defmodule Riverside.Connection do
  @behaviour :cowboy_websocket

  require Logger

  alias Riverside.AuthRequest
  alias Riverside.AuthError
  alias Riverside.ExceptionGuard
  alias Riverside.IO.Random
  alias Riverside.LocalDelivery
  alias Riverside.PeerAddress
  alias Riverside.Session
  alias Riverside.Stats
  alias Riverside.Util.CowboyUtil

  @type shutdown_reason :: :too_many_messages

  @type t :: %__MODULE__{
          handler: module,
          session: Session.t(),
          shutdown_reason: shutdown_reason | nil,
          handler_state: any
        }

  defstruct handler: nil,
            session: nil,
            shutdown_reason: nil,
            handler_state: nil

  @spec new(
          handler :: module,
          user_id :: Session.user_id(),
          session_id :: Session.session_id(),
          peer :: PeerAddress.t(),
          handler_state :: any
        ) :: t

  def new(handler, user_id, session_id, peer, handler_state) do
    %__MODULE__{
      handler: handler,
      session: Session.new(user_id, session_id, peer),
      shutdown_reason: nil,
      handler_state: handler_state
    }
  end

  def init(req, opts) do
    ExceptionGuard.guard(
      "<Riverside.Connection:#{inspect(self())}> init",
      fn -> {:ok, CowboyUtil.response(req, 500, %{})} end,
      fn ->
        peer = PeerAddress.gather(req)

        handler = Keyword.fetch!(opts, :handler)

        if handler.__config__.show_debug_logs do
          Logger.debug("<Riverside.Connection:#{inspect(self())}> incoming new request: #{peer}")
        end

        if Stats.number_of_current_connections() >=
             handler.__config__.max_connections do
          Logger.warn(
            "<Riverside.Connection:#{inspect(self())}> connection number reached the limit."
          )

          # :cow_http.status/1 doesn't support 508, so use 503 instead
          {:ok, CowboyUtil.response(req, 503, %{}), {:unset, handler.__config__.show_debug_logs}}
        else
          auth_req = AuthRequest.new(req, peer)

          case handler.__handle_authentication__(auth_req) do
            {:ok, user_id, handler_state} ->
              timeout = handler.__config__.idle_timeout
              session_id = Random.hex(20)
              state = new(handler, user_id, session_id, peer, handler_state)
              {:cowboy_websocket, req, state, %{idle_timeout: timeout}}

            {:ok, user_id, session_id, handler_state} ->
              timeout = handler.__config__.idle_timeout
              state = new(handler, user_id, session_id, peer, handler_state)
              {:cowboy_websocket, req, state, %{idle_timeout: timeout}}

            {:error, %AuthError{code: code, headers: headers}} ->
              {:ok, CowboyUtil.response(req, code, headers),
               {:unset, handler.__config__.show_debug_logs}}

            other ->
              if handler.__config__.show_debug_logs do
                Logger.debug(
                  "<Riverside.Connection:#{inspect(self())}> failed to authenticate by reason: #{inspect(other)}, shutdown"
                )
              end

              {:ok, CowboyUtil.response(req, 500, %{}),
               {:unset, handler.__config__.show_debug_logs}}
          end
        end
      end
    )
  end

  def websocket_init(state) do
    ExceptionGuard.guard(
      "<Riverside.Connection:#{inspect(self())}>(#{state.session}) websocket_init",
      fn -> {:stop, state} end,
      fn ->
        if state.handler.__config__.show_debug_logs do
          Logger.debug("<Riverside.Connection:#{inspect(self())}>(#{state.session}) @init")
        end

        if Stats.number_of_current_connections() >=
             state.handler.__config__.max_connections do
          Logger.warn("<Riverside.Connection:#{inspect(self())}> connection number is over limit")

          {:stop, state}
        else
          Process.flag(:trap_exit, true)

          send(self(), :post_init)

          Stats.countup_connections()

          LocalDelivery.register(state.session.user_id, state.session.id)

