feat: add reservation QR retrieval

backend/bookings/services.py

@@ -40,6 +40,10 @@ class AlreadyConfirmedReservation(BookingServiceError):
     pass
 
 
+class ReservationNotConfirmed(BookingServiceError):
+    pass
+
+
 @dataclass(frozen=True)
 class PendingReservationResult:
     reservation: Reservation
@@ -59,6 +63,13 @@ class ConfirmedReservationResult:
     qr_code_url: str
 
 
+@dataclass(frozen=True)
+class ReservationQRResult:
+    reservation: Reservation
+    qr_code_image: str
+    qr_code_url: str
+
+
 def calculate_available_seats(performance):
     confirmed_seats = (
         Reservation.objects.filter(
@@ -184,9 +195,32 @@ def confirm_reservation_from_token(raw_token):
         available_seats=available_seats - reservation.party_size,
         qr_code_image=generate_check_in_qr_base64(
             reservation=reservation,
-            raw_check_in_token=raw_check_in_token,
+            raw_check_in_token=raw_token,
         ),
-        qr_code_url=build_check_in_preview_url(raw_check_in_token),
+        qr_code_url=build_check_in_preview_url(raw_token),
+    )
+
+
+def retrieve_reservation_qr_from_token(raw_token):
+    try:
+        confirmation_token = ReservationToken.objects.select_related("reservation").get(
+            token_hash=ReservationToken.hash_token(raw_token),
+            purpose=ReservationToken.Purpose.CONFIRMATION,
+        )
+    except ReservationToken.DoesNotExist as exc:
+        raise InvalidToken("Confirmation token is invalid.") from exc
+
+    reservation = confirmation_token.reservation
+    if reservation.status != Reservation.Status.CONFIRMED:
+        raise ReservationNotConfirmed("Reservation must be confirmed before QR retrieval.")
+
+    return ReservationQRResult(
+        reservation=reservation,
+        qr_code_image=generate_check_in_qr_base64(
+            reservation=reservation,
+            raw_check_in_token=raw_token,
+        ),
+        qr_code_url=build_check_in_preview_url(raw_token),
     )