Block check-in for bookings not scheduled for today

docs/API_REFERENCE.txt

@@ -1778,7 +1778,7 @@ BOOKING APIS
   - 401 Unauthorized
   - 403 Forbidden
   - 404 Not Found (booking/room)
-  - 409 Conflict (booking not open/room unavailable)
+  - 409 Conflict (booking not open/room unavailable/future booking can't be checked in)
 
 
 - Expected checkout API is this one:

src/main/kotlin/com/android/trisolarisserver/controller/booking/BookingFlow.kt

@@ -473,6 +473,12 @@ class BookingFlow(
         if (booking.status != BookingStatus.OPEN) {
             throw ResponseStatusException(HttpStatus.CONFLICT, "Booking not open")
         }
+        val propertyZone = resolveZoneId(booking.property.timezone)
+        val today = OffsetDateTime.now(propertyZone).toLocalDate()
+        val expectedCheckInDate = booking.expectedCheckinAt?.atZoneSameInstant(propertyZone)?.toLocalDate()
+        if (expectedCheckInDate != null && expectedCheckInDate != today) {
+            throw ResponseStatusException(HttpStatus.CONFLICT, "Future booking can't be checked in")
+        }
 
         val roomIds = request.stays.map { it.roomId }
         if (roomIds.distinct().size != roomIds.size) {