feat: setup dataset enrichment app codebase and scripts

backend/api/common.py

@@ -0,0 +1,35 @@
+"""Helpers shared by the route modules."""
+
+import io
+import os
+from functools import lru_cache
+
+from fastapi import HTTPException
+
+from backend import projects as project_store
+
+
+def project_or_404(project_id: int) -> dict:
+    project = project_store.get(project_id)
+    if project is None:
+        raise HTTPException(404, "No such project")
+    return project
+
+
+@lru_cache(maxsize=512)
+def _thumbnail_cached(path: str, width: int, mtime: float) -> bytes:
+    from PIL import Image
+
+    with Image.open(path) as image:
+        image = image.convert("RGB")
+        if image.width > width:
+            height = max(1, round(image.height * width / image.width))
+            image = image.resize((width, height), Image.BILINEAR)
+        buffer = io.BytesIO()
+        image.save(buffer, "JPEG", quality=72)
+        return buffer.getvalue()
+
+
+def thumbnail(path: str, width: int) -> bytes:
+    # mtime is part of the key so a re-extracted frame never serves a stale one.
+    return _thumbnail_cached(path, width, os.path.getmtime(path))