Chain context

Move business logic out of ExplorerWeb into context module, Explorer.Chain.  No
code in ExplorerWeb should access Explorer.Repo directly anymore.

.credo.exs

@@ -22,7 +22,12 @@
         # In the latter case `**/*.{ex,exs}` will be used.
         #
         included: ["lib/", "src/", "web/", "apps/*/lib/**/*.{ex,exs}"],
-        excluded: [~r"/_build/", ~r"/deps/", ~r"/node_modules/"]
+        excluded: [
+          ~r"/_build/",
+          ~r"/deps/",
+          ~r"/node_modules/",
+          ~r"/apps/explorer_web/lib/explorer_web.ex"
+        ]
       },
       #
       # If you create your own checks, you must specify the source files for

.gitignore

@@ -1,8 +1,10 @@
 # App artifacts
 /_build
+/apps/*/cover
 /cover
 /db
 /deps
+/doc
 /*.ez
 
 # Generated on crash by the VM

README.md

@@ -38,6 +38,11 @@ You can also run IEx (Interactive Elixir): `iex -S mix phx.server`
 
 Configure your local CCMenu with the following url: [`https://circleci.com/gh/poanetwork/poa-explorer.cc.xml?circle-token=f8823a3d0090407c11f87028c73015a331dbf604`](https://circleci.com/gh/poanetwork/poa-explorer.cc.xml?circle-token=f8823a3d0090407c11f87028c73015a331dbf604)
 
+### Documentation
+
+* `mix docs`
+* `open doc/index.html`
+
 ### Testing
 
 #### Prerequisites

apps/explorer/lib/explorer/application.ex

@@ -5,6 +5,8 @@ defmodule Explorer.Application do
 
   use Application
 
+  import Supervisor.Spec
+
   # See https://hexdocs.pm/elixir/Application.html
   # for more information on OTP Applications
   def start(_type, _args) do
@@ -17,20 +19,17 @@ defmodule Explorer.Application do
   defp children(:test), do: children()
 
   defp children(_) do
-    import Supervisor.Spec
     exq_options = [] |> Keyword.put(:mode, :enqueuer)
 
     children() ++
       [
         supervisor(Exq, [exq_options]),
-        worker(Explorer.Servers.ChainStatistics, []),
+        worker(Explorer.Chain.Statistics.Server, []),
         Explorer.ExchangeRates
       ]
   end
 
   defp children do
-    import Supervisor.Spec
-
     [
       supervisor(Explorer.Repo, []),
       {Task.Supervisor, name: Explorer.ExchangeRateTaskSupervisor}

apps/explorer/lib/explorer/chain.ex

@@ -0,0 +1,544 @@
+defmodule Explorer.Chain do
+  @moduledoc """
+  The chain context.
+  """
+
+  import Ecto.Query, only: [from: 2, order_by: 2, preload: 2, where: 2, where: 3]
+
+  alias Explorer.Chain.{Address, Block, BlockTransaction, InternalTransaction, Log, Transaction}
+  alias Explorer.Repo.NewRelic, as: Repo
+
+  # Types
+
+  @typedoc """
+  The name of an association on the `t:Ecto.Schema.t/0`
+  """
+  @type association :: atom()
+
+  @typedoc """
+  * `:optional` - the association is optional and only needs to be loaded if available
+  * `:required` - the association is required and MUST be loaded.  If it is not available, then the parent struct
+      SHOULD NOT be returned.
+  """
+  @type necessity :: :optional | :required
+
+  @typedoc """
+  The `t:necessity/0` of each association that should be loaded
+  """
+  @type necessity_by_association :: %{association => necessity}
+
+  @typedoc """
+  Pagination params used by `scrivener`
+  """
+  @type pagination :: map()
+
+  @typep necessity_by_association_option :: {:necessity_by_association, necessity_by_association}
+  @typep pagination_option :: {:pagination, pagination}
+
+  # Functions
+
+  @doc """
+  Finds all `t:Explorer.Chain.Transaction.t/0` in the `t:Explorer.Chain.Block.t/0`.
+
+  ## Options
+
+  * `:necessity_by_association` - use to load `t:association/0` as `:required` or `:optional`.  If an association is
+      `:required`, and the `t:Explorer.Chain.Transaction.t/0` has no associated record for that association, then the
+      `t:Explorer.Chain.Transaction.t/0` will not be included in the page `entries`.
+  * `:pagination` - pagination params to pass to scrivener.
+  """
+  @spec block_to_transactions(Block.t()) :: %Scrivener.Page{entries: [Transaction.t()]}
+  @spec block_to_transactions(Block.t(), [necessity_by_association_option | pagination_option]) ::
+          %Scrivener.Page{entries: [Transaction.t()]}
+  def block_to_transactions(%Block{id: block_id}, options \\ []) when is_list(options) do
+    necessity_by_association = Keyword.get(options, :necessity_by_association, %{})
+    pagination = Keyword.get(options, :pagination, %{})
+
+    query =
+      from(
+        transaction in Transaction,
+        inner_join: block in assoc(transaction, :block),
+        where: block.id == ^block_id,
+        order_by: [desc: transaction.inserted_at]
+      )
+
+    query
+    |> join_associations(necessity_by_association)
+    |> Repo.paginate(pagination)
+  end
+
+  @doc """
+  Counts the number of `t:Explorer.Chain.Transaction.t/0` in the `block`.
+  """
+  @spec block_to_transaction_count(Block.t()) :: non_neg_integer()
+  def block_to_transaction_count(%Block{id: block_id}) do
+    query =
+      from(
+        block_transaction in BlockTransaction,
+        join: block in assoc(block_transaction, :block),
+        where: block_transaction.block_id == ^block_id
+      )
+
+    Repo.aggregate(query, :count, :block_id)
+  end
+
+  @doc """
+  How many blocks have confirmed `block` based on the current `max_block_number`
+  """
+  @spec confirmations(Block.t(), [{:max_block_number, Block.block_number()}]) :: non_neg_integer()
+  def confirmations(%Block{number: number}, named_arguments) when is_list(named_arguments) do
+    max_block_number = Keyword.fetch!(named_arguments, :max_block_number)
+
+    max_block_number - number
+  end
+
+  @doc """
+  Creates an address.
+
+  ## Examples
+
+      iex> Explorer.Addresses.create_address(%{field: value})
+      {:ok, %Address{}}
+
+      iex> Explorer.Addresses.create_address(%{field: bad_value})
+      {:error, %Ecto.Changeset{}}
+
+  """
+  @spec create_address(map()) :: {:ok, Address.t()} | {:error, Ecto.Changeset.t()}
+  def create_address(attrs \\ %{}) do
+    %Address{}
+    |> Address.changeset(attrs)
+    |> Repo.insert()
+  end
+
+  @doc """
+  Ensures that an `t:Explorer.Address.t/0` exists with the given `hash`.
+
+  If a `t:Explorer.Address.t/0` with `hash` already exists, it is returned
+
+      iex> Explorer.Addresses.ensure_hash_address(existing_hash)
+      {:ok, %Address{}}
+
+  If a `t:Explorer.Address.t/0` does not exist with `hash`, it is created and returned
+
+      iex> Explorer.Addresses.ensure_hash_address(new_hash)
+      {:ok, %Address{}}
+
+  There is a chance of a race condition when interacting with the database: the `t:Explorer.Address.t/0` may not exist
+  when first checked, then already exist when it is tried to be created because another connection creates the addres,
+  then another process deletes the address after this process's connection see it was created, but before it can be
+  retrieved.  In scenario, the address may be not found as only one retry is attempted to prevent infinite loops.
+
+      iex> Explorer.Addresses.ensure_hash_address(flicker_hash)
+      {:error, :not_found}
+
+  """
+  @spec ensure_hash_address(Address.hash()) :: {:ok, Address.t()} | {:error, :not_found}
+  def ensure_hash_address(hash) when is_binary(hash) do
+    with {:error, :not_found} <- hash_to_address(hash),
+         {:error, _} <- create_address(%{hash: hash}) do
+      # assume race condition occurred and someone else created the address between the first
+      # hash_to_address and create_address
+      hash_to_address(hash)
+    end
+  end
+
+  @doc """
+  `t:Explorer.Chain.Transaction/0`s from `address`.
+
+  ## Options
+
+  * `:necessity_by_association` - use to load `t:association/0` as `:required` or `:optional`.  If an association is
+      `:required`, and the `t:Explorer.Chain.Transaction.t/0` has no associated record for that association, then the
+      `t:Explorer.Chain.Transaction.t/0` will not be included in the page `entries`.
+  * `:pagination` - pagination params to pass to scrivener.
+
+  """
+  @spec from_address_to_transactions(Address.t(), [
+          necessity_by_association_option | pagination_option
+        ]) :: %Scrivener.Page{entries: [Transaction.t()]}
+  def from_address_to_transactions(address = %Address{}, options \\ [])
+      when is_list(options) do
+    address_to_transactions(address, Keyword.put(options, :direction, :from))
+  end
+
+  @doc """
+  Converts `t:Explorer.Chain.Address.t/0` `hash` to the `t:Explorer.Chain.Address.t/0` with that `hash`.
+
+  Returns `{:ok, %Explorer.Chain.Address{}}` if found
+
+      iex> hash_to_address("0x0addressaddressaddressaddressaddressaddr")
+      {:ok, %Explorer.Chain.Address{}}
+
+  Returns `{:error, :not_found}` if not found
+
+      iex> hash_to_address("0x1addressaddressaddressaddressaddressaddr")
+      {:error, :not_found}
+
+  """
+  @spec hash_to_address(Address.hash()) :: {:ok, Address.t()} | {:error, :not_found}
+  def hash_to_address(hash) do
+    Address
+    |> where_hash(hash)
+    |> preload([:credit, :debit])
+    |> Repo.one()
+    |> case do
+      nil -> {:error, :not_found}
+      address -> {:ok, address}
+    end
+  end
+
+  @doc """
+  Converts `t:Explorer.Chain.Transaction.t/0` `hash` to the `t:Explorer.Chain.Transaction.t/0` with that `hash`.
+
+  Returns `{:ok, %Explorer.Chain.Transaction{}}` if found
+
+      iex> hash_to_transaction("0x0addressaddressaddressaddressaddressaddr")
+      {:ok, %Explorer.Chain.Transaction{}}
+
+  Returns `{:error, :not_found}` if not found
+
+      iex> hash_to_transaction("0x1addressaddressaddressaddressaddressaddr")
+      {:error, :not_found}
+
+  ## Options
+
+  * `:necessity_by_association` - use to load `t:association/0` as `:required` or `:optional`.  If an association is
+      `:required`, and the `t:Explorer.Chain.Transaction.t/0` has no associated record for that association, then the
+      `t:Explorer.Chain.Transaction.t/0` will not be included in the page `entries`.
+  """
+  @spec hash_to_transaction(Transaction.hash(), [necessity_by_association_option]) ::
+          {:ok, Transaction.t()} | {:error, :not_found}
+  def hash_to_transaction(hash, options \\ []) when is_list(options) do
+    necessity_by_association = Keyword.get(options, :necessity_by_association, %{})
+
+    Transaction
+    |> join_associations(necessity_by_association)
+    |> where_hash(hash)
+    |> Repo.one()
+    |> case do
+      nil -> {:error, :not_found}
+      transaction -> {:ok, transaction}
+    end
+  end
+
+  @doc """
+  Converts `t:Explorer.Address.t/0` `id` to the `t:Explorer.Address.t/0` with that `id`.
+
+  Returns `{:ok, %Explorer.Address{}}` if found
+
+      iex> id_to_address(123)
+      {:ok, %Address{}}
+
+  Returns `{:error, :not_found}` if not found
+
+      iex> id_to_address(456)
+      {:error, :not_found}
+
+  """
+  @spec id_to_address(id :: non_neg_integer()) :: {:ok, Address.t()} | {:error, :not_found}
+  def id_to_address(id) do
+    Address
+    |> Repo.get(id)
+    |> case do
+      nil ->
+        {:error, :not_found}
+
+      address ->
+        {:ok, Repo.preload(address, [:credit, :debit])}
+    end
+  end
+
+  @doc """
+  The last `t:Explorer.Chain.Transaction.t/0` `id`.
+  """
+  @spec last_transaction_id([{:pending, boolean()}]) :: non_neg_integer()
+  def last_transaction_id(options \\ []) when is_list(options) do
+    query =
+      from(
+        t in Transaction,
+        select: t.id,
+        order_by: [desc: t.id],
+        limit: 1
+      )
+
+    query
+    |> where_pending(options)
+    |> Repo.one()
+    |> Kernel.||(0)
+  end
+
+  @doc """
+  Finds all `t:Explorer.Chain.Transaction.t/0` in the `t:Explorer.Chain.Block.t/0`.
+
+  ## Options
+
+  * `:necessity_by_association` - use to load `t:association/0` as `:required` or `:optional`.  If an association is
+      `:required`, and the `t:Explorer.Chain.Block.t/0` has no associated record for that association, then the
+      `t:Explorer.Chain.Transaction.t/0` will not be included in the page `entries`.
+  * `:pagination` - pagination params to pass to scrivener.
+
+  """
+  @spec list_blocks([necessity_by_association_option | pagination_option]) :: %Scrivener.Page{
+          entries: [Block.t()]
+        }
+  def list_blocks(options \\ []) when is_list(options) do
+    necessity_by_association = Keyword.get(options, :necessity_by_association, %{})
+    pagination = Keyword.get(options, :pagination, %{})
+
+    Block
+    |> join_associations(necessity_by_association)
+    |> order_by(desc: :number)
+    |> Repo.paginate(pagination)
+  end
+
+  @doc """
+  The maximum `t:Explorer.Chain.Block.t/0` `number`
+  """
+  @spec max_block_number() :: Block.block_number()
+  def max_block_number do
+    Repo.aggregate(Block, :max, :number)
+  end
+
+  @doc """
+  Finds `t:Explorer.Chain.Block.t/0` with `number`
+  """
+  @spec number_to_block(Block.block_number()) :: {:ok, Block.t()} | {:error, :not_found}
+  def number_to_block(number) do
+    Block
+    |> where(number: ^number)
+    |> Repo.one()
+    |> case do
+      nil -> {:error, :not_found}
+      block -> {:ok, block}
+    end
+  end
+
+  @doc """
+  `t:Explorer.Chain.Transaction/0`s to `address`.
+
+  ## Options
+
+  * `:necessity_by_association` - use to load `t:association/0` as `:required` or `:optional`.  If an association is
+      `:required`, and the `t:Explorer.Chain.Transaction.t/0` has no associated record for that association, then the
+      `t:Explorer.Chain.Transaction.t/0` will not be included in the page `entries`.
+  * `:pagination` - pagination params to pass to scrivener.
+
+  """
+  @spec to_address_to_transactions(Address.t(), [
+          necessity_by_association_option | pagination_option
+        ]) :: %Scrivener.Page{entries: [Transaction.t()]}
+  def to_address_to_transactions(address = %Address{}, options \\ []) when is_list(options) do
+    address_to_transactions(address, Keyword.put(options, :direction, :to))
+  end
+
+  @doc """
+  Count of `t:Explorer.Chain.Transaction.t/0`.
+
+  ## Options
+
+  * `:pending`
+    * `true` - only count pending transactions
+    * `false` - count all transactions
+
+  """
+  @spec transaction_count([{:pending, boolean()}]) :: non_neg_integer()
+  def transaction_count(options \\ []) when is_list(options) do
+    Transaction
+    |> where_pending(options)
+    |> Repo.aggregate(:count, :id)
+  end
+
+  @doc """
+  `t:Explorer.Chain.InternalTransaction/0`s in `t:Explorer.Chain.Transaction.t/0` with `hash`
+
+  ## Options
+
+  * `:necessity_by_association` - use to load `t:association/0` as `:required` or `:optional`.  If an association is
+      `:required`, and the `t:Explorer.Chain.InternalTransaction.t/0` has no associated record for that association,
+      then the `t:Explorer.Chain.InternalTransaction.t/0` will not be included in the list.
+
+  """
+  @spec transaction_hash_to_internal_transactions(Transaction.hash()) :: [InternalTransaction.t()]
+  def transaction_hash_to_internal_transactions(hash, options \\ [])
+      when is_binary(hash) and is_list(options) do
+    necessity_by_association = Keyword.get(options, :necessity_by_association, %{})
+
+    InternalTransaction
+    |> for_parent_transaction(hash)
+    |> join_associations(necessity_by_association)
+    |> Repo.all()
+  end
+
+  @doc """
+  Returns the list of transactions that occurred recently (10) before `t:Explorer.Chain.Transaction.t/0` `id`.
+
+  ## Examples
+
+      iex> Explorer.Chain.list_transactions_before_id(id)
+      [%Explorer.Chain.Transaction{}, ...]
+
+  ## Options
+
+  * `:necessity_by_association` - use to load `t:association/0` as `:required` or `:optional`.  If an association is
+      `:required`, and the `t:Explorer.Chain.InternalTransaction.t/0` has no associated record for that association,
+      then the `t:Explorer.Chain.InternalTransaction.t/0` will not be included in the list.
+
+  """
+  @spec transactions_recently_before_id(id :: non_neg_integer, [necessity_by_association_option]) ::
+          [
+            Transaction.t()
+          ]
+  def transactions_recently_before_id(id, options \\ []) when is_list(options) do
+    necessity_by_association = Keyword.get(options, :necessity_by_association, %{})
+
+    Transaction
+    |> join_associations(necessity_by_association)
+    |> recently_before_id(id)
+    |> where_pending(options)
+    |> Repo.all()
+  end
+
+  @doc """
+  Finds all `t:Explorer.Chain.Log.t/0`s for `t:Explorer.Chain.Transaction.t/0`.
+
+  ## Options
+
+  * `:necessity_by_association` - use to load `t:association/0` as `:required` or `:optional`.  If an association is
+      `:required`, and the `t:Explorer.Chain.Log.t/0` has no associated record for that association, then the
+      `t:Explorer.Chain.Log.t/0` will not be included in the page `entries`.
+  * `:pagination` - pagination params to pass to scrivener.
+
+  """
+  @spec transaction_to_logs(Transaction.t(), [
+          necessity_by_association_option | pagination_option
+        ]) :: %Scrivener.Page{entries: [Log.t()]}
+  def transaction_to_logs(%Transaction{hash: hash}, options \\ []) when is_list(options) do
+    transaction_hash_to_logs(hash, options)
+  end
+
+  @doc """
+  Updates `balance` of `t:Explorer.Address.t/0` with `hash`.
+
+  If `t:Explorer.Address.t/0` with `hash` does not already exist, it is created first.
+  """
+  @spec update_balance(Address.hash(), Address.balance()) ::
+          {:ok, Address.t()} | {:error, Ecto.Changeset.t()} | {:error, reason :: term}
+  def update_balance(hash, balance) when is_binary(hash) do
+    changes = %{
+      balance: balance
+    }
+
+    with {:ok, address} <- ensure_hash_address(hash) do
+      address
+      |> Address.balance_changeset(changes)
+      |> Repo.update()
+    end
+  end
+
+  ## Private Functions
+
+  defp address_id_to_transactions(address_id, named_arguments)
+       when is_integer(address_id) and is_list(named_arguments) do
+    field =
+      case Keyword.fetch!(named_arguments, :direction) do
+        :to -> :to_address_id
+        :from -> :from_address_id
+      end
+
+    necessity_by_association = Keyword.get(named_arguments, :necessity_by_association, %{})
+    pagination = Keyword.get(named_arguments, :pagination, %{})
+
+    Transaction
+    |> join_associations(necessity_by_association)
+    |> chronologically()
+    |> where([t], field(t, ^field) == ^address_id)
+    |> Repo.paginate(pagination)
+  end
+
+  defp address_to_transactions(%Address{id: address_id}, options) when is_list(options) do
+    address_id_to_transactions(address_id, options)
+  end
+
+  defp chronologically(query) do
+    from(q in query, order_by: [desc: q.inserted_at, desc: q.id])
+  end
+
+  defp for_parent_transaction(query, hash) when is_binary(hash) do
+    from(
+      child in query,
+      inner_join: transaction in assoc(child, :transaction),
+      where: fragment("lower(?)", transaction.hash) == ^String.downcase(hash)
+    )
+  end
+
+  defp join_association(query, association, necessity) when is_atom(association) do
+    case necessity do
+      :optional ->
+        preload(query, ^association)
+
+      :required ->
+        from(q in query, inner_join: a in assoc(q, ^association), preload: [{^association, a}])
+    end
+  end
+
+  defp join_associations(query, necessity_by_association) when is_map(necessity_by_association) do
+    Enum.reduce(necessity_by_association, query, fn {association, join}, acc_query ->
+      join_association(acc_query, association, join)
+    end)
+  end
+
+  defp recently_before_id(query, id) do
+    from(
+      q in query,
+      where: q.id < ^id,
+      order_by: [desc: q.id],
+      limit: 10
+    )
+  end
+
+  defp transaction_hash_to_logs(transaction_hash, options)
+       when is_binary(transaction_hash) and is_list(options) do
+    lower_transaction_hash = String.downcase(transaction_hash)
+    necessity_by_association = Keyword.get(options, :necessity_by_association, %{})
+    pagination = Keyword.get(options, :pagination, %{})
+
+    query =
+      from(
+        log in Log,
+        join: transaction in assoc(log, :transaction),
+        where: fragment("lower(?)", transaction.hash) == ^lower_transaction_hash,
+        order_by: [asc: :index]
+      )
+
+    query
+    |> join_associations(necessity_by_association)
+    |> Repo.paginate(pagination)
+  end
+
+  defp where_hash(query, hash) do
+    from(
+      q in query,
+      where: fragment("lower(?)", q.hash) == ^String.downcase(hash)
+    )
+  end
+
+  defp where_pending(query, options) when is_list(options) do
+    pending = Keyword.get(options, :pending, false)
+
+    where_pending(query, pending)
+  end
+
+  defp where_pending(query, false), do: query
+
+  defp where_pending(query, true) do
+    from(
+      transaction in query,
+      where:
+        fragment(
+          "NOT EXISTS (SELECT true FROM receipts WHERE receipts.transaction_id = ?)",
+          transaction.id
+        )
+    )
+  end
+end

