Module livekit.agents.beta.translation

@dataclass
class InputSpeechStarted:
    """The speaker began a turn, as the model heard it."""

@dataclass
class InputSpeechStopped:
    """The speaker ended a turn, as the model heard it."""

@dataclass
class InputTranscript:
    """What the model heard, in the language it was spoken."""

    text: str
    is_final: bool
    language: str | None = None
    speaker_id: str | None = None

@dataclass
class OutputSpeechStopped:
    """The model finished speaking a translation; its audio up to here is one segment.

    Yielded by :attr:`TranslationModelSession.audio_stream` rather than emitted as an event,
    so it cannot overtake audio the model has already queued ahead of it.
    """

@dataclass
class OutputTranscript:
    """What the model said, in the language it translates into."""

    text: str
    is_final: bool
    language: str | None = None

@dataclass
class TranslatedAudioFrame:
    """One frame of the translation the model speaks."""

    frame: rtc.AudioFrame
    language: str | None = None
    """The language spoken in this frame, for a provider that stamps its audio."""

@dataclass
class TranslationCapabilities:
    """What varies between translation providers."""

    input_transcription: bool = False
    """Whether the model transcribes the speech it hears, in the language it was spoken."""
    output_transcription: bool = False
    """Whether the model transcribes the translation it speaks."""
    turn_reporting: bool = False
    """Whether the model reports where the speaker's turns start and end.

    About the speech it hears. For the speech it speaks, see ``output_segmentation``.
    """
    output_segmentation: bool = False
    """Whether the model marks where each translation it speaks ends.

    When it does, the session ends a playout segment on that mark alone. When it does not,
    the session falls back to a silence timer, which cannot tell a pause inside a sentence
    from the end of one.
    """
    retargetable: bool = False
    """Whether the target language can be changed on a running session."""

class TranslationModel(ABC):
    """A model that hears speech in one language and speaks it in another.

    Its own primitive, beside :class:`~livekit.agents.llm.LLM`,
    :class:`~livekit.agents.llm.RealtimeModel` and :class:`~livekit.agents.llm.DuplexModel`: a
    translator holds no conversation, so it takes no instructions, carries no chat context,
    calls no tools and never decides to reply. What it has instead is a language it translates
    into. Run one with
    :class:`~livekit.agents.beta.translation.TranslationSession`.
    """

    def __init__(
        self,
        *,
        capabilities: TranslationCapabilities,
        target_language: str,
        source_language: str | None = None,
    ) -> None:
        """
        Args:
            capabilities: What this provider can do.
            target_language: The language the model speaks its translation in.
            source_language: The language the model expects to hear, or ``None`` when it
                detects the language itself.
        """
        self._capabilities = capabilities
        self._target_language = target_language
        self._source_language = source_language
        self._label = f"{type(self).__module__}.{type(self).__name__}"

    @property
    def model(self) -> str:
        return "unknown"

    @property
    def provider(self) -> str:
        return "unknown"

    @property
    def capabilities(self) -> TranslationCapabilities:
        return self._capabilities

    @property
    def label(self) -> str:
        return self._label

    @property
    def target_language(self) -> str:
        """The language the model speaks its translation in."""
        return self._target_language

    @property
    def source_language(self) -> str | None:
        """The language the model expects to hear, or ``None`` when it detects it itself."""
        return self._source_language

    def update_options(self, *, target_language: str) -> None:
        """Point the model at another language.

        Takes effect on the sessions opened after it. To retarget a running session, call
        :meth:`TranslationModelSession.update_options` on the session itself, which a
        provider only serves when ``capabilities.retargetable``.
        """
        self._target_language = target_language

    @abstractmethod
    def session(self) -> TranslationModelSession:
        """Open a session; the caller pushes audio into it and reads its translation out."""

    @abstractmethod
    async def aclose(self) -> None: ...

    async def __aenter__(self) -> TranslationModel:
        return self

    async def __aexit__(
        self,
        exc_type: type[BaseException] | None,
        exc: BaseException | None,
        exc_tb: TracebackType | None,
    ) -> None:
        await self.aclose()

class TranslationModelError(BaseModel):
    model_config = ConfigDict(arbitrary_types_allowed=True)
    type: Literal["translation_model_error"] = "translation_model_error"
    timestamp: float
    label: str
    error: Exception = Field(..., exclude=True)
    recoverable: bool

class TranslationModelSession(
    ABC, rtc.EventEmitter[TranslationEventTypes | TEvent], Generic[TEvent]
):
    """One run of a :class:`TranslationModel`: audio in, translated audio out.

