Tunetti/player.py

"""Audio player using QMediaPlayer + yt-dlp with queue and local-file playback.

Instead of streaming YouTube audio URLs directly (which expire within seconds
and cause "Connection reset by peer" / "Demuxing failed" errors), we download
each song to a temporary file and play from the local filesystem.  This is
reliable because QMediaPlayer never touches the network directly.

Architecture
------------
A single persistent ``DownloadWorker`` lives on a background ``QThread`` for
the entire player lifetime.  Work is sent via Qt signals — no thread
creation/teardown, no signal-disconnect dances, no ``quit()``/``wait()``
timeouts.  Every download is tagged with a monotonically-increasing
``task_id``; stale results (from superseded requests) are simply discarded.

State machine::

    IDLE ──▶ LOADING ──▶ READY ──▶ PLAYING ──▶ ENDED
     ▲          │           │          │  ▲        │
     │          ▼           │          │  │        │
     │        FAILED ───────┘          ▼  │        │
     └───────────────────────────────── PAUSED     │
                                      │  ▲        │
                                      └──┘        │
                                                  │
                                    (queue empty)─┘

Set ``TEST_MODE = True`` below to bypass yt-dlp and generate a short test-tone
WAV instead — useful for UI development without network access.
"""

import logging
import os
import struct
import tempfile
import atexit
import math
import shutil
import threading
from typing import Optional

import yt_dlp
from PySide6.QtCore import QObject, QThread, Signal, Slot, QUrl
from PySide6.QtMultimedia import QMediaPlayer, QAudioOutput

log = logging.getLogger("tunetti.player")

# ── User-settable flags ────────────────────────────────────────────────────
TEST_MODE: bool = False    # skip yt-dlp, use local test-tone WAV instead
VERBOSE:   bool = False    # enable yt-dlp debug output


# ═══════════════════════════════════════════════════════════════════════════════
# Temp-file housekeeping
# ═══════════════════════════════════════════════════════════════════════════════

_TUNETTI_TMP: str | None = None


def _tmp_dir() -> str:
    """Return a scoped temp directory that lives for the process lifetime."""
    global _TUNETTI_TMP
    if _TUNETTI_TMP is None:
        _TUNETTI_TMP = tempfile.mkdtemp(prefix="tunetti_")
        atexit.register(shutil.rmtree, _TUNETTI_TMP, ignore_errors=True)
    return _TUNETTI_TMP


def _stale_files(video_id: str) -> list[str]:
    """Return paths of existing non-temp files for *video_id*, newest first."""
    td = _tmp_dir()
    result = []
    for fn in os.listdir(td):
        if fn.startswith(video_id) and ".temp." not in fn:
            path = os.path.join(td, fn)
            if os.path.isfile(path) and os.path.getsize(path) > 0:
                result.append(path)
    result.sort(key=lambda p: os.path.getmtime(p), reverse=True)
    return result


# ═══════════════════════════════════════════════════════════════════════════════
# Test-tone generator (used when TEST_MODE = True)
# ═══════════════════════════════════════════════════════════════════════════════

def _generate_test_wav(path: str, duration_s: int = 15) -> None:
    """Write a 440 Hz sine wave to *path* as a 16-bit mono WAV file."""
    sample_rate = 44100
    num_samples = sample_rate * duration_s
    frequency = 440.0
    amplitude = 0.3

    with open(path, "wb") as f:
        data_size = num_samples * 2
        f.write(b"RIFF")
        f.write(struct.pack("<I", 36 + data_size))
        f.write(b"WAVE")
        f.write(b"fmt ")
        f.write(struct.pack("<I", 16))
        f.write(struct.pack("<H", 1))
        f.write(struct.pack("<H", 1))
        f.write(struct.pack("<I", sample_rate))
        f.write(struct.pack("<I", sample_rate * 2))
        f.write(struct.pack("<H", 2))
        f.write(struct.pack("<H", 16))
        f.write(b"data")
        f.write(struct.pack("<I", data_size))
        for i in range(num_samples):
            t = i / sample_rate
            sample = int(amplitude * math.sin(2 * math.pi * frequency * t) * 32767)
            f.write(struct.pack("<h", sample))


# ═══════════════════════════════════════════════════════════════════════════════
# Download worker — lives on a single persistent QThread
# ═══════════════════════════════════════════════════════════════════════════════

class DownloadWorker(QObject):
    """Downloads song audio to temporary files via yt-dlp.