apps/explorer/lib/explorer/chain/address.ex

@@ -0,0 +1,66 @@
+defmodule Explorer.Chain.Address do
+  @moduledoc """
+  A stored representation of a web3 address.
+  """
+
+  use Explorer.Schema
+
+  alias Explorer.Chain.{Credit, Debit}
+
+  @typedoc """
+  Hash of the public key for this address.
+  """
+  @type hash :: Hash.t()
+
+  @typedoc """
+  * `balance` - `credit.value - debit.value`
+  * `balance_updated_at` - the last time `balance` was recalculated
+  * `credit` - accumulation of all credits to the address `hash`
+  * `debit` - accumulation of all debits to the address `hash`
+  * `inserted_at` - when this address was inserted
+  * `updated_at` when this address was last updated
+  """
+  @type t :: %__MODULE__{
+          balance: Decimal.t(),
+          balance_updated_at: DateTime.t(),
+          credit: Ecto.Association.NotLoaded.t() | Credit.t() | nil,
+          debit: Ecto.Association.NotLoaded.t() | Debit.t() | nil,
+          hash: hash(),
+          inserted_at: DateTime.t(),
+          updated_at: DateTime.t()
+        }
+
+  schema "addresses" do
+    field(:balance, :decimal)
+    field(:balance_updated_at, Timex.Ecto.DateTime)
+    field(:hash, :string)
+
+    timestamps()
+
+    has_one(:credit, Credit)
+    has_one(:debit, Debit)
+  end
+
+  @required_attrs ~w(hash)a
+  @optional_attrs ~w()a
+
+  def changeset(%__MODULE__{} = address, attrs) do
+    address
+    |> cast(attrs, @required_attrs, @optional_attrs)
+    |> validate_required(@required_attrs)
+    |> update_change(:hash, &String.downcase/1)
+    |> unique_constraint(:hash)
+  end
+
+  def balance_changeset(%__MODULE__{} = address, attrs) do
+    address
+    |> cast(attrs, [:balance])
+    |> validate_required([:balance])
+    |> put_balance_updated_at()
+  end
+
+  defp put_balance_updated_at(changeset) do
+    changeset
+    |> put_change(:balance_updated_at, Timex.now())
+  end
+end

apps/explorer/lib/explorer/chain/block.ex

@@ -0,0 +1,105 @@
+defmodule Explorer.Chain.Block do
+  @moduledoc """
+  A package of data that contains zero or more transactions, the hash of the previous block ("parent"), and optionally
+  other data. Because each block (except for the initial "genesis block") points to the previous block, the data
+  structure that they form is called a "blockchain".
+  """
+
+  use Explorer.Schema
+
+  alias Explorer.Chain.{BlockTransaction, Hash, Transaction}
+
+  # Types
+
+  @typedoc """
+  How much work is required to find a hash with some number of leading 0s.  It is measured in hashes for PoW
+  (Proof-of-Work) chains like Ethereum.  In PoA (Proof-of-Authority) chains, it does not apply as blocks are validated
+  in a round-robin fashion, and so the value is always `Decimal.new(0)`.
+  """
+  @type difficulty :: Decimal.t()
+
+  @typedoc """
+  A measurement roughly equivalent to computational steps.  Every operation has a gas expenditure; for most operations
+  it is ~3-10, although some expensive operations have expenditures up to 700 and a transaction itself has an
+  expenditure of 21000.
+  """
+  @type gas :: non_neg_integer()
+
+  @typedoc """
+  Number of the block in the chain.
+  """
+  @type block_number :: non_neg_integer()
+
+  @typedoc """
+  * `block_transactions` - The `t:Explorer.Chain.BlockTransaction.t/0`s joins this block to its `transactions`
+  * `difficulty` - how hard the block was to mine.
+  * `gas_limit` - If the total number of gas used by the computation spawned by the transaction, including the original
+      message and any sub-messages that may be triggered, is less than or equal to the gas limit, then the transaction
+      processes. If the total gas exceeds the gas limit, then all changes are reverted, except that the transaction is
+      still valid and the fee can still be collected by the miner.
+  * `gas_used` - The actual `t:gas/0` used to mine/validate the transactions in the block.
+  * `hash` - the hash of the block.
+  * `miner` - the hash of the `t:Explorer.Address.t/0` of the miner.  In Proof-of-Authority chains, this is the
+      validator.
+  * `nonce` - the hash of the generated proof-of-work.  Not used in Proof-of-Authority chains.
+  * `number` - which block this is along the chain.
+  * `parent_hash` - the hash of the parent block, which should have the previous `number`
+  * `size` - The size of the block in bytes.
+  * `timestamp` - When the block was collated
+  * `total_diffficulty` - the total `difficulty` of the chain until this block.
+  * `transactions` - the `t:Explorer.Chain.Transaction.t/0` in this block.
+  """
+  @type t :: %__MODULE__{
+          block_transactions: %Ecto.Association.NotLoaded{} | [BlockTransaction.t()],
+          difficulty: difficulty(),
+          gas_limit: gas(),
+          gas_used: gas(),
+          hash: Hash.t(),
+          miner: Address.hash(),
+          nonce: Hash.t(),
+          number: block_number(),
+          parent_hash: Hash.t(),
+          size: non_neg_integer(),
+          timestamp: DateTime.t(),
+          total_difficulty: difficulty(),
+          transactions: %Ecto.Association.NotLoaded{} | [Transaction.t()]
+        }
+
+  schema "blocks" do
+    field(:difficulty, :decimal)
+    field(:gas_limit, :integer)
+    field(:gas_used, :integer)
+    field(:hash, :string)
+    field(:miner, :string)
+    field(:nonce, :string)
+    field(:number, :integer)
+    field(:parent_hash, :string)
+    field(:size, :integer)
+    field(:timestamp, Timex.Ecto.DateTime)
+    field(:total_difficulty, :decimal)
+
+    timestamps()
+
+    has_many(:block_transactions, BlockTransaction)
+    many_to_many(:transactions, Transaction, join_through: "block_transactions")
+  end
+
+  @required_attrs ~w(number hash parent_hash nonce miner difficulty
+                     total_difficulty size gas_limit gas_used timestamp)a
+
+  @doc false
+  def changeset(%__MODULE__{} = block, attrs) do
+    block
+    |> cast(attrs, @required_attrs)
+    |> validate_required(@required_attrs)
+    |> update_change(:hash, &String.downcase/1)
+    |> unique_constraint(:hash)
+    |> cast_assoc(:transactions)
+  end
+
+  def null, do: %__MODULE__{number: -1, timestamp: :calendar.universal_time()}
+
+  def latest(query) do
+    query |> order_by(desc: :number)
+  end
+end

apps/explorer/lib/explorer/chain/block_transaction.ex

@@ -1,20 +1,20 @@
-defmodule Explorer.BlockTransaction do
+defmodule Explorer.Chain.BlockTransaction do
   @moduledoc "Connects a Block to a Transaction"
 
-  alias Explorer.BlockTransaction
-
   use Explorer.Schema
 
+  alias Explorer.Chain.{Block, Transaction}
+
   @primary_key false
   schema "block_transactions" do
-    belongs_to(:block, Explorer.Block)
-    belongs_to(:transaction, Explorer.Transaction, primary_key: true)
+    belongs_to(:block, Block)
+    belongs_to(:transaction, Transaction, primary_key: true)
     timestamps()
   end
 
   @required_attrs ~w(block_id transaction_id)a
 
-  def changeset(%BlockTransaction{} = block_transaction, attrs \\ %{}) do
+  def changeset(%__MODULE__{} = block_transaction, attrs \\ %{}) do
     block_transaction
     |> cast(attrs, @required_attrs)
     |> validate_required(@required_attrs)

apps/explorer/lib/explorer/chain/credit.ex

@@ -1,4 +1,4 @@
-defmodule Explorer.Credit do
+defmodule Explorer.Chain.Credit do
   @moduledoc """
     A materialized view representing the credits to an address.
   """
@@ -6,15 +6,17 @@ defmodule Explorer.Credit do
   use Explorer.Schema
 
   alias Ecto.Adapters.SQL
-  alias Explorer.Address
+  alias Explorer.Chain.Address
   alias Explorer.Repo
 
   @primary_key false
   schema "credits" do
-    belongs_to(:address, Address, primary_key: true)
-    field(:value, :decimal)
     field(:count, :integer)
+    field(:value, :decimal)
+
     timestamps()
+
+    belongs_to(:address, Address, primary_key: true)
   end
 
   def refresh do

apps/explorer/lib/explorer/chain/debit.ex

@@ -1,4 +1,4 @@
-defmodule Explorer.Debit do
+defmodule Explorer.Chain.Debit do
   @moduledoc """
     A materialized view representing the debits from an address.
   """
@@ -6,15 +6,17 @@ defmodule Explorer.Debit do
   use Explorer.Schema
 
   alias Ecto.Adapters.SQL
-  alias Explorer.Address
+  alias Explorer.Chain.Address
   alias Explorer.Repo
 
   @primary_key false
   schema "debits" do
-    belongs_to(:address, Address, primary_key: true)
-    field(:value, :decimal)
     field(:count, :integer)
+    field(:value, :decimal)
+
     timestamps()
+
+    belongs_to(:address, Address, primary_key: true)
   end
 
   def refresh do

apps/explorer/lib/explorer/chain/from_address.ex

@@ -1,18 +1,19 @@
-defmodule Explorer.FromAddress do
+defmodule Explorer.Chain.FromAddress do
   @moduledoc false
 
   use Explorer.Schema
 
-  alias Explorer.FromAddress
+  alias Explorer.Chain.{Address, Transaction}
 
   @primary_key false
   schema "from_addresses" do
-    belongs_to(:transaction, Explorer.Transaction, primary_key: true)
-    belongs_to(:address, Explorer.Address)
+    belongs_to(:address, Address)
+    belongs_to(:transaction, Transaction, primary_key: true)
+
     timestamps()
   end
 
-  def changeset(%FromAddress{} = to_address, attrs \\ %{}) do
+  def changeset(%__MODULE__{} = to_address, attrs \\ %{}) do
     to_address
     |> cast(attrs, [:transaction_id, :address_id])
     |> unique_constraint(:transaction_id, name: :from_addresses_transaction_id_index)

apps/explorer/lib/explorer/chain/hash.ex

@@ -0,0 +1,10 @@
+defmodule Explorer.Chain.Hash do
+  @moduledoc """
+  Hash used throughout Ethereum chains.
+  """
+
+  @typedoc """
+  [KECCAK-256](https://en.wikipedia.org/wiki/SHA-3) hash as a string.
+  """
+  @type t :: String.t()
+end

apps/explorer/lib/explorer/chain/internal_transaction.ex

@@ -1,32 +1,32 @@
-defmodule Explorer.InternalTransaction do
+defmodule Explorer.Chain.InternalTransaction do
   @moduledoc "Models internal transactions."
 
   use Explorer.Schema
 
-  alias Explorer.InternalTransaction
-  alias Explorer.Transaction
-  alias Explorer.Address
+  alias Explorer.Chain.{Address, Transaction}
 
   schema "internal_transactions" do
-    belongs_to(:transaction, Transaction)
-    belongs_to(:from_address, Address)
-    belongs_to(:to_address, Address)
-    field(:index, :integer)
     field(:call_type, :string)
-    field(:trace_address, {:array, :integer})
-    field(:value, :decimal)
     field(:gas, :decimal)
     field(:gas_used, :decimal)
+    field(:index, :integer)
     field(:input, :string)
     field(:output, :string)
+    field(:trace_address, {:array, :integer})
+    field(:value, :decimal)
+
     timestamps()
+
+    belongs_to(:from_address, Address)
+    belongs_to(:to_address, Address)
+    belongs_to(:transaction, Transaction)
   end
 
   @required_attrs ~w(index call_type trace_address value gas gas_used
     transaction_id from_address_id to_address_id)a
   @optional_attrs ~w(input output)
 
-  def changeset(%InternalTransaction{} = internal_transaction, attrs \\ %{}) do
+  def changeset(%__MODULE__{} = internal_transaction, attrs \\ %{}) do
     internal_transaction
     |> cast(attrs, @required_attrs ++ @optional_attrs)
     |> validate_required(@required_attrs)
@@ -36,5 +36,5 @@ defmodule Explorer.InternalTransaction do
     |> unique_constraint(:transaction_id, name: :internal_transactions_transaction_id_index_index)
   end
 
-  def null, do: %InternalTransaction{}
+  def null, do: %__MODULE__{}
 end

apps/explorer/lib/explorer/chain/log.ex

@@ -1,32 +1,32 @@
-defmodule Explorer.Log do
+defmodule Explorer.Chain.Log do
   @moduledoc "Captures a Web3 log entry generated by a transaction"
 
   use Explorer.Schema
 
-  alias Explorer.Address
-  alias Explorer.Log
-  alias Explorer.Receipt
+  alias Explorer.Chain.{Address, Receipt}
 
-  @required_attrs ~w(index data type)a
+  @required_attrs ~w(address_id data index type)a
   @optional_attrs ~w(
-    first_topic second_topic third_topic fourth_topic address_id
+    first_topic second_topic third_topic fourth_topic
   )a
 
   schema "logs" do
-    belongs_to(:receipt, Receipt)
-    belongs_to(:address, Address)
-    has_one(:transaction, through: [:receipt, :transaction])
-    field(:index, :integer)
     field(:data, :string)
-    field(:type, :string)
     field(:first_topic, :string)
+    field(:fourth_topic, :string)
+    field(:index, :integer)
     field(:second_topic, :string)
     field(:third_topic, :string)
-    field(:fourth_topic, :string)
+    field(:type, :string)
+
     timestamps()
+
+    belongs_to(:address, Address)
+    belongs_to(:receipt, Receipt)
+    has_one(:transaction, through: [:receipt, :transaction])
   end
 
-  def changeset(%Log{} = log, attrs \\ %{}) do
+  def changeset(%__MODULE__{} = log, attrs \\ %{}) do
     log
     |> cast(attrs, @required_attrs)
     |> cast(attrs, @optional_attrs)

apps/explorer/lib/explorer/chain/receipt.ex

@@ -1,11 +1,9 @@
-defmodule Explorer.Receipt do
+defmodule Explorer.Chain.Receipt do
   @moduledoc "Captures a Web3 Transaction Receipt."
 
   use Explorer.Schema
 
-  alias Explorer.Transaction
-  alias Explorer.Log
-  alias Explorer.Receipt
+  alias Explorer.Chain.{Log, Transaction}
 
   @required_attrs ~w(cumulative_gas_used gas_used status index)a
   @optional_attrs ~w(transaction_id)a
@@ -20,7 +18,7 @@ defmodule Explorer.Receipt do
     timestamps()
   end
 
-  def changeset(%Receipt{} = transaction_receipt, attrs \\ %{}) do
+  def changeset(%__MODULE__{} = transaction_receipt, attrs \\ %{}) do
     transaction_receipt
     |> cast(attrs, @required_attrs)
     |> cast(attrs, @optional_attrs)
@@ -31,5 +29,5 @@ defmodule Explorer.Receipt do
     |> unique_constraint(:transaction_id)
   end
 
-  def null, do: %Receipt{}
+  def null, do: %__MODULE__{}
 end

apps/explorer/lib/explorer/chain/statistics.ex

@@ -1,4 +1,4 @@
-defmodule Explorer.Chain do
+defmodule Explorer.Chain.Statistics do
   @moduledoc """
     Represents statistics about the chain.
   """
@@ -6,21 +6,11 @@ defmodule Explorer.Chain do
   import Ecto.Query
 
   alias Ecto.Adapters.SQL
-  alias Explorer.Block
-  alias Explorer.Transaction
-  alias Explorer.Repo, as: Repo
+  alias Explorer.Chain.{Block, Transaction}
+  alias Explorer.Repo
   alias Timex.Duration
 