    The speech the model hears is pushed in frame by frame with :meth:`push_audio`; the
    translation it speaks is read out of :attr:`audio_stream`, which also carries an
    :class:`OutputSpeechStopped` where each spoken translation ends. What it heard and what it
    said arrive as ``input_transcript`` and ``output_transcript`` events, and the speaker's
    turns as ``input_speech_started`` and ``input_speech_stopped``.
    """

    def __init__(self, translation_model: TranslationModel) -> None:
        super().__init__()
        self._translation_model = translation_model
        self._closing = False

    @property
    def translation_model(self) -> TranslationModel:
        return self._translation_model

    @property
    def capabilities(self) -> TranslationCapabilities:
        return self._translation_model.capabilities

    @property
    @abstractmethod
    def audio_stream(self) -> AsyncIterable[TranslatedAudioFrame | OutputSpeechStopped]:
        """The translation the model speaks, and where each one ends.

        A model whose ``capabilities.output_segmentation`` is set yields an
        :class:`OutputSpeechStopped` after the last frame of each translation. Because it
        travels in the stream, it is always read after the audio it closes.
        """

    @abstractmethod
    def push_audio(self, frame: rtc.AudioFrame) -> None:
        """Hand the model one frame of the speech to translate."""

    def clear_audio(self) -> None:
        """Drop the translation the model has not spoken yet.

        A no-op for a provider that cannot discard what it has already produced.
        """

    def update_options(self, *, target_language: str) -> None:
        """Point this running session at another language.

        Raises:
            RuntimeError: If the provider fixes the target language for the session's life.
        """
        raise RuntimeError(
            f"{self._translation_model.label} translates into a language fixed for the "
            "session's life; start a new session to translate into another"
        )

    @abstractmethod
    async def aclose(self) -> None: ...

class TranslationRoomIO:
    """Wires a :class:`~livekit.agents.beta.translation.TranslationSession` to a room.

    Its own wiring rather than ``RoomIO``: that one serves an ``AgentSession``, reaching for
    turn timers, chat input and an away timer a translator has none of. What is left is the
    part a translator does use — link a track, take its audio, publish the translated track,
    and publish both transcripts.

    What it links is a *track*, not a participant: the transcript a translator publishes is
    attributed to a track on the wire, a participant may publish more than one, and the
    publisher's identity is read off the track rather than the other way round.
    """

    def __init__(
        self,
        session: TranslationSession,
        room: rtc.Room,
        *,
        options: NotGivenOr[TranslationRoomOptions] = NOT_GIVEN,
    ) -> None:
        self._session, self._room = session, room
        self._options = options if is_given(options) else TranslationRoomOptions()
        self._track_sid = self._options.track if is_given(self._options.track) else None
        self._participant_identity = (
            self._options.participant_identity
            if is_given(self._options.participant_identity)
            else None
        )

        self._audio_input: _ParticipantAudioInputStream | None = None
        self._audio_output: _ParticipantAudioOutput | None = None
        self._input_tr_output: _ParticipantTranscriptionOutput | None = None
        self._output_tr_output: _ParticipantTranscriptionOutput | None = None
        self._tr_synchronizer: TranscriptSynchronizer | None = None
        self._pre_connect_audio_handler: PreConnectAudioHandler | None = None

        self._track_available_fut = asyncio.Future[_LinkedTrack]()
        self._room_connected_fut = asyncio.Future[None]()
        self._ready_fut = asyncio.Future[None]()
        self._init_atask: asyncio.Task[None] | None = None
        self._input_transcript_ch: aio.Chan[tuple[str, bool]] | None = None
        self._input_transcript_atask: asyncio.Task[None] | None = None
        self._tasks: set[asyncio.Task[Any]] = set()

    async def start(self) -> None:
        audio_input_options = self._options.get_audio_input_options()
        if audio_input_options:
            if audio_input_options.pre_connect_audio:
                self._pre_connect_audio_handler = PreConnectAudioHandler(
                    room=self._room, timeout=audio_input_options.pre_connect_audio_timeout
                )
                self._pre_connect_audio_handler.register()

            self._audio_input = _ParticipantAudioInputStream(
                self._room,
                track_source=[
                    rtc.TrackSource.SOURCE_MICROPHONE,
                    rtc.TrackSource.SOURCE_SCREENSHARE_AUDIO,
                ],
                sample_rate=audio_input_options.sample_rate,
                num_channels=audio_input_options.num_channels,
                frame_size_ms=audio_input_options.frame_size_ms,
                noise_cancellation=audio_input_options.noise_cancellation,
                auto_gain_control=(
                    audio_input_options.auto_gain_control
                    if is_given(audio_input_options.auto_gain_control)
                    else (
                        audio_input_options.noise_cancellation is None
                        or callable(audio_input_options.noise_cancellation)
                    )
                ),
                pre_connect_audio_handler=self._pre_connect_audio_handler,
            )

        audio_output_options = self._options.get_audio_output_options()
        if audio_output_options:
            self._audio_output = _ParticipantAudioOutput(
                self._room,
                sample_rate=audio_output_options.sample_rate,
                num_channels=audio_output_options.num_channels,
                track_publish_options=audio_output_options.track_publish_options,
                track_name=(
                    audio_output_options.track_name
                    if is_given(audio_output_options.track_name)
                    else "roomio_audio"
                ),
            )

