How to check availabity of a space for Booking

I am currently developing a project for space bookings. Its an API project. I have done till Booking API. But want to check availability check and validations for booking. How to write logic code for checking availability of the space and to do validations on weather the space is available or not. The spaces I am using in this project is meeting rooms, private space, and desks

This is my space creation JSON

{
    "space": {
        "name": "Star Bucks",
        "email": "stabucks@mail.com",
        "website" : "www.starbucks.com",
        "phone" : "7907653366",
        "amenities_attributes": [
            {
                "name": "wifi",
                "available": true
            },
            {
                "name": "ac",
                "available": true
            }
        ],
        "meeting_rooms_attributes": [
            {
                "count": 5,
                "capacity": 6
            }
        ],
        "private_offices_attributes": [
            {
                "count": 2,
                "capacity": 6
            }
        ],
        "desks_attributes": [
            {
                "count": 12,
                "desk_type": "open_desk"
            }
        ],
        "operating_hours_attributes": [
            {
                "day": "Mon-Fri",
                "slot": "10:00-5:00"
            }
        ]
    }
}

This is my Space booking request JSON

{
   "booking": {
       "space_id": 17,
       "booking_items_attributes": [
           {
               "entity_type": "PrivateOffice",
               "entity_id": 20,
               "count": 1
           },
           {
               "entity_type": "Desk",
               "entity_id": 20,
               "count": 2
           }
       ],
        "booking_dates_attributes": [
           {
               "from_date": "2020-03-18",
               "to_date": "2020-03-18",
               "from_time": "2020-03-18 10:00:00 ",
               "to_time": "2020-03-18 14:00:00 "
           }]
   }
}

Booking Controller

class Api::V1::BookingsController < ApiController
 before_action :fetch_space, only: [:show]

 def index
   bookings = Booking.all
   render_collection(bookings, { name: 'bookings' }, each_serializer: BookingItemSerializer)
 end

 def create
   if booking = current_user.bookings.create(booking_params)
     render_object(booking, { name: 'booking' }, { serializer: BookingSerializer })
   else
     render_error(booking.errors.full_messages)
   end
 end

 private


 def booking_params
   params.require(:booking).permit(:space_id,
                                    booking_items_attributes: [:id, :entity_type, :entity_id, :count],
                                    booking_dates_attributes: [:id, :from_date, :to_date, :from_time, :to_time])
 end
end

Booking Serializer

class BookingSerializer < ActiveModel::Serializer


  attributes :id, :user_id, :space_id, :status, :booked

 # has_many :booking_items, serializer: BookingItemSerializer

  def booked
    object.booking_items.entity_type.sum(:count)
  end


end

Booking Item Serializer

class BookingItemSerializer < ActiveModel::Serializer
  attributes :id, :availabitity


  belongs_to :booking,  serializer: BookingItemSerializer


  # def availabitity
  #   availabitity =   object.meeting.sum(:count) - booked
  # end
end