defmodule ECBRates do
  @moduledoc """
  This is the entrypoint for fetching EUR rates from ECB.
  """

  @doc """
  Fetches the rates for a given date (as Date struct or as a string in ISO8601 format).
  """
  def fetch(%Date{} = date), do: date |> Date.to_iso8601() |> fetch()

  def fetch(date) when is_binary(date) do
    value = ECBRates.Cache.get()

    case Map.get(value, date) do
      nil ->
        {:error, "No rate for #{date}"}

      data ->
        {:ok, data}
    end
  end

  @doc """
  Fetches the rates for a given date (as Date struct or as a string in ISO8601 format)
  and currency (using three letter symbol).
  """
  def fetch(date, currency) do
    case fetch(date) do
      {:error, reason} ->
        {:error, reason}

      {:ok, data} ->
        case Map.get(data, currency) do
          nil ->
            {:error, "No rate for #{currency} on #{date}"}

          rate ->
            {:ok, rate}
        end
    end
  end
end