        text_output_options = self._options.get_text_output_options()
        if text_output_options:
            # _input_tr_output is built in _init_task, once there is a track to stamp it with
            self._input_transcript_ch = aio.Chan[tuple[str, bool]]()
            self._input_transcript_atask = asyncio.create_task(
                self._forward_input_transcript(self._input_transcript_ch)
            )

            self._output_tr_output = _ParticipantTranscriptionOutput(
                room=self._room,
                is_delta_stream=True,
                participant=None,
                next_in_chain=text_output_options.next_in_chain,
                json_format=text_output_options.json_format,
            )

            if text_output_options.sync_transcription is not False and (
                audio_output := self._audio_output or self._session.output.audio
            ):
                self._tr_synchronizer = TranscriptSynchronizer(
                    next_in_chain_audio=audio_output,
                    next_in_chain_text=self._output_tr_output,
                    speed=text_output_options.transcription_speed_factor,
                )

        self._room.on("track_published", self._on_track_published)
        self._room.on("participant_connected", self._on_participant_connected)
        self._room.on("participant_disconnected", self._on_participant_disconnected)
        self._room.on("connection_state_changed", self._on_connection_state_changed)
        if self._room.isconnected():
            self._on_connection_state_changed(rtc.ConnectionState.CONN_CONNECTED)

        self._init_atask = asyncio.create_task(self._init_task())

        if self.audio_input:
            self._session.input.audio = self.audio_input
        if self.audio_output:
            self._session.output.audio = self.audio_output
        if self.transcription_output:
            self._session.output.transcription = self.transcription_output

        self._session.on("user_input_transcribed", self._on_input_transcribed)

    async def aclose(self) -> None:
        self._room.off("track_published", self._on_track_published)
        self._room.off("participant_connected", self._on_participant_connected)
        self._room.off("participant_disconnected", self._on_participant_disconnected)
        self._room.off("connection_state_changed", self._on_connection_state_changed)
        self._session.off("user_input_transcribed", self._on_input_transcribed)

        if self._init_atask:
            await aio.cancel_and_wait(self._init_atask)

        if self._input_transcript_ch:
            self._input_transcript_ch.close()
        if self._input_transcript_atask:
            await aio.cancel_and_wait(self._input_transcript_atask)

        if self._pre_connect_audio_handler:
            await self._pre_connect_audio_handler.aclose()

        if self._audio_input:
            await self._audio_input.aclose()

        if self._tr_synchronizer:
            await self._tr_synchronizer.aclose()

        if self._input_tr_output:
            await self._input_tr_output.aclose()
        if self._output_tr_output:
            await self._output_tr_output.aclose()

        if self._audio_output:
            await self._audio_output.aclose()

        await aio.cancel_and_wait(*self._tasks)
        self._tasks.clear()

    @property
    def room(self) -> rtc.Room:
        return self._room

    @property
    def audio_input(self) -> AudioInput | None:
        return self._audio_input

    @property
    def audio_output(self) -> AudioOutput | None:
        if self._tr_synchronizer:
            return self._tr_synchronizer.audio_output

        return self._audio_output

    @property
    def transcription_output(self) -> TextOutput | None:
        if self._tr_synchronizer:
            return self._tr_synchronizer.text_output

        return self._output_tr_output

    @property
    def linked_track(self) -> _LinkedTrack | None:
        """The track being translated, with the participant publishing it."""
        if not self._track_available_fut.done():
            return None

        return self._track_available_fut.result()

    @property
    def linked_participant(self) -> rtc.RemoteParticipant | None:
        """The participant publishing the linked track."""
        linked = self.linked_track
        return linked.participant if linked else None

    @property
    def subscribed_fut(self) -> asyncio.Future[None] | None:
        if self._audio_output:
            return self._audio_output.subscribed
        return None

    async def wait_for_ready(self) -> None:
        """Wait until the source track is linked and the translated track is published."""
        await self._ready_fut

    def set_track(self, track_sid: str | None) -> None:
        """Translate another track.

        The publisher is read off the track, so nothing else has to be supplied. A track that
        has not been published yet is accepted: it is linked once it appears.

