"Rogues", Sсhiller

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace HotelAccounting
{
    public class AccountingModel : ModelBase
    {
        private double price;
        public double Price
        {
            get { return price; }
            set
            {
                price = value >= 0 ? value : throw new ArgumentException();
                Notify(nameof(Price));
                total = Price * NightsCount * (1 - Discount / 100) >= 0 ? Price * NightsCount * (1 - Discount / 100) : throw new ArgumentException();
                Notify(nameof(Total));
            }
        }

        private int nightsCount;
        public int NightsCount
        {
            get { return nightsCount; }
            set
            {
                nightsCount = value > 0 ? value : throw new ArgumentException();
                Notify(nameof(NightsCount));
                total = Price * NightsCount * (1 - Discount / 100) >= 0 ? Price * NightsCount * (1 - Discount / 100) : throw new ArgumentException();
                Notify(nameof(Total));
            }
        }

        private double discount;
        public double Discount
        {
            get { return discount; }
            set
            {
                discount = value;
                Notify(nameof(Discount));
                total = Price * NightsCount * (1 - Discount / 100) >= 0 ? Price * NightsCount * (1 - Discount / 100) : throw new ArgumentException();
                Notify(nameof(Total));
            }
        }

        private double total;
        public double Total
        {
            get { return total; }
            set
            {
                total = value >= 0 ? value : throw new ArgumentException();
                Notify(nameof(Total));
                discount = 100 - 100 * total / (Price * NightsCount);
                Notify(nameof(Discount));
            }
        }
    }
}