US01-05: Generate and Serve Managed Thumbnails (#50)

photo_pipeline/api/routes/thumbnails.py

@@ -0,0 +1,35 @@
+"""Thumbnail endpoint: previews addressed only by asset ID and bounded size.
+
+The browser never supplies a filesystem path. Errors return a consistent JSON
+envelope with the service's typed code and status; successful responses carry the
+image with an immutable cache header (the URL's identity comes from the versioned,
+content-keyed cache).
+"""
+
+from __future__ import annotations
+
+from fastapi import APIRouter, Query, Request
+from fastapi.responses import FileResponse, JSONResponse
+
+from photo_pipeline.services.thumbnails import ThumbnailError, ThumbnailService
+
+router = APIRouter(tags=["thumbnails"])
+
+
+@router.get("/assets/{asset_id}/thumbnail")
+def get_thumbnail(asset_id: str, request: Request, size: int = Query(512)):
+    service = ThumbnailService(
+        request.app.state.session_factory, request.app.state.config
+    )
+    try:
+        path = service.generate(asset_id, size)
+    except ThumbnailError as error:
+        return JSONResponse(
+            status_code=error.http_status,
+            content={"error": {"code": error.code, "message": str(error)}},
+        )
+    return FileResponse(
+        path,
+        media_type="image/webp",
+        headers={"Cache-Control": "public, max-age=31536000, immutable"},
+    )