defmodule Membrane.Gemini.Endpoint do
  @moduledoc false
  # This module is internally used by Membrane.Gemini.Bin

  use Membrane.Endpoint

  alias Membrane.RawAudio

  def_input_pad :audio_input,
    accepted_format: %RawAudio{sample_format: :s16le, channels: 1, sample_rate: 16_000}

  def_input_pad :text_input,
    accepted_format: %Membrane.RemoteStream{type: :bytestream}

  def_output_pad :output,
    accepted_format: %RawAudio{sample_format: :s16le, channels: 1, sample_rate: 24_000},
    flow_control: :push

  def_options model: [spec: nil | String.t()],
              system_instruction: [spec: nil | String.t()],
              mode: [spec: :paced | :raw],
              extra_opts: [spec: Keyword.t()]

  defmodule State do
    @moduledoc false

    @type t :: %__MODULE__{
            status:
              :standby
              | :text_sent
              | :text_interrupt
              | :receiving
              | :interrupted
              | :eos,
            mode: :paced | :raw,
            gemini_opts: map(),
            session_pid: pid(),
            audio_eos_received?: boolean(),
            text_eos_received?: boolean()
          }

    @enforce_keys [
      :mode,
      :gemini_opts,
      :session_pid
    ]

    defstruct @enforce_keys ++
                [
                  status: :standby,
                  audio_eos_received?: false,
                  text_eos_received?: false
                ]
  end

  @impl true
  def handle_init(_ctx, opts) do
    session_pid = create_session(opts)
    {[], %State{mode: opts.mode, gemini_opts: opts, session_pid: session_pid}}
  end

  @impl true
  def handle_setup(_ctx, %State{session_pid: session_pid} = state) do
    case Gemini.Live.Session.connect(session_pid) do
      :ok -> :ok
      {:error, error} -> raise "Failed to start Gemini Live API session, error: #{inspect(error)}"
    end

    {[], state}
  end

  @impl true
  def handle_playing(_ctx, state) do
    {[
       stream_format:
         {:output, %RawAudio{sample_format: :s16le, channels: 1, sample_rate: 24_000}}
     ], state}
  end

  @impl true
  def handle_buffer(
        :audio_input,
        %Membrane.Buffer{payload: payload},
        _ctx,
        %State{session_pid: session_pid} = state
      ) do
    case Gemini.Live.Session.send_realtime_input(session_pid,
           audio: Gemini.Live.Audio.create_input_blob(payload)
         ) do
      :ok ->
        :ok

      {:error, reason} ->
        Membrane.Logger.warning("sending audio payload failed: #{inspect(reason)}")
    end

    {[], state}
  end

  @impl true
  def handle_buffer(
        :text_input,
        %Membrane.Buffer{payload: payload},
        _ctx,
        %State{session_pid: session_pid, status: status} = state
      ) do
    case Gemini.Live.Session.send_realtime_input(session_pid, text: payload) do
      :ok ->
        case status do
          :receiving ->
            {[event: {:output, %Membrane.Gemini.Events.ResponseEnd{interrupted?: true}}],
             %{state | status: :text_interrupt}}

          :text_interrupt ->
            {[], state}

          _other ->
            {[], %{state | status: :text_sent}}
        end

      {:error, reason} ->
        Membrane.Logger.warning("sending text payload failed: #{inspect(reason)}")
        {[], state}
    end
  end

  @impl true
  def handle_info(msg, _ctx, %State{status: :eos} = state) do
    Membrane.Logger.info("Message received after element went into EOS status: #{inspect(msg)}")
    {[], state}
  end

  @impl true
  def handle_info({:on_message, msg}, ctx, state), do: handle_server_message(msg, ctx, state)

  @impl true
  def handle_info({:on_transcription, {:input, %{"text" => text}}}, _ctx, state),
    do:
      {[event: {:output, %Membrane.Gemini.Events.Transcript{audio_origin: :client, text: text}}],
       state}

  @impl true
  def handle_info(
        {:on_transcription, {:output, _text}},
        _ctx,
        %State{status: status} = state
      )
      when status in [:text_interrupt, :interrupted],
      do: {[], state}