        Raises:
            ValueError: If ``track_sid`` names a publication that is not audio.
        """
        if track_sid is None:
            self.unset_track()
            return

        linked = self.linked_track
        if linked is not None and linked.publication.sid == track_sid:
            # already on it, but pin it all the same: unpinned, a later search is free to
            # settle on another of the publisher's microphones
            self._track_sid = track_sid
            if self._audio_input:
                self._audio_input.set_track_sid(track_sid)
            return

        found: _LinkedTrack | None = None
        for participant in self._room.remote_participants.values():
            if (publication := participant.track_publications.get(track_sid)) is not None:
                if publication.kind != rtc.TrackKind.KIND_AUDIO:
                    # the model is handed audio; linking a camera would only close what is
                    # playing and leave nothing in its place
                    raise ValueError(
                        f"track {track_sid} is {rtc.TrackKind.Name(publication.kind)}, not audio"
                    )

                found = _LinkedTrack(publication, participant)
                break

        if self._track_available_fut.done():
            self._track_available_fut = asyncio.Future[_LinkedTrack]()

        self._track_sid = track_sid
        if found is not None:
            self._track_available_fut.set_result(found)
            self._apply_link(found)
        elif self._audio_input:
            # pinned now, so whatever the publisher is currently sending is dropped until
            # the named track appears and _on_track_published links it
            self._audio_input.set_track_sid(track_sid)

    def _apply_link(self, linked: _LinkedTrack) -> None:
        """Point the input and the transcript at a linked track."""
        self._participant_identity = linked.participant.identity
        track_sid = linked.publication.sid

        if self._audio_input:
            # pinned before the participant, so set_participant's scan of existing
            # publications cannot latch a different audio track of theirs first
            self._audio_input.set_track_sid(track_sid)
            self._audio_input.set_participant(self._participant_identity)
        if self._input_tr_output:
            self._input_tr_output.set_participant(self._participant_identity)
            # the transcript follows the track, or later speech keeps the old stamp
            self._input_tr_output.set_track(track_sid)

        logger.info(
            "TranslationRoomIO linked to track",
            extra={
                trace_types.ATTR_TRACK_SID: track_sid,
                trace_types.ATTR_PARTICIPANT_IDENTITY: self._participant_identity,
                trace_types.ATTR_ROOM_NAME: self._room.name,
            },
        )

    def unset_track(self) -> None:
        """Stop translating any track, leaving the session with nothing to hear."""
        self._track_sid = None
        self._participant_identity = None
        self._track_available_fut = asyncio.Future[_LinkedTrack]()
        if self._audio_input:
            self._audio_input.set_track_sid(None)
            self._audio_input.set_participant(None)
        if self._input_tr_output:
            self._input_tr_output.set_participant(None)
            self._input_tr_output.set_track(None)

    @log_exceptions(logger=logger)
    async def _init_task(self) -> None:
        await self._room_connected_fut

        for participant in self._room.remote_participants.values():
            self._on_participant_connected(participant)

        linked = await self._track_available_fut

        if self._options.get_text_output_options() is not None:
            # stamped with the track itself, not whichever microphone track its publisher
            # happens to own, and attributed to that publisher on the wire
            self._input_tr_output = _ParticipantTranscriptionOutput(
                room=self._room,
                is_delta_stream=False,
                participant=linked.participant.identity,
                track=linked.publication.sid,
            )

        self._apply_link(linked)

        if self._output_tr_output:
            self._output_tr_output.set_participant(self._room.local_participant.identity)

        if self._audio_output:
            await self._audio_output.start()

        if not self._ready_fut.done():
            self._ready_fut.set_result(None)

    @log_exceptions(logger=logger)
    async def _forward_input_transcript(self, event_ch: aio.Chan[tuple[str, bool]]) -> None:
        async for transcript, is_final in event_ch:
            if self._input_tr_output is None:
                continue

            await self._input_tr_output.capture_text(transcript)
            if is_final:
                self._input_tr_output.flush()

    def _on_input_transcribed(self, ev: Any) -> None:
        if self._input_transcript_ch:
            self._input_transcript_ch.send_nowait((ev.transcript, ev.is_final))

    def _on_connection_state_changed(self, state: rtc.ConnectionState.ValueType) -> None:
        if self._room.isconnected() and not self._room_connected_fut.done():
            self._room_connected_fut.set_result(None)

    def _on_participant_connected(self, participant: rtc.RemoteParticipant) -> None:
        for publication in participant.track_publications.values():
            self._on_track_published(publication, participant)

    def _on_track_published(
        self, publication: rtc.RemoteTrackPublication, participant: rtc.RemoteParticipant
    ) -> None:
        if self._track_available_fut.done() or publication.kind != rtc.TrackKind.KIND_AUDIO:
            return

