defmodule Membrane.RTC.Engine.Endpoint.RTSP.ConnectionManager do
  @moduledoc false
  use Connection

  require Membrane.Logger

  alias Membrane.RTSP

  defmodule ConnectionStatus do
    @moduledoc false
    use Bunch.Access

    @type t :: %__MODULE__{
            stream_uri: binary(),
            rtsp_session: pid(),
            endpoint: pid(),
            keep_alive: pid(),
            endpoint_options: map(),
            reconnect_delay: non_neg_integer(),
            keep_alive_interval: non_neg_integer(),
            max_reconnect_attempts: non_neg_integer() | :infinity,
            reconnect_attempt: non_neg_integer()
          }

    @enforce_keys [
      :stream_uri,
      :endpoint,
      :endpoint_options,
      :reconnect_delay,
      :keep_alive_interval,
      :max_reconnect_attempts,
      :reconnect_attempt
    ]

    defstruct @enforce_keys ++
                [
                  :rtsp_session,
                  :keep_alive
                ]
  end

  @spec reconnect(GenServer.server()) :: :ok
  def reconnect(connection_manager) do
    GenServer.cast(connection_manager, :reconnect)
  end

  @spec start_link(Keyword.t()) :: GenServer.on_start()
  def start_link(args) do
    Membrane.Logger.debug("ConnectionManager: start_link, args: #{inspect(args)}")

    Connection.start_link(__MODULE__, args)
  end

  @impl true
  def init(opts) do
    Membrane.Logger.debug("ConnectionManager: Initializing")

    {:connect, :init,
     %ConnectionStatus{
       stream_uri: opts[:stream_uri],
       endpoint_options: %{
         port: opts[:port],
         rtpmap: nil,
         fmtp: nil,
         control: nil,
         server_port: nil
       },
       endpoint: opts[:endpoint],
       reconnect_delay: opts[:reconnect_delay],
       keep_alive_interval: opts[:keep_alive_interval],
       max_reconnect_attempts: opts[:max_reconnect_attempts],
       reconnect_attempt: 0
     }}
  end

  @impl true
  def connect(info, %ConnectionStatus{} = connection_status) do
    Membrane.Logger.debug("ConnectionManager: Connecting (info: #{inspect(info)})")

    rtsp_session = start_rtsp_session(connection_status)
    connection_status = %{connection_status | rtsp_session: rtsp_session}

    if is_nil(rtsp_session) do
      maybe_reconnect(connection_status)
    else
      with {:ok, connection_status} <- get_rtsp_description(connection_status),
           {:ok, connection_status} <- setup_rtsp_connection(connection_status),
           {:ok, connection_status} <- start_keep_alive(connection_status),
           :ok <- play(connection_status) do
        Membrane.Logger.debug(~s"""
        ConnectionManager processes:
          RTSP session: #{inspect(connection_status.rtsp_session)},
          Endpoint: #{inspect(connection_status.endpoint)},
          RTSP keep alive: #{inspect(connection_status.keep_alive)}
        """)

        send(
          connection_status.endpoint,
          {:rtsp_setup_complete, connection_status.endpoint_options}
        )

        {:ok, %{connection_status | reconnect_attempt: 0}}
      else
        {:error, :unauthorized} ->
          Membrane.Logger.debug(
            "ConnectionManager: Unauthorized. Attempting immediate reconnect..."
          )

          {:backoff, 0, connection_status}

        {:error, error} ->
          Membrane.Logger.debug("ConnectionManager: Connection failed: #{inspect(error)}")

          send(connection_status.endpoint, {:connection_info, {:connection_failed, error}})

          maybe_reconnect(connection_status)
      end
    end
  end

  @impl true
  def disconnect(message, %ConnectionStatus{} = connection_status) do
    Membrane.Logger.debug("ConnectionManager: Disconnecting: #{message}")

    kill_children(connection_status)

    connection_status = %{
      connection_status
      | rtsp_session: nil,
        keep_alive: nil
    }

    send(connection_status.endpoint, {:connection_info, :disconnected})