    Lives on a *persistent* background ``QThread`` that is created once
    when the ``AudioPlayer`` is initialised and never torn down until
    shutdown.  This avoids all the fragile ``quit()``/``wait()``/signal-
    disconnect races that plagued the previous design.

    Work is requested via :attr:`download_requested` and cancellation is
    signalled via :attr:`cancel_requested`.  Results are delivered on the
    main thread via :attr:`download_finished`.
    """

    # ── Input (main thread → worker thread, queued connection) ──────────
    download_requested = Signal(int, dict)   # task_id, song dict
    cancel_requested   = Signal()            # discard current download

    # ── Output (worker thread → main thread, queued connection) ─────────
    download_succeeded = Signal(int, dict)  # task_id, resolved song dict
    download_failed    = Signal(int)        # task_id

    def __init__(self, parent: Optional[QObject] = None):
        super().__init__(parent)
        self._lock = threading.Lock()
        self._cancelled = False
        self._task_id: Optional[int] = None

    @Slot(int, dict)
    def _do_download(self, task_id: int, song: dict) -> None:
        """Entry point — invoked on the worker thread."""
        self._task_id = task_id
        self._cancelled = False

        video_id = song.get("videoId") or song.get("video_id", "")
        temp_path: Optional[str] = None

        try:
            # Keep the stale cleanup at the start of each new download.
            for stale in _stale_files(video_id):
                try:
                    os.unlink(stale)
                except OSError:
                    pass

            # ── TEST MODE ────────────────────────────────────────────
            if TEST_MODE:
                wav_path = os.path.join(_tmp_dir(), f"{video_id}.wav")
                _generate_test_wav(wav_path)
                resolved = dict(song)
                resolved["_local_path"] = wav_path
                resolved["duration"] = 15
                resolved["thumbnail"] = ""
                resolved["title"] = song.get("title", f"Test {video_id}")
                with self._lock:
                    if not self._cancelled:
                        self.download_succeeded.emit(task_id, resolved)
                return

            # ── Real download ────────────────────────────────────────
            tmpl = os.path.join(_tmp_dir(), f"{video_id}.%(ext)s")
            ydl_opts: dict = {
                "quiet": not VERBOSE,
                "no_warnings": not VERBOSE,
                "verbose": VERBOSE,
                "format": "worstaudio/worst",
                "outtmpl": tmpl,
                "noprogress": not VERBOSE,
                "extract_flat": False,
            }

            with yt_dlp.YoutubeDL(ydl_opts) as ydl:
                info = ydl.extract_info(
                    f"https://music.youtube.com/watch?v={video_id}",
                    download=True,
                )

            # Construct the expected path from the output template.
            # The outtmpl is <tmp_dir>/<video_id>.%(ext)s and yt-dlp resolves
            # %(ext)s from the downloaded format.  We avoid relying on
            # info["requested_downloads"][0]["filepath"] because that key
            # may be set *before* post-processor fixup renames the file.
            actual_ext = info.get("ext", "")
            expected_path = os.path.join(_tmp_dir(), f"{video_id}.{actual_ext}") if actual_ext else ""

            temp_path = self._resolve_temp_path(video_id, expected_path)
            if not temp_path:
                raise RuntimeError(
                    f"Download produced empty/missing file for {video_id}"
                )

            resolved = self._build_resolved_dict(song, info, temp_path)

            with self._lock:
                if not self._cancelled:
                    self.download_succeeded.emit(task_id, resolved)

        except Exception as exc:
            log.error("Download error for %s: %s", video_id, exc)
            self._cleanup_path(temp_path)
            with self._lock:
                if not self._cancelled:
                    self.download_failed.emit(task_id)

    def _resolve_temp_path(self, video_id: str, expected_path: str) -> Optional[str]:
        """Resolve the actual temp file path after a download.