-  defstruct number: -1,
-            timestamp: :calendar.universal_time(),
-            average_time: %Duration{seconds: 0, megaseconds: 0, microseconds: 0},
-            lag: %Duration{seconds: 0, megaseconds: 0, microseconds: 0},
-            transaction_count: 0,
-            skipped_blocks: 0,
-            block_velocity: 0,
-            transaction_velocity: 0,
-            blocks: [],
-            transactions: []
+  # Constants
 
   @average_time_query """
     SELECT coalesce(avg(difference), interval '0 seconds')
@@ -69,6 +59,60 @@ defmodule Explorer.Chain do
       WHERE transactions.inserted_at > NOW() - interval '1 minute'
   """
 
+  # Types
+
+  @typedoc """
+  The number of `t:Explorer.Chain.Block.t/0` mined/validated per minute.
+  """
+  @type blocks_per_minute :: non_neg_integer()
+
+  @typedoc """
+  The number of `t:Explorer.Chain.Transaction.t/0` mined/validated per minute.
+  """
+  @type transactions_per_minute :: non_neg_integer()
+
+  @typedoc """
+  * `average_time` - the average time it took to mine/validate the last <= 100 `t:Explorer.Chain.Block.t/0`
+  * `block_velocity` - the number of `t:Explorer.Chain.Block.t/0` mined/validated in the last minute
+  * `blocks` - the last <= 5 `t:Explorer.Chain.Block.t/0`
+  * `lag` - the average time over the last hour between when the block was mined/validated
+      (`t:Explorer.Chain.Block.t/0` `timestamp`) and when it was inserted into the databasse
+      (`t:Explorer.Chain.Block.t/0` `inserted_at`)
+  * `number` - the latest `t:Explorer.Chain.Block.t/0` `number`
+  * `skipped_blocks` - the number of blocks that were mined/validated, but do not exist as `t:Explorer.Chain.Block.t/0`
+  * `timestamp` - when the last `t:Explorer.Chain.Block.t/0` was mined/validated
+  * `transaction_count` - the number of transactions confirmed in blocks that were mined/validated in the last day
+  * `transaction_velocity` - the number of `t:Explorer.Chain.Block.t/0` mined/validated in the last minute
+  * `transactions` - the last <= 5 `t:Explorer.Chain.Transaction.t/0`
+  """
+  @type t :: %__MODULE__{
+          average_time: Duration.t(),
+          block_velocity: blocks_per_minute(),
+          blocks: [Block.t()],
+          lag: Duration.t(),
+          number: Block.number(),
+          skipped_blocks: non_neg_integer(),
+          timestamp: :calendar.datetime(),
+          transaction_count: non_neg_integer(),
+          transaction_velocity: transactions_per_minute(),
+          transactions: [Transaction.t()]
+        }
+
+  # Struct
+
+  defstruct average_time: %Duration{seconds: 0, megaseconds: 0, microseconds: 0},
+            block_velocity: 0,
+            blocks: [],
+            lag: %Duration{seconds: 0, megaseconds: 0, microseconds: 0},
+            number: -1,
+            skipped_blocks: 0,
+            timestamp: :calendar.universal_time(),
+            transaction_count: 0,
+            transaction_velocity: 0,
+            transactions: []
+
+  # Functions
+
   def fetch do
     blocks =
       from(
@@ -90,7 +134,7 @@ defmodule Explorer.Chain do
     last_block = Block |> Block.latest() |> limit(1) |> Repo.one()
     latest_block = last_block || Block.null()
 
-    %Explorer.Chain{
+    %__MODULE__{
       number: latest_block.number,
       timestamp: latest_block.timestamp,
       average_time: query_duration(@average_time_query),

apps/explorer/lib/explorer/chain/statistics/server.ex

@@ -0,0 +1,49 @@
+defmodule Explorer.Chain.Statistics.Server do
+  @moduledoc "Stores the latest chain statistics."
+
+  use GenServer
+
+  alias Explorer.Chain.Statistics
+
+  @interval 1_000
+
+  @spec fetch() :: Statistics.t()
+  def fetch do
+    case GenServer.whereis(__MODULE__) do
+      nil -> Statistics.fetch()
+      _ -> GenServer.call(__MODULE__, :fetch)
+    end
+  end
+
+  def start_link, do: start_link(true)
+
+  def start_link(refresh) do
+    GenServer.start_link(__MODULE__, refresh, name: __MODULE__)
+  end
+
+  def init(true) do
+    {:noreply, chain} = handle_cast({:update, Statistics.fetch()}, %Statistics{})
+    {:ok, chain}
+  end
+
+  def init(false), do: {:ok, Statistics.fetch()}
+
+  def handle_info(:refresh, %Statistics{} = statistics) do
+    Task.start_link(fn ->
+      GenServer.cast(__MODULE__, {:update, Statistics.fetch()})
+    end)
+
+    {:noreply, statistics}
+  end
+
+  def handle_info(_, %Statistics{} = statistics), do: {:noreply, statistics}
+  def handle_call(:fetch, _, %Statistics{} = statistics), do: {:reply, statistics, statistics}
+  def handle_call(_, _, %Statistics{} = statistics), do: {:noreply, statistics}
+
+  def handle_cast({:update, %Statistics{} = statistics}, %Statistics{} = _) do
+    Process.send_after(self(), :refresh, @interval)
+    {:noreply, statistics}
+  end
+
+  def handle_cast(_, %Statistics{} = statistics), do: {:noreply, statistics}
+end

apps/explorer/lib/explorer/chain/to_address.ex

@@ -1,17 +1,18 @@
-defmodule Explorer.ToAddress do
+defmodule Explorer.Chain.ToAddress do
   @moduledoc false
-  alias Explorer.ToAddress
 
   use Explorer.Schema
 
+  alias Explorer.Chain.{Address, Transaction}
+
   @primary_key false
   schema "to_addresses" do
-    belongs_to(:transaction, Explorer.Transaction, primary_key: true)
-    belongs_to(:address, Explorer.Address)
+    belongs_to(:address, Address)
+    belongs_to(:transaction, Transaction, primary_key: true)
     timestamps()
   end
 
-  def changeset(%ToAddress{} = to_address, attrs \\ %{}) do
+  def changeset(%__MODULE__{} = to_address, attrs \\ %{}) do
     to_address
     |> cast(attrs, [:transaction_id, :address_id])
     |> unique_constraint(:transaction_id, name: :to_addresses_transaction_id_index)

apps/explorer/lib/explorer/chain/transaction.ex

@@ -1,13 +1,9 @@
-defmodule Explorer.Transaction do
+defmodule Explorer.Chain.Transaction do
   @moduledoc "Models a Web3 transaction."
 
   use Explorer.Schema
 
-  alias Explorer.Address
-  alias Explorer.BlockTransaction
-  alias Explorer.InternalTransaction
-  alias Explorer.Receipt
-  alias Explorer.Transaction
+  alias Explorer.Chain.{Address, BlockTransaction, InternalTransaction, Receipt}
 
   schema "transactions" do
     has_one(:receipt, Receipt)
@@ -37,7 +33,7 @@ defmodule Explorer.Transaction do
   @optional_attrs ~w(to_address_id from_address_id)a
 
   @doc false
-  def changeset(%Transaction{} = transaction, attrs \\ %{}) do
+  def changeset(%__MODULE__{} = transaction, attrs \\ %{}) do
     transaction
     |> cast(attrs, @required_attrs ++ @optional_attrs)
     |> validate_required(@required_attrs)
@@ -46,5 +42,5 @@ defmodule Explorer.Transaction do
     |> unique_constraint(:hash)
   end
 
-  def null, do: %Transaction{}
+  def null, do: %__MODULE__{}
 end

apps/explorer/lib/explorer/exchange_rates/source/coin_market_cap.ex

@@ -3,10 +3,8 @@ defmodule Explorer.ExchangeRates.Source.CoinMarketCap do
   Adapter for fetching exchange rates from https://coinmarketcap.com.
   """
 
-  alias Explorer.ExchangeRates.Rate
-  alias Explorer.ExchangeRates.Source
-  alias HTTPoison.Error
-  alias HTTPoison.Response
+  alias Explorer.ExchangeRates.{Rate, Source}
+  alias HTTPoison.{Error, Response}
 
   @behaviour Source
 

apps/explorer/lib/explorer/importers/balance_importer.ex

@@ -1,18 +1,17 @@
 defmodule Explorer.BalanceImporter do
   @moduledoc "Imports a balance for a given address."
 
-  alias Explorer.Address.Service, as: Address
-  alias Explorer.Ethereum
+  alias Explorer.{Chain, Ethereum}
 
   def import(hash) do
-    hash
-    |> Ethereum.download_balance()
-    |> persist_balance(hash)
+    encoded_balance = Ethereum.download_balance(hash)
+
+    persist_balance(hash, encoded_balance)
   end
 
-  defp persist_balance(balance, hash) do
-    balance
-    |> Ethereum.decode_integer_field()
-    |> Address.update_balance(hash)
+  defp persist_balance(hash, encoded_balance) when is_binary(hash) do
+    decoded_balance = Ethereum.decode_integer_field(encoded_balance)
+
+    Chain.update_balance(hash, decoded_balance)
   end
 end

apps/explorer/lib/explorer/importers/block_importer.ex

@@ -4,8 +4,8 @@ defmodule Explorer.BlockImporter do
   import Ecto.Query
   import Ethereumex.HttpClient, only: [eth_get_block_by_number: 2]
 
-  alias Explorer.Block
-  alias Explorer.Ethereum
+  alias Explorer.{BlockImporter, Ethereum}
+  alias Explorer.Chain.Block
   alias Explorer.Repo.NewRelic, as: Repo
   alias Explorer.Workers.ImportTransaction
 
@@ -26,7 +26,6 @@ defmodule Explorer.BlockImporter do
 
   @dialyzer {:nowarn_function, import: 1}
   def import(block_number) do
-    alias Explorer.BlockImporter
     block_number |> download_block() |> BlockImporter.import()
   end
 

apps/explorer/lib/explorer/importers/internal_transaction_importer.ex

@@ -3,12 +3,8 @@ defmodule Explorer.InternalTransactionImporter do
 
   import Ecto.Query
 
-  alias Explorer.Address.Service, as: Address
-  alias Explorer.Ethereum
-  alias Explorer.EthereumexExtensions
-  alias Explorer.InternalTransaction
-  alias Explorer.Repo
-  alias Explorer.Transaction
+  alias Explorer.{Chain, Ethereum, EthereumexExtensions, Repo}
+  alias Explorer.Chain.{InternalTransaction, Transaction}
 
   @dialyzer {:nowarn_function, import: 1}
   def import(hash) do
@@ -77,6 +73,8 @@ defmodule Explorer.InternalTransactionImporter do
   end
 
   defp address_id(hash) do
-    Address.find_or_create_by_hash(hash).id
+    {:ok, address} = Chain.ensure_hash_address(hash)
+
+    address.id
   end
 end

apps/explorer/lib/explorer/importers/receipt_importer.ex

@@ -4,10 +4,8 @@ defmodule Explorer.ReceiptImporter do
   import Ecto.Query
   import Ethereumex.HttpClient, only: [eth_get_transaction_receipt: 1]
 
-  alias Explorer.Address.Service, as: Address
-  alias Explorer.Repo
-  alias Explorer.Transaction
-  alias Explorer.Receipt
+  alias Explorer.{Chain, Repo}
+  alias Explorer.Chain.{Receipt, Transaction}
 
   def import(hash) do
     transaction = hash |> find_transaction()
@@ -59,7 +57,7 @@ defmodule Explorer.ReceiptImporter do
   end
 
   defp extract_log(log) do
-    address = Address.find_or_create_by_hash(log["address"])
+    {:ok, address} = Chain.ensure_hash_address(log["address"])
 
     %{
       address_id: address.id,

apps/explorer/lib/explorer/importers/transaction_importer.ex

@@ -4,13 +4,8 @@ defmodule Explorer.TransactionImporter do
   import Ecto.Query
   import Ethereumex.HttpClient, only: [eth_get_transaction_by_hash: 1]
 
-  alias Explorer.Address.Service, as: Address
-  alias Explorer.Block
-  alias Explorer.BlockTransaction
-  alias Explorer.Ethereum
-  alias Explorer.Repo
-  alias Explorer.Transaction
-  alias Explorer.BalanceImporter
+  alias Explorer.{Chain, Ethereum, Repo, BalanceImporter}
+  alias Explorer.Chain.{Block, BlockTransaction, Transaction}
 
   def import(hash) when is_binary(hash) do
     hash |> download_transaction() |> persist_transaction()
@@ -126,7 +121,9 @@ defmodule Explorer.TransactionImporter do
   def from_address(hash) when is_bitstring(hash), do: hash
 
   def fetch_address(hash) when is_bitstring(hash) do
-    Address.find_or_create_by_hash(hash)
+    {:ok, address} = Chain.ensure_hash_address(hash)
+
+    address
   end
 
   defp refresh_account_balances(raw_transaction) do

apps/explorer/lib/explorer/resource.ex

@@ -1,56 +0,0 @@
-defmodule Explorer.Resource do
-  @moduledoc "Looks up and fetches resource based on its handle (either an id or hash)"
-
-  import Ecto.Query, only: [from: 2]
-
-  alias Explorer.Block
-  alias Explorer.Address
-  alias Explorer.Repo.NewRelic, as: Repo
-  alias Explorer.Transaction
-
-  def lookup(hash) when byte_size(hash) > 42, do: fetch_transaction(hash)
-
-  def lookup(hash) when byte_size(hash) == 42, do: fetch_address(hash)
-
-  def lookup(number), do: fetch_block(number)
-
-  def fetch_address(hash) do
-    query =
-      from(
-        address in Address,
-        where: fragment("lower(?)", address.hash) == ^String.downcase(hash),
-        limit: 1
-      )
-
-    Repo.one(query)
-  end
-
-  def fetch_transaction(hash) do
-    query =
-      from(
-        transaction in Transaction,
-        where: fragment("lower(?)", transaction.hash) == ^String.downcase(hash),
-        limit: 1
-      )
-
-    Repo.one(query)
-  end
-
-  def fetch_block(block_number) when is_bitstring(block_number) do
-    case Integer.parse(block_number) do
-      {number, ""} -> fetch_block(number)
-      _ -> nil
-    end
-  end
-
-  def fetch_block(number) when is_integer(number) do
-    query =
-      from(
-        b in Block,
-        where: b.number == ^number,
-        limit: 1
-      )
-
-    Repo.one(query)
-  end
-end

apps/explorer/lib/explorer/schema.ex

@@ -5,8 +5,7 @@ defmodule Explorer.Schema do
     quote do
       use Ecto.Schema
 
-      import Ecto.Changeset
-      import Ecto.Query
+      import Ecto.{Changeset, Query}
 
       @timestamps_opts [
         type: Timex.Ecto.DateTime,

apps/explorer/lib/explorer/schemas/address.ex

@@ -1,43 +0,0 @@
-defmodule Explorer.Address do
-  @moduledoc """
-    A stored representation of a web3 address.
-  """
-
-  use Explorer.Schema
-
-  alias Explorer.Address
-  alias Explorer.Credit
-  alias Explorer.Debit
-
-  schema "addresses" do
-    has_one(:credit, Credit)
-    has_one(:debit, Debit)
-    field(:hash, :string)
-    field(:balance, :decimal)
-    field(:balance_updated_at, Timex.Ecto.DateTime)
-    timestamps()
-  end
-
-  @required_attrs ~w(hash)a
-  @optional_attrs ~w()a
-
-  def changeset(%Address{} = address, attrs) do
-    address
-    |> cast(attrs, @required_attrs, @optional_attrs)
-    |> validate_required(@required_attrs)
-    |> update_change(:hash, &String.downcase/1)
-    |> unique_constraint(:hash)
-  end
-
-  def balance_changeset(%Address{} = address, attrs) do
-    address
-    |> cast(attrs, [:balance])
-    |> validate_required([:balance])
-    |> put_balance_updated_at()
-  end
-
-  defp put_balance_updated_at(changeset) do
-    changeset
-    |> put_change(:balance_updated_at, Timex.now())
-  end
-end

apps/explorer/lib/explorer/schemas/block.ex

@@ -1,48 +0,0 @@
-defmodule Explorer.Block do
-  @moduledoc """
-    Stores a web3 block.
-  """
-
-  use Explorer.Schema
-
-  alias Explorer.Block
-  alias Explorer.BlockTransaction
-  alias Explorer.Transaction
-
-  schema "blocks" do
-    has_many(:block_transactions, BlockTransaction)
-    many_to_many(:transactions, Transaction, join_through: "block_transactions")
-
-    field(:number, :integer)
-    field(:hash, :string)
-    field(:parent_hash, :string)
-    field(:nonce, :string)
-    field(:miner, :string)
-    field(:difficulty, :decimal)
-    field(:total_difficulty, :decimal)
-    field(:size, :integer)
-    field(:gas_limit, :integer)
-    field(:gas_used, :integer)
-    field(:timestamp, Timex.Ecto.DateTime)
-    timestamps()
-  end
-
-  @required_attrs ~w(number hash parent_hash nonce miner difficulty
-                     total_difficulty size gas_limit gas_used timestamp)a
-
-  @doc false
-  def changeset(%Block{} = block, attrs) do
-    block
-    |> cast(attrs, @required_attrs)
-    |> validate_required(@required_attrs)
-    |> update_change(:hash, &String.downcase/1)
-    |> unique_constraint(:hash)
-    |> cast_assoc(:transactions)
-  end
-
-  def null, do: %Block{number: -1, timestamp: :calendar.universal_time()}
-
-  def latest(query) do
-    query |> order_by(desc: :number)
-  end
-end

apps/explorer/lib/explorer/servers/chain_statistics.ex

@@ -1,48 +0,0 @@
-defmodule Explorer.Servers.ChainStatistics do
-  @moduledoc "Stores the latest chain statistics."
-
-  use GenServer
-
-  alias Explorer.Chain
-
-  @interval 1_000
-
-  def fetch do
-    case GenServer.whereis(__MODULE__) do
-      nil -> Chain.fetch()
-      _ -> GenServer.call(__MODULE__, :fetch)
-    end
-  end
-
-  def start_link, do: start_link(true)
-
-  def start_link(refresh) do
-    GenServer.start_link(__MODULE__, refresh, name: __MODULE__)
-  end
-
-  def init(true) do
-    {:noreply, chain} = handle_cast({:update, Chain.fetch()}, %Chain{})
-    {:ok, chain}
-  end
-
-  def init(false), do: {:ok, Chain.fetch()}
-
-  def handle_info(:refresh, %Chain{} = chain) do
-    Task.start_link(fn ->
-      GenServer.cast(__MODULE__, {:update, Chain.fetch()})
-    end)
-
-    {:noreply, chain}
-  end
-
-  def handle_info(_, %Chain{} = chain), do: {:noreply, chain}
-  def handle_call(:fetch, _, %Chain{} = chain), do: {:reply, chain, chain}
-  def handle_call(_, _, %Chain{} = chain), do: {:noreply, chain}
-
-  def handle_cast({:update, %Chain{} = chain}, %Chain{} = _) do
-    Process.send_after(self(), :refresh, @interval)
-    {:noreply, chain}
-  end
-
-  def handle_cast(_, %Chain{} = chain), do: {:noreply, chain}
-end