        # a named track is taken whoever published it; otherwise the search is narrowed the
        # way RoomIO narrows its participant search
        if self._track_sid is not None:
            if publication.sid != self._track_sid:
                return
        else:
            if publication.source != rtc.TrackSource.SOURCE_MICROPHONE:
                return

            if self._participant_identity is not None:
                if participant.identity != self._participant_identity:
                    return
            elif (
                participant.attributes.get(ATTRIBUTE_PUBLISH_ON_BEHALF)
                == self._room.local_participant.identity
            ):
                return

            accepted_kinds = (
                self._options.participant_kinds
                if is_given(self._options.participant_kinds)
                else DEFAULT_PARTICIPANT_KINDS
            )
            if participant.kind not in accepted_kinds:
                return

        linked = _LinkedTrack(publication, participant)
        self._track_available_fut.set_result(linked)

        if self._init_atask is not None and self._init_atask.done():
            # startup has finished, so nothing else will pick this up
            self._apply_link(linked)

    def _on_participant_disconnected(self, participant: rtc.RemoteParticipant) -> None:
        if not (linked := self.linked_participant) or participant.identity != linked.identity:
            return

        self._track_available_fut = asyncio.Future[_LinkedTrack]()

        if (
            self._options.close_on_disconnect
            and participant.disconnect_reason in DEFAULT_CLOSE_ON_DISCONNECT_REASONS
        ):
            logger.info(
                "closing translation session due to participant disconnect "
                "(disable via `TranslationRoomOptions.close_on_disconnect=False`)",
                extra={
                    trace_types.ATTR_ROOM_NAME: self._room.name,
                    trace_types.ATTR_PARTICIPANT_IDENTITY: participant.identity,
                },
            )
            self._session._close_soon(reason=CloseReason.PARTICIPANT_DISCONNECTED)

@dataclass
class TranslationRoomOptions:
    """How a :class:`~livekit.agents.beta.translation.TranslationSession` reaches a room.

    The subset of ``RoomOptions`` a translator can use: it hears one participant and speaks
    its translation back into the room, and there is no text input to answer.
    """

    audio_input: AudioInputOptions | bool = True
    """The speech to translate. Pass ``False`` to feed the session audio yourself."""
    audio_output: AudioOutputOptions | bool = True
    """The track the translation is spoken on. Pass ``False`` to take the audio yourself."""
    text_output: TextOutputOptions | bool = True
    """Transcripts published to the room: what was heard, and what was spoken back."""
    track: NotGivenOr[str] = NOT_GIVEN
    """The sid of the audio track to translate. If not given, the first eligible one
    published. A track is the unit here rather than a participant: a participant can publish
    more than one, and only a track can be transcribed and attributed on the wire."""
    participant_identity: NotGivenOr[str] = NOT_GIVEN
    """Narrows the automatic search to one participant's tracks. Ignored when ``track`` names
    a publication outright."""
    participant_kinds: NotGivenOr[list[rtc.ParticipantKind.ValueType]] = NOT_GIVEN
    """Participant kinds accepted when searching automatically."""
    close_on_disconnect: bool = True
    """Close the session when the linked track's publisher leaves of their own accord."""

    def get_audio_input_options(self) -> AudioInputOptions | None:
        if isinstance(self.audio_input, AudioInputOptions):
            return self.audio_input
        return AudioInputOptions() if self.audio_input else None

    def get_audio_output_options(self) -> AudioOutputOptions | None:
        if isinstance(self.audio_output, AudioOutputOptions):
            return self.audio_output
        return AudioOutputOptions() if self.audio_output else None

    def get_text_output_options(self) -> TextOutputOptions | None:
        if isinstance(self.text_output, TextOutputOptions):
            return self.text_output
        return TextOutputOptions() if self.text_output else None

class TranslationSession(rtc.EventEmitter[EventTypes], Generic[Userdata_T]):
    """Runs a :class:`TranslationModel` against a room: speech in, translation out.

    Its own primitive rather than an ``AgentSession``: a translator holds no conversation. It
    takes no instructions, keeps no chat context, calls no tools, and never decides to reply —
    so there is no ``Agent`` to supply and no turn to take. What is left it does carry: room
    I/O, both transcripts, user and agent state, and a close that reports why.

    A model reports the speaker's turns itself, so no VAD runs here, and nothing waits for the
    speaker to stop before speaking over them.

    Example:
        ```python
        session = TranslationSession(model=VoiceModel(target_language="es"))
        await session.start(room=ctx.room)
        ```
    """

    def __init__(
        self,
        *,
        model: TranslationModel,
        userdata: NotGivenOr[Userdata_T] = NOT_GIVEN,
        output_segment_timeout: float = DEFAULT_OUTPUT_SEGMENT_TIMEOUT,
        loop: asyncio.AbstractEventLoop | None = None,
    ) -> None:
        """
        Args:
            model: The translation model this session runs.
            userdata: Arbitrary state carried on the session.
            output_segment_timeout: Seconds of silence from the model that end a segment of
                its speech. Used only when the model's ``capabilities.output_segmentation``
                is unset; a model that marks its own boundaries ends a segment on the mark,
                so a pause inside a sentence does not split it.
            loop: Event loop to run on.
        """
        super().__init__()
        self._loop = loop or asyncio.get_event_loop()
        self._model = model
        self._userdata: Userdata_T | None = userdata if is_given(userdata) else None
        self._output_segment_timeout = output_segment_timeout

        self._input = io.AgentInput(self._on_video_input_changed, self._on_audio_input_changed)
        self._output = io.AgentOutput(
            self._on_video_output_changed,
            self._on_audio_output_changed,
            self._on_text_output_changed,
        )