        First checks the *expected_path* (built from the extension yt-dlp reported),
        then falls back to scanning the temp directory for stale files.
        """
        # Debug: list every file in the temp dir for this video_id
        td = _tmp_dir()
        try:
            all_matches = [
                (fn, os.path.getsize(os.path.join(td, fn)))
                for fn in os.listdir(td)
                if fn.startswith(video_id)
            ]
            all_matches.sort()
            log.debug("Temp files for %s: %s", video_id, all_matches)
        except OSError as exc:
            log.debug("Temp dir listing failed: %s", exc)

        if expected_path:
            log.debug("Checking expected path: %s", expected_path)
        if expected_path and os.path.isfile(expected_path) and os.path.getsize(expected_path) > 0:
            return expected_path

        # Fallback: scan the temp directory for the most recent valid file.
        candidates = _stale_files(video_id)
        log.debug("_stale_files fallback for %s: %s", video_id, candidates)
        if candidates:
            return candidates[0]

        return None

    @staticmethod
    def _build_resolved_dict(song: dict, info: dict, temp_path: str) -> dict:
        """Build the resolved song dict with local path and metadata."""
        resolved = dict(song)
        resolved["_local_path"] = temp_path
        resolved["duration"] = info.get("duration") or song.get("duration", 0)
        resolved["thumbnail"] = info.get("thumbnail") or song.get("thumbnail", "")
        resolved["title"] = info.get("title", song.get("title", ""))
        return resolved

    @Slot()
    def _do_cancel(self) -> None:
        """Mark the current download as cancelled."""
        with self._lock:
            self._cancelled = True

    @staticmethod
    def _cleanup_path(path: Optional[str]) -> None:
        if path and os.path.isfile(path):
            try:
                os.unlink(path)
            except OSError:
                pass


# ═══════════════════════════════════════════════════════════════════════════════
# Search worker
# ═══════════════════════════════════════════════════════════════════════════════

class SearchWorker(QObject):
    """Runs a ytmusicapi search in a background thread.

    Searches both songs and videos, returning categorised results
    as a dict with ``"songs"`` and ``"videos"`` keys each containing
    a list of normalised song dicts.
    """

    results_ready = Signal(dict)
    failed        = Signal(str)

    def __init__(self, query: str):
        super().__init__()
        self._query = query

    @Slot()
    def run(self) -> None:
        if TEST_MODE:
            dummy = [
                {"videoId": f"dummy_{i}", "title": f"Test Song {i}",
                 "artists": [{"name": f"Artist {i}"}],
                 "album": None, "duration_seconds": 15,
                 "duration": "0:15", "thumbnails": [],
                 "videoType": "MUSIC_VIDEO_TYPE_ATV",
                 "resultType": "song"}
                for i in range(5)
            ]
            self.results_ready.emit({"songs": dummy, "videos": []})
            return

        from ytmusicapi import YTMusic
        try:
            yt = YTMusic()
            # Always search both categories so the UI can display them
            # side by side with a "Videos" and "Songs" header.
            raw_songs = yt.search(self._query, filter="songs", limit=20)
            raw_videos = yt.search(self._query, filter="videos", limit=20)

            songs = [
                _build_song_dict(r) for r in raw_songs if r.get("videoId")
            ]
            videos = [
                _build_song_dict(r) for r in raw_videos if r.get("videoId")
            ]
            self.results_ready.emit({"songs": songs, "videos": videos})
        except Exception as exc:
            log.error("Search failed: %s", exc)
            self.failed.emit(str(exc))


# ═══════════════════════════════════════════════════════════════════════════════
# Main AudioPlayer
# ═══════════════════════════════════════════════════════════════════════════════

class AudioPlayer(QObject):
    """QObject-based audio player wrapping QMediaPlayer with local-file playback.

    Every song is downloaded to a temporary file before playing.  A single
    persistent ``DownloadWorker`` on a background ``QThread`` handles all
    downloads — no thread creation/teardown, no signal-disconnect races, no
    ``quit()``/``wait()`` timeouts.

    Signals
    -------
    loading(video_id)
    song_started(song_dict)
    song_ended(video_id)
    paused(song_dict)
    resumed(song_dict)
    error(dict)
    position_changed(ms: int)
    duration_changed(ms: int)
    playback_state_changed(state: str)  — "playing"|"paused"|"stopped"
    """

    loading               = Signal(str)
    song_loaded           = Signal(bool)
    song_started          = Signal(dict)
    song_ended            = Signal(str)
    paused                = Signal(dict)
    resumed               = Signal(dict)
    error                 = Signal(dict)
    position_changed      = Signal(int)
    duration_changed      = Signal(int)
    playback_state_changed = Signal(str)
    seeked                = Signal(int)  # position_ms after seek

    def __init__(self, parent: Optional[QObject] = None):
        super().__init__(parent)