  @impl true
  def handle_info({:on_transcription, {:output, %{"text" => text}}}, _ctx, state),
    do:
      maybe_start_response(
        [event: {:output, %Membrane.Gemini.Events.Transcript{audio_origin: :server, text: text}}],
        state
      )

  @impl true
  def handle_info({:on_error, msg}, _ctx, state) do
    Membrane.Logger.error("Unhandled error received by session: #{inspect(msg)}")
    {[], state}
  end

  @impl true
  def handle_info(
        {:on_go_away, go_away_message},
        _ctx,
        %State{session_pid: session_pid, gemini_opts: gemini_opts, status: status} = state
      ) do
    if status != :standby do
      Membrane.Logger.warning("Unexpected go_away received in non-idle state: #{inspect(status)}")
    end

    resume_handle =
      case go_away_message do
        %{handle: resume_handle, time_left_ms: _time_left_ms} ->
          Membrane.Logger.debug(
            "go_away received, restarting session using resume handle: #{inspect(resume_handle)}"
          )

          resume_handle

        %{time_left_ms: time_left_ms} ->
          Membrane.Logger.info("""
          go_away received without a resume handle, time left: #{inspect(time_left_ms)}
          The Gemini session will be restarted without previous context.
          """)

          nil

        other ->
          Membrane.Logger.warning("""
          Received go_away with unexpected message structure: #{inspect(other)}
          The Gemini session will be restarted without previous context.
          """)

          nil
      end

    new_session_pid = restart_session(session_pid, gemini_opts, resume_handle)
    {[], %{state | status: :standby, session_pid: new_session_pid}}
  end

  @impl true
  def handle_info(message, _ctx, state) do
    Membrane.Logger.warning("Unrecognised message received by endpoint: #{inspect(message)}")
    {[], state}
  end

  @impl true
  def handle_parent_notification(:reset_session, _ctx, %State{status: :eos} = state),
    do: {[], state}

  @impl true
  def handle_parent_notification(
        :reset_session,
        _ctx,
        %State{
          status: prev_status,
          session_pid: session_pid,
          gemini_opts: gemini_opts
        } = state
      ) do
    new_session_pid = restart_session(session_pid, gemini_opts)

    state = %{state | status: :standby, session_pid: new_session_pid}

    case prev_status do
      :receiving ->
        {maybe_eos_action, state} = maybe_eos(state)

        {[event: {:output, %Membrane.Gemini.Events.ResponseEnd{interrupted?: true}}] ++
           maybe_eos_action, state}

      :standby ->
        {[], state}

      status when status in [:text_sent, :text_interrupt, :interrupted] ->
        maybe_eos(state)
    end
  end

  @impl true
  def handle_end_of_stream(:audio_input, _ctx, %State{session_pid: session_pid} = state) do
    # Flushes cached audio
    case Gemini.Live.Session.send_realtime_input(session_pid, audio_stream_end: true) do
      :ok -> :ok
      {:error, reason} -> Membrane.Logger.warning("Audio cache flush failed: #{inspect(reason)}")
    end

    maybe_eos(%{state | audio_eos_received?: true})
  end

  @impl true
  def handle_end_of_stream(:text_input, _ctx, state) do
    maybe_eos(%{state | text_eos_received?: true})
  end

  @spec create_session(gemini_opts :: %__MODULE__{}, resume_handle :: nil | String.t()) :: pid()
  defp create_session(gemini_opts, resume_handle \\ nil) do
    Membrane.Logger.debug("Creating new session with config: #{inspect(gemini_opts)}")
    filter_pid = self()

    gemini_callbacks =
      [
        :on_message,
        :on_error,
        :on_go_away,
        :on_transcription
      ]
      |> Enum.map(fn callback_atom ->
        {
          callback_atom,
          &send(filter_pid, {callback_atom, &1})
        }
      end)