apps/explorer/lib/explorer/services/address.ex

@@ -1,58 +0,0 @@
-defmodule Explorer.Address.Service do
-  @moduledoc "Service module for interacting with Addresses"
-
-  alias Explorer.Address
-  alias Explorer.Repo.NewRelic, as: Repo
-  alias Explorer.Address.Service.Query
-
-  def by_hash(hash) do
-    Address
-    |> Query.by_hash(hash)
-    |> Query.include_credit_and_debit()
-    |> Repo.one()
-  end
-
-  def update_balance(balance, hash) do
-    changes = %{
-      balance: balance
-    }
-
-    hash
-    |> find_or_create_by_hash()
-    |> Address.balance_changeset(changes)
-    |> Repo.update()
-  end
-
-  def find_or_create_by_hash(hash) do
-    Address
-    |> Query.by_hash(hash)
-    |> Repo.one()
-    |> case do
-      nil -> Repo.insert!(Address.changeset(%Address{}, %{hash: hash}))
-      address -> address
-    end
-  end
-
-  defmodule Query do
-    @moduledoc "Query module for pulling in aspects of Addresses."
-
-    import Ecto.Query, only: [from: 2]
-
-    def by_hash(query, hash) do
-      from(
-        q in query,
-        where: fragment("lower(?)", q.hash) == ^String.downcase(hash),
-        limit: 1
-      )
-    end
-
-    def include_credit_and_debit(query) do
-      from(
-        q in query,
-        left_join: credit in assoc(q, :credit),
-        left_join: debit in assoc(q, :debit),
-        preload: [:credit, :debit]
-      )
-    end
-  end
-end

apps/explorer/lib/explorer/services/transaction.ex

@@ -1,118 +0,0 @@
-defmodule Explorer.Transaction.Service do
-  @moduledoc "Service module for interacting with Transactions"
-
-  alias Explorer.InternalTransaction
-  alias Explorer.Repo.NewRelic, as: Repo
-  alias Explorer.Transaction.Service.Query
-
-  def internal_transactions(hash) do
-    InternalTransaction
-    |> Query.for_parent_transaction(hash)
-    |> Query.join_from_and_to_addresses()
-    |> Repo.all()
-  end
-
-  defmodule Query do
-    @moduledoc "Helper module to hold Transaction-related query fragments"
-
-    import Ecto.Query, only: [from: 2]
-
-    def to_address(query, to_address_id) do
-      from(q in query, where: q.to_address_id == ^to_address_id)
-    end
-
-    def from_address(query, from_address_id) do
-      from(q in query, where: q.from_address_id == ^from_address_id)
-    end
-
-    def recently_seen(query, last_seen) do
-      from(
-        q in query,
-        where: q.id < ^last_seen,
-        order_by: [desc: q.id],
-        limit: 10
-      )
-    end
-
-    def by_hash(query, hash) do
-      from(
-        q in query,
-        where: fragment("lower(?)", q.hash) == ^String.downcase(hash),
-        limit: 1
-      )
-    end
-
-    def include_addresses(query) do
-      from(
-        q in query,
-        inner_join: to_address in assoc(q, :to_address),
-        inner_join: from_address in assoc(q, :from_address),
-        preload: [
-          to_address: to_address,
-          from_address: from_address
-        ]
-      )
-    end
-
-    def include_receipt(query) do
-      from(
-        q in query,
-        left_join: receipt in assoc(q, :receipt),
-        preload: [
-          receipt: receipt
-        ]
-      )
-    end
-
-    def include_block(query) do
-      from(
-        q in query,
-        left_join: block in assoc(q, :block),
-        preload: [
-          block: block
-        ]
-      )
-    end
-
-    def require_receipt(query) do
-      from(
-        q in query,
-        inner_join: receipt in assoc(q, :receipt),
-        preload: [
-          receipt: receipt
-        ]
-      )
-    end
-
-    def require_block(query) do
-      from(
-        q in query,
-        inner_join: block in assoc(q, :block),
-        preload: [
-          block: block
-        ]
-      )
-    end
-
-    def for_parent_transaction(query, hash) do
-      from(
-        child in query,
-        inner_join: transaction in assoc(child, :transaction),
-        where: fragment("lower(?)", transaction.hash) == ^String.downcase(hash)
-      )
-    end
-
-    def join_from_and_to_addresses(query) do
-      from(
-        q in query,
-        inner_join: to_address in assoc(q, :to_address),
-        inner_join: from_address in assoc(q, :from_address),
-        preload: [:to_address, :from_address]
-      )
-    end
-
-    def chron(query) do
-      from(q in query, order_by: [desc: q.inserted_at])
-    end
-  end
-end

apps/explorer/lib/explorer/skipped_balances.ex

@@ -1,8 +1,8 @@
 defmodule Explorer.SkippedBalances do
   @moduledoc "Gets a list of Addresses that do not have balances."
 
-  alias Explorer.Address
-  alias Explorer.Repo
+  alias Explorer.Chain.Address
+  alias Explorer.Repo.NewRelic, as: Repo
 
   import Ecto.Query, only: [from: 2]
 

apps/explorer/lib/explorer/skipped_blocks.ex

@@ -3,7 +3,8 @@ defmodule Explorer.SkippedBlocks do
     Fill in older blocks that were skipped during processing.
   """
   import Ecto.Query, only: [from: 2, limit: 2]
-  alias Explorer.Block
+
+  alias Explorer.Chain.Block
   alias Explorer.Repo.NewRelic, as: Repo
 
   @missing_number_query "SELECT generate_series(?, 0, -1) AS missing_number"

apps/explorer/lib/explorer/skipped_internal_transactions.ex

@@ -4,7 +4,7 @@ defmodule Explorer.SkippedInternalTransactions do
   """
   import Ecto.Query, only: [from: 2]
 
-  alias Explorer.Transaction
+  alias Explorer.Chain.Transaction
   alias Explorer.Repo.NewRelic, as: Repo
 
   def first, do: first(1)

apps/explorer/lib/explorer/skipped_receipts.ex

@@ -4,7 +4,7 @@ defmodule Explorer.SkippedReceipts do
   """
   import Ecto.Query, only: [from: 2]
 
-  alias Explorer.Transaction
+  alias Explorer.Chain.Transaction
   alias Explorer.Repo.NewRelic, as: Repo
 
   def first, do: first(1)

apps/explorer/lib/explorer/workers/import_transaction.ex

@@ -4,8 +4,7 @@ defmodule Explorer.Workers.ImportTransaction do
   """
 
   alias Explorer.TransactionImporter
-  alias Explorer.Workers.ImportReceipt
-  alias Explorer.Workers.ImportInternalTransaction
+  alias Explorer.Workers.{ImportInternalTransaction, ImportReceipt}
 
   @dialyzer {:nowarn_function, perform: 1}
   def perform(hash) when is_binary(hash) do

apps/explorer/lib/explorer/workers/refresh_balance.ex

@@ -4,8 +4,7 @@ defmodule Explorer.Workers.RefreshBalance do
   """
 
   alias Ecto.Adapters.SQL
-  alias Explorer.Credit
-  alias Explorer.Debit
+  alias Explorer.Chain.{Credit, Debit}
   alias Explorer.Repo
 
   def perform("credit"), do: unless(refreshing("credits"), do: Credit.refresh())

apps/explorer/lib/mix/tasks/exq.start.ex

@@ -1,8 +1,8 @@
 defmodule Mix.Tasks.Exq.Start do
   @moduledoc "Starts the Exq worker"
   use Mix.Task
-  alias Explorer.Repo
-  alias Explorer.Scheduler
+
+  alias Explorer.{Repo, Scheduler}
 
   def run(["scheduler"]) do
     [:postgrex, :ecto, :ethereumex, :tzdata]

apps/explorer/lib/mix/tasks/scrape.balances.ex

@@ -3,9 +3,7 @@ defmodule Mix.Tasks.Scrape.Balances do
 
   use Mix.Task
 
-  alias Explorer.Repo
-  alias Explorer.SkippedBalances
-  alias Explorer.BalanceImporter
+  alias Explorer.{BalanceImporter, Repo, SkippedBalances}
 
   def run([]), do: run(1)
 

apps/explorer/lib/mix/tasks/scrape.blocks.ex

@@ -1,9 +1,9 @@
 defmodule Mix.Tasks.Scrape.Blocks do
   @moduledoc "Scrapes blocks from web3"
+
   use Mix.Task
-  alias Explorer.Repo
-  alias Explorer.SkippedBlocks
-  alias Explorer.BlockImporter
+
+  alias Explorer.{BlockImporter, Repo, SkippedBlocks}
 
   def run([]), do: run(1)
 

apps/explorer/lib/mix/tasks/scrape.internal_transactions.ex

@@ -1,10 +1,9 @@
 defmodule Mix.Tasks.Scrape.InternalTransactions do
   @moduledoc "Backfill Internal Transactions via Parity Trace."
+
   use Mix.Task
 
-  alias Explorer.Repo
-  alias Explorer.SkippedInternalTransactions
-  alias Explorer.InternalTransactionImporter
+  alias Explorer.{InternalTransactionImporter, Repo, SkippedInternalTransactions}
 
   def run([]), do: run(1)
 

apps/explorer/lib/mix/tasks/scrape.receipts.ex

@@ -1,10 +1,9 @@
 defmodule Mix.Tasks.Scrape.Receipts do
   @moduledoc "Scrapes blocks from web3"
+
   use Mix.Task
 
-  alias Explorer.Repo
-  alias Explorer.SkippedReceipts
-  alias Explorer.ReceiptImporter
+  alias Explorer.{ReceiptImporter, Repo, SkippedReceipts}
 
   def run([]), do: run(1)
 

apps/explorer/mix.exs

@@ -71,7 +71,7 @@ defmodule Explorer.Mixfile do
   defp deps do
     [
       {:bypass, "~> 0.8", only: :test},
-      {:credo, "~> 0.8", only: [:dev, :test], runtime: false},
+      {:credo, "0.9.1", only: [:dev, :test], runtime: false},
       {:crontab, "~> 1.1"},
       {:dialyxir, "~> 0.5", only: [:dev, :test], runtime: false},
       {:ethereumex, "~> 0.3"},
@@ -107,6 +107,7 @@ defmodule Explorer.Mixfile do
   # See the documentation for `Mix` for more info on aliases.
   defp aliases do
     [
+      compile: "compile --warnings-as-errors",
       "ecto.setup": ["ecto.create", "ecto.migrate", "run priv/repo/seeds.exs"],
       "ecto.reset": ["ecto.drop", "ecto.setup"],
       test: ["ecto.create --quiet", "ecto.migrate", "test"]

apps/explorer/test/explorer/chain/address_test.exs

@@ -1,6 +1,7 @@
-defmodule Explorer.AddressTest do
+defmodule Explorer.Chain.AddressTest do
   use Explorer.DataCase
-  alias Explorer.Address
+
+  alias Explorer.Chain.Address
 
   describe "changeset/2" do
     test "with valid attributes" do

apps/explorer/test/explorer/chain/block_test.exs

@@ -1,9 +1,10 @@
-defmodule Explorer.BlockTest do
+defmodule Explorer.Chain.BlockTest do
   use Explorer.DataCase
 
-  alias Explorer.Block
   import Ecto.Query, only: [order_by: 2]
 
+  alias Explorer.Chain.Block
+
   describe "changeset/2" do
     test "with valid attributes" do
       changeset = build(:block) |> Block.changeset(%{})

apps/explorer/test/explorer/chain/block_transaction_test.exs

@@ -1,6 +1,7 @@
-defmodule Explorer.BlockTransactionTest do
+defmodule Explorer.Chain.BlockTransactionTest do
   use Explorer.DataCase
-  alias Explorer.BlockTransaction
+
+  alias Explorer.Chain.BlockTransaction
 
   describe "changeset/2" do
     test "with empty attributes" do

apps/explorer/test/explorer/chain/credit_test.exs

@@ -1,7 +1,7 @@
-defmodule Explorer.CreditTest do
+defmodule Explorer.Chain.CreditTest do
   use Explorer.DataCase
 
-  alias Explorer.Credit
+  alias Explorer.Chain.Credit
 
   describe "Repo.all/1" do
     test "returns no rows when there are no addresses" do

apps/explorer/test/explorer/chain/debit_test.exs

@@ -1,7 +1,7 @@
-defmodule Explorer.DebitTest do
+defmodule Explorer.Chain.DebitTest do
   use Explorer.DataCase
 
-  alias Explorer.Debit
+  alias Explorer.Chain.Debit
 
   describe "Repo.all/1" do
     test "returns no rows when there are no addresses" do

apps/explorer/test/explorer/chain/from_address_test.exs

@@ -1,6 +1,7 @@
-defmodule Explorer.FromAddressTest do
+defmodule Explorer.Chain.FromAddressTest do
   use Explorer.DataCase
-  alias Explorer.FromAddress
+
+  alias Explorer.Chain.FromAddress
 
   describe "changeset/2" do
     test "with valid attributes" do

apps/explorer/test/explorer/chain/internal_transaction_test.exs

@@ -1,7 +1,7 @@
-defmodule Explorer.InternalTransactionTest do
+defmodule Explorer.Chain.InternalTransactionTest do
   use Explorer.DataCase
 
-  alias Explorer.InternalTransaction
+  alias Explorer.Chain.InternalTransaction
 
   describe "changeset/2" do
     test "with valid attributes" do

apps/explorer/test/explorer/chain/log_test.exs

@@ -1,7 +1,7 @@
-defmodule Explorer.LogTest do
+defmodule Explorer.Chain.LogTest do
   use Explorer.DataCase
 
-  alias Explorer.Log
+  alias Explorer.Chain.Log
 
   describe "changeset/2" do
     test "accepts valid attributes" do

apps/explorer/test/explorer/chain/receipt_test.exs

@@ -1,7 +1,7 @@
-defmodule Explorer.ReceiptTest do
+defmodule Explorer.Chain.ReceiptTest do
   use Explorer.DataCase
 
-  alias Explorer.Receipt
+  alias Explorer.Chain.Receipt
 
   describe "changeset/2" do
     test "accepts valid attributes" do

apps/explorer/test/explorer/chain/statistics/server_test.exs

@@ -0,0 +1,89 @@
+defmodule Explorer.Chain.Statistics.ServerTest do
+  use Explorer.DataCase
+
+  alias Explorer.Chain.Statistics
+  alias Explorer.Chain.Statistics.Server
+
+  describe "init/1" do
+    test "returns a new chain when not told to refresh" do
+      {:ok, statistics} = Server.init(false)
+
+      assert statistics.number == Statistics.fetch().number
+    end
+
+    test "returns a new chain when told to refresh" do
+      {:ok, statistics} = Server.init(true)
+
+      assert statistics == Statistics.fetch()
+    end
+
+    test "refreshes when told to refresh" do
+      {:ok, _} = Server.init(true)
+
+      assert_receive :refresh, 2_000
+    end
+  end
+
+  describe "fetch/0" do
+    test "fetches the chain when not started" do
+      original = Statistics.fetch()
+
+      assert Server.fetch() == original
+    end
+  end
+
+  describe "handle_info/2" do
+    test "returns the original chain when sent a :refresh message" do
+      original = Statistics.fetch()
+
+      assert {:noreply, ^original} = Server.handle_info(:refresh, original)
+    end
+
+    test "launches an update when sent a :refresh message" do
+      original = Statistics.fetch()
+      {:ok, pid} = Server.start_link()
+      chain = Server.fetch()
+      :ok = GenServer.stop(pid)
+
+      assert original.number == chain.number
+    end
+
+    test "does not reply when sent any other message" do
+      assert {:noreply, _} = Server.handle_info(:ham, %Statistics{})
+    end
+  end
+
+  describe "handle_call/3" do
+    test "replies with statistics when sent a :fetch message" do
+      original = Statistics.fetch()
+
+      assert {:reply, _, ^original} = Server.handle_call(:fetch, self(), original)
+    end
+
+    test "does not reply when sent any other message" do
+      assert {:noreply, _} = Server.handle_call(:ham, self(), %Statistics{})
+    end
+  end
+
+  describe "handle_cast/2" do
+    test "schedules a refresh of the statistics when sent an update" do
+      statistics = Statistics.fetch()
+
+      Server.handle_cast({:update, statistics}, %Statistics{})
+
+      assert_receive :refresh, 2_000
+    end
+
+    test "returns a noreply and the new incoming chain when sent an update" do
+      original = Statistics.fetch()
+
+      assert {:noreply, ^original} = Server.handle_cast({:update, original}, %Statistics{})
+    end
+
+    test "returns a noreply and the old chain when sent any other cast" do
+      original = Statistics.fetch()
+
+      assert {:noreply, ^original} = Server.handle_cast(:ham, original)
+    end
+  end
+end

apps/explorer/test/explorer/chain/statistics_test.exs

@@ -0,0 +1,116 @@
+defmodule Explorer.Chain.StatisticsTest do
+  use Explorer.DataCase
+
+  alias Explorer.Chain.Statistics
+  alias Timex.Duration
+
+  describe "fetch/0" do
+    test "returns -1 for the number when there are no blocks" do
+      assert %Statistics{number: -1} = Statistics.fetch()
+    end
+
+    test "returns the highest block number when there is a block" do
+      insert(:block, number: 1)
+
+      max_number = 100
+      insert(:block, number: max_number)
+
+      assert %Statistics{number: ^max_number} = Statistics.fetch()
+    end
+
+    test "returns the latest block timestamp" do
+      time = DateTime.utc_now()
+      insert(:block, timestamp: time)
+
+      statistics = Statistics.fetch()
+
+      assert Timex.diff(statistics.timestamp, time, :seconds) == 0
+    end
+
+    test "returns the average time between blocks" do
+      time = DateTime.utc_now()
+      next_time = Timex.shift(time, seconds: 5)
+      insert(:block, timestamp: time)
+      insert(:block, timestamp: next_time)
+
+      assert %Statistics{
+               average_time: %Duration{
+                 seconds: 5,
+                 megaseconds: 0,
+                 microseconds: 0
+               }
+             } = Statistics.fetch()
+    end
+
+    test "returns the count of transactions from blocks in the last day" do
+      time = DateTime.utc_now()
+      last_week = Timex.shift(time, days: -8)
+      block = insert(:block, timestamp: time)
+      old_block = insert(:block, timestamp: last_week)
+      transaction = insert(:transaction)
+      old_transaction = insert(:transaction)
+      insert(:block_transaction, block: block, transaction: transaction)
+      insert(:block_transaction, block: old_block, transaction: old_transaction)
+
+      assert %Statistics{transaction_count: 1} = Statistics.fetch()
+    end
+
+    test "returns the number of skipped blocks" do
+      insert(:block, %{number: 0})
+      insert(:block, %{number: 2})
+
+      statistics = Statistics.fetch()
+
+      assert statistics.skipped_blocks == 1
+    end
+
+    test "returns the lag between validation and insertion time" do
+      validation_time = DateTime.utc_now()
+      inserted_at = validation_time |> Timex.shift(seconds: 5)
+      insert(:block, timestamp: validation_time, inserted_at: inserted_at)
+
+      assert %Statistics{lag: %Duration{seconds: 5, megaseconds: 0, microseconds: 0}} =
+               Statistics.fetch()
+    end
+
+    test "returns the number of blocks inserted in the last minute" do
+      old_inserted_at = Timex.shift(DateTime.utc_now(), days: -1)
+      insert(:block, inserted_at: old_inserted_at)
+      insert(:block)
+
+      statistics = Statistics.fetch()
+
+      assert statistics.block_velocity == 1
+    end
+
+    test "returns the number of transactions inserted in the last minute" do
+      old_inserted_at = Timex.shift(DateTime.utc_now(), days: -1)
+      insert(:transaction, inserted_at: old_inserted_at)
+      insert(:transaction)
+
+      assert %Statistics{transaction_velocity: 1} = Statistics.fetch()
+    end
+
+    test "returns the last five blocks" do
+      insert_list(6, :block)
+
+      statistics = Statistics.fetch()
+
+      assert statistics.blocks |> Enum.count() == 5
+    end
+
+    test "returns the last five transactions with blocks" do
+      block = insert(:block)
+
+      6
+      |> insert_list(:transaction)
+      |> Enum.map(fn transaction ->
+        insert(:block_transaction, block: block, transaction: transaction)
+      end)
+
+      statistics = Statistics.fetch()
+
+      assert statistics.transactions |> Enum.count() == 5
+    end
+  end
+end

apps/explorer/test/explorer/chain/to_address_test.exs

@@ -1,6 +1,7 @@
-defmodule Explorer.ToAddressTest do
+defmodule Explorer.Chain.ToAddressTest do
   use Explorer.DataCase
-  alias Explorer.ToAddress
+
+  alias Explorer.Chain.ToAddress
 
   describe "changeset/2" do
     test "with valid attributes" do

apps/explorer/test/explorer/chain/transaction_test.exs

@@ -1,7 +1,7 @@
-defmodule Explorer.TransactionTest do
+defmodule Explorer.Chain.TransactionTest do
   use Explorer.DataCase
 
