"""On-demand web image resizing with disk cache (srcset helpers)."""

from __future__ import annotations

import logging
import tempfile
from pathlib import Path
from urllib.parse import quote

from PIL import Image

from . import config

logger = logging.getLogger("livef12.images")

# Allowed ?w= values for /jobs/.../files/... — keep in sync with templates.
SRCSET_WIDTHS: tuple[int, ...] = (320, 640, 960, 1280)

# Default sizes for the 1/2/4-column job + variant grids.
GRID_SIZES = "(min-width: 960px) 25vw, (min-width: 640px) 50vw, 100vw"
# Original/rembg pair is always two columns.
PAIR_SIZES = "(min-width: 640px) 50vw, 50vw"


def file_url(job_id: str, filename: str, width: int | None = None) -> str:
    base = f"/jobs/{quote(job_id, safe='')}/files/{quote(filename, safe='')}"
    if width is None:
        return base
    return f"{base}?w={width}"


def srcset_for(job_id: str, filename: str) -> str:
    return ", ".join(f"{file_url(job_id, filename, w)} {w}w" for w in SRCSET_WIDTHS)


def img_attrs(job_id: str, filename: str, *, sizes: str = GRID_SIZES) -> dict[str, str]:
    """Attrs for responsive <img>: src, srcset, sizes, full_src (lightbox)."""
    return {
        "src": file_url(job_id, filename, 640),
        "srcset": srcset_for(job_id, filename),
        "sizes": sizes,
        # Lightbox: large webp, not the multi-MB master PNG/JPEG.
        "full_src": file_url(job_id, filename, SRCSET_WIDTHS[-1]),
    }


def get_or_create_resized(source: Path, width: int) -> Path:
    """Return a cached WebP whose longest edge is at most `width` (no upscale)."""
    if width not in SRCSET_WIDTHS:
        raise ValueError(f"unsupported width: {width}")
    if not source.is_file():
        raise FileNotFoundError(source)

    config.WEB_CACHE_DIR.mkdir(parents=True, exist_ok=True)
    cache_path = config.WEB_CACHE_DIR / f"{source.name}.w{width}.webp"
    try:
        if cache_path.is_file() and cache_path.stat().st_mtime >= source.stat().st_mtime:
            return cache_path
    except OSError:
        pass

    _write_resized(source, cache_path, width)
    return cache_path


def _write_resized(source: Path, dest: Path, width: int) -> None:
    with Image.open(source) as img:
        img.load()
        if img.mode == "P":
            img = img.convert("RGBA" if "transparency" in img.info else "RGB")
        elif img.mode not in ("RGB", "RGBA"):
            img = img.convert("RGB")

        if img.width > width:
            new_h = max(1, round(img.height * (width / img.width)))
            img = img.resize((width, new_h), Image.Resampling.LANCZOS)

        dest.parent.mkdir(parents=True, exist_ok=True)
        with tempfile.NamedTemporaryFile(
            dir=dest.parent, suffix=".webp", delete=False
        ) as tmp:
            tmp_path = Path(tmp.name)
        try:
            img.save(tmp_path, format="WEBP", quality=78, method=4)
            tmp_path.replace(dest)
        except Exception:
            tmp_path.unlink(missing_ok=True)
            raise
        logger.debug("cached %s -> %s (%dx%d)", source.name, dest.name, img.width, img.height)