using System;
using System.ComponentModel;

namespace TipCalc
{
    class TipCalcModel : INotifyPropertyChanged
    {
        double subTotal, postTaxTotal, tipPercent, tipAmount, total;

        public event PropertyChangedEventHandler PropertyChanged;

        public double SubTotal
        {
            set
            {
                 if (subTotal != value)
                 {
                     subTotal = value;
                     OnPropertyChanged("SubTotal");
                     Recalculate();
                 }
            }
            get
            {
                return subTotal;
            }
        }

        public double PostTaxTotal
        {
            set
            {
                if (postTaxTotal != value)
                {
                    postTaxTotal = value;
                    OnPropertyChanged("PostTaxTotal");
                    Recalculate();
                }
            }
            get
            {
                return postTaxTotal;
            }
        }

        public double TipPercent
        {
            set
            {
                if (tipPercent != value)
                {
                    tipPercent = value;
                    OnPropertyChanged("TipPercent");
                    Recalculate();
                }
            }
            get
            {
                return tipPercent;
            }
        }

        public double TipAmount
        {
            set
            {
                if (tipAmount != value)
                {
                    tipAmount = value;
                    OnPropertyChanged("TipAmount");
                }
            }
            get
            {
                return tipAmount;
            }
        }

        public double Total
        {
            set
            {
                if (total != value)
                {
                    total = value;
                    OnPropertyChanged("Total");
                }
            }
            get
            {
                return total;
            }
        }

        void Recalculate()
        {
            this.TipAmount = Math.Round(this.TipPercent * this.SubTotal / 100, 2);

            // Round total to nearest quarter.
            this.Total = Math.Round(4 * (this.PostTaxTotal + this.TipAmount)) / 4;
        }

        protected void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}