# Source code for mopidy.core.playback

    import logging
    import urllib

    from pykka.messages import ProxyCall

    from mopidy.audio import PlaybackState
    from mopidy.core import listener
    from mopidy.internal import deprecation, models, validation

    logger = logging.getLogger(__name__)

    class PlaybackController:
        def __init__(self, audio, backends, core):
            # TODO: these should be internal
            self.backends = backends
            self.core = core
            self._audio = audio

            self._stream_title = None
            self._state = PlaybackState.STOPPED

            self._current_tl_track = None
            self._pending_tl_track = None

            self._pending_position = None
            self._last_position = None
            self._previous = False

            self._start_at_position = None
            self._start_paused = False

            if self._audio:
                self._audio.set_about_to_finish_callback(
                    self._on_about_to_finish_callback
                )

        def _get_backend(self, tl_track):
            if tl_track is None:
                return None
            uri_scheme = urllib.parse.urlparse(tl_track.track.uri).scheme
            return self.backends.with_playback.get(uri_scheme, None)

        def get_current_tl_track(self):
            """Get the currently playing or selected track.

            Returns a :class:`mopidy.models.TlTrack` or :class:`None`.
            """
            return self._current_tl_track

        def _set_current_tl_track(self, value):
            """Set the currently playing or selected track.

            *Internal:* This is only for use by Mopidy's test suite.
            """
            self._current_tl_track = value

        def get_current_track(self):
            """
            Get the currently playing or selected track.

            Extracted from :meth:`get_current_tl_track` for convenience.

            Returns a :class:`mopidy.models.Track` or :class:`None`.
            """
            return getattr(self.get_current_tl_track(), "track", None)

        def get_current_tlid(self):
            """
            Get the currently playing or selected TLID.

            Extracted from :meth:`get_current_tl_track` for convenience.

            Returns a :class:`int` or :class:`None`.

            .. versionadded:: 1.1
            """
            return getattr(self.get_current_tl_track(), "tlid", None)

        def get_stream_title(self):
            """Get the current stream title or :class:`None`."""
            return self._stream_title

        def get_state(self):
            """Get The playback state."""

            return self._state

        def set_state(self, new_state):
            """Set the playback state.

            Must be :attr:`PLAYING`, :attr:`PAUSED`, or :attr:`STOPPED`.

            Possible states and transitions:

            .. digraph:: state_transitions

                "STOPPED" -> "PLAYING" [ label="play" ]
                "STOPPED" -> "PAUSED" [ label="pause" ]
                "PLAYING" -> "STOPPED" [ label="stop" ]
                "PLAYING" -> "PAUSED" [ label="pause" ]
                "PLAYING" -> "PLAYING" [ label="play" ]
                "PAUSED" -> "PLAYING" [ label="resume" ]
                "PAUSED" -> "STOPPED" [ label="stop" ]
            """
            validation.check_choice(new_state, validation.PLAYBACK_STATES)

            (old_state, self._state) = (self.get_state(), new_state)
            logger.debug("Changing state: %s -> %s", old_state, new_state)

            self._trigger_playback_state_changed(old_state, new_state)

        def get_time_position(self):
            """Get time position in milliseconds."""
            if self._pending_position is not None:
                return self._pending_position
            backend = self._get_backend(self.get_current_tl_track())
            if backend:
                # TODO: Wrap backend call in error handling.
                return backend.playback.get_time_position().get()
            else:
                return 0

        def _on_end_of_stream(self):
            self.set_state(PlaybackState.STOPPED)
            if self._current_tl_track:
                self._trigger_track_playback_ended(self.get_time_position())
            self._set_current_tl_track(None)

        def _on_stream_changed(self, uri):
            if self._last_position is None:
                position = self.get_time_position()
            else:
                # This code path handles the stop() case, uri should be none.
                position, self._last_position = self._last_position, None

            if self._pending_position is None:
                self._trigger_track_playback_ended(position)

            self._stream_title = None
            if self._pending_tl_track:
                self._set_current_tl_track(self._pending_tl_track)
                self._pending_tl_track = None