          {:ok, state}
        end
      end
    )
  end

  def websocket_info(:post_init, state) do
    ExceptionGuard.guard(
      "<Riverside.Connection:#{inspect(self())}>(#{state.session}) websocket_info",
      fn -> {:stop, state} end,
      fn ->
        if state.handler.__config__.show_debug_logs do
          Logger.debug("<Riverside.#{inspect(self())}>(#{state.session}) @post_init")
        end

        case state.handler.init(state.session, state.handler_state) do
          {:ok, session2, handler_state2} ->
            if state.handler.__config__.connection_max_age != :infinity do
              Process.send_after(self(), :over_age, state.handler.__config__.connection_max_age)
            end

            state2 = %{state | session: session2, handler_state: handler_state2}
            {:ok, state2, :hibernate}

          {:error, reason} ->
            Logger.info(
              "<Riverside.Connection:#{inspect(self())}>(#{state.session}) failed to initialize: #{inspect(reason)}"
            )

            {:stop, state}
        end
      end
    )
  end

  def websocket_info(:over_age, state) do
    if state.handler.__config__.show_debug_logs do
      Logger.debug("<Riverside.Connection:#{inspect(self())}>(#{state.session}) @over_age")
    end

    {:stop, %{state | shutdown_reason: :over_age}}
  end

  def websocket_info(:stop, state) do
    if state.handler.__config__.show_debug_logs do
      Logger.debug("<Riverside.Connection:#{inspect(self())}>(#{state.session}) @stop")
    end

    {:stop, state}
  end

  def websocket_info({:deliver, type, msg}, state) do
    if state.handler.__config__.show_debug_logs do
      Logger.debug("<Riverside.Connection:#{inspect(self())}>(#{state.session}) @deliver")
    end

    Stats.countup_outgoing_messages()

    {:reply, {type, msg}, state, :hibernate}
  end

  def websocket_info({:EXIT, pid, reason}, %{session: session} = state) do
    ExceptionGuard.guard(
      "<Riverside.Connection:#{inspect(self())}>(#{session}) websocket_info",
      fn -> {:stop, state} end,
      fn ->
        if state.handler.__config__.show_debug_logs do
          Logger.debug(
            "<Riverside.Connection:#{inspect(self())}>(#{session}) @exit: #{inspect(pid)} -> #{inspect(self())}"
          )
        end

        if Session.should_delegate_exit?(session, pid) do
          session2 = Session.forget_to_trap_exit(session, pid)

          state2 = %{state | session: session2}

          handler_info({:EXIT, pid, reason}, state2)
        else
          {:stop, state}
        end
      end
    )
  end

  def websocket_info(event, state) do
    ExceptionGuard.guard(
      "<Riverside.Connection:#{inspect(self())}>(#{state.session}) websocket_info",
      fn -> {:stop, state} end,
      fn ->
        if state.handler.__config__.show_debug_logs do
          Logger.debug(
            "<Riverside.Connection:#{inspect(self())}>(#{state.session}) @info: #{inspect(event)}"
          )
        end

        handler_info(event, state)
      end
    )
  end

  defp handler_info(event, state) do
    case state.handler.handle_info(event, state.session, state.handler_state) do
      {:ok, session2, handler_state2} ->
        state2 = %{state | session: session2, handler_state: handler_state2}
        {:ok, state2}

      {:stop, reason, handler_state2} ->
        {:stop, %{state | shutdown_reason: reason, handler_state: handler_state2}}