    # TODO: change once RTSP Endpoint supports reconnecting to the same stream
    {:noconnect, connection_status, :hibernate}
  end

  defp kill_children(%ConnectionStatus{keep_alive: keep_alive, rtsp_session: rtsp_session}) do
    if !is_nil(keep_alive) and Process.alive?(keep_alive),
      do: Process.exit(keep_alive, :normal)

    if !is_nil(rtsp_session) and Process.alive?(rtsp_session), do: RTSP.close(rtsp_session)
  end

  @impl true
  def handle_cast(:reconnect, %ConnectionStatus{} = connection_status) do
    Membrane.Logger.debug("ConnectionManager: Received reconnect request")

    connection_status = %{connection_status | reconnect_attempt: 1}

    if is_nil(connection_status.rtsp_session) do
      {:connect, :reload, connection_status}
    else
      Membrane.Logger.debug("ConnectionManager: RTSP session up, ignoring reconnect request")
      {:noreply, connection_status}
    end
  end

  @impl true
  def handle_info(
        {:DOWN, _ref, :process, pid, reason},
        %ConnectionStatus{
          rtsp_session: rtsp_session,
          keep_alive: keep_alive
        } = connection_status
      )
      when reason != :normal do
    Membrane.Logger.debug("ConnectionManager: Received DOWN message from #{inspect(pid)}")

    Membrane.Logger.debug(~s"""
    ConnectionManager processes:
      RTSP session: #{inspect(rtsp_session)},
      RTSP keep alive: #{inspect(keep_alive)}
    """)

    case pid do
      ^rtsp_session ->
        Membrane.Logger.warn("RTSP.ConnectionManager: RTSP session crashed")

      ^keep_alive ->
        Membrane.Logger.warn("RTSP.ConnectionManager: Keep_alive process crashed")

      process ->
        Membrane.Logger.warn("RTSP.ConnectionManager: #{inspect(process)} process crashed")
    end

    {:disconnect, :reload, connection_status}
  end

  @impl true
  def handle_info({:DOWN, _ref, :process, _pid, reason}, connection_status)
      when reason == :normal do
    {:noreply, connection_status}
  end

  @impl true
  def handle_info({:EXIT, _from, reason}, connection_status) do
    {:disconnect, {:error, reason}, connection_status}
  end

  defp maybe_reconnect(
         %ConnectionStatus{
           endpoint: endpoint,
           reconnect_attempt: attempt,
           max_reconnect_attempts: max_attempts,
           reconnect_delay: delay
         } = connection_status
       ) do
    connection_status = %{connection_status | reconnect_attempt: attempt + 1}

    # This works with :infinity, since integers < atoms
    if attempt < max_attempts do
      {:backoff, delay, connection_status}
    else
      Membrane.Logger.debug("ConnectionManager: Max reconnect attempts reached. Hibernating")
      send(endpoint, {:connection_info, :max_reconnects})
      {:ok, connection_status, :hibernate}
    end
  end

  defp start_rtsp_session(%ConnectionStatus{
         rtsp_session: nil,
         stream_uri: stream_uri,
         endpoint: endpoint
       }) do
    case RTSP.start(stream_uri) do
      {:ok, session} ->
        Process.monitor(session)
        session

