"""Thin on-disk cache + proxy helpers for Plex poster/art images.

Posters/art/cast-photos are proxied on demand; without a cache every scroll re-hits Plex over the
LAN (janky). We cache the fetched bytes on local disk keyed by a stable id, so repeat views (and
other users) serve instantly from disk. On-demand + bounded by the library size; no eviction (a
few hundred MB at most for a big library — acceptable, matching the download disk trade-offs).

The cache directory (``cache.CACHE_DIR``) is shared with the subtitle cache (see ``subtitles.py``).
"""

from fastapi import Response
from sqlalchemy.orm import Session

from app import logs
from app.models import PlexCollection, PlexItem, PlexSeason, PlexShow
from app.plex.cache import CACHE_DIR
from app.plex.lookups import by_rating_key

log = logs.get_logger(__name__)

_EXT_CT = [("jpg", "image/jpeg"), ("png", "image/png"), ("webp", "image/webp")]
_CT_EXT = {ct: ext for ext, ct in _EXT_CT}
# Target box per variant — Plex resizes to these server-side. Posters fill ≤176px cells (grid/info/
# strips), so 400px covers 2× DPR; the faint backdrop art only needs ~1280px. Keeps images ~tens of KB.
SIZES = {"thumb": (400, 600), "art": (1280, 720)}


def key_for(db: Session, rating_key: str, variant: str) -> str | None:
    """The stored Plex image path for a known rating_key (item/show/season). Only mirrored keys
    are proxyable — this is not an open image proxy."""
    it = by_rating_key(db, PlexItem, rating_key)
    if it is not None:
        return it.art_key if variant == "art" else it.thumb_key
    sh = by_rating_key(db, PlexShow, rating_key)
    if sh is not None:
        return sh.art_key if variant == "art" else sh.thumb_key
    se = by_rating_key(db, PlexSeason, rating_key)
    if se is not None:
        return se.thumb_key
    col = by_rating_key(db, PlexCollection, rating_key)
    if col is not None:
        return col.thumb_key
    return None


def read(key: str) -> tuple[bytes, str] | None:
    for ext, ct in _EXT_CT:
        p = CACHE_DIR / f"{key}.{ext}"
        try:
            if p.exists() and p.stat().st_size > 0:
                return p.read_bytes(), ct
        # silent-ok: a miss. The caller fetches from Plex and writes the file again, and the write
        # path below is the one that reports a cache that cannot be used.
        except OSError:
            pass
    return None


def write(key: str, data: bytes, ct: str) -> None:
    ext = _CT_EXT.get((ct or "").split(";")[0].strip(), "jpg")
    try:
        CACHE_DIR.mkdir(parents=True, exist_ok=True)
        tmp = CACHE_DIR / f"{key}.{ext}.tmp"
        tmp.write_bytes(data)
        tmp.replace(CACHE_DIR / f"{key}.{ext}")  # atomic publish
    except OSError as exc:
        # Best-effort, and silently so: with an unwritable cache every poster on every grid goes
        # to Plex live, for as long as nobody notices. Debug, because a grid is ~100 images and
        # the point is the condition, not the count.
        log.debug(
            "the Plex image cache could not be written",
            extra=logs.event("plex.imgcache.write_failed", reason=type(exc).__name__),
        )


def response(data: bytes, ct: str) -> Response:
    return Response(content=data, media_type=ct, headers={"Cache-Control": "public, max-age=86400"})