defmodule Wideact do
	@moduledoc """
	This is Wideact: an inter-lingual actor system.
	"""

	use Application

	@doc """
	Starts the application with arguments being an array containing only the port number (default: 40444).
	"""
	def start(_type, args) do
		import Supervisor.Spec

		Process.register(spawn(StaleMail, :start, []), :stalemail)

		children = [
			supervisor(Task.Supervisor, [[ name: Wideact.TaskSupervisor ]]),
			worker(Task, [ Wideact, :accept, args ])
		]

		opts = [ strategy: :one_for_one, name: Wideact.Supervisor ]
		Supervisor.start_link(children, opts)
	end

	@doc """
	Opens a listener port and starts accepting connections.
	"""
	def accept(port) do
		{ :ok, socket } = :gen_tcp.listen(port, 
			[ :binary, packet: :line, active: false, reuseaddr: true, send_timeout: 40 ])
		loop_acceptor(socket)
	end

	@doc """
	Loops and accepts clients, setting up the consumer connections in the process.
	"""
	defp loop_acceptor(socket) do
		{ :ok, client } = :gen_tcp.accept(socket)
		{ :ok, pid } = Task.Supervisor.start_child(Wideact.TaskSupervisor, fn -> setup(client) end)
		:gen_tcp.controlling_process(client, pid)
			
		loop_acceptor(socket)
	end

	@doc """
	A receiving loop, checking the stale mail for messages.
	"""
	defp recvloop(client, name) do
		receive do
			{ :received_message, sender, message } ->

				case :gen_tcp.send(client, "MESSAGE #{sender} #{message}\n") do
					:ok -> 
						send :stalemail, { :got_mail, name }
					{ :error, _reason } -> 
						exit(:normal)
				end
			_ -> exit(:normal)
		after 
			10 -> send :stalemail, { :new_mail, name, self() } 
		end

		recvloop(client, name)
	end

	@doc """
	Sets the connection up. If the first message isn't a [ CONNECT name ] message, stop the client, because of protocol breach.
	"""
	defp setup(socket) do
		case :gen_tcp.recv(socket, 0) do
			{ :ok, data } ->
				case data |> String.split(" ", parts: 2) do
					[ "CONNECT", name ] ->
						send :stalemail, { :new_mailbox, name, self() }
						spawn(fn ->
							recvloop(socket, name) 
						end)
						serve(socket, name)
					_ ->
						:gen_tcp.close(socket)
						exit(:normal)
				end
			_ -> 
				:gen_tcp.close(socket)
				exit(:normal)
		end
	end

	@doc """
	Serve the content to the socket under a given name.
	""" 
	defp serve(socket, name) do
		case :gen_tcp.recv(socket, 0) do
			{ :ok, data } ->
				case data |> String.split(" ", parts: 3) do
					[ "MESSAGE", receiver, message ] ->
						send :stalemail, { :pass_message, receiver, message, name }
				end
			{ :error, _reason } -> nil
		end

		serve(socket, name)
	end
end