                if self._pending_position is None:
                    self.set_state(PlaybackState.PLAYING)
                    self._trigger_track_playback_started()
                    seek_ok = False
                    if self._start_at_position:
                        seek_ok = self.seek(self._start_at_position)
                        self._start_at_position = None
                    if not seek_ok and self._start_paused:
                        self.pause()
                        self._start_paused = False
                else:
                    self._seek(self._pending_position)
                    self.set_state(PlaybackState.PLAYING)
                    self._trigger_track_playback_started()

        def _on_position_changed(self, position):
            if self._pending_position is not None:
                self._trigger_seeked(self._pending_position)
                self._pending_position = None
                if self._start_paused:
                    self._start_paused = False
                    self.pause()

        def _on_about_to_finish_callback(self):
            """Callback that performs a blocking actor call to the real callback.

            This is passed to audio, which is allowed to call this code from the
            audio thread. We pass execution into the core actor to ensure that
            there is no unsafe access of state in core. This must block until
            we get a response.
            """
            self.core.actor_ref.ask(
                ProxyCall(
                    attr_path=["playback", "_on_about_to_finish"],
                    args=[],
                    kwargs={},
                )
            )

        def _on_about_to_finish(self):
            if self._state == PlaybackState.STOPPED:
                return

            # Unless overridden by other calls (e.g. next / previous / stop) this
            # will be the last position recorded until the track gets reassigned.
            # TODO: Check if case when track.length isn't populated needs to be
            # handled.
            self._last_position = self._current_tl_track.track.length

            pending = self.core.tracklist.eot_track(self._current_tl_track)
            # avoid endless loop if 'repeat' is 'true' and no track is playable
            # * 2 -> second run to get all playable track in a shuffled playlist
            count = self.core.tracklist.get_length() * 2

            while pending:
                backend = self._get_backend(pending)
                if backend:
                    try:
                        if backend.playback.change_track(pending.track).get():
                            self._pending_tl_track = pending
                            break
                    except Exception:
                        logger.exception(
                            "%s backend caused an exception.",
                            backend.actor_ref.actor_class.__name__,
                        )

                self.core.tracklist._mark_unplayable(pending)
                pending = self.core.tracklist.eot_track(pending)
                count -= 1
                if not count:
                    logger.info("No playable track in the list.")
                    break

        def _on_tracklist_change(self):
            """
            Tell the playback controller that the current playlist has changed.

            Used by :class:`mopidy.core.TracklistController`.
            """
            tl_tracks = self.core.tracklist.get_tl_tracks()
            if not tl_tracks:
                self.stop()
                self._set_current_tl_track(None)
            elif self.get_current_tl_track() not in tl_tracks:
                self._set_current_tl_track(None)

        def next(self):
            """
            Change to the next track.

            The current playback state will be kept. If it was playing, playing
            will continue. If it was paused, it will still be paused, etc.
            """
            state = self.get_state()
            current = self._pending_tl_track or self._current_tl_track
            # avoid endless loop if 'repeat' is 'true' and no track is playable
            # * 2 -> second run to get all playable track in a shuffled playlist
            count = self.core.tracklist.get_length() * 2

            while current:
                pending = self.core.tracklist.next_track(current)
                if self._change(pending, state):
                    break
                else:
                    self.core.tracklist._mark_unplayable(pending)
                # TODO: this could be needed to prevent a loop in rare cases
                # if current == pending:
                #     break
                current = pending
                count -= 1
                if not count:
                    logger.info("No playable track in the list.")
                    break

            # TODO return result?

        def pause(self):
            """Pause playback."""
            backend = self._get_backend(self.get_current_tl_track())
            # TODO: Wrap backend call in error handling.
            if not backend or backend.playback.pause().get():
                # TODO: switch to:
                # backend.track(pause)
                # wait for state change?
                self.set_state(PlaybackState.PAUSED)
                self._trigger_track_playback_paused()

        def play(self, tl_track=None, tlid=None):
            """
            Play the given track, or if the given tl_track and tlid is
            :class:`None`, play the currently active track.

            Note that the track **must** already be in the tracklist.

            .. deprecated:: 3.0
                The ``tl_track`` argument. Use ``tlid`` instead.

