feat: support complet des images — arborescence, visionneuse, indexation #108

backend/media_thumbs.py

@@ -0,0 +1,74 @@
+"""Image thumbnail generation and disk cache (roadmap #108-C).
+
+Thumbnails are generated on demand with Pillow and cached under
+``<OBSIGATE_DATA_DIR>/.obsigate-cache/thumbs/<sha1>.webp``. The cache key
+embeds the source path, mtime (ns) and size, so an edited image naturally
+invalidates its stale thumbnail without any explicit cleanup.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import os
+from pathlib import Path
+
+DEFAULT_THUMB_SIZE = 256
+
+# Extensions Pillow cannot decode without extra native libraries: served as-is.
+_UNDECODABLE = {".svg"}
+
+
+def thumbs_cache_dir() -> Path:
+    """Return (and create) the thumbnail cache directory."""
+    base = Path(os.environ.get("OBSIGATE_DATA_DIR", "data")) / ".obsigate-cache" / "thumbs"
+    base.mkdir(parents=True, exist_ok=True)
+    return base
+
+
+def thumb_cache_path(file_path: Path, size: int) -> Path:
+    """Compute the deterministic cache path for *file_path* at *size*."""
+    try:
+        st = file_path.stat()
+        stamp = f"{st.st_mtime_ns}:{st.st_size}"
+    except OSError:
+        stamp = "0:0"
+    key = hashlib.sha1(f"{file_path}:{stamp}:{size}".encode()).hexdigest()
+    return thumbs_cache_dir() / f"{key}.webp"
+
+
+def is_decodable(file_path: Path) -> bool:
+    """True when Pillow can be expected to decode *file_path*."""
+    return file_path.suffix.lower() not in _UNDECODABLE
+
+
+def generate_thumbnail(file_path: Path, size: int = DEFAULT_THUMB_SIZE) -> Path | None:
+    """Generate (or reuse) a WebP thumbnail and return its path.
+
+    Returns ``None`` when the file cannot be decoded (e.g. SVG) or Pillow is
+    unavailable, so the caller can fall back to serving the original.
+    """
+    cache_path = thumb_cache_path(file_path, size)
+    if cache_path.exists():
+        return cache_path
+
+    try:
+        from PIL import Image, ImageOps
+    except Exception:  # pragma: no cover - Pillow is an optional runtime dep
+        return None
+
+    try:
+        with Image.open(file_path) as opened:
+            # Animated formats: keep only the first frame.
+            if getattr(opened, "is_animated", False):
+                opened.seek(0)
+            img = ImageOps.exif_transpose(opened) or opened
+            if img.mode not in ("RGB", "RGBA"):
+                img = img.convert("RGBA")
+            img.thumbnail((size, size))
+
+            tmp = cache_path.with_suffix(".tmp")
+            img.save(tmp, "WEBP", quality=80)
+        os.replace(tmp, cache_path)
+        return cache_path
+    except Exception:
+        return None