    {:ok, session_pid} =
      Gemini.Live.Session.start_link(
        [
          auth: :gemini,
          api_version: "v1beta",
          input_audio_transcription: %{},
          output_audio_transcription: %{},
          session_resumption: %{},
          generation_config: %{
            response_modalities: [:audio],
            thinking_config: %{
              thinking_budget: 1024,
              include_thoughts: true
            }
          }
        ] ++
          gemini_opts.extra_opts ++
          [
            resume_handle: resume_handle,
            model: gemini_opts.model || Gemini.Live.Models.resolve(:audio),
            system_instruction: gemini_opts.system_instruction
          ] ++
          gemini_callbacks
      )

    session_pid
  end

  @spec restart_session(
          session_pid :: pid(),
          gemini_opts :: %__MODULE__{},
          resume_handle :: nil | String.t()
        ) :: pid()
  defp restart_session(session_pid, gemini_opts, resume_handle \\ nil) do
    Gemini.Live.Session.close(session_pid)
    new_session_pid = create_session(gemini_opts, resume_handle)

    case Gemini.Live.Session.connect(new_session_pid) do
      :ok -> :ok
      {:error, error} -> raise "Failed to connect to Gemini Live API, error: #{inspect(error)}"
    end

    new_session_pid
  end

  @spec handle_server_message(
          Gemini.Types.Live.ServerMessage.t(),
          Membrane.Element.CallbackContext.t(),
          State.t()
        ) :: {[Membrane.Element.Action.t()], State.t()}
  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{model_turn: %{parts: parts}}
         },
         _ctx,
         %State{status: status} = state
       )
       when status in [:text_interrupt, :interrupted] and is_list(parts),
       do: {[], state}

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{model_turn: %{parts: parts}}
         },
         _ctx,
         state
       )
       when is_list(parts) do
    mime_type = Gemini.Live.Audio.output_mime_type()

    # Note: `parts` seems to always be a singleton,
    # and the thinking prompt and audio come in through different invocations
    # Either way, we process the response as if `parts` could contain more than one element.
    actions =
      parts
      |> Enum.map(fn
        %{inline_data: %{"data" => data, "mimeType" => ^mime_type}} ->
          {:buffer, {:output, %Membrane.Buffer{payload: Base.decode64!(data)}}}

        %{text: text} ->
          {:event, {:output, %Membrane.Gemini.Events.Thinking{text: text}}}

        other ->
          Membrane.Logger.warning("Unrecognised response part received: #{inspect(other)}")
          nil
      end)
      |> Enum.reject(&Kernel.is_nil/1)

    maybe_start_response(actions, state)
  end

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           setup_complete: %Gemini.Types.Live.SetupComplete{session_id: id}
         },
         _ctx,
         state
       ) do
    Membrane.Logger.debug("Gemini setup complete, session id: #{inspect(id)}")
    {[], state}
  end

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{generation_complete: true}
         },
         _ctx,
         state
       ) do
    Membrane.Logger.debug("Received generation_complete: true")
    handle_generation_complete(state)
  end

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{turn_complete: true},
           usage_metadata: %Gemini.Types.Live.UsageMetadata{} = usage_metadata
         },
         _ctx,
         state
       ) do
    Membrane.Logger.debug("Turn metadata received: #{inspect(usage_metadata)}")
    Membrane.Logger.debug("Received turn_complete: true, status: #{inspect(state.status)}")
    handle_turn_complete(state)
  end

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{interrupted: true}
         },
         _ctx,
         %State{status: :receiving} = state
       ) do
    Membrane.Logger.debug("Interruption detected, status: :receiving")

    {[event: {:output, %Membrane.Gemini.Events.ResponseEnd{interrupted?: true}}],
     %{state | status: :interrupted}}
  end

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{interrupted: true}
         },
         _ctx,
         %State{status: :text_interrupt} = state
       ),
       do: {[], %{state | status: :interrupted}}

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{interrupted: true}
         },
         _ctx,
         state
       ),
       do: {[], state}

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           go_away: %Gemini.Types.Live.GoAway{time_left: time_left}
         },
         _ctx,
         state
       ) do
    Membrane.Logger.debug("go_away received, time left: #{inspect(time_left)}")
    {[], state}
  end