            :param tl_track: track to play
            :type tl_track: :class:`mopidy.models.TlTrack` or :class:`None`
            :param tlid: TLID of the track to play
            :type tlid: :class:`int` or :class:`None`
            """
            if sum(o is not None for o in [tl_track, tlid]) > 1:
                raise ValueError('At most one of "tl_track" and "tlid" may be set')

            tl_track is None or validation.check_instance(tl_track, models.TlTrack)
            tlid is None or validation.check_integer(tlid, min=1)

            if tl_track:
                deprecation.warn("core.playback.play:tl_track_kwarg")

            if tl_track is None and tlid is not None:
                for tl_track in self.core.tracklist.get_tl_tracks():
                    if tl_track.tlid == tlid:
                        break
                else:
                    tl_track = None

            if tl_track is not None:
                # TODO: allow from outside tracklist, would make sense given refs?
                if tl_track not in self.core.tracklist.get_tl_tracks():
                    raise AssertionError
            elif tl_track is None and self.get_state() == PlaybackState.PAUSED:
                self.resume()
                return

            current = self._pending_tl_track or self._current_tl_track
            pending = tl_track or current or self.core.tracklist.next_track(None)
            # avoid endless loop if 'repeat' is 'true' and no track is playable
            # * 2 -> second run to get all playable track in a shuffled playlist
            count = self.core.tracklist.get_length() * 2

            while pending:
                if self._change(pending, PlaybackState.PLAYING):
                    break
                else:
                    self.core.tracklist._mark_unplayable(pending)
                current = pending
                pending = self.core.tracklist.next_track(current)
                count -= 1
                if not count:
                    logger.info("No playable track in the list.")
                    break

            # TODO return result?

        def _change(self, pending_tl_track, state):
            self._pending_tl_track = pending_tl_track

            if not pending_tl_track:
                self.stop()
                self._on_end_of_stream()  # pretend an EOS happened for cleanup
                return True

            backend = self._get_backend(pending_tl_track)
            if not backend:
                return False

            # This must happen before prepare_change gets called, otherwise the
            # backend flushes the information of the track.
            self._last_position = self.get_time_position()

            # TODO: Wrap backend call in error handling.
            backend.playback.prepare_change()

            try:
                if not backend.playback.change_track(pending_tl_track.track).get():
                    return False
            except Exception:
                logger.exception(
                    "%s backend caused an exception.",
                    backend.actor_ref.actor_class.__name__,
                )
                return False

            # TODO: Wrap backend calls in error handling.
            if state == PlaybackState.PLAYING:
                try:
                    return backend.playback.play().get()
                except TypeError:
                    # TODO: check by binding against underlying play method using
                    # inspect and otherwise re-raise?
                    logger.error(
                        "%s needs to be updated to work with this "
                        "version of Mopidy.",
                        backend,
                    )
                    return False
            elif state == PlaybackState.PAUSED:
                return backend.playback.pause().get()
            elif state == PlaybackState.STOPPED:
                # TODO: emit some event now?
                self._current_tl_track = self._pending_tl_track
                self._pending_tl_track = None
                return True

            raise Exception(f"Unknown state: {state}")

        def previous(self):
            """
            Change to the previous track.

            The current playback state will be kept. If it was playing, playing
            will continue. If it was paused, it will still be paused, etc.
            """
            self._previous = True
            state = self.get_state()
            current = self._pending_tl_track or self._current_tl_track
            # avoid endless loop if 'repeat' is 'true' and no track is playable
            # * 2 -> second run to get all playable track in a shuffled playlist
            count = self.core.tracklist.get_length() * 2

            while current:
                pending = self.core.tracklist.previous_track(current)
                if self._change(pending, state):
                    break
                else:
                    self.core.tracklist._mark_unplayable(pending)
                # TODO: this could be needed to prevent a loop in rare cases
                # if current == pending:
                #     break
                current = pending
                count -= 1
                if not count:
                    logger.info("No playable track in the list.")
                    break

            # TODO: no return value?

        def resume(self):
            """If paused, resume playing the current track."""
            if self.get_state() != PlaybackState.PAUSED:
                return
            backend = self._get_backend(self.get_current_tl_track())
            # TODO: Wrap backend call in error handling.
            if backend and backend.playback.resume().get():
                self.set_state(PlaybackState.PLAYING)
                # TODO: trigger via gst messages
                self._trigger_track_playback_resumed()

            # TODO: switch to:
            # backend.resume()
            # wait for state change?

        def seek(self, time_position):
            """
            Seeks to time position given in milliseconds.