        # ── QMediaPlayer ──────────────────────────────────────────────
        self._player = QMediaPlayer(self)
        self._audio_output = QAudioOutput(self)
        self._player.setAudioOutput(self._audio_output)
        self._audio_output.setVolume(0.5)

        self._player.mediaStatusChanged.connect(self._on_media_status)
        self._player.positionChanged.connect(self._on_position)
        self._player.durationChanged.connect(self._on_duration)
        self._player.playbackStateChanged.connect(self._on_playback_state)
        self._player.errorOccurred.connect(self._on_player_error_occurred)

        # ── Queue & state ─────────────────────────────────────────────
        self._queue: list[dict] = []
        self._current: Optional[dict] = None
        self._history: list[dict] = []
        self._loop_mode = False

        # ── Download worker (single persistent thread) ────────────────
        self._next_task_id = 0
        # The task ID that is "current" — results with other IDs are stale.
        self._active_task_id: Optional[int] = None
        # The task ID of the in-progress prefetch (if any).
        self._prefetch_task_id: Optional[int] = None
        # Cache of prefetched results: video_id → resolved dict with _local_path.
        self._prefetch_cache: dict[str, dict] = {}

        self._worker_thread = QThread(self)
        self._worker = DownloadWorker()
        self._worker.moveToThread(self._worker_thread)

        # Connect worker signals (cross-thread → queued delivery).
        self._worker.download_requested.connect(self._worker._do_download)
        self._worker.cancel_requested.connect(self._worker._do_cancel)
        self._worker.download_succeeded.connect(self._on_download_succeeded)
        self._worker.download_failed.connect(self._on_download_failed)
        self._worker_thread.start()

    # ═══════════════════════════════════════════════════════════════════════
    # Public API
    # ═══════════════════════════════════════════════════════════════════════

    # ── Volume ──────────────────────────────────────────────────────────────

    def set_volume(self, percent: int) -> None:
        self._audio_output.setVolume(max(0, min(100, percent)) / 100.0)

    def volume(self) -> int:
        return int(self._audio_output.volume() * 100)

    # ── Seek ────────────────────────────────────────────────────────────────

    def seek(self, ms: int) -> None:
        self._player.setPosition(max(0, ms))
        self.seeked.emit(max(0, ms))

    # ── Play / Queue ────────────────────────────────────────────────────────

    def play(self, song: dict) -> None:
        """Clear the queue and play *song* immediately."""
        self._cleanup_temp_files()
        self._queue.clear()
        self._prefetch_cache.clear()
        self._loop_mode = False
        self._request_download(song)

    def queue_song(self, song: dict) -> None:
        self._queue.append(song)
        if self._current is None and self._active_task_id is None:
            self._pop_and_play()

    def queue_next(self, song: dict) -> None:
        """Insert *song* to play immediately after the current one."""
        self._queue.insert(0, song)

    def queue_list(self, songs: list[dict]) -> None:
        self._queue.extend(songs)

    def skip(self) -> None:
        """Skip to the next song."""
        # Push current song to history before moving on.
        if self._current is not None:
            self._history.append(self._current)
        self._cancel_active_downloads()
        self._player.stop()
        self._advance()

    def previous(self) -> None:
        """Go back to the previous song, if available."""
        if not self._history:
            return
        prev = self._history.pop()
        self._cancel_active_downloads()
        self._player.stop()
        self._queue.insert(0, prev)
        self._try_next_song()

    def has_previous(self) -> bool:
        """Whether a previous song is available."""
        return len(self._history) > 0

    def is_loaded(self) -> bool:
        """Whether any song is currently loaded (playing or paused)."""
        return self._current is not None

    def stop_playback(self) -> None:
        """Soft stop: halt playback, clear queue, cancel downloads."""
        self._cancel_active_downloads()
        self._cleanup_temp_files()
        self._queue.clear()
        self._prefetch_cache.clear()
        self._history.clear()
        self._loop_mode = False
        self._current = None
        self._player.stop()
        self.song_loaded.emit(False)
        self.playback_state_changed.emit("stopped")

    @Slot()
    def _pop_and_play(self) -> None:
        """Pop the next song from the queue and start downloading it.

