feat: add booking service layer

backend/bookings/services.py

@@ -0,0 +1,188 @@
+from dataclasses import dataclass
+from datetime import timedelta
+
+from django.db import transaction
+from django.db.models import Sum
+from django.utils import timezone
+
+from shows.models import Performance
+
+from .models import Reservation, ReservationToken
+
+
+CONFIRMATION_TOKEN_TTL = timedelta(hours=48)
+CHECK_IN_TOKEN_AFTER_PERFORMANCE_TTL = timedelta(days=1)
+
+
+class BookingServiceError(Exception):
+    """Base class for booking service domain errors."""
+
+
+class PerformanceNotAvailable(BookingServiceError):
+    pass
+
+
+class NotEnoughSeats(BookingServiceError):
+    pass
+
+
+class InvalidToken(BookingServiceError):
+    pass
+
+
+class ExpiredToken(BookingServiceError):
+    pass
+
+
+class AlreadyConfirmedReservation(BookingServiceError):
+    pass
+
+
+@dataclass(frozen=True)
+class PendingReservationResult:
+    reservation: Reservation
+    confirmation_token: ReservationToken
+    raw_confirmation_token: str
+    available_seats: int
+
+
+@dataclass(frozen=True)
+class ConfirmedReservationResult:
+    reservation: Reservation
+    confirmation_token: ReservationToken
+    check_in_token: ReservationToken
+    raw_check_in_token: str
+    available_seats: int
+
+
+def calculate_available_seats(performance):
+    confirmed_seats = (
+        Reservation.objects.filter(
+            performance=performance,
+            status=Reservation.Status.CONFIRMED,
+        ).aggregate(total=Sum("party_size"))["total"]
+        or 0
+    )
+    return performance.configured_capacity - confirmed_seats
+
+
+def create_pending_reservation(
+    *,
+    performance_id,
+    name,
+    email,
+    party_size,
+    phone="",
+    notes="",
+    confirmation_expires_at=None,
+):
+    with transaction.atomic():
+        performance = _get_locked_bookable_performance(performance_id)
+        available_seats = calculate_available_seats(performance)
+        if party_size > available_seats:
+            raise NotEnoughSeats("Not enough seats are available for this performance.")
+
+        reservation = Reservation(
+            performance=performance,
+            name=name,
+            email=email,
+            phone=phone,
+            party_size=party_size,
+            notes=notes,
+        )
+        reservation.full_clean()
+        reservation.save()
+
+        confirmation_token, raw_confirmation_token = generate_confirmation_token(
+            reservation,
+            expires_at=confirmation_expires_at,
+        )
+
+    return PendingReservationResult(
+        reservation=reservation,
+        confirmation_token=confirmation_token,
+        raw_confirmation_token=raw_confirmation_token,
+        available_seats=available_seats,
+    )
+
+
+def generate_confirmation_token(reservation, *, expires_at=None):
+    return ReservationToken.create_token(
+        reservation=reservation,
+        purpose=ReservationToken.Purpose.CONFIRMATION,
+        expires_at=expires_at or timezone.now() + CONFIRMATION_TOKEN_TTL,
+    )
+
+
+def confirm_reservation_from_token(raw_token):
+    token_hash = ReservationToken.hash_token(raw_token)
+    token_was_expired = False
+
+    with transaction.atomic():
+        try:
+            confirmation_token = (
+                ReservationToken.objects.select_for_update()
+                .select_related("reservation")
+                .get(token_hash=token_hash, purpose=ReservationToken.Purpose.CONFIRMATION)
+            )
+        except ReservationToken.DoesNotExist as exc:
+            raise InvalidToken("Confirmation token is invalid.") from exc
+
+        reservation = Reservation.objects.select_for_update().get(pk=confirmation_token.reservation_id)
+
+        if confirmation_token.is_used:
+            if reservation.status == Reservation.Status.CONFIRMED:
+                raise AlreadyConfirmedReservation("Reservation is already confirmed.")
+            raise InvalidToken("Confirmation token has already been used.")
+
+        if confirmation_token.is_expired:
+            if reservation.status == Reservation.Status.PENDING:
+                reservation.status = Reservation.Status.EXPIRED
+                reservation.save(update_fields=["status", "updated_at"])
+            token_was_expired = True
+
+        if not token_was_expired and reservation.status == Reservation.Status.CONFIRMED:
+            raise AlreadyConfirmedReservation("Reservation is already confirmed.")
+
+        if not token_was_expired and reservation.status != Reservation.Status.PENDING:
+            raise InvalidToken("Confirmation token is not valid for this reservation.")
+
+        if not token_was_expired:
+            performance = _get_locked_bookable_performance(reservation.performance_id)
+            available_seats = calculate_available_seats(performance)
+            if reservation.party_size > available_seats:
+                raise NotEnoughSeats("Not enough seats are available for this performance.")
+
+            reservation.confirm()
+            confirmation_token.mark_used()
+
+            check_in_token, raw_check_in_token = ReservationToken.create_token(
+                reservation=reservation,
+                purpose=ReservationToken.Purpose.CHECK_IN,
+                expires_at=performance.starts_at + CHECK_IN_TOKEN_AFTER_PERFORMANCE_TTL,
+            )
+            reservation.qr_code_generated_at = timezone.now()
+            reservation.save(update_fields=["qr_code_generated_at", "updated_at"])
+
+    if token_was_expired:
+        raise ExpiredToken("Confirmation token has expired.")
+
+    return ConfirmedReservationResult(
+        reservation=reservation,
+        confirmation_token=confirmation_token,
+        check_in_token=check_in_token,
+        raw_check_in_token=raw_check_in_token,
+        available_seats=available_seats - reservation.party_size,
+    )
+
+
+def _get_locked_bookable_performance(performance_id):
+    try:
+        performance = Performance.objects.select_for_update().get(pk=performance_id)
+    except Performance.DoesNotExist as exc:
+        raise PerformanceNotAvailable("Performance is not available for booking.") from exc
+
+    if not performance.is_booking_enabled:
+        raise PerformanceNotAvailable("Performance is not available for booking.")
+
+    return performance