feat(T05): Dateiablage pro Fahrzeug + File UI with thumbnails and gallery

backend/app/utils/thumbnails.py

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+"""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