"""Thumbnail generation utilities using Pillow.

Generates 200x200 thumbnails for image files (jpg, png, webp).
Non-image files return None (no thumbnail).
"""

import logging
from pathlib import Path
from typing import Optional

from PIL import Image, ImageOps

logger = logging.getLogger(__name__)

THUMBNAIL_SIZE = (200, 200)
IMAGE_MIME_TYPES = {
    "image/jpeg",
    "image/png",
    "image/webp",
}
IMAGE_EXTENSIONS = {"jpg", "jpeg", "png", "webp"}


def is_image_mime_type(mime_type: str) -> bool:
    """Check if the given MIME type is a supported image type."""
    return mime_type.lower() in IMAGE_MIME_TYPES


def generate_thumbnail(
    source_path: str | Path,
    thumbnail_dir: str | Path,
    stored_filename: str,
) -> Optional[str]:
    """Generate a 200x200 thumbnail for an image file.

    Args:
        source_path: Path to the original image file.
        thumbnail_dir: Directory where thumbnails are stored.
        stored_filename: The stored filename of the original file.

    Returns:
        Relative path to the thumbnail file, or None if the file is not
        a supported image or thumbnail generation fails.
    """
    source_path = Path(source_path)
    thumbnail_dir = Path(thumbnail_dir)

    # Check if the file extension is a supported image type
    ext = source_path.suffix.lower().lstrip(".")
    if ext not in IMAGE_EXTENSIONS:
        return None

    try:
        thumbnail_dir.mkdir(parents=True, exist_ok=True)

        thumbnail_name = f"thumb_{stored_filename}"
        # Use .jpg for thumbnails to save space
        if ext in ("jpg", "jpeg"):
            thumbnail_name = f"thumb_{Path(stored_filename).stem}.jpg"
        elif ext == "png":
            thumbnail_name = f"thumb_{Path(stored_filename).stem}.png"
        elif ext == "webp":
            thumbnail_name = f"thumb_{Path(stored_filename).stem}.webp"

        thumbnail_path = thumbnail_dir / thumbnail_name

        with Image.open(source_path) as img:
            # Convert to RGB if necessary (e.g., for RGBA/P mode images)
            if img.mode in ("RGBA", "P", "LA"):
                # Create a white background for transparency
                background = Image.new("RGB", img.size, (255, 255, 255))
                if img.mode == "P":
                    img = img.convert("RGBA")
                background.paste(img, mask=img.split()[-1] if img.mode in ("RGBA", "LA") else None)
                img = background
            elif img.mode != "RGB":
                img = img.convert("RGB")

            # Use ImageOps.fit for a centered crop to exact thumbnail size
            thumbnail = ImageOps.fit(img, THUMBNAIL_SIZE, method=Image.Resampling.LANCZOS)
            thumbnail.save(thumbnail_path, quality=85, optimize=True)

        logger.info("Thumbnail generated: %s", thumbnail_path)
        return str(thumbnail_path)

    except Exception as exc:
        logger.error("Failed to generate thumbnail for %s: %s", source_path, exc)
        return None