      {:error, error} ->
        Membrane.Logger.debug(
          "ConnectionManager: Starting RTSP session failed - #{inspect(error)}"
        )

        send(endpoint, {:connection_info, {:connection_failed, error}})

        nil
    end
  end

  defp start_rtsp_session(%ConnectionStatus{rtsp_session: rtsp_session}) do
    rtsp_session
  end

  defp get_rtsp_description(%ConnectionStatus{rtsp_session: rtsp_session} = connection_status) do
    Membrane.Logger.debug("ConnectionManager: Setting up RTSP description")

    case RTSP.describe(rtsp_session) do
      {:ok, %{status: 200} = response} ->
        attributes = get_video_attributes(response)

        connection_status =
          connection_status
          |> put_in([:endpoint_options, :control], get_attribute(attributes, "control", ""))
          |> put_in([:endpoint_options, :fmtp], get_attribute(attributes, ExSDP.Attribute.FMTP))
          |> put_in(
            [:endpoint_options, :rtpmap],
            get_attribute(attributes, ExSDP.Attribute.RTPMapping)
          )

        {:ok, connection_status}

      {:ok, %{status: 401}} ->
        {:error, :unauthorized}

      _result ->
        {:error, :getting_rtsp_description_failed}
    end
  end

  defp setup_rtsp_connection(
         %ConnectionStatus{
           rtsp_session: rtsp_session,
           endpoint_options: endpoint_options
         } = connection_status
       ) do
    Membrane.Logger.debug("ConnectionManager: Setting up RTSP connection")

    case RTSP.setup(rtsp_session, endpoint_options.control, [
           {"Transport", "RTP/AVP;unicast;client_port=#{endpoint_options.port}"}
         ]) do
      {:ok, %{status: 200, headers: headers}} ->
        # Parse server port to be able to combat NAT later
        server_port = parse_server_port(headers)

        {:ok, put_in(connection_status, [:endpoint_options, :server_port], server_port)}

      result ->
        Membrane.Logger.debug(
          "ConnectionManager: Setting up RTSP connection failed: #{inspect(result)}"
        )

        {:error, :setting_up_sdp_connection_failed}
    end
  end

  defp play(%ConnectionStatus{rtsp_session: rtsp_session, endpoint: _endpoint}) do
    Membrane.Logger.debug("ConnectionManager: Setting RTSP on play mode")

    case RTSP.play(rtsp_session) do
      {:ok, %{status: 200}} ->
        :ok

      _result ->
        {:error, :play_rtsp_failed}
    end
  end

  defp start_keep_alive(%ConnectionStatus{} = connection_status) do
    Membrane.Logger.debug("ConnectionManager: Starting Keep alive process")

    {keep_alive, _ref} =
      spawn_monitor(fn ->
        rtsp_keep_alive(connection_status.rtsp_session, connection_status.keep_alive_interval)
      end)

    {:ok, %{connection_status | keep_alive: keep_alive}}
  end

  defp rtsp_keep_alive(rtsp_session, keep_alive_interval) do
    if Process.alive?(rtsp_session) do
      case RTSP.get_parameter(rtsp_session) do
        {:ok, %RTSP.Response{status: 200}} ->
          Process.sleep(keep_alive_interval)
          rtsp_keep_alive(rtsp_session, keep_alive_interval)

        error ->
          Membrane.Logger.debug("RTSP ping failed: #{inspect(error)}")
          Process.exit(self(), :connection_failed)
      end
    else
      Process.exit(self(), :rtsp_session_closed)
    end
  end

  defp get_video_attributes(%{body: %ExSDP{media: media_list}}) do
    media_list |> Enum.find(fn elem -> elem.type == :video end)
  end

  defp get_attribute(video_attributes, attribute, default \\ nil) do
    case ExSDP.Media.get_attribute(video_attributes, attribute) do
      {^attribute, value} -> value
      %^attribute{} = value -> value
      _other -> default
    end
  end

  defp parse_server_port(headers) do
    Enum.find_value(headers, fn entry ->
      case entry do
        {"Transport", value} -> value
        _other -> false
      end
    end)
    |> String.split(";")
    |> Enum.find_value(fn entry ->
      String.split(entry, "=")
      |> List.to_tuple()
      |> case do
        {"server_port", port_range} ->
          [range_start | _range_end] = String.split(port_range, "-")
          String.to_integer(range_start)

        _other ->
          false
      end
    end)
  end
end