"""Apply album art to existing library files.

Two jobs, both reusing the post-processing standard so the user's
``album_art_order`` preference is honored and embedded art matches cover.jpg:

- Detect whether an album already has art ON DISK (embedded in the audio file
  or a cover.jpg/folder.jpg sidecar) — the Cover Art Filler previously only
  looked at the DB ``thumb_url``, so albums whose files were artless but whose
  DB row had a URL were never flagged.
- Embed found art into the album's audio files (``embed_album_art_metadata``)
  and write a cover.jpg (``download_cover_art``). Only ADDS art — it does not
  clear or rewrite the user's existing tags.
"""

from __future__ import annotations

import contextlib
import errno
import os
from typing import Iterable

from core.metadata.artwork import download_cover_art, embed_album_art_metadata
from core.metadata.common import get_mutagen_symbols
from utils.logging_config import get_logger

logger = get_logger("metadata.art_apply")

# Folder-level cover files recognised across players (matches soulsync_client).
_COVER_SIDECARS = (
    "cover.jpg", "cover.jpeg", "cover.png",
    "folder.jpg", "folder.jpeg", "folder.png",
)


def folder_has_cover_sidecar(folder: str) -> bool:
    """True if the album folder already carries a cover.jpg/folder.jpg sidecar."""
    if not folder:
        return False
    try:
        for name in _COVER_SIDECARS:
            if os.path.isfile(os.path.join(folder, name)):
                return True
    except OSError:
        return False
    return False


def file_has_embedded_art(file_path: str) -> bool:
    """True if the audio file already has embedded cover art (FLAC picture,
    ID3 APIC, MP4 covr, or a Vorbis metadata_block_picture)."""
    if not file_path or not os.path.isfile(file_path):
        return False
    symbols = get_mutagen_symbols()
    if not symbols:
        return False
    try:
        return _audio_has_art(symbols.File(file_path), symbols)
    except Exception as exc:
        logger.debug("art presence check failed for %s: %s", file_path, exc)
        return False


def _audio_has_art(audio, symbols) -> bool:
    """True if an already-open mutagen object carries embedded cover art."""
    if audio is None:
        return False
    # FLAC / Ogg expose picture blocks directly.
    if getattr(audio, "pictures", None):
        return True
    if isinstance(audio, symbols.MP4):
        return bool(audio.get("covr"))
    tags = getattr(audio, "tags", None)
    if tags is None:
        return False
    with contextlib.suppress(Exception):
        if isinstance(tags, symbols.ID3):
            return bool(tags.getall("APIC"))
    with contextlib.suppress(Exception):
        if "metadata_block_picture" in tags:
            return True
    return False


def album_has_art_on_disk(rep_file_path: str) -> bool:
    """Does this album have art on disk?

    Checks the folder for a cover sidecar first (cheap stat) and only opens the
    representative audio file when there's no sidecar. Returns True when there's
    no local file to inspect (e.g. a media-server-only album) so such albums
    aren't wrongly flagged as missing file art.
    """
    if not rep_file_path:
        return True
    folder = os.path.dirname(rep_file_path)
    if folder_has_cover_sidecar(folder):
        return True
    return file_has_embedded_art(rep_file_path)


def apply_art_to_album_files(
    file_paths: Iterable[str],
    metadata: dict,
    album_info: dict,
    folder: str = None,
    context: dict = None,
) -> dict:
    """Embed art into each audio file + write cover.jpg, reusing the standard.

    ``metadata`` feeds ``embed_album_art_metadata`` (needs album_artist/artist/
    album, optionally musicbrainz_release_id and album_art_url as the fallback
    URL). ``album_info`` feeds ``download_cover_art`` (album_name/album_image_url/
    musicbrainz_release_id). Existing tags are preserved — only art is added.

    Returns counts; never raises (unwritable/read-only files are skipped).
    ``read_only_fs`` is True when the target filesystem itself rejects writes
    (EROFS — a docker ``:ro`` volume mount; chmod can't fix that) so callers
    can tell the user the actual cure instead of a generic failure.
    """
    result = {"embedded": 0, "failed": 0, "skipped": 0, "cover_written": False,
              "read_only_fs": False}
    symbols = get_mutagen_symbols()
    paths = [p for p in (file_paths or []) if p]
    if not symbols:
        return result

    # Pre-flight: if the mount is read-only, every save below would fail with
    # EROFS one by one (Tim's report: a wall of per-file warnings and a 777
    # chmod that couldn't help). statvfs asks the kernel without writing.
    probe_dir = folder or (os.path.dirname(paths[0]) if paths else None)
    if probe_dir:
        try:
            if os.statvfs(probe_dir).f_flag & os.ST_RDONLY:
                logger.warning(
                    "Art apply skipped: %s is on a READ-ONLY filesystem "
                    "(docker ':ro' volume mount — chmod cannot fix this)",
                    probe_dir)
                result["read_only_fs"] = True
                result["failed"] = len(paths)
                return result
        except OSError:
            pass  # statvfs unavailable/odd fs — fall through to per-file handling

    for fp in paths:
        if not os.path.isfile(fp):
            result["skipped"] += 1
            continue
        try:
            audio = symbols.File(fp)
            if audio is None:
                result["skipped"] += 1
                continue
            # Purely additive: never touch a file that already has art. Embedding
            # again would APPEND a duplicate picture on FLAC (add_picture doesn't
            # replace), so leave already-arted files alone.
            if _audio_has_art(audio, symbols):
                result["skipped"] += 1
                continue
            # ID3 needs a tag container before APIC can be added.
            if getattr(audio, "tags", None) is None and hasattr(audio, "add_tags"):
                with contextlib.suppress(Exception):
                    audio.add_tags()
            if embed_album_art_metadata(audio, metadata):
                audio.save()
                result["embedded"] += 1
            else:
                result["failed"] += 1
        except Exception as exc:
            # Read-only mounts / permission errors land here — skip, don't crash.
            if getattr(exc, "errno", None) == errno.EROFS:
                result["read_only_fs"] = True
            logger.warning("Could not embed art into %s: %s", fp, exc)
            result["failed"] += 1

    target_dir = folder or (os.path.dirname(paths[0]) if paths else None)
    if target_dir and os.path.isdir(target_dir):
        try:
            download_cover_art(album_info, target_dir, context)
            result["cover_written"] = folder_has_cover_sidecar(target_dir)
        except Exception as exc:
            if getattr(exc, "errno", None) == errno.EROFS:
                result["read_only_fs"] = True
            logger.warning("cover.jpg write failed for %s: %s", target_dir, exc)
    return result