defmodule WechatPay do
  @moduledoc """
  WechatPay provide toolkit for Wechat Payment Platform.

  ### Setup

  You need to define you own pay module, then `use` WechatPay:

  ```elixir
  defmodule MyPay do
    use WechatPay, otp_app: :my_app
  end
  ```

  Then config your app in `config/config.exs`:

  ```elixir
  config :my_app, MyPay,
    appid: "the-appid",
    mch_id: "the-mch-id",
    apikey: "the-apikey",
    ssl_cacert: File.read!("fixture/certs/rootca.pem"),
    ssl_cert: File.read!("fixture/certs/apiclient_cert.pem"),
    ssl_key: File.read!("fixture/certs/apiclient_key.pem")
  ```

  If this does not fit your needs, you might want to check [Configuration](configuration.html).

  > NOTE: WechatPay provide `Mix.Tasks.WechatPay.GetSandboxSignkey` to
  > fetch the Sandbox API Key.

  ### Payment methods

  When `use` WechatPay in `MyPay` module, it will generate following
  modules for you:

  - `MyPay.App` - Implements the `WechatPay.App.Behaviour` behaviour
  - `MyPay.JSAPI` - Implements the `WechatPay.JSAPI.Behaviour` behaviour
  - `MyPay.Native` - Implements the `WechatPay.Native.Behaviour` behaviour

  ### Plug

  WechatPay will also generate some [Plugs](https://github.com/elixir-plug/plug) to
  simplify the process of handling notification from Wechat's Payment Gateway:

  - `MyPay.Plug.Payment` - Implements the `WechatPay.Plug.Payment` behaviour
  - `MyPay.Plug.Refund` - Implements the `WechatPay.Plug.Refund` behaviour

  ### JSON Encoder

  By default, `WechatPay` use `Jason` to encode JSON, if you want to use `Poison`,
  you can configure `:wechat_pay` application with:

  ```elixir
  config :wechat_pay, :json_library, Poison
  ```
  """

  alias WechatPay.Config

  defmacro __using__(opts) do
    opts =
      opts
      |> Enum.into(%{})

    config_ast =
      case opts do
        %{otp_app: otp_app} ->
          quote do
            @behaviour Config

            def config do
              unquote(otp_app)
              |> Application.fetch_env!(__MODULE__)
              |> Config.new()
            end
          end

        _ ->
          quote do
            @behaviour Config
          end
      end

    module_ast =
      quote do
        # define module `MyModule.App`
        __MODULE__
        |> Module.concat(:App)
        |> Module.create(
          quote do
            use WechatPay.App, unquote(__MODULE__)
          end,
          Macro.Env.location(__ENV__)
        )

        # define module `MyModule.JSAPI`
        __MODULE__
        |> Module.concat(:JSAPI)
        |> Module.create(
          quote do
            use WechatPay.JSAPI, unquote(__MODULE__)
          end,
          Macro.Env.location(__ENV__)
        )

        # define module `MyModule.Native`
        __MODULE__
        |> Module.concat(:Native)
        |> Module.create(
          quote do
            use WechatPay.Native, unquote(__MODULE__)
          end,
          Macro.Env.location(__ENV__)
        )

        # define module `MyModule.Plug.Payment` & `MyModule.Plug.Refund`
        if Code.ensure_loaded?(Plug) do
          [__MODULE__, :Plug, :Payment]
          |> Module.concat()
          |> Module.create(
            quote do
              use WechatPay.Plug.Payment, unquote(__MODULE__)
            end,
            Macro.Env.location(__ENV__)
          )

          [__MODULE__, :Plug, :Refund]
          |> Module.concat()
          |> Module.create(
            quote do
              use WechatPay.Plug.Refund, unquote(__MODULE__)
            end,
            Macro.Env.location(__ENV__)
          )
        end
      end

    [config_ast, module_ast]
  end
end