        If it was already prefetched, the download is instant (already cached).
        """
        if not self._queue:
            return
        song = self._queue.pop(0)
        vid = song.get("videoId") or song.get("video_id", "")
        cached = self._prefetch_cache.pop(vid, None)
        if cached is not None:
            # Prefetched — play directly without downloading.
            self._start_playback(cached)
        else:
            self._request_download(song)

    # ── Pause / Resume ──────────────────────────────────────────────────────

    def pause(self) -> None:
        if self._player.playbackState() == QMediaPlayer.PlaybackState.PlayingState:
            self._player.pause()

    def resume(self) -> None:
        if self._player.playbackState() == QMediaPlayer.PlaybackState.PausedState:
            self._player.play()

    def toggle_pause(self) -> bool:
        state = self._player.playbackState()
        if state == QMediaPlayer.PlaybackState.PlayingState:
            self._player.pause()
            return True
        elif state == QMediaPlayer.PlaybackState.PausedState:
            self._player.play()
            return False
        return False

    def is_paused(self) -> bool:
        return self._player.playbackState() == QMediaPlayer.PlaybackState.PausedState

    def is_playing(self) -> bool:
        return self._player.playbackState() == QMediaPlayer.PlaybackState.PlayingState

    def is_stopped(self) -> bool:
        return self._player.playbackState() == QMediaPlayer.PlaybackState.StoppedState

    # ── Queue introspection ────────────────────────────────────────────────

    def get_current(self) -> Optional[dict]:
        return self._current

    def get_queue(self) -> list[dict]:
        return list(self._queue)

    def get_queue_length(self) -> int:
        return len(self._queue)

    def get_loop(self) -> bool:
        return self._loop_mode

    def get_position(self) -> int:
        return self._player.position()

    def set_loop(self, enabled: bool) -> None:
        self._loop_mode = enabled

    # ═══════════════════════════════════════════════════════════════════════
    # Download lifecycle
    # ═══════════════════════════════════════════════════════════════════════

    def _request_download(self, song: dict) -> None:
        """Request a download via the persistent worker.

        Cancels any in-progress download and prefetch first, then assigns a
        fresh task ID and emits the request signal.
        """
        vid = song.get("videoId") or song.get("video_id", "")

        # Guard: don't re-download what's already playing.
        current_vid = (
            (self._current or {}).get("videoId")
            or (self._current or {}).get("video_id", "")
        )
        if vid and vid == current_vid:
            log.debug("Ignoring duplicate download request for %s", vid)
            return

        # Fast path: already has a local file (e.g. from prefetch cache).
        if song.get("_local_path"):
            self._start_playback(song)
            return

        # Cancel any in-flight work — this is a new intent.
        self._cancel_active_downloads()

        task_id = self._next_task_id
        self._next_task_id += 1
        self._active_task_id = task_id

        self.loading.emit(vid)
        self._worker.download_requested.emit(task_id, song)

    def _cancel_active_downloads(self) -> None:
        """Tell the worker to discard its current work and forget about it."""
        if self._active_task_id is not None or self._prefetch_task_id is not None:
            self._worker.cancel_requested.emit()
        self._active_task_id = None
        self._prefetch_task_id = None

    @Slot(int, dict)
    def _on_download_succeeded(self, task_id: int, song: dict) -> None:
        """Called on the main thread when a download succeeds.

        Checks *task_id* against ``_active_task_id`` and ``_prefetch_task_id``
        to discard stale results from superseded requests.
        """
        log.debug("Download succeeded: task_id=%d, active=%s, prefetch=%s",
                   task_id, self._active_task_id, self._prefetch_task_id)

        # ── Stale check for active download ──────────────────────────
        if task_id == self._active_task_id:
            self._active_task_id = None

            local_path = song.get("_local_path")
            if not local_path or not os.path.isfile(local_path):
                log.error("Download succeeded but file missing: %s", local_path)
                self.error.emit({
                    "video_id": song.get("videoId", ""),
                    "error": "Downloaded file went missing",
                })
                self._try_next_song()
                return

            self._start_playback(song)
            return

        # ── Stale check for prefetch download ────────────────────────
        if task_id == self._prefetch_task_id:
            self._prefetch_task_id = None

            vid = song.get("videoId") or song.get("video_id", "")
            # Only cache if the song is still in the active queue.
            if any(
                (s.get("videoId") or s.get("video_id", "")) == vid
                for s in self._queue
            ):
                log.debug("Caching prefetched result for %s (task %d)", vid, task_id)
                self._prefetch_cache[vid] = song
            else:
                log.debug("Prefetched %s no longer in queue, discarding", vid)
            return

