defmodule EthereumJSONRPC do
  @moduledoc """
  Ethereum JSONRPC client.

  ## Configuration

  Configuration for parity URLs can be provided with the following mix config:

      config :ethereum_jsonrpc,
        url: "https://sokol.poa.network",
        trace_url: "https://sokol-trace.poa.network",
        http: [recv_timeout: 60_000, timeout: 60_000, hackney: [pool: :ethereum_jsonrpc]]

  Note: the tracing node URL is provided separately from `:url`, via `:trace_url`. The trace URL and is used for
  `fetch_internal_transactions`, which is only a supported method on tracing nodes. The `:http` option is passed
  directly to the HTTP library (`HTTPoison`), which forwards the options down to `:hackney`.
  """

  require Logger

  alias EthereumJSONRPC.{Blocks, Parity, Receipts, Transactions}

  @typedoc """
  Truncated 20-byte [KECCAK-256](https://en.wikipedia.org/wiki/SHA-3) hash encoded as a hexadecimal number in a
  `String.t`.
  """
  @type address :: String.t()

  @typedoc """
  Binary data encoded as a single hexadecimal number in a `String.t`
  """
  @type data :: String.t()

  @typedoc """
  A full 32-byte [KECCAK-256](https://en.wikipedia.org/wiki/SHA-3) hash encoded as a hexadecimal number in a `String.t`

  ## Example

     "0xe670ec64341771606e55d6b4ca35a1a6b75ee3d5145a99d05921026d1527331"

  """
  @type hash :: String.t()

  @typedoc """
  8 byte [KECCAK-256](https://en.wikipedia.org/wiki/SHA-3) hash of the proof-of-work.
  """
  @type nonce :: String.t()

  @typedoc """
  A number encoded as a hexadecimal number in a `String.t`

  ## Example

      "0x1b4"

  """
  @type quantity :: String.t()

  @typedoc """
  A logic block tag that can be used in place of a block number.

  | Tag          | Description                    |
  |--------------|--------------------------------|
  | `"earliest"` | The first block in the chain   |
  | `"latest"`   | The latest collated block.     |
  | `"pending"`  | The next block to be collated. |
  """
  @type tag :: String.t()

  @typedoc """
  Unix timestamp encoded as a hexadecimal number in a `String.t`
  """
  @type timestamp :: String.t()

  @doc """
  Fetches configuration for this module under `key`

  Configuration can be set a compile time using `config`

      config :ethereume_jsonrpc, key, value

  Configuration can be set a runtime using `Application.put_env/3`

      Application.put_env(:ethereume_jsonrpc, key, value)

  """
  def config(key) do
    Application.fetch_env!(:ethereum_jsonrpc, key)
  end

  @doc """
  Fetches address balances by address hashes.
  """
  def fetch_balances_by_hash(address_hashes) do
    address_hashes
    |> get_balance_requests()
    |> json_rpc(config(:url))
    |> handle_balances()
  end

  defp handle_balances({:ok, results}) do
    native_results =
      for response <- results, into: %{} do
        {response["id"], hexadecimal_to_integer(response["result"])}
      end

    {:ok, native_results}
  end

  defp handle_balances({:error, _reason} = err), do: err

  @doc """
  Fetches blocks by block hashes.

  Transaction data is included for each block.
  """
  def fetch_blocks_by_hash(block_hashes) do
    block_hashes
    |> get_block_by_hash_requests()
    |> json_rpc(config(:url))
    |> handle_get_blocks()
    |> case do
      {:ok, _next, results} -> {:ok, results}
      {:error, reason} -> {:error, reason}
    end
  end

  @doc """
  Fetches blocks by block number range.
  """
  def fetch_blocks_by_range(block_start, block_end) do
    block_start
    |> get_block_by_number_requests(block_end)
    |> json_rpc(config(:url))
    |> handle_get_blocks()
  end

  @doc """
  Fetches block number by `t:tag/0`.

  The `"earliest"` tag is the earlist block number, which is `0`.

      iex> EthereumJSONRPC.fetch_block_number_by_tag("earliest")
      {:ok, 0}

  ## Returns

   * `{:ok, number}` - the block number for the given `tag`.
   * `{:error, :invalid_tag}` - When `tag` is not a valid `t:tag/0`.
   * `{:error, reason}` - other JSONRPC error.

  """
  @spec fetch_block_number_by_tag(tag()) :: {:ok, non_neg_integer()} | {:error, reason :: :invalid_tag | term()}
  def fetch_block_number_by_tag(tag) when tag in ~w(earliest latest pending) do
    tag
    |> get_block_by_tag_request()
    |> json_rpc(config(:url))
    |> handle_get_block_by_tag()
  end

  @doc """
  Fetches internal transactions from client-specific API.
  """
  def fetch_internal_transactions(hashes) when is_list(hashes) do
    Parity.fetch_internal_transactions(hashes)
  end

  def fetch_transaction_receipts(hashes) when is_list(hashes) do
    Receipts.fetch(hashes)
  end

  @doc """
    1. POSTs JSON `payload` to `url`
    2. Decodes the response
    3. Handles the response

  ## Returns

    * Handled response
    * `{:error, reason}` if POST failes
  """
  def json_rpc(payload, url) do
    json = encode_json(payload)
    headers = [{"Content-Type", "application/json"}]

    case HTTPoison.post(url, json, headers, config(:http)) do
      {:ok, %HTTPoison.Response{body: body, status_code: code}} ->
        body |> decode_json(payload, url) |> handle_response(code)

