"""Responsive JPEG variants for hero images."""

from __future__ import annotations

import re
from pathlib import Path

from PIL import Image

VARIANT_WIDTHS = (360, 560, 800)
JPEG_QUALITY = 82
DATE_IMAGE_RE = re.compile(r"^(\d{4}-\d{2}-\d{2})\.jpg$")


def image_public_path(date_iso: str, width: int | None = None) -> str:
    if width is None:
        return f"/img/{date_iso}.jpg"
    return f"/img/{date_iso}-{width}w.jpg"


def build_srcset(date_iso: str, widths: list[int], full_width: int) -> str:
    parts = [f"{image_public_path(date_iso, w)} {w}w" for w in widths]
    parts.append(f"{image_public_path(date_iso)} {full_width}w")
    return ", ".join(parts)


def create_responsive_variants(img_dir: Path, date_iso: str) -> dict[str, str] | None:
    source = img_dir / f"{date_iso}.jpg"
    if not source.exists():
        return None

    with Image.open(source) as im:
        im = im.convert("RGB")
        full_width, full_height = im.size
        generated: list[int] = []

        for width in VARIANT_WIDTHS:
            if width >= full_width:
                continue
            height = round(full_height * width / full_width)
            resized = im.resize((width, height), Image.Resampling.LANCZOS)
            out = img_dir / f"{date_iso}-{width}w.jpg"
            resized.save(out, "JPEG", quality=JPEG_QUALITY, optimize=True)
            generated.append(width)

        im.save(source, "JPEG", quality=JPEG_QUALITY, optimize=True)

    srcset = build_srcset(date_iso, generated, full_width)
    default_src = image_public_path(date_iso, 560) if 560 in generated else image_public_path(date_iso)
    thumb_src = image_public_path(date_iso, 360) if 360 in generated else image_public_path(date_iso)

    return {
        "src": default_src,
        "srcset": srcset,
        "sizes": "(max-width: 768px) 100vw, 560px",
        "og": image_public_path(date_iso),
        "thumb_src": thumb_src,
        "thumb_srcset": srcset,
        "thumb_sizes": "(max-width: 640px) 50vw, 360px",
    }


def load_image_descriptor(img_dir: Path, date_iso: str) -> dict[str, str] | None:
    if not (img_dir / f"{date_iso}.jpg").exists():
        return None
    if not (img_dir / f"{date_iso}-360w.jpg").exists():
        return create_responsive_variants(img_dir, date_iso)
    widths = [w for w in VARIANT_WIDTHS if (img_dir / f"{date_iso}-{w}w.jpg").exists()]
    with Image.open(img_dir / f"{date_iso}.jpg") as im:
        full_width = im.size[0]
    srcset = build_srcset(date_iso, widths, full_width)
    return {
        "src": image_public_path(date_iso, 560) if 560 in widths else image_public_path(date_iso),
        "srcset": srcset,
        "sizes": "(max-width: 768px) 100vw, 560px",
        "og": image_public_path(date_iso),
        "thumb_src": image_public_path(date_iso, 360) if 360 in widths else image_public_path(date_iso),
        "thumb_srcset": srcset,
        "thumb_sizes": "(max-width: 640px) 50vw, 360px",
    }


def iter_source_images(img_dir: Path) -> list[Path]:
    if not img_dir.exists():
        return []
    sources = []
    for path in sorted(img_dir.glob("*.jpg")):
        if DATE_IMAGE_RE.match(path.name):
            sources.append(path)
    return sources