        # ── Otherwise: truly stale — discard ────────────────────────────
        log.debug("Discarding stale download result for task %d (task_id=%d, active=%s, prefetch=%s)",
                   task_id, task_id, self._active_task_id, self._prefetch_task_id)

    @Slot(int)
    def _on_download_failed(self, task_id: int) -> None:
        """Called on the main thread when a download fails."""
        log.debug("Download failed: task_id=%d, active=%s, prefetch=%s",
                   task_id, self._active_task_id, self._prefetch_task_id)

        if task_id == self._active_task_id:
            self._active_task_id = None
            log.warning("Download failed for task %d", task_id)
            self.error.emit({
                "video_id": "",
                "error": "Failed to resolve audio URL",
            })
            self._try_next_song()
        elif task_id == self._prefetch_task_id:
            self._prefetch_task_id = None
            log.debug("Prefetch failed for task %d (harmless)", task_id)
        else:
            log.debug("Ignoring stale download failure for task %d", task_id)

    # ── Playback ───────────────────────────────────────────────────────

    def _start_playback(self, song: dict) -> None:
        """Begin playing a resolved song (already has ``_local_path``).

        Always called on the main thread.
        """
        # Remove the previous song's temp file BEFORE updating _current.
        self._cleanup_current_temp()

        local_path = song.get("_local_path", "")
        log.debug("Starting playback: path=%s, exists=%s, size=%s",
                   local_path,
                   os.path.isfile(local_path) if local_path else "N/A",
                   os.path.getsize(local_path) if local_path and os.path.isfile(local_path) else "N/A")

        self._player.stop()
        self._current = song

        self._player.setSource(QUrl.fromLocalFile(local_path))
        self._player.play()
        self.song_started.emit(song)
        self.song_loaded.emit(True)

        # Kick off prefetch for the next queued song.
        self._start_prefetch()

    # ═══════════════════════════════════════════════════════════════════════
    # End-of-song handling
    # ═══════════════════════════════════════════════════════════════════════

    def _on_media_status(self, status: QMediaPlayer.MediaStatus) -> None:
        if status == QMediaPlayer.MediaStatus.EndOfMedia:
            self._advance()
        elif status == QMediaPlayer.MediaStatus.InvalidMedia:
            if self._current is None:
                return
            if self._player.playbackState() == QMediaPlayer.PlaybackState.StoppedState:
                return
            self.error.emit({
                "video_id": (self._current or {}).get("videoId", ""),
                "error": "Invalid media",
            })
            # Don't call _advance here — the player will go to stopped state,
            # and _on_playback_state will handle advancing if appropriate.
            # But let's advance immediately for invalid media.
            self._advance()

    def _advance(self) -> None:
        """Move to the next song (or stop if the queue is empty).

        This is the single exit point from an actively-playing song.
        It handles loop re-queuing, song_ended emission, and queue popping.
        """
        if self._current is None:
            return

        finished_song = self._current
        finished_vid = finished_song.get("videoId") or finished_song.get(
            "video_id", ""
        )
        self._current = None

        self.song_ended.emit(finished_vid)

        # Re-queue for loop mode.
        if self._loop_mode:
            self._queue.insert(0, finished_song)

        self._try_next_song()

    def _try_next_song(self) -> None:
        """Attempt to play the next song, or stop if the queue is empty."""
        if self._queue:
            self._pop_and_play()
        else:
            self.playback_state_changed.emit("stopped")

    # ── Position / duration / state ────────────────────────────────────

    @Slot(int)
    def _on_position(self, ms: int) -> None:
        self.position_changed.emit(ms)

    @Slot(int)
    def _on_duration(self, ms: int) -> None:
        self.duration_changed.emit(ms)

    @Slot(QMediaPlayer.PlaybackState)
    def _on_playback_state(self, state: QMediaPlayer.PlaybackState) -> None:
        if state == QMediaPlayer.PlaybackState.PlayingState:
            self.playback_state_changed.emit("playing")
            if self._current:
                self.resumed.emit(self._current)
        elif state == QMediaPlayer.PlaybackState.PausedState:
            self.playback_state_changed.emit("paused")
            if self._current:
                self.paused.emit(self._current)
        else:
            self.playback_state_changed.emit("stopped")

