feat(api): add input validation on public endpoints

- Add days query param to GET /public/trends/{product_id} (ge=1, le=365)
- Add category query param to GET /public/store-comparison
- Add category and period query params to GET /public/inflation
- Add boundary and malicious input test cases

Co-Authored-By: Paperclip <noreply@paperclip.ing>

api/src/cartsnitch_api/routes/public.py

@@ -18,10 +18,14 @@ router = APIRouter(prefix="/public", tags=["public"])
 
 
 @router.get("/trends/{product_id}", response_model=PublicTrendResponse)
-async def public_price_trend(product_id: UUID, db: AsyncSession = Depends(get_db)):
+async def public_price_trend(
+    product_id: UUID,
+    days: int = Query(90, ge=1, le=365),
+    db: AsyncSession = Depends(get_db),
+):
     svc = PublicService(db)
     try:
-        return await svc.get_trend(product_id)
+        return await svc.get_trend(product_id, days=days)
     except LookupError:
         raise HTTPException(
             status_code=status.HTTP_404_NOT_FOUND, detail="Product not found"
@@ -31,6 +35,7 @@ async def public_price_trend(product_id: UUID, db: AsyncSession = Depends(get_db
 @router.get("/store-comparison", response_model=PublicStoreComparisonResponse)
 async def public_store_comparison(
     product_ids: Annotated[list[UUID], Query(max_length=20)],
+    category: str | None = Query(None, max_length=100, pattern=r"^[a-zA-Z0-9 _-]+$"),
     db: AsyncSession = Depends(get_db),
 ):
     if not product_ids:
@@ -39,10 +44,14 @@ async def public_store_comparison(
             detail="At least one product_id is required",
         )
     svc = PublicService(db)
-    return await svc.get_store_comparison(product_ids)
+    return await svc.get_store_comparison(product_ids, category=category)
 
 
 @router.get("/inflation", response_model=PublicInflationResponse)
-async def public_inflation(db: AsyncSession = Depends(get_db)):
+async def public_inflation(
+    category: str | None = Query(None, max_length=100, pattern=r"^[a-zA-Z0-9 _-]+$"),
+    period: str = Query("all-time", pattern=r"^(all-time|1y|6m|3m|1m)$"),
+    db: AsyncSession = Depends(get_db),
+):
     svc = PublicService(db)
-    return await svc.get_inflation()
+    return await svc.get_inflation(category=category, period=period)

api/src/cartsnitch_api/services/public.py

@@ -1,5 +1,6 @@
 """Public service — unauthenticated price transparency endpoints."""
 
+from datetime import date, timedelta
 from uuid import UUID
 
 from sqlalchemy import and_, func, select
@@ -13,7 +14,7 @@ class PublicService:
     def __init__(self, db: AsyncSession) -> None:
         self.db = db
 
-    async def get_trend(self, product_id: UUID) -> dict:
+    async def get_trend(self, product_id: UUID, days: int = 90) -> dict:
         from cartsnitch_api.models import NormalizedProduct, PriceHistory
 
         result = await self.db.execute(
@@ -23,9 +24,13 @@ class PublicService:
         if not product:
             raise LookupError("Product not found")
 
+        date_threshold = date.today() - timedelta(days=days)
         prices_result = await self.db.execute(
             select(PriceHistory)
-            .where(PriceHistory.normalized_product_id == product_id)
+            .where(
+                PriceHistory.normalized_product_id == product_id,
+                PriceHistory.observed_date >= date_threshold,
+            )
             .options(selectinload(PriceHistory.store))
             .order_by(PriceHistory.observed_date)
         )
@@ -45,20 +50,25 @@ class PublicService:
             ],
         }
 
-    async def get_store_comparison(self, product_ids: list[UUID]) -> dict:
+    async def get_store_comparison(
+        self, product_ids: list[UUID], category: str | None = None
+    ) -> dict:
         from cartsnitch_api.models import NormalizedProduct, PriceHistory
 
         if not product_ids:
             return {"products": []}
 
-        # Fetch all products in one query
-        prod_result = await self.db.execute(
-            select(NormalizedProduct).where(NormalizedProduct.id.in_(product_ids))
-        )
+        product_query = select(NormalizedProduct).where(NormalizedProduct.id.in_(product_ids))
+        if category:
+            product_query = product_query.where(NormalizedProduct.category == category)
+        prod_result = await self.db.execute(product_query)
         products_by_id = {p.id: p for p in prod_result.scalars().all()}
 
-        # Latest prices for all requested products in one query
-        subq = latest_price_per_store(product_ids)
+        if not products_by_id:
+            return {"products": []}
+
+        filtered_product_ids = list(products_by_id.keys())
+        subq = latest_price_per_store(filtered_product_ids)
         prices_result = await self.db.execute(
             select(PriceHistory)
             .join(
@@ -69,18 +79,17 @@ class PublicService:
                     PriceHistory.normalized_product_id == subq.c.normalized_product_id,
                 ),
             )
-            .where(PriceHistory.normalized_product_id.in_(product_ids))
+            .where(PriceHistory.normalized_product_id.in_(filtered_product_ids))
             .options(selectinload(PriceHistory.store))
         )
         all_prices = prices_result.scalars().all()
 