-  alias Explorer.Transaction
+  alias Explorer.Chain.Transaction
 
   describe "changeset/2" do
     test "with valid attributes" do

apps/explorer/test/explorer/chain_test.exs

@@ -1,103 +1,757 @@
 defmodule Explorer.ChainTest do
   use Explorer.DataCase
 
-  alias Explorer.Chain
-  alias Timex.Duration
+  alias Explorer.{Chain, Repo}
 
-  describe "fetch/0" do
-    test "returns -1 for the number when there are no blocks" do
-      chain = Chain.fetch()
-      assert chain.number == -1
+  alias Explorer.Chain.{Address, Block, InternalTransaction, Log, Receipt, Transaction}
+
+  # Constants
+
+  @invalid_attrs %{hash: nil}
+  @valid_attrs %{hash: "some hash"}
+
+  # Tests
+
+  describe "block_to_transactions/1" do
+    test "without transactions" do
+      block = insert(:block)
+
+      assert Repo.aggregate(Transaction, :count, :id) == 0
+
+      assert %Scrivener.Page{
+               entries: [],
+               page_number: 1,
+               total_entries: 0
+             } = Chain.block_to_transactions(block)
+    end
+
+    test "with transactions" do
+      block = %Block{id: block_id} = insert(:block)
+      %Transaction{id: transaction_id} = insert(:transaction)
+      insert(:block_transaction, block_id: block_id, transaction_id: transaction_id)
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^transaction_id}],
+               page_number: 1,
+               total_entries: 1
+             } = Chain.block_to_transactions(block)
+    end
+
+    test "with transaction with receipt required without receipt does not return transaction" do
+      block = %Block{id: block_id} = insert(:block)
+
+      %Transaction{id: transaction_id_with_receipt} = insert(:transaction)
+      insert(:receipt, transaction_id: transaction_id_with_receipt)
+      insert(:block_transaction, block_id: block_id, transaction_id: transaction_id_with_receipt)
+
+      %Transaction{id: transaction_id_without_receipt} = insert(:transaction)
+
+      insert(
+        :block_transaction,
+        block_id: block_id,
+        transaction_id: transaction_id_without_receipt
+      )
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^transaction_id_with_receipt, receipt: %Receipt{}}],
+               page_number: 1,
+               total_entries: 1
+             } =
+               Chain.block_to_transactions(
+                 block,
+                 necessity_by_association: %{receipt: :required}
+               )
+
+      assert %Scrivener.Page{
+               entries: transactions,
+               page_number: 1,
+               total_entries: 2
+             } =
+               Chain.block_to_transactions(
+                 block,
+                 necessity_by_association: %{receipt: :optional}
+               )
+
+      assert length(transactions) == 2
+
+      transaction_by_id =
+        Enum.into(transactions, %{}, fn transaction = %Transaction{id: id} ->
+          {id, transaction}
+        end)
+
+      assert %Transaction{receipt: %Receipt{}} = transaction_by_id[transaction_id_with_receipt]
+      assert %Transaction{receipt: nil} = transaction_by_id[transaction_id_without_receipt]
+    end
+
+    test "with transactions can be paginated" do
+      block = %Block{id: block_id} = insert(:block)
+
+      transactions = insert_list(2, :transaction)
+
+      Enum.each(transactions, fn %Transaction{id: transaction_id} ->
+        insert(:block_transaction, block_id: block_id, transaction_id: transaction_id)
+      end)
+
+      [%Transaction{id: first_transaction_id}, %Transaction{id: second_transaction_id}] =
+        transactions
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^first_transaction_id}],
+               page_number: 1,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } = Chain.block_to_transactions(block, pagination: %{page_size: 1})
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^second_transaction_id}],
+               page_number: 2,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } = Chain.block_to_transactions(block, pagination: %{page: 2, page_size: 1})
+    end
+  end
+
+  describe "block_to_transaction_bound/1" do
+    test "without transactions" do
+      block = insert(:block)
+
+      assert Chain.block_to_transaction_count(block) == 0
+    end
+
+    test "with transactions" do
+      block = insert(:block)
+      %Transaction{id: transaction_id} = insert(:transaction)
+      insert(:block_transaction, block_id: block.id, transaction_id: transaction_id)
+
+      assert Chain.block_to_transaction_count(block) == 1
+    end
+  end
+
+  describe "confirmations/1" do
+    test "with block.number == max_block_number " do
+      block = insert(:block)
+      max_block_number = Chain.max_block_number()
+
+      assert block.number == max_block_number
+      assert Chain.confirmations(block, max_block_number: max_block_number) == 0
+    end
+
+    test "with block.number < max_block_number" do
+      block = insert(:block)
+      max_block_number = block.number + 2
+
+      assert block.number < max_block_number
+
+      assert Chain.confirmations(block, max_block_number: max_block_number) ==
+               max_block_number - block.number
+    end
+  end
+
+  describe "create_address/1" do
+    test "with valid data creates a address" do
+      assert {:ok, %Address{} = address} = Chain.create_address(@valid_attrs)
+      assert address.hash == "some hash"
+    end
+
+    test "with invalid data returns error changeset" do
+      assert {:error, %Ecto.Changeset{}} = Chain.create_address(@invalid_attrs)
+    end
+  end
+
+  describe "ensure_hash_address/1" do
+    test "creates a new address when one does not exist" do
+      Chain.ensure_hash_address("0xFreshPrince")
+
+      assert {:ok, _} = Chain.hash_to_address("0xfreshprince")
+    end
+
+    test "when the address already exists doesn't insert a new address" do
+      insert(:address, %{hash: "bigmouthbillybass"})
+
+      before = Repo.aggregate(Address, :count, :id)
+
+      assert {:ok, _} = Chain.ensure_hash_address("bigmouthbillybass")
+
+      assert Repo.aggregate(Address, :count, :id) == before
+    end
+
+    test "when there is no hash it blows up" do
+      assert {:error, :not_found} = Chain.ensure_hash_address("")
+    end
+  end
+
+  describe "from_address_to_transactions/2" do
+    test "without transactions" do
+      address = insert(:address)
+
+      assert Repo.aggregate(Transaction, :count, :id) == 0
+
+      assert %Scrivener.Page{
+               entries: [],
+               page_number: 1,
+               total_entries: 0
+             } = Chain.from_address_to_transactions(address)
+    end
+
+    test "with transactions" do
+      %Transaction{from_address_id: from_address_id, id: transaction_id} = insert(:transaction)
+      address = Repo.get!(Address, from_address_id)
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^transaction_id}],
+               page_number: 1,
+               total_entries: 1
+             } = Chain.from_address_to_transactions(address)
+    end
+
+    test "with transactions with receipt required without receipt does not return transaction" do
+      address = %Address{id: from_address_id} = insert(:address)
+
+      %Transaction{id: transaction_id_with_receipt} =
+        insert(:transaction, from_address_id: from_address_id)
+
+      insert(:receipt, transaction_id: transaction_id_with_receipt)
+
+      %Transaction{id: transaction_id_without_receipt} =
+        insert(:transaction, from_address_id: from_address_id)
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^transaction_id_with_receipt, receipt: %Receipt{}}],
+               page_number: 1,
+               total_entries: 1
+             } =
+               Chain.from_address_to_transactions(
+                 address,
+                 necessity_by_association: %{receipt: :required}
+               )
+
+      assert %Scrivener.Page{
+               entries: transactions,
+               page_number: 1,
+               total_entries: 2
+             } =
+               Chain.from_address_to_transactions(
+                 address,
+                 necessity_by_association: %{receipt: :optional}
+               )
+
+      assert length(transactions) == 2
+
+      transaction_by_id =
+        Enum.into(transactions, %{}, fn transaction = %Transaction{id: id} ->
+          {id, transaction}
+        end)
+
+      assert %Transaction{receipt: %Receipt{}} = transaction_by_id[transaction_id_with_receipt]
+      assert %Transaction{receipt: nil} = transaction_by_id[transaction_id_without_receipt]
+    end
+
+    test "with transactions can be paginated" do
+      adddress = %Address{id: from_address_id} = insert(:address)
+      transactions = insert_list(2, :transaction, from_address_id: from_address_id)
+
+      [%Transaction{id: oldest_transaction_id}, %Transaction{id: newest_transaction_id}] =
+        transactions
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^newest_transaction_id}],
+               page_number: 1,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } = Chain.from_address_to_transactions(adddress, pagination: %{page_size: 1})
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^oldest_transaction_id}],
+               page_number: 2,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } =
+               Chain.from_address_to_transactions(adddress, pagination: %{page: 2, page_size: 1})
+    end
+  end
+
+  describe "hash_to_address/1" do
+    test "without address returns {:error, :not_found}" do
+      assert {:error, :not_found} = Chain.hash_to_address("unknown")
+    end
+
+    test "with address returns {:ok, address}" do
+      hash = "0xandesmints"
+      %Address{id: address_id} = insert(:address, hash: hash)
+
+      assert {:ok, %Address{id: ^address_id}} = Chain.hash_to_address(hash)
+    end
+  end
+
+  describe "hash_to_transaction/2" do
+    test "without transaction returns {:error, :not_found}" do
+      assert {:error, :not_found} = Chain.hash_to_transaction("unknown")
+    end
+
+    test "with transaction returns {:ok, transaction}" do
+      hash = "0xandesmints"
+      %Transaction{id: transaction_id} = insert(:transaction, hash: hash)
+
+      assert {:ok, %Transaction{id: ^transaction_id}} = Chain.hash_to_transaction(hash)
+    end
+
+    test "with transaction with receipt required without receipt returns {:error, :not_found}" do
+      %Transaction{hash: hash_with_receipt, id: transaction_id_with_receipt} =
+        insert(:transaction)
+
+      insert(:receipt, transaction_id: transaction_id_with_receipt)
+
+      %Transaction{hash: hash_without_receipt} = insert(:transaction)
+
+      assert {:ok, %Transaction{hash: ^hash_with_receipt}} =
+               Chain.hash_to_transaction(
+                 hash_with_receipt,
+                 necessity_by_association: %{receipt: :required}
+               )
+
+      assert {:error, :not_found} =
+               Chain.hash_to_transaction(
+                 hash_without_receipt,
+                 necessity_by_association: %{receipt: :required}
+               )
+
+      assert {:ok, %Transaction{hash: ^hash_without_receipt}} =
+               Chain.hash_to_transaction(
+                 hash_without_receipt,
+                 necessity_by_association: %{receipt: :optional}
+               )
+    end
+  end
+
+  describe "id_to_address/1" do
+    test "returns the address with given id" do
+      %Address{id: id} = insert(:address)
+
+      assert {:ok, %Address{id: ^id}} = Chain.id_to_address(id)
+    end
+  end
+
+  describe "last_transaction_id/1" do
+    test "without transactions returns 0" do
+      assert Chain.last_transaction_id() == 0
+    end
+
+    test "with transaction returns last created transaction's id" do
+      insert(:transaction)
+      %Transaction{id: id} = insert(:transaction)
+
+      assert Chain.last_transaction_id() == id
+    end
+
+    test "with transaction with pending: true returns last pending transaction id, not the last transaction" do
+      %Transaction{id: pending_transaction_id} = insert(:transaction)
+
+      %Transaction{id: transaction_id} = insert(:transaction)
+      insert(:receipt, transaction_id: transaction_id)
+
+      assert pending_transaction_id < transaction_id
+
+      assert Chain.last_transaction_id(pending: true) == pending_transaction_id
+      assert Chain.last_transaction_id(pending: false) == transaction_id
+      assert Chain.last_transaction_id() == transaction_id
     end
+  end
+
+  describe "list_blocks/2" do
+    test "without blocks" do
+      assert %Scrivener.Page{
+               entries: [],
+               page_number: 1,
+               total_entries: 0,
+               total_pages: 1
+             } = Chain.list_blocks()
+    end
+
+    test "with blocks" do
+      %Block{id: id} = insert(:block)
+
+      assert %Scrivener.Page{
+               entries: [%Block{id: ^id}],
+               page_number: 1,
+               total_entries: 1
+             } = Chain.list_blocks()
+    end
+
+    test "with blocks can be paginated" do
+      blocks = insert_list(2, :block)
+
+      [%Block{number: lesser_block_number}, %Block{number: greater_block_number}] = blocks
+
+      assert %Scrivener.Page{
+               entries: [%Block{number: ^greater_block_number}],
+               page_number: 1,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } = Chain.list_blocks(pagination: %{page_size: 1})
+
+      assert %Scrivener.Page{
+               entries: [%Block{number: ^lesser_block_number}],
+               page_number: 2,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } = Chain.list_blocks(pagination: %{page: 2, page_size: 1})
+    end
+  end
+
+  describe "max_block_number/0" do
+    test "without blocks is nil" do
+      assert Chain.max_block_number() == nil
+    end
+
+    test "with blocks is max number regardless of insertion order" do
+      max_number = 2
+      insert(:block, number: max_number)
 
-    test "returns the highest block number when there is a block" do
       insert(:block, number: 1)
-      insert(:block, number: 100)
-      chain = Chain.fetch()
-      assert chain.number == 100
+
+      assert Chain.max_block_number() == max_number
+    end
   end
 
-    test "returns the latest block timestamp" do
-      time = DateTime.utc_now()
-      insert(:block, timestamp: time)
-      chain = Chain.fetch()
-      assert Timex.diff(chain.timestamp, time, :seconds) == 0
+  describe "number_to_block/1" do
+    test "without block" do
+      assert {:error, :not_found} = Chain.number_to_block(-1)
     end
 
-    test "returns the average time between blocks" do
-      time = DateTime.utc_now()
-      next_time = Timex.shift(time, seconds: 5)
-      insert(:block, timestamp: time)
-      insert(:block, timestamp: next_time)
-      chain = Chain.fetch()
+    test "with block" do
+      %Block{number: number} = insert(:block)
 
-      assert chain.average_time == %Duration{
-               seconds: 5,
-               megaseconds: 0,
-               microseconds: 0
-             }
+      assert {:ok, %Block{number: ^number}} = Chain.number_to_block(number)
+    end
   end
 
-    test "returns the count of transactions from blocks in the last day" do
-      time = DateTime.utc_now()
-      last_week = Timex.shift(time, days: -8)
-      block = insert(:block, timestamp: time)
-      old_block = insert(:block, timestamp: last_week)
-      transaction = insert(:transaction)
-      old_transaction = insert(:transaction)
-      insert(:block_transaction, block: block, transaction: transaction)
-      insert(:block_transaction, block: old_block, transaction: old_transaction)
-      chain = Chain.fetch()
-      assert chain.transaction_count == 1
+  describe "to_address_to_transactions/2" do
+    test "without transactions" do
+      address = insert(:address)
+
+      assert Repo.aggregate(Transaction, :count, :id) == 0
+
+      assert %Scrivener.Page{
+               entries: [],
+               page_number: 1,
+               total_entries: 0
+             } = Chain.to_address_to_transactions(address)
     end
 
-    test "returns the number of skipped blocks" do
-      insert(:block, %{number: 0})
-      insert(:block, %{number: 2})
-      chain = Chain.fetch()
-      assert chain.skipped_blocks == 1
+    test "with transactions" do
+      %Transaction{to_address_id: to_address_id, id: transaction_id} = insert(:transaction)
+      address = Repo.get!(Address, to_address_id)
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^transaction_id}],
+               page_number: 1,
+               total_entries: 1
+             } = Chain.to_address_to_transactions(address)
     end
 
-    test "returns the lag between validation and insertion time" do
-      validation_time = DateTime.utc_now()
-      inserted_at = validation_time |> Timex.shift(seconds: 5)
-      insert(:block, timestamp: validation_time, inserted_at: inserted_at)
-      chain = Chain.fetch()
-      assert chain.lag == %Duration{seconds: 5, megaseconds: 0, microseconds: 0}
+    test "with transactions with receipt required without receipt does not return transaction" do
+      address = %Address{id: to_address_id} = insert(:address)
+
+      %Transaction{id: transaction_id_with_receipt} =
+        insert(:transaction, to_address_id: to_address_id)
+
+      insert(:receipt, transaction_id: transaction_id_with_receipt)
+
+      %Transaction{id: transaction_id_without_receipt} =
+        insert(:transaction, to_address_id: to_address_id)
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^transaction_id_with_receipt, receipt: %Receipt{}}],
+               page_number: 1,
+               total_entries: 1
+             } =
+               Chain.to_address_to_transactions(
+                 address,
+                 necessity_by_association: %{receipt: :required}
+               )
+
+      assert %Scrivener.Page{
+               entries: transactions,
+               page_number: 1,
+               total_entries: 2
+             } =
+               Chain.to_address_to_transactions(
+                 address,
+                 necessity_by_association: %{receipt: :optional}
+               )
+
+      assert length(transactions) == 2
+
+      transaction_by_id =
+        Enum.into(transactions, %{}, fn transaction = %Transaction{id: id} ->
+          {id, transaction}
+        end)
+
+      assert %Transaction{receipt: %Receipt{}} = transaction_by_id[transaction_id_with_receipt]
+      assert %Transaction{receipt: nil} = transaction_by_id[transaction_id_without_receipt]
     end
 