            :param time_position: time position in milliseconds
            :type time_position: int
            :rtype: :class:`True` if successful, else :class:`False`
            """
            # TODO: seek needs to take pending tracks into account :(
            validation.check_integer(time_position)

            if time_position < 0:
                logger.debug("Client seeked to negative position. Seeking to zero.")
                time_position = 0

            if not self.core.tracklist.get_length():
                return False

            if self.get_state() == PlaybackState.STOPPED:
                self.play()

            # We need to prefer the still playing track, but if nothing is playing
            # we fall back to the pending one.
            tl_track = self._current_tl_track or self._pending_tl_track
            if tl_track and tl_track.track.length is None:
                return False

            if time_position < 0:
                time_position = 0
            elif time_position > tl_track.track.length:
                # TODO: GStreamer will trigger a about-to-finish for us, use that?
                self.next()
                return True

            # Store our target position.
            self._pending_position = time_position

            # Make sure we switch back to previous track if we get a seek while we
            # have a pending track.
            if self._current_tl_track and self._pending_tl_track:
                self._change(self._current_tl_track, self.get_state())
            else:
                # TODO: Avoid returning False here when STOPPED (seek is deferred)?
                return self._seek(time_position)

        def _seek(self, time_position):
            backend = self._get_backend(self.get_current_tl_track())
            if not backend:
                return False
            # TODO: Wrap backend call in error handling.
            return backend.playback.seek(time_position).get()

        def stop(self):
            """Stop playing."""
            if self.get_state() != PlaybackState.STOPPED:
                self._last_position = self.get_time_position()
                backend = self._get_backend(self.get_current_tl_track())
                # TODO: Wrap backend call in error handling.
                if not backend or backend.playback.stop().get():
                    self.set_state(PlaybackState.STOPPED)

        def _trigger_track_playback_paused(self):
            logger.debug("Triggering track playback paused event")
            if self.get_current_tl_track() is None:
                return
            listener.CoreListener.send(
                "track_playback_paused",
                tl_track=self.get_current_tl_track(),
                time_position=self.get_time_position(),
            )

        def _trigger_track_playback_resumed(self):
            logger.debug("Triggering track playback resumed event")
            if self.get_current_tl_track() is None:
                return
            listener.CoreListener.send(
                "track_playback_resumed",
                tl_track=self.get_current_tl_track(),
                time_position=self.get_time_position(),
            )

        def _trigger_track_playback_started(self):
            if self.get_current_tl_track() is None:
                return

            logger.debug("Triggering track playback started event")
            tl_track = self.get_current_tl_track()
            self.core.tracklist._mark_playing(tl_track)
            self.core.history._add_track(tl_track.track)
            listener.CoreListener.send("track_playback_started", tl_track=tl_track)

        def _trigger_track_playback_ended(self, time_position_before_stop):
            tl_track = self.get_current_tl_track()
            if tl_track is None:
                return

            logger.debug("Triggering track playback ended event")

            if not self._previous:
                self.core.tracklist._mark_played(self._current_tl_track)
            self._previous = False

            # TODO: Use the lowest of track duration and position.
            listener.CoreListener.send(
                "track_playback_ended",
                tl_track=tl_track,
                time_position=time_position_before_stop,
            )

        def _trigger_playback_state_changed(self, old_state, new_state):
            logger.debug("Triggering playback state change event")
            listener.CoreListener.send(
                "playback_state_changed", old_state=old_state, new_state=new_state
            )

        def _trigger_seeked(self, time_position):
            # TODO: Trigger this from audio events?
            logger.debug("Triggering seeked event")
            listener.CoreListener.send("seeked", time_position=time_position)

        def _save_state(self):
            return models.PlaybackState(
                tlid=self.get_current_tlid(),
                time_position=self.get_time_position(),
                state=self.get_state(),
            )

        def _load_state(self, state, coverage):
            if state and "play-last" in coverage and state.tlid is not None:
                if state.state == PlaybackState.PAUSED:
                    self._start_paused = True
                if state.state in (PlaybackState.PLAYING, PlaybackState.PAUSED):
                    self._start_at_position = state.time_position
                    self.play(tlid=state.tlid)