-        # Group by product
         prices_by_product: dict[UUID, list] = {}
         for ph in all_prices:
             prices_by_product.setdefault(ph.normalized_product_id, []).append(ph)
 
         products = []
-        for pid in product_ids:
+        for pid in filtered_product_ids:
             product = products_by_id.get(pid)
             if not product:
                 continue
@@ -102,19 +111,29 @@ class PublicService:
 
         return {"products": products}
 
-    async def get_inflation(self) -> dict:
+    async def get_inflation(self, category: str | None = None, period: str = "all-time") -> dict:
         """Aggregate price change stats. Compares average prices across periods."""
         from cartsnitch_api.models import NormalizedProduct, PriceHistory
 
-        # Get average prices grouped by category for recent vs older data
-        result = await self.db.execute(
-            select(
-                NormalizedProduct.category,
-                func.avg(PriceHistory.regular_price),
-            )
-            .join(NormalizedProduct)
-            .group_by(NormalizedProduct.category)
-        )
+        date_threshold = None
+        if period != "all-time":
+            days_map = {"1y": 365, "6m": 180, "3m": 90, "1m": 30}
+            days = days_map.get(period, 365)
+            date_threshold = date.today() - timedelta(days=days)
+
+        query = select(
+            NormalizedProduct.category,
+            func.avg(PriceHistory.regular_price),
+        ).join(NormalizedProduct)
+
+        if category:
+            query = query.where(NormalizedProduct.category == category)
+        if date_threshold:
+            query = query.where(PriceHistory.observed_date >= date_threshold)
+
+        query = query.group_by(NormalizedProduct.category)
+
+        result = await self.db.execute(query)
         categories = {}
         for row in result.all():
             cat, avg_price = row
@@ -122,7 +141,7 @@ class PublicService:
                 categories[cat] = float(avg_price) if avg_price else 0.0
 
         return {
-            "period": "all-time",
+            "period": period,
             "cartsnitch_index": sum(categories.values()) / max(len(categories), 1),
             "cpi_baseline": 100.0,
             "categories": categories,

api/tests/test_routes/test_public.py

@@ -71,3 +71,97 @@ async def test_public_inflation(client, public_data):
     data = resp.json()
     assert "categories" in data
     assert "cartsnitch_index" in data
+
+
+@pytest.mark.asyncio
+async def test_trend_invalid_uuid(client):
+    resp = await client.get("/public/trends/not-a-uuid")
+    assert resp.status_code == 422
+    assert "detail" in resp.json()
+    assert "stack" not in resp.json()
+
+
+@pytest.mark.asyncio
+async def test_trend_days_zero(client, public_data):
+    pid = str(public_data["product"].id)
+    resp = await client.get(f"/public/trends/{pid}?days=0")
+    assert resp.status_code == 422
+    assert "detail" in resp.json()
+    assert "stack" not in resp.json()
+
+
+@pytest.mark.asyncio
+async def test_trend_days_negative(client, public_data):
+    pid = str(public_data["product"].id)
+    resp = await client.get(f"/public/trends/{pid}?days=-1")
+    assert resp.status_code == 422
+    assert "detail" in resp.json()
+    assert "stack" not in resp.json()
+
+
+@pytest.mark.asyncio
+async def test_trend_days_over_max(client, public_data):
+    pid = str(public_data["product"].id)
+    resp = await client.get(f"/public/trends/{pid}?days=999")
+    assert resp.status_code == 422
+    assert "detail" in resp.json()
+    assert "stack" not in resp.json()
+
+
+@pytest.mark.asyncio
+async def test_trend_days_valid(client, public_data):
+    pid = str(public_data["product"].id)
+    resp = await client.get(f"/public/trends/{pid}?days=30")
+    assert resp.status_code == 200
+    assert "product_name" in resp.json()
+
+
+@pytest.mark.asyncio
+async def test_store_comparison_empty_list(client):
+    resp = await client.get("/public/store-comparison")
+    assert resp.status_code == 400
+    assert "detail" in resp.json()
+
+
+@pytest.mark.asyncio
+async def test_store_comparison_category_xss(client, public_data):
+    pid = str(public_data["product"].id)
+    resp = await client.get(
+        f"/public/store-comparison?product_ids={pid}&category=<script>alert(1)</script>"
+    )
+    assert resp.status_code == 422
+    assert "detail" in resp.json()
+    assert "stack" not in resp.json()
+
+
+@pytest.mark.asyncio
+async def test_store_comparison_category_sql_injection(client, public_data):
+    pid = str(public_data["product"].id)
+    resp = await client.get(f"/public/store-comparison?product_ids={pid}&category='; DROP TABLE--")
+    assert resp.status_code == 422
+    assert "detail" in resp.json()
+    assert "stack" not in resp.json()
+
+
+@pytest.mark.asyncio
+async def test_inflation_invalid_period(client, public_data):
+    resp = await client.get("/public/inflation?period=10years")
+    assert resp.status_code == 422
+    assert "detail" in resp.json()
+    assert "stack" not in resp.json()
+
+
+@pytest.mark.asyncio
+async def test_inflation_valid_periods(client, public_data):
+    for period in ["all-time", "1y", "6m", "3m", "1m"]:
+        resp = await client.get(f"/public/inflation?period={period}")
+        assert resp.status_code == 200, f"period={period} failed"
+
+
+@pytest.mark.asyncio
+async def test_inflation_category_too_long(client, public_data):
+    long_category = "x" * 200
+    resp = await client.get(f"/public/inflation?category={long_category}")
+    assert resp.status_code == 422
+    assert "detail" in resp.json()
+    assert "stack" not in resp.json()