        self._room_io: TranslationRoomIO | None = None
        self._model_session: TranslationModelSession | None = None

        self._user_state: UserState = "listening"

        self._started = False
        self._closing_task: asyncio.Task[None] | None = None
        self._job_context_cb_registered = False
        self._lock = asyncio.Lock()

        self._forward_input_atask: asyncio.Task[None] | None = None
        self._forward_output_atask: asyncio.Task[None] | None = None
        self._output_transcript_ch: aio.Chan[OutputTranscript] | None = None
        self._output_transcript_atask: asyncio.Task[None] | None = None
        self._segment_timer: asyncio.TimerHandle | None = None
        self._segment_tasks: set[asyncio.Task[None]] = set()
        # serialises capturing a frame against ending a segment, so a tail the resampler
        # holds cannot be flushed out from under a frame being captured
        self._output_lock = asyncio.Lock()
        self._resampler: rtc.AudioResampler | None = None
        self._resampler_key: tuple[int, int, int | None] | None = None
        self._resampler_sink: io.AudioOutput | None = None

    @property
    def model(self) -> TranslationModel:
        """The translation model this session runs."""
        return self._model

    @property
    def input(self) -> io.AgentInput:
        return self._input

    @property
    def output(self) -> io.AgentOutput:
        return self._output

    @property
    def user_state(self) -> UserState:
        return self._user_state

    @property
    def room_io(self) -> TranslationRoomIO | None:
        return self._room_io

    @property
    def userdata(self) -> Userdata_T:
        if self._userdata is None:
            raise ValueError("TranslationSession userdata is not set")

        return self._userdata

    @userdata.setter
    def userdata(self, value: Userdata_T) -> None:
        self._userdata = value

    def set_target_language(self, language: str) -> None:
        """Point the model at another language.

        Before :meth:`start` this only changes what the next session is opened with. On a
        running session it reaches the model, which a provider serves only when its
        ``capabilities.retargetable``.

        Raises:
            RuntimeError: If the session is running and its model cannot be retargeted.
        """
        if self._model_session is not None and not self._model.capabilities.retargetable:
            raise RuntimeError(
                f"{self._model.label} translates into a language fixed for the session's "
                "life; start a new session to translate into another"
            )

        # the running session first: it can refuse a language the capability allows in
        # general, and the model setting must not claim a language being spoken
        if self._model_session is not None:
            self._model_session.update_options(target_language=language)

        self._model.update_options(target_language=language)

    async def start(
        self,
        *,
        room: NotGivenOr[rtc.Room] = NOT_GIVEN,
        room_options: NotGivenOr[TranslationRoomOptions] = NOT_GIVEN,
    ) -> None:
        """Start translating.

        Args:
            room: The room to listen to and speak into. Omit it to drive the session's
                ``input``/``output`` yourself.
            room_options: How the session reaches that room.
        """
        async with self._lock:
            if self._started:
                return

            job_ctx = get_job_context(required=False)

            if is_given(room) and self._room_io is None:
                options = room_options if is_given(room_options) else TranslationRoomOptions()

                if self.input.audio is not None and options.audio_input:
                    logger.warning(
                        "room audio input is enabled but input.audio is already set, ignoring.."
                    )
                    options.audio_input = False

                if self.output.audio is not None and options.audio_output:
                    logger.warning(
                        "room audio output is enabled but output.audio is already set, ignoring.."
                    )
                    options.audio_output = False

                self._room_io = TranslationRoomIO(self, room, options=options)
                await self._room_io.start()

                if job_ctx:
                    await job_ctx.connect()

            if job_ctx and not self._job_context_cb_registered:
                job_ctx.add_shutdown_callback(
                    lambda: self._aclose_impl(reason=CloseReason.JOB_SHUTDOWN)
                )
                self._job_context_cb_registered = True

            self._model_session = self._model.session()
            self._model_session.on("input_speech_started", self._on_input_speech_started)
            self._model_session.on("input_speech_stopped", self._on_input_speech_stopped)
            self._model_session.on("input_transcript", self._on_input_transcript)
            self._model_session.on("output_transcript", self._on_output_transcript)
            self._model_session.on("error", self._on_model_error)

            self._output_transcript_ch = aio.Chan[OutputTranscript]()
            self._output_transcript_atask = asyncio.create_task(
                self._forward_output_transcript_task(self._output_transcript_ch),
                name="_forward_output_transcript_task",
            )

            self._closing_task = None
            self._started = True

            if self.input.audio is not None:
                self._forward_input_atask = asyncio.create_task(
                    self._forward_input_audio_task(), name="_forward_input_audio_task"
                )

            self._forward_output_atask = asyncio.create_task(
                self._forward_output_audio_task(self._model_session),
                name="_forward_output_audio_task",
            )

    async def aclose(self) -> None:
        """Stop translating and release the model and the room."""
        await self._aclose_impl(reason=CloseReason.USER_INITIATED)

    def shutdown(self) -> None:
        """Close the session without waiting for it."""
        self._close_soon(reason=CloseReason.USER_INITIATED)

    def _close_soon(self, *, reason: CloseReason) -> None:
        if self._closing_task:
            return

        self._closing_task = asyncio.create_task(self._aclose_impl(reason=reason))