      {:error, %HTTPoison.Error{reason: reason}} ->
        {:error, reason}
    end
  end

  @doc """
  Converts `t:nonce/0` to `t:non_neg_integer/0`
  """
  def nonce_to_integer(nonce) do
    hexadecimal_to_integer(nonce)
  end

  @doc """
  Converts `t:quantity/0` to `t:non_neg_integer/0`.
  """
  def quantity_to_integer(quantity) do
    hexadecimal_to_integer(quantity)
  end

  @doc """
  Converts `t:timestamp/0` to `t:DateTime.t/0`
  """
  def timestamp_to_datetime(timestamp) do
    timestamp
    |> hexadecimal_to_integer()
    |> Timex.from_unix()
  end

  defp get_balance_requests(address_hashes) do
    for address_hash <- address_hashes do
      get_balance_request(%{id: address_hash, hash: address_hash})
    end
  end

  defp get_balance_request(%{id: id, hash: hash}) do
    request(%{id: id, method: "eth_getBalance", params: [hash, "latest"]})
  end

  defp get_block_by_hash_requests(block_hashes) do
    for block_hash <- block_hashes do
      get_block_by_hash_request(%{id: block_hash, hash: block_hash, transactions: :full})
    end
  end

  defp get_block_by_hash_request(%{id: id} = options) do
    request(%{id: id, method: "eth_getBlockByHash", params: get_block_by_hash_params(options)})
  end

  defp get_block_by_hash_params(%{hash: hash} = options) do
    [hash, get_block_transactions(options)]
  end

  defp get_block_by_number_requests(block_start, block_end) do
    for current <- block_start..block_end do
      get_block_by_number_request(%{id: current, quantity: current, transactions: :full})
    end
  end

  defp get_block_by_number_request(%{id: id} = options) do
    request(%{id: id, method: "eth_getBlockByNumber", params: get_block_by_number_params(options)})
  end

  defp get_block_by_tag_request(tag) do
    # eth_getBlockByNumber accepts either a number OR a tag
    get_block_by_number_request(%{id: tag, tag: tag, transactions: :hashes})
  end

  defp request(%{id: id, method: method, params: params}) do
    %{
      "id" => id,
      "jsonrpc" => "2.0",
      "method" => method,
      "params" => params
    }
  end

  defp get_block_by_number_params(options) do
    [get_block_by_number_subject(options), get_block_transactions(options)]
  end

  defp get_block_by_number_subject(options) do
    case {Map.fetch(options, :quantity), Map.fetch(options, :tag)} do
      {{:ok, quantity}, :error} ->
        int_to_hash_string(quantity)

      {:error, {:ok, tag}} ->
        tag

      {{:ok, _}, {:ok, _}} ->
        raise ArgumentError, "Only one of :quantity or :tag can be passed to get_block_by_number_request"

      {:error, :error} ->
        raise ArgumentError, "One of :quantity or :tag MUST be passed to get_block_by_number_request"
    end
  end

  defp get_block_transactions(%{transactions: transactions}) do
    case transactions do
      :full -> true
      :hashes -> false
    end
  end

  defp encode_json(data), do: Jason.encode_to_iodata!(data)

  defp decode_json(body, posted_payload, url) do
    Jason.decode!(body)
  rescue
    Jason.DecodeError ->
      Logger.error("""
      failed to decode json payload:

          url: #{inspect(url)}

          body: #{inspect(body)}

          posted payload: #{inspect(posted_payload)}

      """)

      raise("bad jason")
  end

  defp handle_get_blocks({:ok, results}) do
    {blocks, next} =
      Enum.reduce(results, {[], :more}, fn
        %{"result" => nil}, {blocks, _} -> {blocks, :end_of_chain}
        %{"result" => %{} = block}, {blocks, next} -> {[block | blocks], next}
      end)

    elixir_blocks = Blocks.to_elixir(blocks)
    elixir_transactions = Blocks.elixir_to_transactions(elixir_blocks)
    blocks_params = Blocks.elixir_to_params(elixir_blocks)
    transactions_params = Transactions.elixir_to_params(elixir_transactions)

    {:ok, next,
     %{
       blocks: blocks_params,
       transactions: transactions_params
     }}
  end

  defp handle_get_blocks({:error, _} = error), do: error

  defp handle_get_block_by_tag({:ok, %{"number" => quantity}}) do
    {:ok, quantity_to_integer(quantity)}
  end

  defp handle_get_block_by_tag({:error, %{"code" => -32602}}), do: {:error, :invalid_tag}
  defp handle_get_block_by_tag({:error, _} = error), do: error

  defp handle_response(resp, 200) do
    case resp do
      [%{} | _] = batch_resp -> {:ok, batch_resp}
      %{"error" => error} -> {:error, error}
      %{"result" => result} -> {:ok, result}
    end
  end

  defp handle_response(resp, _status) do
    {:error, resp}
  end

  defp hexadecimal_to_integer("0x" <> hexadecimal_digits) do
    String.to_integer(hexadecimal_digits, 16)
  end

  defp int_to_hash_string(number), do: "0x" <> Integer.to_string(number, 16)
end