mammoth

defmodule Mammoth do
  @moduledoc ~S"""
  Mammoth: A STOMP client.

  Use `Mammoth` as the primary API and `Mammoth.Message` for working with received messages.

  ## Example
      {:ok, callback_pid} = Mammoth.DefaultCallbackHandler.start_link
      {:ok, pid} = Mammoth.start_link(callback_pid)
      Mammoth.connect(pid, {127,0,0,1}, 61613, "admin", "admin")
      Mammoth.subscribe(pid, "foo.bar")
      Mammoth.disconnect(pid)

  ## Starting in a supervision tree

      children = [
        worker(Mammoth, [%{}, [name: Mammoth]])
      ]
  """

  use GenServer

  require Logger
  alias Mammoth.{Message, Receiver, Socket, Subscriber}

  def init(args) do
    {
      :ok,
      args
      |> Map.put_new(:socket, nil)
      |> Map.put_new(:receiver, nil)
      |> Map.put_new(:subscriber, nil)
    }
  end

  def start_link(callback_handler, state \\ %{}, opts \\ []) do
    GenServer.start_link(
      __MODULE__,
      state |> Map.put_new(:callback_handler, callback_handler),
      opts
    )
  end

  @doc """
  Connect to server.

  `host` must be `inet:socket_address() | inet:hostname()`, for example `{127,0,0,1}`.
  """
  def connect(pid, host, port, login, password) do
    GenServer.call(pid, {:connect, host, port, login, password})
  end

  @doc """
  Subscribe to a queue.
  """
  def subscribe(pid, destination) do
    GenServer.call(pid, {:subscribe, destination})
  end

  @doc """
  Unsubscribe from a queue.
  """
  def unsubscribe(pid, destination) do
    GenServer.call(pid, {:unsubscribe, destination})
  end

  @doc """
  Receive messages from the TCP socket.

  Is called automatically when necessary. Should not be called manually.
  """
  def receive(pid, message) do
    GenServer.call(pid, {:receive, message})
  end

  @doc """
  Disconnect from server.
  """
  def disconnect(pid) do
    GenServer.call(pid, :disconnect)
  end

  def handle_call(
        {:receive, message},
        _from,
        state = %{callback_handler: callback_handler}
      ) do
    Kernel.send(callback_handler, {:mammoth, :receive_frame, message})

    {:reply, :ok, state}
  end

  def handle_call({:connect, host, port, login, password}, _from, state) do
    # todo: handle {:error, :econnrefused} response
    {:ok, socket} = Socket.connect(host, port)
    Socket.send(socket, connect_message(login, password))

    {:ok, subscriber} = Subscriber.start_link()
    {:ok, receiver} = Receiver.start_link(%{socket: socket, consumer: self()})
    Receiver.listen(receiver)

    {:reply, socket, %{state | socket: socket, subscriber: subscriber, receiver: receiver}}
  end

  @doc """
  Requests disconnection from the remote server
  """
  def handle_call(
        :disconnect,
        _from,
        state = %{
          socket: socket
        }
      ) do
    receipt_id = Enum.random(1000..1_000_000)
    Socket.send(socket, disconnect_message(receipt_id))

    {:noreply, Map.put(state, :disconnect_id, receipt_id)}
  end

  def handle_call(
        {:subscribe, destination},
        _from,
        state = %{socket: socket, subscriber: subscriber}
      ) do
    {:ok, entry} = Subscriber.subscribe(subscriber, destination)
    message = subscribe_message(destination, entry.id)
    Socket.send(socket, message)
    {:reply, {:ok, entry}, state}
  end

  def handle_call(
        {:unsubscribe, destination},
        _from,
        state = %{socket: socket, subscriber: subscriber}
      ) do
    {:ok, entry} = Subscriber.unsubscribe(subscriber, destination)
    message = unsubscribe_message(entry.id)
    Socket.send(socket, message)
    {:reply, :ok, state}
  end

  def handle_cast(
        :disconnected,
        state = %{
          subscriber: subscriber,
          receiver: receiver,
          callback_handler: callback_handler,
          disconnect_id: _disconnect_id
        }
      ) do
    Subscriber.stop(subscriber)
    Receiver.stop(receiver)

    Kernel.send(callback_handler, {:mammoth, :disconnected, true})

    {:noreply, state}
  end

  def handle_cast(
        :disconnected,
        state = %{
          subscriber: subscriber,
          receiver: receiver,
          callback_handler: callback_handler
        }
      ) do
    Subscriber.stop(subscriber)
    Receiver.stop(receiver)

    Kernel.send(callback_handler, {:mammoth, :disconnected, false})

    {:noreply, state}
  end

  defp connect_message(login, password) do
    %Message{
      command: :connect,
      headers: [
        {"accept-version", "1.2"},
        {"host", "localhost"},
        {"login", login},
        {"passcode", password}
      ]
    }
  end

  defp disconnect_message(receipt_id) do
    %Message{
      command: :disconnect,
      headers: [
        {"receipt-id", receipt_id}
      ]
    }
  end

  defp subscribe_message(destination, id) do
    %Message{
      command: :subscribe,
      headers: [
        {"destination", destination},
        {"ack", "auto"},
        {"id", id}
      ]
    }
  end

  defp unsubscribe_message(id) do
    %Message{
      command: :unsubscribe,
      headers: [
        {"id", id}
      ]
    }
  end
end