    @log_exceptions(logger=logger)
    async def _aclose_impl(self, *, reason: CloseReason) -> None:
        async with self._lock:
            if not self._started:
                return

            self._started = False
            self._cancel_segment_timer()
            if self._segment_tasks:
                await aio.cancel_and_wait(*self._segment_tasks)
                self._segment_tasks.clear()

            await aio.cancel_and_wait(
                *[
                    task
                    for task in (self._forward_input_atask, self._forward_output_atask)
                    if task is not None
                ]
            )
            self._forward_input_atask = self._forward_output_atask = None

            if self._output_transcript_ch:
                self._output_transcript_ch.close()
                self._output_transcript_ch = None
            if self._output_transcript_atask:
                await aio.cancel_and_wait(self._output_transcript_atask)
                self._output_transcript_atask = None

            if self._model_session:
                await self._model_session.aclose()
                self._model_session = None

            # detach what room io made, since it closes those on the way out and a restart
            # would otherwise reuse the closed devices. A caller's own stay attached: they
            # were never closed here, and losing the reference would strand them
            if (room_io := self._room_io) is not None:
                if self.input.audio is room_io.audio_input:
                    self.input.audio = None
                if self.output.audio is room_io.audio_output:
                    self.output.audio = None
                if self.output.transcription is room_io.transcription_output:
                    self.output.transcription = None

            self.emit("close", CloseEvent(reason=reason))

            if self._room_io:
                await self._room_io.aclose()
                self._room_io = None

            self._discard_resampler()
            self._user_state = "listening"

    # -- model session --

    @log_exceptions(logger=logger)
    async def _forward_input_audio_task(self) -> None:
        audio_input = self.input.audio
        if audio_input is None:
            return

        async for frame in audio_input:
            if (model_session := self._model_session) is not None:
                model_session.push_audio(frame)

    @log_exceptions(logger=logger)
    async def _forward_output_audio_task(self, model_session: TranslationModelSession) -> None:
        marks_segments = self._model.capabilities.output_segmentation
        try:
            async for ev in model_session.audio_stream:
                if isinstance(ev, OutputSpeechStopped):
                    # read in order behind the audio it closes, so nothing it ended is
                    # still waiting to be captured. Honoured even while the output is
                    # muted: whatever was captured before the mute is still a segment, and
                    # dropping the mark would merge the next translation into it
                    await self._close_output_segment()
                    continue

                if self.output.audio is None or not self.output.audio_enabled:
                    continue

                async with self._output_lock:
                    if (audio_output := self.output.audio) is None:
                        continue

                    await self._capture_output_frame(ev.frame, audio_output)

                if not marks_segments:
                    self._arm_segment_timer()
        finally:
            self._cancel_segment_timer()
            async with self._output_lock:
                await self._drain_resampler()

    @log_exceptions(logger=logger)
    async def _forward_output_transcript_task(self, event_ch: aio.Chan[OutputTranscript]) -> None:
        async for ev in event_ch:
            transcription_output = self.output.transcription
            if transcription_output is None or not self.output.transcription_enabled:
                continue

            await transcription_output.capture_text(ev.text)
            if ev.is_final:
                transcription_output.flush()

    def _on_input_speech_started(self, _: InputSpeechStarted) -> None:
        self._update_user_state("speaking")

    def _on_input_speech_stopped(self, _: InputSpeechStopped) -> None:
        self._update_user_state("listening")

    def _on_input_transcript(self, ev: InputTranscript) -> None:
        self.emit(
            "user_input_transcribed",
            UserInputTranscribedEvent(
                transcript=ev.text,
                is_final=ev.is_final,
                language=ev.language,
                speaker_id=ev.speaker_id,
            ),
        )

    def _on_output_transcript(self, ev: OutputTranscript) -> None:
        if self._output_transcript_ch is not None:
            self._output_transcript_ch.send_nowait(ev)

        self.emit(
            "translation_transcribed",
            TranslationTranscribedEvent(
                transcript=ev.text,
                is_final=ev.is_final,
                language=ev.language if ev.language is not None else self._model.target_language,
            ),
        )

    def _on_model_error(self, ev: TranslationModelError) -> None:
        self.emit("error", ErrorEvent(error=ev, source=self._model))

        if not ev.recoverable:
            logger.error(
                "translation model error, closing the session",
                extra={"label": ev.label, "error": str(ev.error)},
            )
            self._close_soon(reason=CloseReason.ERROR)

    # -- output segments --

    async def _capture_output_frame(
        self, frame: rtc.AudioFrame, audio_output: io.AudioOutput
    ) -> None:
        """Hand one frame to the sink, at the rate that sink plays at.

