defmodule Money.ExchangeRates.Cache do
  @moduledoc """
  Defines a cache behaviour and default inplementation
  of a cache for exchange rates
  """

  @doc """
  Initialize the cache when the exchange rates
  retriever is started
  """
  @callback init() :: any()

  @doc """
  Terminate the cache when the retriver process
  stops normally
  """
  @callback terminate() :: any()

  @doc """
  Retrieve the latest exchange rates from the
  cache.
  """
  @callback latest_rates() :: {:ok, Map.t} | {:error, {Exception.t, String.t}}

  @doc """
  Returns the exchange rates for a given
  date.
  """
  @callback historic_rates(Date.t) :: {:ok, Map.t} | {:error, {Exception.t, String.t}}

  @doc """
  Store the latest exchange rates in the cache.
  """
  @callback store_latest_rates(Map.t, DateTime.t) :: :ok

  @doc """
  Store the historic exchange rates for a given
  date in the cache.
  """
  @callback store_historic_rates(Map.t, Date.t) :: :ok

  @doc """
  Return the value for a given key in the
  cache.
  """
  @callback get(any()) :: any()

  @doc """
  Put the given value under the given
  key in the cache.
  """
  @callback put(any(), any()) :: any()

  def latest_rates do
    cache().latest_rates
  end

  def historic_rates(date) do
    cache().historic_rates(date)
  end

  def cache do
    Money.ExchangeRates.Retriever.config.cache_module
  end
end