fix double booked day validation

db/booking.ts

@@ -4,7 +4,8 @@ import { dateFormatBackend, getDays, nowInTz } from '../helpers/date'
 
 import { Bill } from './bill'
 import { Booker } from './booker'
-import { BOOKING_STATUS } from './enums'
+import { BOOKING_STATUS, VALIDATION_ERRORS } from './enums'
+import { getBookedDays } from './index'
 
 export interface Booking {
   uuid: string
@@ -71,6 +72,19 @@ const BookingSchema = new mongoose.Schema<BookingDocument>(
     days: {
       type: [String],
       required: true,
+      validate: {
+        validator: async function (days: string[]) {
+          const bookedDays = await getBookedDays()
+
+          const doubleBookedDays = days.filter((day: string) =>
+            bookedDays.includes(day)
+          )
+          return doubleBookedDays.length === 0
+        },
+        message: (props: { value: string[] }) =>
+          `At least one day is of ${props.value.join(',')} is already booked`,
+        type: VALIDATION_ERRORS.AT_LEAST_ONE_DAY_BOOKED,
+      },
     },
     status: {
       type: String,
@@ -89,7 +103,7 @@ const BookingSchema = new mongoose.Schema<BookingDocument>(
   }
 )
 
-BookingSchema.pre('save', function (next) {
+BookingSchema.pre('validate', function (next: () => void) {
   const booking = this as BookingDocument
   booking.days = getDays({
     startDate: new Date(booking.startDate),