"""
Index-time enrichment for the Music group app: embedded tag/cover
extraction (mutagen) and filename-parse fallback for a newly-added audio
IndexEntry (docs/musicbay.md §2.1, §6).

Runs through its own small bounded worker pool, the same discipline as the
Videos app's `enrich.py` — separate from any other pool, never blocking a
scan or the watchdog. Unlike `enrich.py`, this one shells out to nothing:
`mutagen` is pure Python, synchronous I/O only, so there is no subprocess to
spawn, no pipe to drain, and no ffmpeg-shaped deadlock risk here at all —
the bounded pool exists to keep a large library's indexing burst bounded,
not to contain a process. Reads run via `asyncio.to_thread` so they never
block the event loop.

MusicBrainz lookups are **not** done here. Tag/cover extraction is free and
local, so it runs for every audio file the Music app is enabled for,
regardless of whether MusicBrainz itself is turned on for the group — the
flat view (docs/musicbay.md §5.2) needs nothing more than this. MusicBrainz
is a separate, lazy, per-request enrichment (`music_meta_req`, handled in
webrtc_server.py), the same "fetched on demand, cached once" shape TMDB
already uses.
"""

import asyncio
import logging
import re
from collections.abc import Awaitable, Callable
from pathlib import Path

import blake3
from meshbay_common.protocol import IndexEntry
from mutagen import File as MutagenFile

from meshbay_node.indexer import title_parse
from meshbay_node.media_cache import MediaCache

log = logging.getLogger(__name__)

# Higher than the video pool's default (2): mutagen reads a few KB of tag
# data synchronously, no subprocess, no decode — cheap enough that a wider
# pool doesn't cost much and finishes a large library's initial scan sooner.
DEFAULT_MAX_CONCURRENT = 4
READ_TIMEOUT_SECS = 10

_TRACK_NO_RE = re.compile(r"\d+")


def _extract_cover(mf) -> bytes | None:
    """
    Best-effort embedded cover art across the tag formats mutagen exposes
    differently: ID3 (MP3) keeps pictures as APIC frames on `.tags`, FLAC
    exposes `.pictures` on the file object itself, MP4/M4A keeps a `covr`
    atom on `.tags`. Returns the first picture found, or None — most of a
    real library has no embedded art at all, which is not an error.
    """
    tags = mf.tags
    if tags is not None and hasattr(tags, "getall"):
        pics = tags.getall("APIC")
        if pics:
            return bytes(pics[0].data)
    pictures = getattr(mf, "pictures", None)
    if pictures:
        return bytes(pictures[0].data)
    if tags is not None and hasattr(tags, "get"):
        covr = tags.get("covr")
        if covr:
            return bytes(covr[0])
    return None


def _read_tags_and_cover(path: Path) -> tuple[dict, float | None, bytes | None]:
    """
    Synchronous — always called via asyncio.to_thread. Returns a partial
    `tags` dict (only keys actually found: title/artist/album/track_no),
    duration in seconds (None if unreadable), and raw cover bytes (None if
    absent). Never raises for an unreadable/corrupt file — the caller falls
    back to filename parsing entirely in that case.
    """
    tags: dict = {}
    duration: float | None = None
    try:
        easy = MutagenFile(str(path), easy=True)
    except Exception:
        easy = None
    if easy is not None:
        if easy.info is not None:
            duration = getattr(easy.info, "length", None)
        for field in ("title", "artist", "album"):
            values = easy.get(field)
            if values and str(values[0]).strip():
                tags[field] = str(values[0]).strip()
        track_raw = easy.get("tracknumber")
        if track_raw:
            m = _TRACK_NO_RE.match(str(track_raw[0]))
            if m:
                tags["track_no"] = int(m.group())

    cover: bytes | None = None
    try:
        raw = MutagenFile(str(path))
    except Exception:
        raw = None
    if raw is not None:
        try:
            cover = _extract_cover(raw)
        except Exception:
            cover = None

    return tags, duration, cover


def _artist_album_from_ancestors(file_path: Path) -> tuple[str | None, str | None]:
    """
    `Artist/Album/track.mp3` is the common shape (docs/musicbay.md §2.1) —
    used only to fill whatever the tags left empty. No attempt to validate
    against the group's actual roots (enrich.py's ancestor walks don't
    either): a flat `Artist/track.mp3` layout, or a various-artists
    compilation folder, just yields a plausible-but-not-guaranteed album
    name from the immediate parent and nothing further up — good enough for
    a fallback, not asserted as accurate.
    """
    album_folder = file_path.parent
    if album_folder == album_folder.parent:
        return None, None
    artist_folder = album_folder.parent
    album = album_folder.name or None
    artist = artist_folder.name if artist_folder != artist_folder.parent else None
    return artist, album


class AudioEnricher:
    """Owns the node's bounded audio index-time enrichment pool."""

    def __init__(self, media_cache: MediaCache, max_concurrent: int = DEFAULT_MAX_CONCURRENT):
        self._media_cache = media_cache
        self._sem = asyncio.Semaphore(max_concurrent)
        self._tasks: set[asyncio.Task] = set()

    def spawn(
        self, entry: IndexEntry, file_path: Path,
        on_done: Callable[[str, dict], Awaitable[None]],
    ) -> asyncio.Task:
        """
        Fire-and-forget one file's enrichment — same contract as
        `enrich.Enricher.spawn`: `on_done(file_id, fields)` is awaited with
        the index fields to merge once ready, never blocks the caller, and
        the returned task must be held by the caller for the same reason
        `WebRTCPeerSession._spawn` holds streaming tasks (a bare
        `ensure_future` can be garbage-collected mid-flight).
        """
        task = asyncio.ensure_future(self._run(entry, file_path, on_done))
        self._tasks.add(task)

        def _cleanup(t: asyncio.Task) -> None:
            self._tasks.discard(t)
            if not t.cancelled() and t.exception():
                log.error("Audio enrichment failed for %s: %s", entry.id[:12], t.exception(),
                          exc_info=t.exception())
        task.add_done_callback(_cleanup)
        return task

    async def _run(
        self, entry: IndexEntry, file_path: Path,
        on_done: Callable[[str, dict], Awaitable[None]],
    ) -> None:
        async with self._sem:
            fields: dict = {}
            try:
                tags, duration, cover = await asyncio.wait_for(
                    asyncio.to_thread(_read_tags_and_cover, file_path), timeout=READ_TIMEOUT_SECS)
            except Exception as e:
                log.warning("Tag read failed for %s: %s", file_path, e)
                tags, duration, cover = {}, None, None

            if duration:
                fields["duration"] = int(duration)

            parsed = title_parse.parse_track_filename(entry.name)
            fields["display_title"] = tags.get("title") or parsed.title or parsed.naive_title
            fields["track_no"] = tags.get("track_no") if "track_no" in tags else parsed.track_no

            artist = tags.get("artist")
            album = tags.get("album")
            if not artist or not album:
                fallback_artist, fallback_album = await asyncio.to_thread(
                    _artist_album_from_ancestors, file_path)
                artist = artist or fallback_artist
                album = album or fallback_album
            fields["artist"] = artist
            fields["album"] = album

            if cover:
                thumb_hash = blake3.blake3(cover).hexdigest()
                await self._media_cache.put_thumb(thumb_hash, entry.id, cover)
                fields["thumb_hash"] = thumb_hash

            await on_done(entry.id, fields)