Better form amount parsing

main.py

@@ -22,18 +22,25 @@ async def welcome(request: Request):
     return templates.TemplateResponse(request=request, name="welcome.html.j2")
 
 
-@app.post("/", response_class=RedirectResponse)
+@app.post("/")
-async def pay(request: Request, amount: Annotated[int, Form()]):
+async def pay(request: Request, amount: Annotated[str, Form()]):
-    # Amount is in cents. Depositing less than a euro does not really make sense, so interpret this
+    # Normalize input.
-    # as full Euro's.
+    if "," in amount:
-    if amount < 100:
+        amount = amount.replace(",", ".")
-        amount *= 100
+    if "." not in amount:
+        amount = f"{amount}.00"
+    # Conversion.
+    [i, f] = amount.split(".")
+    cents = int(i) * 100 + int(f)
+    # Sanity checks.
+    if cents < 10_00 or 150_00 < cents:
+        raise HTTPException(status_code=400, detail=f"invalid amount: {amount}")
 
     payment = mollie_client.payments.create(
         {
             "amount": {
                 "currency": "EUR",
-                "value": f"{amount // 100}.{amount % 100:02}",
+                "value": f"{cents // 100}.{cents % 100:02}",
             },
             "description": "Bitlair bar tegoed",
             "redirectUrl": f"{public_url}/return",