module to calculate market cap

apps/explorer/config/test.exs

@@ -27,6 +27,9 @@ if File.exists?(file = "test.secret.exs") do
   import_config file
 end
 
+config :explorer, Explorer.ExchangeRates.Source.TransactionAndLog,
+  secondary_source: Explorer.ExchangeRates.Source.OneCoinSource
+
 variant =
   if is_nil(System.get_env("ETHEREUM_JSONRPC_VARIANT")) do
     "parity"

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

@@ -0,0 +1,50 @@
+defmodule Explorer.ExchangeRates.Source.TransactionAndLog do
+  @moduledoc """
+  Adapter for calculating the market cap and total supply from logs and transactions
+  while still getting other info like price in dollars and bitcoin from a secondary source
+  """
+
+  alias Explorer.ExchangeRates.{Source, Token}
+  alias Explorer.Chain
+
+  @behaviour Source
+
+  @impl Source
+  def fetch_exchange_rates do
+    token_data =
+      secondary_source().fetch_exchange_rates()
+      |> elem(1)
+      |> Enum.find(fn token -> token.symbol == Explorer.coin() end)
+      |> build_struct
+
+    {:ok, [token_data]}
+  end
+
+  defp build_struct(original_token) do
+    %Token{
+      available_supply: to_decimal(Chain.circulating_supply()),
+      btc_value: original_token.btc_value,
+      id: original_token.id,
+      last_updated: original_token.last_updated,
+      market_cap_usd: Decimal.mult(to_decimal(Chain.circulating_supply()), original_token.usd_value),
+      name: original_token.name,
+      symbol: original_token.symbol,
+      usd_value: original_token.usd_value,
+      volume_24h_usd: original_token.volume_24h_usd
+    }
+  end
+
+  defp to_decimal(value) do
+    Decimal.new(value)
+  end
+
+  @spec secondary_source() :: module()
+  defp secondary_source do
+    config(:secondary_source) || Explorer.ExchangeRates.Source.CoinMarketCap
+  end
+
+  @spec config(atom()) :: term
+  defp config(key) do
+    Application.get_env(:explorer, __MODULE__, [])[key]
+  end
+end

apps/explorer/test/explorer/exchange_rates/source/transaction_and_log_test.exs

@@ -0,0 +1,11 @@
+defmodule Explorer.ExchangeRates.Source.TransactionAndLogTest do
+  use Explorer.DataCase
+  alias Explorer.ExchangeRates.Source.TransactionAndLog
+  alias Explorer.ExchangeRates.Token
+
+  describe "fetch_exchange_rates/1" do
+    test "bring a list with one %Token{}" do
+      assert {:ok, [%Token{}]} = TransactionAndLog.fetch_exchange_rates()
+    end
+  end
+end

apps/explorer/test/support/fakes/one_coin_source.ex

@@ -0,0 +1,25 @@
+defmodule Explorer.ExchangeRates.Source.OneCoinSource do
+  @moduledoc false
+
+  alias Explorer.ExchangeRates.Source
+  alias Explorer.ExchangeRates.Token
+
+  @behaviour Source
+
+  @impl Source
+  def fetch_exchange_rates do
+    pseudo_token = %Token{
+      available_supply: Decimal.new(10_000_000),
+      btc_value: Decimal.new(1),
+      id: "",
+      last_updated: Timex.now(),
+      name: "",
+      market_cap_usd: Decimal.new(10_000_000),
+      symbol: Explorer.coin(),
+      usd_value: Decimal.new(1),
+      volume_24h_usd: Decimal.new(1)
+    }
+
+    {:ok, [pseudo_token]}
+  end
+end