      # TODO support reply?
      _other ->
        {:stop, state}
    end
  end

  def websocket_handle(:ping, state) do
    ExceptionGuard.guard(
      "<Riverrise.Connection:#{inspect(self())}> websocket_handle",
      fn -> {:stop, state} end,
      fn ->
        if state.handler.__config__.show_debug_logs do
          Logger.debug("<Riverside.Connection:#{inspect(self())}>(#{state.session}) @ping")
        end

        handle_frame(:ping, nil, state)
      end
    )
  end

  def websocket_handle({:binary, data}, state) do
    ExceptionGuard.guard(
      "<Riverside.Connection:#{inspect(self())}> websocket_handle",
      fn -> {:stop, state} end,
      fn ->
        if state.handler.__config__.show_debug_logs do
          Logger.debug("<Riverside.Connection:#{inspect(self())}>(#{state.session}) @binary")
        end

        handle_frame(:binary, data, state)
      end
    )
  end

  def websocket_handle({:text, data}, state) do
    ExceptionGuard.guard(
      "<Riverside.Connection:#{inspect(self())}>(#{state.session}) websocket_handle",
      fn -> {:stop, state} end,
      fn ->
        if state.handler.__config__.show_debug_logs do
          Logger.debug("<Riverside.Connection:#{inspect(self())}>(#{state.session}) @text")
        end

        handle_frame(:text, data, state)
      end
    )
  end

  def websocket_handle(event, state) do
    if state.handler.__config__.show_debug_logs do
      Logger.debug(
        "<Riverside.Connection:#{inspect(self())}>(#{state.session}) handle: unsupported event #{inspect(event)}"
      )
    end

    {:ok, state}
  end

  def terminate(reason, _req, {:unset, show_debug_logs}) do
    if show_debug_logs do
      Logger.debug("<Riverside.Connection:#{inspect(self())}> @terminate: #{inspect(reason)}")
    end

    :ok
  end

  def terminate(reason, _req, %{shutdown_reason: nil} = state) do
    ExceptionGuard.guard(
      "<Riverside.Connection:#{inspect(self())}>(#{state.session}) terminate",
      fn -> :ok end,
      fn ->
        if state.handler.__config__.show_debug_logs do
          Logger.debug(
            "<Riverside.Connection:#{inspect(self())}>(#{state.session}) @terminate: #{inspect(reason)}"
          )
        end

        state.handler.terminate(reason, state.session, state.handler_state)

        Stats.countdown_connections()

        :ok
      end
    )
  end

  def terminate(reason, _req, state) do
    ExceptionGuard.guard(
      "<Riverside.Connection:#{inspect(self())}>(#{state.session}) terminate",
      fn -> :ok end,
      fn ->
        if state.handler.__config__.show_debug_logs do
          Logger.debug(
            "<Riverside.Connection:#{inspect(self())}>(#{state.session}) @terminate: #{inspect(reason)}"
          )
        end

        state.handler.terminate(state.shutdown_reason, state.session, state.handler_state)

        Stats.countdown_connections()

        :ok
      end
    )
  end

  defp handle_frame(type, data, %{handler: handler, session: session} = state) do
    Stats.countup_incoming_messages()

    case Session.countup_messages(session, handler.__config__.transmission_limit) do
      {:ok, session2} ->
        state2 = %{state | session: session2}

        case handle_data(type, data, state2) do
          {:ok, session3, handler_state3} ->
            state3 = %{state2 | session: session3, handler_state: handler_state3}
            {:ok, state3, :hibernate}

          {:stop, reason, handler_state3} ->
            {:stop, %{state2 | shutdown_reason: reason, handler_state: handler_state3}}

          {:error, reason} ->
            if state.handler.__config__.show_debug_logs do
              Logger.debug(
                "<Riverside.Connection:#{inspect(self())}>(#{session2}) failed to handle frame_type #{inspect(type)}: #{inspect(reason)}"
              )
            end

            {:ok, state2}
        end

      {:error, :too_many_messages} ->
        Logger.debug(
          "<Riverside.Connection:#{inspect(self())}>(#{session}) too many messages: #{Session.peer_address(session)}"
        )

        {:stop, %{state | shutdown_reason: :too_many_messages}}
    end
  end

  defp handle_data(:text, data, state) do
    state.handler.__handle_data__(:text, data, state.session, state.handler_state)
  end

  defp handle_data(:binary, data, state) do
    state.handler.__handle_data__(:binary, data, state.session, state.handler_state)
  end

  defp handle_data(:ping, _data, state) do
    {:ok, state.session, state.handler_state}
  end
end