-    test "returns the number of blocks inserted in the last minute" do
-      old_inserted_at = Timex.shift(DateTime.utc_now(), days: -1)
-      insert(:block, inserted_at: old_inserted_at)
-      insert(:block)
-      chain = Chain.fetch()
-      assert chain.block_velocity == 1
+    test "with transactions can be paginated" do
+      adddress = %Address{id: to_address_id} = insert(:address)
+      transactions = insert_list(2, :transaction, to_address_id: to_address_id)
+
+      [%Transaction{id: oldest_transaction_id}, %Transaction{id: newest_transaction_id}] =
+        transactions
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^newest_transaction_id}],
+               page_number: 1,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } = Chain.to_address_to_transactions(adddress, pagination: %{page_size: 1})
+
+      assert %Scrivener.Page{
+               entries: [%Transaction{id: ^oldest_transaction_id}],
+               page_number: 2,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } = Chain.to_address_to_transactions(adddress, pagination: %{page: 2, page_size: 1})
+    end
   end
 
-    test "returns the number of transactions inserted in the last minute" do
-      old_inserted_at = Timex.shift(DateTime.utc_now(), days: -1)
-      insert(:transaction, inserted_at: old_inserted_at)
+  describe "transaction_count/0" do
+    test "without transactions" do
+      assert Chain.transaction_count() == 0
+    end
+
+    test "with transactions" do
+      count = 2
+      insert_list(count, :transaction)
+
+      assert Chain.transaction_count() == count
+    end
+
+    test "with transaction pending: true counts only pending transactions" do
       insert(:transaction)
-      chain = Chain.fetch()
-      assert chain.transaction_velocity == 1
+
+      %Transaction{id: transaction_id} = insert(:transaction)
+      insert(:receipt, transaction_id: transaction_id)
+
+      assert Chain.transaction_count(pending: true) == 1
+      assert Chain.transaction_count(pending: false) == 2
+      assert Chain.transaction_count() == 2
+    end
   end
 
-    test "returns the last five blocks" do
-      insert_list(6, :block)
-      chain = Chain.fetch()
-      assert chain.blocks |> Enum.count() == 5
+  describe "transaction_hash_to_internal_transactions/1" do
+    test "without transaction" do
+      assert Chain.transaction_hash_to_internal_transactions("unknown") == []
     end
 
-    test "returns the last five transactions with blocks" do
-      block = insert(:block)
+    test "with transaction without internal transactions" do
+      %Transaction{hash: hash} = insert(:transaction)
+
+      assert Chain.transaction_hash_to_internal_transactions(hash) == []
+    end
+
+    test "with transaction with internal transactions returns all internal transactions for a given transaction hash" do
+      transaction = insert(:transaction)
+      internal_transaction = insert(:internal_transaction, transaction_id: transaction.id)
+
+      result = hd(Chain.transaction_hash_to_internal_transactions(transaction.hash))
 
-      insert_list(6, :transaction)
-      |> Enum.map(fn transaction ->
-        insert(:block_transaction, block: block, transaction: transaction)
+      assert result.id == internal_transaction.id
+    end
+
+    test "with transaction with internal transactions loads associations with in necessity_by_assocation" do
+      %Transaction{hash: hash, id: transaction_id} = insert(:transaction)
+      insert(:internal_transaction, transaction_id: transaction_id)
+
+      assert [
+               %InternalTransaction{
+                 from_address: %Ecto.Association.NotLoaded{},
+                 to_address: %Ecto.Association.NotLoaded{},
+                 transaction: %Ecto.Association.NotLoaded{}
+               }
+             ] = Chain.transaction_hash_to_internal_transactions(hash)
+
+      assert [
+               %InternalTransaction{
+                 from_address: %Address{},
+                 to_address: %Address{},
+                 transaction: %Transaction{}
+               }
+             ] =
+               Chain.transaction_hash_to_internal_transactions(
+                 hash,
+                 necessity_by_association: %{
+                   from_address: :optional,
+                   to_address: :optional,
+                   transaction: :optional
+                 }
+               )
+    end
+  end
+
+  describe "transactions_recently_before_id" do
+    test "returns at most 10 transactions" do
+      count = 12
+
+      assert 10 < count
+
+      transactions = insert_list(count, :transaction)
+      %Transaction{id: last_transaction_id} = List.last(transactions)
+
+      recent_transactions = Chain.transactions_recently_before_id(last_transaction_id)
+
+      assert length(recent_transactions) == 10
+    end
+
+    test "with pending: true returns only pending transactions" do
+      count = 12
+
+      transactions = insert_list(count, :transaction)
+      %Transaction{id: last_transaction_id} = List.last(transactions)
+
+      transactions
+      |> Enum.take(3)
+      |> Enum.each(fn %Transaction{id: id} ->
+        insert(:receipt, transaction_id: id)
       end)
 
-      chain = Chain.fetch()
-      assert chain.transactions |> Enum.count() == 5
+      assert length(Chain.transactions_recently_before_id(last_transaction_id, pending: true)) ==
+               8
+
+      assert length(Chain.transactions_recently_before_id(last_transaction_id, pending: false)) ==
+               10
+
+      assert length(Chain.transactions_recently_before_id(last_transaction_id)) == 10
+    end
+  end
+
+  describe "transaction_to_logs/2" do
+    test "without logs" do
+      transaction = insert(:transaction)
+
+      assert %Scrivener.Page{
+               entries: [],
+               page_number: 1,
+               total_entries: 0,
+               total_pages: 1
+             } = Chain.transaction_to_logs(transaction)
+    end
+
+    test "with logs" do
+      transaction = insert(:transaction)
+      %Receipt{id: receipt_id} = insert(:receipt, transaction_id: transaction.id)
+      %Log{id: id} = insert(:log, receipt_id: receipt_id)
+
+      assert %Scrivener.Page{
+               entries: [%Log{id: ^id}],
+               page_number: 1,
+               total_entries: 1,
+               total_pages: 1
+             } = Chain.transaction_to_logs(transaction)
+    end
+
+    test "with logs can be paginated" do
+      transaction = insert(:transaction)
+      %Receipt{id: receipt_id} = insert(:receipt, transaction_id: transaction.id)
+      logs = insert_list(2, :log, receipt_id: receipt_id)
+
+      [%Log{id: first_log_id}, %Log{id: second_log_id}] = logs
+
+      assert %Scrivener.Page{
+               entries: [%Log{id: ^first_log_id}],
+               page_number: 1,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } = Chain.transaction_to_logs(transaction, pagination: %{page_size: 1})
+
+      assert %Scrivener.Page{
+               entries: [%Log{id: ^second_log_id}],
+               page_number: 2,
+               page_size: 1,
+               total_entries: 2,
+               total_pages: 2
+             } = Chain.transaction_to_logs(transaction, pagination: %{page: 2, page_size: 1})
+    end
+
+    test "with logs necessity_by_association loads associations" do
+      transaction = insert(:transaction)
+      %Receipt{id: receipt_id} = insert(:receipt, transaction_id: transaction.id)
+      insert(:log, receipt_id: receipt_id)
+
+      assert %Scrivener.Page{
+               entries: [
+                 %Log{
+                   address: %Address{},
+                   receipt: %Receipt{},
+                   transaction: %Transaction{}
+                 }
+               ],
+               page_number: 1,
+               total_entries: 1,
+               total_pages: 1
+             } =
+               Chain.transaction_to_logs(
+                 transaction,
+                 necessity_by_association: %{
+                   address: :optional,
+                   receipt: :optional,
+                   transaction: :optional
+                 }
+               )
+
+      assert %Scrivener.Page{
+               entries: [
+                 %Log{
+                   address: %Ecto.Association.NotLoaded{},
+                   receipt: %Ecto.Association.NotLoaded{},
+                   transaction: %Ecto.Association.NotLoaded{}
+                 }
+               ],
+               page_number: 1,
+               total_entries: 1,
+               total_pages: 1
+             } = Chain.transaction_to_logs(transaction)
+    end
+  end
+
+  describe "update_balance/2" do
+    test "updates the balance" do
+      hash = "0xwarheads"
+      insert(:address, hash: hash)
+
+      Chain.update_balance(hash, 5)
+
+      expected_balance = Decimal.new(5)
+
+      assert {:ok, %Address{balance: ^expected_balance}} = Chain.hash_to_address(hash)
+    end
+
+    test "updates the balance timestamp" do
+      hash = "0xtwizzlers"
+      insert(:address, hash: hash)
+
+      Chain.update_balance(hash, 88)
+
+      assert {:ok, %Address{balance_updated_at: balance_updated_at}} =
+               Chain.hash_to_address("0xtwizzlers")
+
+      refute is_nil(balance_updated_at)
+    end
+
+    test "creates an address if one does not exist" do
+      Chain.update_balance("0xtwizzlers", 88)
+
+      expected_balance = Decimal.new(88)
+
+      assert {:ok, %Address{balance: ^expected_balance}} = Chain.hash_to_address("0xtwizzlers")
     end
   end
 end

apps/explorer/test/explorer/importers/balance_importer_test.exs

@@ -1,15 +1,19 @@
 defmodule Explorer.BalanceImporterTest do
   use Explorer.DataCase
 
-  alias Explorer.Address.Service, as: Address
-  alias Explorer.BalanceImporter
+  alias Explorer.{Chain, BalanceImporter}
+  alias Explorer.Chain.Address
 
   describe "import/1" do
     test "it updates the balance for an address" do
       insert(:address, hash: "0x5cc18cc34175d358ff8e19b7f98566263c4106a0", balance: 5)
+
       BalanceImporter.import("0x5cc18cc34175d358ff8e19b7f98566263c4106a0")
-      address = Address.by_hash("0x5cc18cc34175d358ff8e19b7f98566263c4106a0")
-      assert address.balance == Decimal.new(1_572_374_181_095_000_000)
+
+      expected_balance = Decimal.new(1_572_374_181_095_000_000)
+
+      assert {:ok, %Address{balance: ^expected_balance}} =
+               Chain.hash_to_address("0x5cc18cc34175d358ff8e19b7f98566263c4106a0")
     end
 
     test "it updates the balance update time for an address" do
@@ -20,13 +24,17 @@ defmodule Explorer.BalanceImporterTest do
       )
 
       BalanceImporter.import("0x5cc18cc34175d358ff8e19b7f98566263c4106a0")
-      address = Address.by_hash("0x5cc18cc34175d358ff8e19b7f98566263c4106a0")
-      refute is_nil(address.balance_updated_at)
+
+      assert {:ok, %Address{balance_updated_at: balance_updated_at}} =
+               Chain.hash_to_address("0x5cc18cc34175d358ff8e19b7f98566263c4106a0")
+
+      refute is_nil(balance_updated_at)
     end
 
     test "it creates an address if one does not exist" do
       BalanceImporter.import("0x5cc18cc34175d358ff8e19b7f98566263c4106a0")
-      assert Address.by_hash("0x5cc18cc34175d358ff8e19b7f98566263c4106a0")
+
+      assert {:ok, _} = Chain.hash_to_address("0x5cc18cc34175d358ff8e19b7f98566263c4106a0")
     end
   end
 end

apps/explorer/test/explorer/importers/block_importer_test.exs

@@ -3,9 +3,8 @@ defmodule Explorer.BlockImporterTest do
 
   import Mock
 
-  alias Explorer.Block
-  alias Explorer.Transaction
   alias Explorer.BlockImporter
+  alias Explorer.Chain.{Block, Transaction}
   alias Explorer.Workers.ImportTransaction
 
   describe "import/1" do

apps/explorer/test/explorer/importers/internal_transaction_importer_test.exs

@@ -1,7 +1,7 @@
 defmodule Explorer.InternalTransactionImporterTest do
   use Explorer.DataCase
 
-  alias Explorer.InternalTransaction
+  alias Explorer.Chain.InternalTransaction
   alias Explorer.InternalTransactionImporter
 
   describe "import/1" do

apps/explorer/test/explorer/importers/receipt_importer_test.exs

@@ -1,8 +1,7 @@
 defmodule Explorer.ReceiptImporterTest do
   use Explorer.DataCase
 
-  alias Explorer.Receipt
-  alias Explorer.Log
+  alias Explorer.Chain.{Log, Receipt}
   alias Explorer.ReceiptImporter
 
   describe "import/1" do

apps/explorer/test/explorer/importers/transaction_importer_test.exs

@@ -1,9 +1,7 @@
 defmodule Explorer.TransactionImporterTest do
   use Explorer.DataCase
 
-  alias Explorer.Address
-  alias Explorer.BlockTransaction
-  alias Explorer.Transaction
+  alias Explorer.Chain.{Address, BlockTransaction, Transaction}
   alias Explorer.TransactionImporter
 
   @raw_transaction %{

apps/explorer/test/explorer/resource_test.exs

@@ -1,45 +0,0 @@
-defmodule Explorer.ResourceTest do
-  use Explorer.DataCase
-
-  alias Explorer.Resource
-
-  describe "lookup/1" do
-    test "finds a block by block number with a valid block number" do
-      insert(:block, number: 37)
-      block = Resource.lookup("37")
-
-      assert block.number == 37
-    end
-
-    test "finds a transaction by hash" do
-      transaction = insert(:transaction)
-
-      resource = Resource.lookup(transaction.hash)
-
-      assert transaction.hash == resource.hash
-    end
-
-    test "finds an address by hash" do
-      address = insert(:address)
-
-      resource = Resource.lookup(address.hash)
-
-      assert address.hash == resource.hash
-    end
-
-    test "returns nil when garbage is passed in" do
-      item = Resource.lookup("any ol' thing")
-
-      assert is_nil(item)
-    end
-
-    test "returns nil when it does not find a match" do
-      transaction_hash = String.pad_trailing("0xnonsense", 43, "0")
-      address_hash = String.pad_trailing("0xbaddress", 42, "0")
-
-      assert is_nil(Resource.lookup("38999"))
-      assert is_nil(Resource.lookup(transaction_hash))
-      assert is_nil(Resource.lookup(address_hash))
-    end
-  end
-end

apps/explorer/test/explorer/servers/chain_statistics_test.exs

@@ -1,85 +0,0 @@
-defmodule Explorer.Servers.ChainStatisticsTest do
-  use Explorer.DataCase
-
-  alias Explorer.Chain
-  alias Explorer.Servers.ChainStatistics
-
-  describe "init/1" do
-    test "returns a new chain when not told to refresh" do
-      {:ok, statistics} = ChainStatistics.init(false)
-      assert statistics.number == Chain.fetch().number
-    end
-
-    test "returns a new chain when told to refresh" do
-      {:ok, statistics} = ChainStatistics.init(true)
-      assert statistics == Chain.fetch()
-    end
-
-    test "refreshes when told to refresh" do
-      {:ok, _} = ChainStatistics.init(true)
-      assert_receive :refresh, 2_000
-    end
-  end
-
-  describe "fetch/0" do
-    test "fetches the chain when not started" do
-      original = Chain.fetch()
-      chain = ChainStatistics.fetch()
-      assert chain == original
-    end
-  end
-
-  describe "handle_info/2" do
-    test "returns the original chain when sent a :refresh message" do
-      original = Chain.fetch()
-      {:noreply, chain} = ChainStatistics.handle_info(:refresh, original)
-      assert chain == original
-    end
-
-    test "launches an update when sent a :refresh message" do
-      original = Chain.fetch()
-      {:ok, pid} = Explorer.Servers.ChainStatistics.start_link()
-      chain = ChainStatistics.fetch()
-      :ok = GenServer.stop(pid)
-      assert original.number == chain.number
-    end
-
-    test "does not reply when sent any other message" do
-      {status, _} = ChainStatistics.handle_info(:ham, %Chain{})
-      assert status == :noreply
-    end
-  end
-
-  describe "handle_call/3" do
-    test "replies with statistics when sent a :fetch message" do
-      original = Chain.fetch()
-      {:reply, _, chain} = ChainStatistics.handle_call(:fetch, self(), original)
-      assert chain == original
-    end
-
-    test "does not reply when sent any other message" do
-      {status, _} = ChainStatistics.handle_call(:ham, self(), %Chain{})
-      assert status == :noreply
-    end
-  end
-
-  describe "handle_cast/2" do
-    test "schedules a refresh of the statistics when sent an update" do
-      chain = Chain.fetch()
-      ChainStatistics.handle_cast({:update, chain}, %Chain{})
-      assert_receive :refresh, 2_000
-    end
-
-    test "returns a noreply and the new incoming chain when sent an update" do
-      original = Chain.fetch()
-      {:noreply, chain} = ChainStatistics.handle_cast({:update, original}, %Chain{})
-      assert chain == original
-    end
-
-    test "returns a noreply and the old chain when sent any other cast" do
-      original = Chain.fetch()
-      {:noreply, chain} = ChainStatistics.handle_cast(:ham, original)
-      assert chain == original
-    end
-  end
-end

apps/explorer/test/explorer/services/address_test.exs

@@ -1,56 +0,0 @@
-defmodule Explorer.Address.ServiceTest do
-  use Explorer.DataCase
-
-  alias Explorer.Address.Service
-  alias Explorer.Address
-
-  describe "by_hash/1" do
-    test "it returns an address with that hash" do
-      address = insert(:address, hash: "0xandesmints")
-      result = Service.by_hash("0xandesmints")
-      assert result.id == address.id
-    end
-  end
-
-  describe "update_balance/2" do
-    test "it updates the balance" do
-      insert(:address, hash: "0xwarheads")
-      Service.update_balance(5, "0xwarheads")
-      result = Service.by_hash("0xwarheads")
-      assert result.balance == Decimal.new(5)
-    end
-
-    test "it updates the balance timestamp" do
-      insert(:address, hash: "0xtwizzlers")
-      Service.update_balance(88, "0xtwizzlers")
-      result = Service.by_hash("0xtwizzlers")
-      refute is_nil(result.balance_updated_at)
-    end
-
-    test "it creates an address if one does not exist" do
-      Service.update_balance(88, "0xtwizzlers")
-      result = Service.by_hash("0xtwizzlers")
-      assert result.balance == Decimal.new(88)
-    end
-  end
-
-  describe "find_or_create_by_hash/1" do
-    test "that it creates a new address when one does not exist" do
-      Service.find_or_create_by_hash("0xFreshPrince")
-      assert Service.by_hash("0xfreshprince")
-    end
-
-    test "when the address already exists it doesn't insert a new address" do
-      insert(:address, %{hash: "bigmouthbillybass"})
-      Service.find_or_create_by_hash("bigmouthbillybass")
-      number_of_addresses = Address |> Repo.all() |> length
-      assert number_of_addresses == 1
-    end
-
-    test "when there is no hash it blows up" do
-      assert_raise Ecto.InvalidChangesetError, fn ->
-        Service.find_or_create_by_hash("")
-      end
-    end
-  end
-end

apps/explorer/test/explorer/services/transaction_test.exs

@@ -1,16 +0,0 @@
-defmodule Explorer.Transaction.ServiceTest do
-  use Explorer.DataCase
-
-  alias Explorer.Transaction.Service
-
-  describe "internal_transactions/1" do
-    test "it returns all internal transactions for a given hash" do
-      transaction = insert(:transaction)
-      internal_transaction = insert(:internal_transaction, transaction_id: transaction.id)
-
-      result = hd(Service.internal_transactions(transaction.hash))
-
-      assert result.id == internal_transaction.id
-    end
-  end
-end

apps/explorer/test/explorer/workers/import_balance_test.exs

@@ -1,16 +1,20 @@
 defmodule Explorer.Workers.ImportBalanceTest do
   import Mock
 