        The resampler is rebuilt whenever the model's format or the sink changes, since one
        built for the old pair would tag frames with a rate the new one does not play.
        """
        target_rate = audio_output.sample_rate
        key = (frame.sample_rate, frame.num_channels, target_rate)

        if self._resampler is not None and (
            self._resampler_key != key or self._resampler_sink is not audio_output
        ):
            if self._resampler_sink is audio_output:
                # same sink, new format: its tail still belongs there, in this segment
                await self._drain_resampler()
            else:
                # the sink was replaced: its segment ends on the sink that received it
                logger.debug("audio output replaced, closing the segment it was given")
                await self._close_segment_locked()

        if target_rate is None or frame.sample_rate == target_rate:
            await audio_output.capture_frame(frame)
            return

        if self._resampler is None:
            self._resampler = rtc.AudioResampler(
                input_rate=frame.sample_rate,
                output_rate=target_rate,
                num_channels=frame.num_channels,
            )
            self._resampler_key = key
            self._resampler_sink = audio_output

        for resampled in self._resampler.push(frame):
            await audio_output.capture_frame(resampled)

    async def _drain_resampler(self) -> None:
        """Push what the resampler still holds to the sink it was built for, then drop it.

        Not to whatever sink is current: those frames were converted for the old one, and
        another sink would replay them at its own rate.
        """
        resampler, sink = self._resampler, self._resampler_sink
        self._discard_resampler()
        if resampler is None or sink is None:
            return

        for frame in resampler.flush():
            await sink.capture_frame(frame)

    def _discard_resampler(self) -> None:
        """Forget the resampler and the pair it was built for, dropping anything it holds.

        Used where that tail cannot be placed, or once :meth:`_drain_resampler` has emptied it.
        """
        self._resampler = None
        self._resampler_key = None
        self._resampler_sink = None

    async def _close_output_segment(self) -> None:
        """End the segment the model has been speaking into."""
        self._cancel_segment_timer()
        async with self._output_lock:
            await self._close_segment_locked()

    async def _close_segment_locked(self) -> None:
        """End the segment on the sink that actually received its audio.

        Drains the resampler first: a partial frame it is still holding belongs to the
        segment being closed, not to whatever the model says next. The sink it was built
        for owns the segment, so replacing ``output.audio`` mid-translation closes the old
        sink's segment rather than flushing the replacement's.
        """
        sink = self._resampler_sink or self.output.audio
        await self._drain_resampler()
        if sink is not None:
            sink.flush()

    def _arm_segment_timer(self) -> None:
        """Restart the silence that ends a segment, for a model that marks none itself.

        Armed after every frame, so the segment ends only once the model has gone quiet for
        ``output_segment_timeout``.
        """
        self._cancel_segment_timer()
        self._segment_timer = self._loop.call_later(
            self._output_segment_timeout, self._close_output_segment_soon
        )

    def _cancel_segment_timer(self) -> None:
        """Disarm the silence timer, leaving the current segment open."""
        if self._segment_timer is not None:
            self._segment_timer.cancel()
            self._segment_timer = None

    def _close_output_segment_soon(self) -> None:
        """Close the segment from the timer, which cannot await the drain itself.

        The work runs as a task, tracked so closing the session can wait on it.
        """
        self._segment_timer = None
        task = asyncio.create_task(self._close_output_segment())
        self._segment_tasks.add(task)
        task.add_done_callback(self._segment_tasks.discard)

    # -- state --

    def _update_user_state(self, state: UserState) -> None:
        if self._user_state == state:
            return

        old_state = self._user_state
        self._user_state = state
        self.emit("user_state_changed", UserStateChangedEvent(old_state=old_state, new_state=state))

    # -- io --

    def _on_audio_input_changed(self) -> None:
        if not self._started:
            return

        if self._forward_input_atask is not None:
            self._forward_input_atask.cancel()
            self._forward_input_atask = None

        if self.input.audio is not None:
            self._forward_input_atask = asyncio.create_task(
                self._forward_input_audio_task(), name="_forward_input_audio_task"
            )

    def _on_video_input_changed(self) -> None:
        if self.input.video is not None:
            logger.warning("a translation model takes no video input, ignoring..")

    def _on_audio_output_changed(self) -> None: ...

    def _on_video_output_changed(self) -> None: ...

    def _on_text_output_changed(self) -> None: ...

class TranslationTranscribedEvent(BaseModel):
    """The translation the model spoke, in the language it translates into."""

    type: Literal["translation_transcribed"] = "translation_transcribed"
    transcript: str
    is_final: bool
    language: str | None = None
    created_at: float = Field(default_factory=time.time)