    # ── errorOccurred handler ─────────────────────────────────────────

    @Slot(QMediaPlayer.Error, str)
    def _on_player_error_occurred(
        self, error: QMediaPlayer.Error, error_string: str
    ) -> None:
        """Handle QMediaPlayer error signals."""
        if error in (QMediaPlayer.Error.NetworkError, QMediaPlayer.Error.ResourceError):
            vid = (self._current or {}).get("videoId", "")
            log.warning("Player error (%s): %s — advancing", error, error_string)
            self.error.emit({
                "video_id": vid,
                "error": f"{error_string} (local file issue)",
            })
            self._advance()

    # ── Prefetch ──────────────────────────────────────────────────────────────

    def _start_prefetch(self) -> None:
        """Request a download of the next queued song (if any).

        Called after playback of the current song starts.  Uses the same
        persistent worker — no separate thread needed.
        """
        if not self._queue:
            return

        next_song = self._queue[0]
        vid = next_song.get("videoId") or next_song.get("video_id", "")

        # Already cached or already downloading.
        if vid in self._prefetch_cache:
            return
        if vid == self._prefetch_task_id:
            return
        # Don't prefetch if it's already the active download target.
        if self._active_task_id is not None:
            # The active download might be for this same song (e.g. if
            # _request_download was called but is still in flight).  Check by
            # tracking task_id alone is enough — if there's an active download,
            # the prefetch is redundant anyway.
            return

        task_id = self._next_task_id
        self._next_task_id += 1
        self._prefetch_task_id = task_id

        self._worker.download_requested.emit(task_id, next_song)

    # ═══════════════════════════════════════════════════════════════════════
    # Temp-file cleanup
    # ═══════════════════════════════════════════════════════════════════════

    def _cleanup_current_temp(self) -> None:
        """Remove the temp file of the song we're about to replace."""
        if self._current is None:
            return
        lp = self._current.get("_local_path")
        if lp and os.path.isfile(lp):
            try:
                os.unlink(lp)
            except OSError:
                pass

    def _cleanup_temp_files(self) -> None:
        """Remove all temp files we know about (current + prefetch cache)."""
        if self._current:
            lp = self._current.get("_local_path")
            if lp and os.path.isfile(lp):
                try:
                    os.unlink(lp)
                except OSError:
                    pass
        for cached in self._prefetch_cache.values():
            lp = cached.get("_local_path")
            if lp and os.path.isfile(lp):
                try:
                    os.unlink(lp)
                except OSError:
                    pass

    # ── Shutdown ──────────────────────────────────────────────────────────────

    def shutdown(self) -> None:
        """Clean shutdown — stop playback, quit worker thread, remove temps."""
        self._player.stop()
        self._cancel_active_downloads()
        self._cleanup_temp_files()
        self._queue.clear()
        self._prefetch_cache.clear()
        self._current = None
        self._loop_mode = False

        # Tear down the persistent worker thread.
        self._worker_thread.quit()
        self._worker_thread.wait(3000)
        # The worker and thread objects are owned by self (parented), so
        # they'll be cleaned up by Qt when the AudioPlayer is destroyed.


# ── Helpers ───────────────────────────────────────────────────────────────────

def _best_thumbnail(thumbnails) -> str:
    if not thumbnails:
        return ""
    if isinstance(thumbnails, str):
        return thumbnails
    if isinstance(thumbnails, list):
        best = thumbnails[-1]
        return best.get("url", "") if isinstance(best, dict) else str(best)
    return str(thumbnails)


def _build_song_dict(search_result: dict) -> dict:
    """Normalise a ytmusicapi result into our standard song dict."""
    return {
        "videoId": search_result.get("videoId", ""),
        "title": search_result.get("title", "Unknown"),
        "artists": search_result.get("artists") or [],
        "album": search_result.get("album"),
        "duration": search_result.get("duration_seconds", 0),
        "duration_label": search_result.get("duration", "?"),
        "thumbnail": _best_thumbnail(search_result.get("thumbnails", [])),
        "videoType": search_result.get("videoType", ""),
        "resultType": search_result.get("resultType", "song"),
    }