defmodule Swoosh.ApiClient do
  @moduledoc """
  Specification for a Swoosh API client.

  It can be set to your own client with:

      config :swoosh, :api_client, MyAPIClient

  Swoosh comes with `Swoosh.ApiClient.Hackney` and `Swoosh.ApiClient.Finch`.
  """

  @type url :: binary()
  @type headers :: [{binary(), binary()}]
  @type body :: binary()
  @type status :: pos_integer()

  @doc """
  Callback to initializes the given api client.
  """
  @callback init() :: :ok

  @doc """
  Callback invoked when posting to a given URL.
  """
  @callback post(url, headers, body, Swoosh.Email.t()) ::
              {:ok, status, headers, body} | {:error, term()}

  @optional_callbacks init: 0

  @doc """
  API used by adapters to post to a given URL with headers, body, and email.
  """
  def post(url, headers, body, email) do
    api_client().post(url, headers, body, email)
  end

  @doc false
  def init do
    client = api_client()

    if Code.ensure_loaded?(client) and function_exported?(client, :init, 0) do
      :ok = client.init()
    end

    :ok
  end

  defp api_client do
    Application.fetch_env!(:swoosh, :api_client)
  end
end