defmodule Slack do
  @moduledoc """
  Slack is a genserver-ish interface for working with the Slack real time
  messaging API through a Websocket connection.

  To use this module you'll need a need a Slack API token which can be retrieved
  by following the [Token Generation Instructions] or by creating a new [bot
  integration].

  [Token Generation Instructions]: https://hexdocs.pm/slack/token_generation_instructions.html
  [bot integration]: https://api.slack.com/bot-users

  ## Examples

  ```
  defmodule Bot do
    use Slack

    def handle_event(message = %{type: "message"}, slack, state) do
      if message.text == "Hi" do
        send_message("Hello to you too!", message.channel, slack)
      end

      {:ok, state}
    end
    def handle_event(_, _, state), do: {:ok, state}
  end

  Slack.Bot.start_link(Bot, [], "API_TOKEN")
  ```

  `handle_*` methods are always passed `slack` and `state` arguments. The
  `slack` argument holds the state of Slack and is kept up to date
  automatically.

  In this example we're just matching against the message type and checking if
  the text content is "Hi" and if so, we reply with our own greeting.

  The message type is pattern matched against because the
  [Slack RTM API](https://api.slack.com/rtm) defines many different types of
  messages that we can receive. Because of this it's wise to write a catch-all
  `handle_event/3` in your bots to prevent crashing.

  ## Callbacks

  * `handle_connect(slack, state)` - called when connected to Slack.
  * `handle_event(message, slack, state)` - called when a message is received.
  * `handle_close(reason, slack, state)` - called when websocket is closed before process is terminated.
  * `handle_info(message, slack, state)` - called when any other message is received in the process mailbox.

  ## Slack argument

  The Slack argument that's passed to each callback is what contains all of the
  state related to Slack including a list of channels, users, groups, bots, and
  even the socket.

  Here's a list of what's stored:

  * me - The current bot/users information stored as a map of properties.
  * team - The current team's information stored as a map of properties.
  * bots - Stored as a map with id's as keys.
  * channels - Stored as a map with id's as keys.
  * groups - Stored as a map with id's as keys.
  * users - Stored as a map with id's as keys.
  * ims (direct message channels) - Stored as a map with id's as keys.
  * socket - The connection to Slack.
  * client - The client that makes calls to Slack.

  For all but `socket` and `client`, you can see what types of data to expect each of the
  types to contain from the [Slack API types] page.

  [Slack API types]: https://api.slack.com/types
  """

  defmacro __using__(_) do
    quote do
      import Slack
      import Slack.Lookups
      import Slack.Sends

      def handle_connect(_slack, state), do: {:ok, state}
      def handle_event(_message, _slack, state), do: {:ok, state}
      def handle_close(_reason, _slack, state), do: :close
      def handle_info(_message, _slack, state), do: {:ok, state}

      def child_spec(_opts) do
        %{
          id: __MODULE__,
          start: {__MODULE__, :start_link, []},
          type: :worker,
          restart: :permanent,
          shutdown: 500
        }
      end

      defoverridable handle_connect: 2,
                     handle_event: 3,
                     handle_close: 3,
                     handle_info: 3,
                     child_spec: 1
    end
  end
end