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{
             input_transcription: %Gemini.Types.Live.Transcription{}
           }
         },
         _ctx,
         state
       ),
       do: {[], state}

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{
             output_transcription: %Gemini.Types.Live.Transcription{}
           }
         },
         _ctx,
         state
       ),
       do: {[], state}

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           server_content: %Gemini.Types.Live.ServerContent{},
           usage_metadata: %Gemini.Types.Live.UsageMetadata{} = usage_metadata
         },
         _ctx,
         state
       ) do
    Membrane.Logger.debug("Turn metadata received: #{inspect(usage_metadata)}")
    {[], state}
  end

  defp handle_server_message(
         %Gemini.Types.Live.ServerMessage{
           setup_complete: nil,
           server_content: %Gemini.Types.Live.ServerContent{
             model_turn: nil,
             generation_complete: nil,
             turn_complete: nil,
             interrupted: nil,
             grounding_metadata: nil,
             input_transcription: nil,
             output_transcription: nil,
             url_context_metadata: nil,
             turn_complete_reason: nil
           },
           tool_call: nil,
           tool_call_cancellation: nil,
           go_away: nil,
           session_resumption_update: nil,
           voice_activity: nil,
           usage_metadata: nil
         },
         _ctx,
         state
       ),
       do: {[], state}

  defp handle_server_message(msg, _ctx, state) do
    Membrane.Logger.warning("Unrecognised message received by session: #{inspect(msg)}")
    {[], state}
  end

  @spec maybe_start_response([Membrane.Element.Action.t()], State.t()) ::
          {[Membrane.Element.Action.t()], State.t()}
  defp maybe_start_response(actions, %State{status: :receiving} = state), do: {actions, state}

  defp maybe_start_response(actions, state),
    do:
      {[{:event, {:output, %Membrane.Gemini.Events.ResponseStart{}}} | actions],
       %{state | status: :receiving}}

  @spec handle_generation_complete(State.t()) :: {[Membrane.Element.Action.t()], State.t()}
  defp handle_generation_complete(%State{mode: :paced} = state) do
    {[], state}
  end

  defp handle_generation_complete(%State{mode: :raw, status: :receiving} = state),
    do: signal_response_completed(state)

  defp handle_generation_complete(%State{mode: :raw, status: :interrupted} = state) do
    {[], %{state | status: :standby}}
  end

  @spec handle_turn_complete(State.t()) :: {[Membrane.Element.Action.t()], State.t()}
  defp handle_turn_complete(%State{mode: :paced, status: :receiving} = state),
    do: signal_response_completed(state)

  defp handle_turn_complete(%State{mode: :paced, status: :interrupted} = state) do
    {[], %{state | status: :standby}}
  end

  defp handle_turn_complete(%State{mode: :paced} = state) do
    # Sometimes user input contains longer pauses between voice activity,
    # which the model might mistake for a turn end. When more of the voice activity follows,
    # but the model hasn't sent its response yet, it will issue a single `turn_complete`
    # message (instead of an `interrupted` message).
    # This clause is used to ignore it explicitly.
    {[], state}
  end

  defp handle_turn_complete(%State{mode: :raw} = state) do
    {[], state}
  end

  @spec signal_response_completed(State.t()) :: {[Membrane.Element.Action.t()], State.t()}
  defp signal_response_completed(%State{status: :receiving} = state) do
    {maybe_eos_action, state} = maybe_eos(%{state | status: :standby})

    {[event: {:output, %Membrane.Gemini.Events.ResponseEnd{interrupted?: false}}] ++
       maybe_eos_action, state}
  end

  @spec maybe_eos(State.t()) ::
          {[Membrane.Element.Action.end_of_stream()], State.t()}
  defp maybe_eos(
         %State{
           status: :standby,
           audio_eos_received?: true,
           text_eos_received?: true,
           session_pid: pid
         } = state
       ) do
    Gemini.Live.Session.close(pid)
    {[end_of_stream: :output], %{state | status: :eos}}
  end

  defp maybe_eos(state), do: {[], state}
end