+  alias Explorer.Chain
+  alias Explorer.Chain.Address
   alias Explorer.Workers.ImportBalance
-  alias Explorer.Address.Service, as: Address
 
   use Explorer.DataCase
 
   describe "perform/1" do
     test "imports the balance for an address" do
       ImportBalance.perform("0x1d12e5716c593b156eb7152ca4360f6224ba3b0a")
-      address = Address.by_hash("0x1d12e5716c593b156eb7152ca4360f6224ba3b0a")
-      assert address.balance == Decimal.new(1_572_374_181_095_000_000)
+
+      expected_balance = Decimal.new(1_572_374_181_095_000_000)
+
+      assert {:ok, %Address{balance: ^expected_balance}} =
+               Chain.hash_to_address("0x1d12e5716c593b156eb7152ca4360f6224ba3b0a")
     end
   end
 
@@ -25,8 +29,11 @@ defmodule Explorer.Workers.ImportBalanceTest do
           )
         end do
         ImportBalance.perform_later("0xskateboards")
-        address = Address.by_hash("0xskateboards")
-        assert address.balance == Decimal.new(66)
+
+        expected_balance = Decimal.new(66)
+
+        assert {:ok, %Address{balance: ^expected_balance}} =
+                 Chain.hash_to_address("0xskateboards")
       end
     end
   end

apps/explorer/test/explorer/workers/import_block_test.exs

@@ -1,11 +1,11 @@
 defmodule Explorer.Workers.ImportBlockTest do
-  alias Explorer.Block
-  alias Explorer.Repo
-  alias Explorer.Workers.ImportBlock
+  use Explorer.DataCase
 
   import Mock
 
-  use Explorer.DataCase
+  alias Explorer.Chain.Block
+  alias Explorer.Repo
+  alias Explorer.Workers.ImportBlock
 
   describe "perform/1" do
     test "imports the requested block number as an integer" do

apps/explorer/test/explorer/workers/import_internal_transaction_test.exs

@@ -2,7 +2,7 @@ defmodule Explorer.Workers.ImportInternalTransactionTest do
   use Explorer.DataCase
 
   alias Explorer.Repo
-  alias Explorer.InternalTransaction
+  alias Explorer.Chain.InternalTransaction
   alias Explorer.Workers.ImportInternalTransaction
 
   describe "perform/1" do

apps/explorer/test/explorer/workers/import_receipt_test.exs

@@ -2,7 +2,7 @@ defmodule Explorer.Workers.ImportReceiptTest do
   use Explorer.DataCase
 
   alias Explorer.Repo
-  alias Explorer.Receipt
+  alias Explorer.Chain.Receipt
   alias Explorer.Workers.ImportReceipt
 
   describe "perform/1" do

apps/explorer/test/explorer/workers/import_skipped_blocks_test.exs

@@ -1,12 +1,11 @@
 defmodule Explorer.Workers.ImportSkippedBlocksTest do
-  alias Explorer.Block
-  alias Explorer.Repo
-  alias Explorer.Workers.ImportBlock
-  alias Explorer.Workers.ImportSkippedBlocks
+  use Explorer.DataCase
 
   import Mock
 
-  use Explorer.DataCase
+  alias Explorer.Chain.Block
+  alias Explorer.Repo
+  alias Explorer.Workers.{ImportBlock, ImportSkippedBlocks}
 
   describe "perform/1" do
     test "imports the requested number of skipped blocks" do

apps/explorer/test/explorer/workers/import_transaction_test.exs

@@ -3,10 +3,8 @@ defmodule Explorer.Workers.ImportTransactionTest do
 
   import Mock
 
-  alias Explorer.InternalTransaction
-  alias Explorer.Receipt
+  alias Explorer.Chain.{InternalTransaction, Receipt, Transaction}
   alias Explorer.Repo
-  alias Explorer.Transaction
   alias Explorer.Workers.ImportInternalTransaction
   alias Explorer.Workers.ImportTransaction
 

apps/explorer/test/explorer/workers/refresh_balance_test.exs

@@ -3,8 +3,7 @@ defmodule Explorer.Workers.RefreshBalanceTest do
 
   import Mock
 
-  alias Explorer.Credit
-  alias Explorer.Debit
+  alias Explorer.Chain.{Credit, Debit}
   alias Explorer.Workers.RefreshBalance
 
   describe "perform/0" do

apps/explorer/test/support/data_case.ex

@@ -39,20 +39,4 @@ defmodule Explorer.DataCase do
 
     :ok
   end
-
-  @doc """
-  A helper that transform changeset errors to a map of messages.
-
-      assert {:error, changeset} = Accounts.create_user(%{password: "short"})
-      assert "password is too short" in errors_on(changeset).password
-      assert %{password: ["password is too short"]} = errors_on(changeset)
-
-  """
-  def errors_on(changeset) do
-    Ecto.Changeset.traverse_errors(changeset, fn {message, opts} ->
-      Enum.reduce(opts, message, fn {key, value}, acc ->
-        String.replace(acc, "%{#{key}}", to_string(value))
-      end)
-    end)
-  end
 end

apps/explorer/test/support/factories/chain/address_factory.ex

@@ -1,8 +1,8 @@
-defmodule Explorer.AddressFactory do
+defmodule Explorer.Chain.AddressFactory do
   defmacro __using__(_opts) do
     quote do
       def address_factory do
-        %Explorer.Address{
+        %Explorer.Chain.Address{
           hash: String.pad_trailing(sequence("0x"), 42, "address")
         }
       end

apps/explorer/test/support/factories/chain/block_factory.ex

@@ -1,8 +1,8 @@
-defmodule Explorer.BlockFactory do
+defmodule Explorer.Chain.BlockFactory do
   defmacro __using__(_opts) do
     quote do
       def block_factory do
-        %Explorer.Block{
+        %Explorer.Chain.Block{
           number: sequence(""),
           hash: sequence("0x"),
           parent_hash: sequence("0x"),

apps/explorer/test/support/factories/chain/block_transaction_factory.ex

@@ -1,8 +1,8 @@
-defmodule Explorer.BlockTransactionFactory do
+defmodule Explorer.Chain.BlockTransactionFactory do
   defmacro __using__(_opts) do
     quote do
       def block_transaction_factory do
-        %Explorer.BlockTransaction{}
+        %Explorer.Chain.BlockTransaction{}
       end
     end
   end

apps/explorer/test/support/factories/chain/from_address_factory.ex

@@ -1,8 +1,8 @@
-defmodule Explorer.FromAddressFactory do
+defmodule Explorer.Chain.FromAddressFactory do
   defmacro __using__(_opts) do
     quote do
       def from_address_factory do
-        %Explorer.FromAddress{}
+        %Explorer.Chain.FromAddress{}
       end
     end
   end

apps/explorer/test/support/factories/chain/internal_transaction_factory.ex

@@ -1,8 +1,8 @@
-defmodule Explorer.InternalTransactionFactory do
+defmodule Explorer.Chain.InternalTransactionFactory do
   defmacro __using__(_opts) do
     quote do
       def internal_transaction_factory do
-        %Explorer.InternalTransaction{
+        %Explorer.Chain.InternalTransaction{
           index: Enum.random(0..9),
           call_type: Enum.random(["call", "creates", "calldelegate"]),
           trace_address: [Enum.random(0..4), Enum.random(0..4)],

apps/explorer/test/support/factories/chain/log_factory.ex

@@ -1,15 +1,16 @@
-defmodule Explorer.LogFactory do
+defmodule Explorer.Chain.LogFactory do
   defmacro __using__(_opts) do
     quote do
       def log_factory do
-        %Explorer.Log{
-          index: sequence(""),
+        %Explorer.Chain.Log{
+          address_id: insert(:address).id,
           data: sequence("0x"),
-          type: sequence("0x"),
           first_topic: nil,
+          fourth_topic: nil,
+          index: sequence(""),
           second_topic: nil,
           third_topic: nil,
-          fourth_topic: nil
+          type: sequence("0x")
         }
       end
     end

apps/explorer/test/support/factories/chain/receipt_factory.ex

@@ -1,8 +1,8 @@
-defmodule Explorer.ReceiptFactory do
+defmodule Explorer.Chain.ReceiptFactory do
   defmacro __using__(_opts) do
     quote do
       def receipt_factory do
-        %Explorer.Receipt{
+        %Explorer.Chain.Receipt{
           cumulative_gas_used: Enum.random(21_000..100_000),
           gas_used: Enum.random(21_000..100_000),
           status: Enum.random(1..2),

apps/explorer/test/support/factories/chain/to_address_factory.ex

@@ -1,8 +1,8 @@
-defmodule Explorer.ToAddressFactory do
+defmodule Explorer.Chain.ToAddressFactory do
   defmacro __using__(_opts) do
     quote do
       def to_address_factory do
-        %Explorer.ToAddress{}
+        %Explorer.Chain.ToAddress{}
       end
     end
   end

apps/explorer/test/support/factories/chain/transaction_factory.ex

@@ -1,12 +1,11 @@
-defmodule Explorer.TransactionFactory do
+defmodule Explorer.Chain.TransactionFactory do
   defmacro __using__(_opts) do
     quote do
-      alias Explorer.Address
-      alias Explorer.BlockTransaction
+      alias Explorer.Chain.{Address, BlockTransaction, Transaction}
       alias Explorer.Repo
 
       def transaction_factory do
-        %Explorer.Transaction{
+        %Transaction{
           hash: String.pad_trailing(sequence("0x"), 43, "action"),
           value: Enum.random(1..100_000),
           gas: Enum.random(21_000..100_000),

apps/explorer/test/support/factory.ex

@@ -1,13 +1,13 @@
 defmodule Explorer.Factory do
   @dialyzer {:nowarn_function, fields_for: 1}
   use ExMachina.Ecto, repo: Explorer.Repo
-  use Explorer.AddressFactory
-  use Explorer.BlockFactory
-  use Explorer.BlockTransactionFactory
-  use Explorer.FromAddressFactory
-  use Explorer.InternalTransactionFactory
-  use Explorer.LogFactory
-  use Explorer.ToAddressFactory
-  use Explorer.TransactionFactory
-  use Explorer.ReceiptFactory
+  use Explorer.Chain.AddressFactory
+  use Explorer.Chain.BlockFactory
+  use Explorer.Chain.BlockTransactionFactory
+  use Explorer.Chain.FromAddressFactory
+  use Explorer.Chain.InternalTransactionFactory
+  use Explorer.Chain.LogFactory
+  use Explorer.Chain.ReceiptFactory
+  use Explorer.Chain.ToAddressFactory
+  use Explorer.Chain.TransactionFactory
 end

apps/explorer_web/lib/explorer_web.ex

@@ -20,9 +20,11 @@ defmodule ExplorerWeb do
   def controller do
     quote do
       use Phoenix.Controller, namespace: ExplorerWeb
-      import Plug.Conn
+
+      import ExplorerWeb.Controller
       import ExplorerWeb.Router.Helpers
       import ExplorerWeb.Gettext
+      import Plug.Conn
     end
   end
 
@@ -38,17 +40,16 @@ defmodule ExplorerWeb do
       # Use all HTML functionality (forms, tags, etc)
       use Phoenix.HTML
 
-      import ExplorerWeb.Router.Helpers
-      import ExplorerWeb.ErrorHelpers
-      import ExplorerWeb.Gettext
-      import Scrivener.HTML
+      import ExplorerWeb.{ErrorHelpers, Gettext, Router.Helpers}
       import ReactPhoenix.ClientSide
+      import Scrivener.HTML
     end
   end
 
   def router do
     quote do
       use Phoenix.Router
+
       import Plug.Conn
       import Phoenix.Controller
     end
@@ -57,6 +58,7 @@ defmodule ExplorerWeb do
   def channel do
     quote do
       use Phoenix.Channel
+
       import ExplorerWeb.Gettext
     end
   end

apps/explorer_web/lib/explorer_web/chain.ex

@@ -0,0 +1,33 @@
+defmodule ExplorerWeb.Chain do
+  @moduledoc """
+  Converts the `param` to the corresponding resource that uses that format of param.
+  """
+
+  import Explorer.Chain, only: [hash_to_address: 1, hash_to_transaction: 1, number_to_block: 1]
+
+  @spec from_param(String.t()) ::
+          {:ok, Address.t() | Transaction.t() | Block.t()} | {:error, :not_found}
+  def from_param(param)
+
+  def from_param(hash) when byte_size(hash) > 42 do
+    hash_to_transaction(hash)
+  end
+
+  def from_param(hash) when byte_size(hash) == 42 do
+    hash_to_address(hash)
+  end
+
+  def from_param(formatted_number) when is_binary(formatted_number) do
+    case param_to_block_number(formatted_number) do
+      {:ok, number} -> number_to_block(number)
+      {:error, :invalid} -> {:error, :not_found}
+    end
+  end
+
+  def param_to_block_number(formatted_number) when is_binary(formatted_number) do
+    case Integer.parse(formatted_number) do
+      {number, ""} -> {:ok, number}
+      _ -> {:error, :invalid}
+    end
+  end
+end

apps/explorer_web/lib/explorer_web/controller.ex

@@ -0,0 +1,18 @@
+defmodule ExplorerWeb.Controller do
+  @moduledoc """
+  Common controller error responses
+  """
+
+  import Phoenix.Controller
+  import Plug.Conn
+
+  @doc """
+  Renders HTML Not Found error
+  """
+  def not_found(conn) do
+    conn
+    |> put_status(:not_found)
+    |> put_view(ExplorerWeb.ErrorView)
+    |> render("404.html")
+  end
+end

apps/explorer_web/lib/explorer_web/controllers/address_controller.ex

@@ -1,10 +1,14 @@
 defmodule ExplorerWeb.AddressController do
   use ExplorerWeb, :controller
 
-  alias Explorer.Address.Service, as: Address
+  alias Explorer.Chain
 
-  def show(conn, %{"id" => id}) do
-    address = id |> Address.by_hash()
-    render(conn, "show.html", address: address)
+  def show(conn, %{"id" => hash}) do
+    hash
+    |> Chain.hash_to_address()
+    |> case do
+      {:ok, address} -> render(conn, "show.html", address: address)
+      {:error, :not_found} -> not_found(conn)
+    end
   end
 end

apps/explorer_web/lib/explorer_web/controllers/address_transaction_from_controller.ex

@@ -5,25 +5,29 @@ defmodule ExplorerWeb.AddressTransactionFromController do
 
   use ExplorerWeb, :controller
 
-  alias Explorer.Address.Service, as: Address
-  alias Explorer.Repo.NewRelic, as: Repo
-  alias Explorer.Transaction
-  alias Explorer.Transaction.Service.Query
+  alias Explorer.Chain
   alias ExplorerWeb.TransactionForm
 
-  def index(conn, %{"address_id" => address_id} = params) do
-    address = Address.by_hash(address_id)
+  def index(conn, %{"address_id" => from_address_hash} = params) do
+    case Chain.hash_to_address(from_address_hash) do
+      {:ok, from_address} ->
+        page =
+          Chain.from_address_to_transactions(
+            from_address,
+            necessity_by_association: %{
+              block: :required,
+              from_address: :optional,
+              to_address: :optional,
+              receipt: :required
+            },
+            pagination: params
+          )
 
-    query =
-      Transaction
-      |> Query.from_address(address.id)
-      |> Query.include_addresses()
-      |> Query.require_receipt()
-      |> Query.require_block()
-      |> Query.chron()
-
-    page = Repo.paginate(query, params)
         entries = Enum.map(page.entries, &TransactionForm.build_and_merge/1)
         render(conn, "index.html", transactions: Map.put(page, :entries, entries))
+
+      {:error, :not_found} ->
+        not_found(conn)
+    end
   end
 end

apps/explorer_web/lib/explorer_web/controllers/address_transaction_to_controller.ex

@@ -5,25 +5,29 @@ defmodule ExplorerWeb.AddressTransactionToController do
 
   use ExplorerWeb, :controller
 
-  alias Explorer.Address.Service, as: Address
-  alias Explorer.Repo.NewRelic, as: Repo
-  alias Explorer.Transaction
-  alias Explorer.Transaction.Service.Query
+  alias Explorer.Chain
   alias ExplorerWeb.TransactionForm
 
-  def index(conn, %{"address_id" => address_id} = params) do
-    address = Address.by_hash(address_id)
+  def index(conn, %{"address_id" => to_address_hash} = params) do
+    case Chain.hash_to_address(to_address_hash) do
+      {:ok, to_address} ->
+        page =
+          Chain.to_address_to_transactions(
+            to_address,
+            necessity_by_association: %{
+              block: :required,
+              from_address: :optional,
+              to_address: :optional,
+              receipt: :required
+            },
+            pagination: params
+          )
 
-    query =
-      Transaction
-      |> Query.to_address(address.id)
-      |> Query.include_addresses()
-      |> Query.require_receipt()
-      |> Query.require_block()
-      |> Query.chron()
-
-    page = Repo.paginate(query, params)
         entries = Enum.map(page.entries, &TransactionForm.build_and_merge/1)
         render(conn, "index.html", transactions: Map.put(page, :entries, entries))
+
+      {:error, :not_found} ->
+        not_found(conn)
+    end
   end
 end

apps/explorer_web/lib/explorer_web/controllers/block_controller.ex

@@ -1,31 +1,25 @@
 defmodule ExplorerWeb.BlockController do
   use ExplorerWeb, :controller
 
-  import Ecto.Query
-
-  alias Explorer.Block
-  alias Explorer.Repo.NewRelic, as: Repo
+  alias Explorer.Chain
   alias ExplorerWeb.BlockForm
 
   def index(conn, params) do
     blocks =
-      from(
-        block in Block,
-        order_by: [desc: block.number],
-        preload: :transactions
-      )
+      Chain.list_blocks(necessity_by_association: %{transactions: :optional}, pagination: params)
 
-    render(conn, "index.html", blocks: Repo.paginate(blocks, params))
+    render(conn, "index.html", blocks: blocks)
   end
 
   def show(conn, %{"id" => number}) do
-    block =
-      Block
-      |> where(number: ^number)
-      |> first
-      |> Repo.one()
-      |> BlockForm.build()
+    case Chain.number_to_block(number) do
+      {:ok, block} ->
+        block_form = BlockForm.build(block)
+
+        render(conn, "show.html", block: block_form)
 
-    render(conn, "show.html", block: block)
+      {:error, :not_found} ->
+        not_found(conn)
+    end
   end
 end

apps/explorer_web/lib/explorer_web/controllers/block_transaction_controller.ex

@@ -1,27 +1,34 @@
 defmodule ExplorerWeb.BlockTransactionController do
   use ExplorerWeb, :controller
 
-  import Ecto.Query
+  import ExplorerWeb.Chain, only: [param_to_block_number: 1]
 
-  alias Explorer.Repo.NewRelic, as: Repo
-  alias Explorer.Transaction
+  alias Explorer.Chain
   alias ExplorerWeb.TransactionForm
 
-  def index(conn, %{"block_id" => block_number} = params) do
-    query =
-      from(
-        transaction in Transaction,
-        join: block in assoc(transaction, :block),
-        join: receipt in assoc(transaction, :receipt),
-        join: from_address in assoc(transaction, :from_address),
-        join: to_address in assoc(transaction, :to_address),
-        preload: [:block, :receipt, :to_address, :from_address],
-        order_by: [desc: transaction.inserted_at],
-        where: block.number == ^block_number
+  def index(conn, %{"block_id" => formatted_block_number} = params) do
+    with {:ok, block_number} <- param_to_block_number(formatted_block_number),
+         {:ok, block} <- Chain.number_to_block(block_number) do
+      page =
+        Chain.block_to_transactions(
+          block,
+          necessity_by_association: %{
+            block: :required,
+            from_address: :required,
+            to_address: :required,
+            receipt: :required
+          },
+          pagination: params
         )
 
-    page = Repo.paginate(query, params)
       entries = Enum.map(page.entries, &TransactionForm.build_and_merge/1)
       render(conn, "index.html", transactions: Map.put(page, :entries, entries))
+    else
+      {:error, :invalid} ->
+        not_found(conn)
+
+      {:error, :not_found} ->
+        not_found(conn)
+    end
   end
 end

apps/explorer_web/lib/explorer_web/controllers/chain_controller.ex

@@ -1,34 +1,35 @@
 defmodule ExplorerWeb.ChainController do
   use ExplorerWeb, :controller
 
-  alias Explorer.Servers.ChainStatistics
-  alias Explorer.Resource
+  alias Explorer.Chain.{Address, Block, Statistics, Transaction}
+  alias ExplorerWeb.Chain
 
   def show(conn, _params) do
-    render(conn, "show.html", chain: ChainStatistics.fetch())
+    render(conn, "show.html", chain: Statistics.fetch())
   end
 
   def search(conn, %{"q" => query}) do
     query
     |> String.trim()
-    |> Resource.lookup()
+    |> Chain.from_param()
     |> case do
-      nil ->
-        conn
-        |> put_status(:not_found)
-        |> put_view(ExplorerWeb.ErrorView)
-        |> render("404.html")
-
-      item ->
+      {:ok, item} ->
         redirect_search_results(conn, item)
+
+      {:error, :not_found} ->
+        not_found(conn)
     end
   end
 
-  defp redirect_search_results(conn, %Explorer.Block{} = item) do
+  defp redirect_search_results(conn, %Address{} = item) do
+    redirect(conn, to: address_path(conn, :show, Gettext.get_locale(), item.hash))
+  end
+
+  defp redirect_search_results(conn, %Block{} = item) do
     redirect(conn, to: block_path(conn, :show, Gettext.get_locale(), item.number))
   end
 
-  defp redirect_search_results(conn, %Explorer.Transaction{} = item) do
+  defp redirect_search_results(conn, %Transaction{} = item) do
     redirect(
       conn,
       to:
@@ -40,8 +41,4 @@ defmodule ExplorerWeb.ChainController do
         )
     )
   end
-
-  defp redirect_search_results(conn, %Explorer.Address{} = item) do
-    redirect(conn, to: address_path(conn, :show, Gettext.get_locale(), item.hash))
-  end
 end

apps/explorer_web/lib/explorer_web/controllers/pending_transaction_controller.ex

@@ -1,55 +1,31 @@
 defmodule ExplorerWeb.PendingTransactionController do
   use ExplorerWeb, :controller
 
-  import Ecto.Query
-
-  alias Explorer.Repo.NewRelic, as: Repo
-  alias Explorer.Transaction
+  alias Explorer.Chain
+  alias Explorer.Chain.Transaction
   alias ExplorerWeb.PendingTransactionForm
 
-  def index(conn, %{"last_seen" => last_seen} = _) do
-    query =
-      from(
-        transaction in Transaction,
-        inner_join: to_address in assoc(transaction, :to_address),
-        inner_join: from_address in assoc(transaction, :from_address),
-        preload: [to_address: to_address, from_address: from_address],
-        where:
-          fragment(
-            "NOT EXISTS (SELECT true FROM receipts WHERE receipts.transaction_id = ?)",
-            transaction.id
-          ),
-        where: transaction.id < ^last_seen,
-        order_by: [desc: transaction.id],
-        limit: 10
-      )
-
-    total_query =
-      from(
-        transaction in Transaction,
-        where:
-          fragment(
-            "NOT EXISTS (SELECT true FROM receipts WHERE receipts.transaction_id = ?)",
-            transaction.id
-          ),
-        order_by: [desc: transaction.id],
-        limit: 1
+  def index(conn, %{"last_seen" => last_seen_id} = _) do
+    total = Chain.transaction_count(pending: true)
+
+    entries =
+      last_seen_id
+      |> Chain.transactions_recently_before_id(
+        necessity_by_association: %{
+          from_address: :optional,
+          to_address: :optional
+        },
+        pending: true
       )
+      |> Enum.map(&PendingTransactionForm.build/1)
 
-    total =
-      case Repo.one(total_query) do
-        nil -> 0
-        total -> total.id
-      end
-
-    entries = Repo.all(query)
     last = List.last(entries) || Transaction.null()
 
     render(
       conn,
       "index.html",
       transactions: %{
-        entries: entries |> Enum.map(&PendingTransactionForm.build/1),
+        entries: entries,
         total_entries: total,
         last_seen: last.id
       }
@@ -57,21 +33,12 @@ defmodule ExplorerWeb.PendingTransactionController do
   end
 
   def index(conn, params) do
-    query =
-      from(
-        transaction in Transaction,
-        select: transaction.id,
-        where:
-          fragment(
-            "NOT EXISTS (SELECT true FROM receipts WHERE receipts.transaction_id = ?)",
-            transaction.id
-          ),
-        order_by: [desc: transaction.id],
-        limit: 1
-      )
+    last_seen =
+      [pending: true]
+      |> Chain.last_transaction_id()
+      |> Kernel.+(1)
+      |> Integer.to_string()
 
-    first_id = Repo.one(query) || 0
-    last_seen = Integer.to_string(first_id + 1)
     index(conn, Map.put(params, "last_seen", last_seen))
   end
 end

apps/explorer_web/lib/explorer_web/controllers/transaction_controller.ex

@@ -1,38 +1,23 @@
 defmodule ExplorerWeb.TransactionController do
   use ExplorerWeb, :controller
 
-  import Ecto.Query
-
-  alias Explorer.Repo.NewRelic, as: Repo
-  alias Explorer.Transaction
-  alias Explorer.Transaction.Service
-  alias Explorer.Transaction.Service.Query
+  alias Explorer.Chain
+  alias Explorer.Chain.Transaction
   alias ExplorerWeb.TransactionForm
 
-  def index(conn, %{"last_seen" => last_seen}) do
-    query =
-      Transaction
-      |> Query.recently_seen(last_seen)
-      |> Query.include_addresses()
-      |> Query.require_receipt()
-      |> Query.require_block()
-
-    total_query =
-      from(
-        transaction in Transaction,
-        order_by: [desc: transaction.id],
-        limit: 1
-      )
-
-    total =
-      case Repo.one(total_query) do
-        nil -> 0
-        total -> total.id
-      end
+  def index(conn, %{"last_seen" => last_seen_id}) do
+    total = Chain.transaction_count()
 
     entries =
-      query
-      |> Repo.all()
+      last_seen_id
+      |> Chain.transactions_recently_before_id(
+        necessity_by_association: %{
+          block: :required,
+          from_address: :optional,
+          to_address: :optional,
+          receipt: :required
+        }
+      )
       |> Enum.map(&TransactionForm.build_and_merge/1)
 
     last = List.last(entries) || Transaction.null()
@@ -49,38 +34,42 @@ defmodule ExplorerWeb.TransactionController do
   end
 
   def index(conn, params) do
-    query =
-      from(
-        t in Transaction,
-        select: t.id,
-        order_by: [desc: t.id],
-        limit: 1
-      )
+    last_seen =
+      Chain.last_transaction_id()
+      |> Kernel.+(1)
+      |> Integer.to_string()
 
-    first_id = Repo.one(query) || 0
-    last_seen = Integer.to_string(first_id + 1)
     index(conn, Map.put(params, "last_seen", last_seen))
   end
 
   def show(conn, params) do
-    transaction = get_transaction(String.downcase(params["id"]))
+    case Chain.hash_to_transaction(
+           params["id"],
+           necessity_by_association: %{
+             block: :optional,
+             from_address: :optional,
+             to_address: :optional,
+             receipt: :optional
+           }
+         ) do
+      {:ok, transaction} ->
+        internal_transactions =
+          Chain.transaction_hash_to_internal_transactions(
+            transaction.hash,
+            necessity_by_association: %{from_address: :required, to_address: :required}
+          )
 
-    internal_transactions = Service.internal_transactions(transaction.hash)
+        transaction_form = TransactionForm.build_and_merge(transaction)
 
         render(
           conn,
+          "show.html",
           internal_transactions: internal_transactions,
-      transaction: transaction
+          transaction: transaction_form
         )
-  end
 
-  defp get_transaction(hash) do
-    Transaction
-    |> Query.by_hash(hash)
-    |> Query.include_addresses()
-    |> Query.include_receipt()
-    |> Query.include_block()
-    |> Repo.one()
-    |> TransactionForm.build_and_merge()
+      {:error, :not_found} ->
+        not_found(conn)
+    end
   end
 end

apps/explorer_web/lib/explorer_web/controllers/transaction_log_controller.ex

@@ -1,41 +1,28 @@
 defmodule ExplorerWeb.TransactionLogController do
   use ExplorerWeb, :controller
 
-  import Ecto.Query
-
-  alias Explorer.Log
-  alias Explorer.Repo.NewRelic, as: Repo
-  alias Explorer.Transaction
-  alias Explorer.Transaction.Service.Query
+  alias Explorer.Chain
   alias ExplorerWeb.TransactionForm
 
-  def index(conn, %{"transaction_id" => transaction_id}) do
-    transaction_hash = String.downcase(transaction_id)
-    transaction = get_transaction(transaction_hash)
-
+  def index(conn, %{"transaction_id" => transaction_hash} = params) do
+    case Chain.hash_to_transaction(
+           transaction_hash,
+           necessity_by_association: %{from_address: :required, to_address: :required}
+         ) do
+      {:ok, transaction} ->
         logs =
-      from(
-        log in Log,
-        join: transaction in assoc(log, :transaction),
-        preload: [:address],
-        where: fragment("lower(?)", transaction.hash) == ^transaction_hash
+          Chain.transaction_to_logs(
+            transaction,
+            necessity_by_association: %{address: :optional},
+            pagination: params
           )
 
-    render(
-      conn,
-      "index.html",
-      logs: Repo.paginate(logs),
-      transaction: transaction
-    )
-  end
+        transaction_form = TransactionForm.build_and_merge(transaction)
+
+        render(conn, "index.html", logs: logs, transaction: transaction_form)
 
-  defp get_transaction(hash) do
-    Transaction
-    |> Query.by_hash(hash)
-    |> Query.include_addresses()
-    |> Query.include_receipt()
-    |> Query.include_block()
-    |> Repo.one()
-    |> TransactionForm.build_and_merge()
+      {:error, :not_found} ->
+        not_found(conn)
+    end
   end
 end

apps/explorer_web/lib/explorer_web/forms/block_form.ex

@@ -1,32 +1,17 @@
 defmodule ExplorerWeb.BlockForm do
   @moduledoc false
-  alias Explorer.Block
-  alias Explorer.BlockTransaction
-  alias Explorer.Repo
-  import Ecto.Query
+
+  alias Explorer.Chain
 
   def build(block) do
     block
     |> Map.merge(%{
-      transactions_count: block |> get_transactions_count,
-      age: block |> calculate_age,
-      formatted_timestamp: block |> format_timestamp
+      age: calculate_age(block),
+      formatted_timestamp: format_timestamp(block),
+      transactions_count: Chain.block_to_transaction_count(block)
     })
   end
 
-  def get_transactions_count(block) do
-    query =
-      from(
-        block_transaction in BlockTransaction,
-        join: block in Block,
-        where: block.id == block_transaction.block_id,
-        where: block.id == ^block.id,
-        select: count(block_transaction.block_id)
-      )
-
-    Repo.one(query)
-  end
-
   def calculate_age(block) do
     block.timestamp |> Timex.from_now()
   end

apps/explorer_web/lib/explorer_web/forms/pending_transaction_form.ex

@@ -3,30 +3,40 @@ defmodule ExplorerWeb.PendingTransactionForm do
 
   import ExplorerWeb.Gettext
 
+  alias Explorer.Chain.{Address, Transaction}
+
+  # Functions
+
   def build(transaction) do
     Map.merge(transaction, %{
-      to_address_hash: transaction |> to_address_hash,
-      from_address_hash: transaction |> from_address_hash,
-      first_seen: transaction |> first_seen,
-      last_seen: transaction |> last_seen,
+      first_seen: first_seen(transaction),
+      formatted_status: gettext("Pending"),
+      from_address_hash: from_address_hash(transaction),
+      last_seen: last_seen(transaction),
       status: :pending,
-      formatted_status: gettext("Pending")
+      to_address_hash: to_address_hash(transaction)
     })
   end
 
-  def to_address_hash(transaction) do
-    (transaction.to_address && transaction.to_address.hash) || nil
+  def first_seen(transaction) do
+    transaction.inserted_at |> Timex.from_now()
   end
 
-  def from_address_hash(transaction) do
-    (transaction.to_address && transaction.from_address.hash) || nil
+  def from_address_hash(%Transaction{from_address: from_address}) do
+    case from_address do
+      %Address{hash: hash} -> hash
+      _ -> nil
     end
-
-  def first_seen(transaction) do
-    transaction.inserted_at |> Timex.from_now()
   end
 
   def last_seen(transaction) do
     transaction.updated_at |> Timex.from_now()
   end
+
+  def to_address_hash(%Transaction{to_address: to_address}) do
+    case to_address do
+      %Address{hash: hash} -> hash
+      _ -> nil
+    end
+  end
 end

apps/explorer_web/lib/explorer_web/forms/transaction_form.ex

@@ -1,17 +1,15 @@
 defmodule ExplorerWeb.TransactionForm do
   @moduledoc "Format a Block and a Transaction for display."
 
-  import Ecto.Query
   import ExplorerWeb.Gettext
 
   alias Cldr.Number
-  alias Explorer.Block
-  alias Explorer.Receipt
-  alias Explorer.Repo
+  alias Explorer.Chain
+  alias Explorer.Chain.{Receipt, Transaction}
 
   def build(transaction) do
-    block = (Ecto.assoc_loaded?(transaction.block) && transaction.block) || nil
-    receipt = Ecto.assoc_loaded?(transaction.receipt) && transaction.receipt
+    block = block(transaction)
+    receipt = receipt(transaction)
     status = status(transaction, receipt || Receipt.null())
 
     %{
@@ -34,47 +32,38 @@ defmodule ExplorerWeb.TransactionForm do
     Map.merge(transaction, build(transaction))
   end
 
-  def block_number(block) do
-    (block && block.number) || ""
+  def block(%Transaction{block: block}) do
+    if Ecto.assoc_loaded?(block) do
+      block
+    else
+      nil
+    end
   end
 
   def block_age(block) do
     (block && block.timestamp |> Timex.from_now()) || gettext("Pending")
   end
 
-  def format_age(block) do
-    (block && "#{block_age(block)} (#{format_timestamp(block)})") || gettext("Pending")
+  def block_number(block) do
+    (block && block.number) || ""
   end
 
-  def format_timestamp(block) do
-    (block && block.timestamp |> Timex.format!("%b-%d-%Y %H:%M:%S %p %Z", :strftime)) ||
-      gettext("Pending")
+  def confirmations(nil), do: 0
+
+  def confirmations(block) do
+    Chain.confirmations(block, max_block_number: Chain.max_block_number())
   end
 
   def cumulative_gas_used(block) do
     (block && block.gas_used |> Number.to_string!()) || gettext("Pending")
   end
 
-  def to_address_hash(transaction) do
-    (transaction.to_address && transaction.to_address.hash) || nil
-  end
-
-  def from_address_hash(transaction) do
-    (transaction.to_address && transaction.from_address.hash) || nil
-  end
-
-  def confirmations(block) do
-    query = from(block in Block, select: max(block.number))
-    (block && Repo.one(query) - block.number) || 0
+  def first_seen(transaction) do
+    transaction.inserted_at |> Timex.from_now()
   end
 
-  def status(transaction, receipt) do
-    %{
-      0 => %{true => :out_of_gas, false => :failed},
-      1 => %{true => :success, false => :success}
-    }
-    |> Map.get(receipt.status, %{true: :pending, false: :pending})
-    |> Map.get(receipt.gas_used == transaction.gas)
+  def format_age(block) do
+    (block && "#{block_age(block)} (#{format_timestamp(block)})") || gettext("Pending")
   end
 
   def format_status(status) do
@@ -87,11 +76,37 @@ defmodule ExplorerWeb.TransactionForm do
     |> Map.fetch!(status)
   end
 
-  def first_seen(transaction) do
-    transaction.inserted_at |> Timex.from_now()
+  def format_timestamp(block) do
+    (block && block.timestamp |> Timex.format!("%b-%d-%Y %H:%M:%S %p %Z", :strftime)) ||
+      gettext("Pending")
+  end
+
+  def from_address_hash(transaction) do
+    (transaction.to_address && transaction.from_address.hash) || nil
   end
 
   def last_seen(transaction) do
     transaction.updated_at |> Timex.from_now()
   end
+
+  def receipt(%Transaction{receipt: receipt}) do
+    if Ecto.assoc_loaded?(receipt) do
+      receipt
+    else
+      nil
+    end
+  end
+
+  def status(transaction, receipt) do
+    %{
+      0 => %{true => :out_of_gas, false => :failed},
+      1 => %{true => :success, false => :success}
+    }
+    |> Map.get(receipt.status, %{true: :pending, false: :pending})
+    |> Map.get(receipt.gas_used == transaction.gas)
+  end
+
+  def to_address_hash(transaction) do
+    (transaction.to_address && transaction.to_address.hash) || nil
+  end
 end