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

namespace EventAndDelegateDemo
{
    //There are 3 rules which are MANDATORY when you are planning to create events
    //Rule 1> The delegate must be defined with two arguments
    //Rule 2> These arguments always represent TWO objects… 
    //          The Publisher (object that raised the event)
    //          Event Information object
    //Rule 3> The 2nd object HAS to be derived from EventArgs

    //Step 1> Create a class that inherits from EventArgs (To comply with Rule 3)
    class NotifyChangeEventArgs : EventArgs
    {
        //constructor to initialize the SpecialNumberOld and SpecialNumberNew property
        public NotifyChangeEventArgs(int SpecialNumberOld, int SpecialNumberNew)
        {
            this.SpecialNumberNew = SpecialNumberNew;
            this.SpecialNumberOld = SpecialNumberOld;
        }
        public int SpecialNumberNew { get; set; }
        public int SpecialNumberOld { get; set; }
    };

    class SpecialNumberClass // Publisher
    {
        //Publisher declares a special delegate and event (Rule 1 & 2)
        public delegate void SpecialNumberHandler(object source, NotifyChangeEventArgs e);
        public event SpecialNumberHandler OnSpecialNumberUpdate;

        //Constructor to set the value of the _specialNumber directly.
        //Notice that we are not setting the SpecialNumber property!
        public SpecialNumberClass(int number)
        {
            _specialNumber = number;
        }

        //This property will fire an event called OnSpecialNumberUpdate whenever called
        //The effect is that is the special number is changed from outside, all the guys
        //would be notified. It is upto them to listen to it or not listen to it.
        private int _specialNumber;
        public int SpecialNumber
        {
            get { return _specialNumber; }
            //Put a breakpoint here on set and step into (F11)
            set
            {
                if (OnSpecialNumberUpdate != null)
                {
                    //This is the guy who would fire that notify event called OnSpecialNumberUpdate
                    //Basically, before you fire that event, you can set up that value for EventArgs
                    //In my case, I have set the value of e's old value and new value...
                    //to the _specialNumber and value (which would be the new value)
                    //Notice that we are just firing the events with appropriate EventArgs...
                    //We haven't thrown any output as such yet!!!!
                    NotifyChangeEventArgs e = new NotifyChangeEventArgs(_specialNumber, value);
                    Console.WriteLine("Raising Events to all the subscribers...\n");
                    OnSpecialNumberUpdate(this, e);
                }
            }
        }
    };

    class SpecialNumberUpdateListener // Subscriber
    {
        //Here we are just creating a new Object called objSN for my SpecialNumberClass
        SpecialNumberClass objSN;

        //In this method, I would go ahead and bind my event
        public SpecialNumberUpdateListener(SpecialNumberClass spClass)
        {
            Console.WriteLine("SpecialNumber listener > Subscribing to the event...\n");
            this.objSN = spClass;

            //Wiring the event so that the event is fired
            spClass.OnSpecialNumberUpdate += new SpecialNumberClass.SpecialNumberHandler(OnSpecialNumberUpdate);
        }

        //This is the event that would be invoked whenever you change the value
        //Try putting a break point here and see how it gets hit when the number changes
        //Also notice how we use the Event args to grab the details and finally print it out
        void OnSpecialNumberUpdate(object source, NotifyChangeEventArgs e)
        {
            Console.WriteLine("The number has changed from {0} to {1} ", e.SpecialNumberOld, e.SpecialNumberNew);
        }
    }

    class EventDemo
    {
        public static void Main()
        {
            //Creating a new Special Number (Publisher) class with initial value of 20
            SpecialNumberClass snc = new SpecialNumberClass(30);
            //Creating a Subscriber/listener class
            SpecialNumberUpdateListener s = new SpecialNumberUpdateListener(snc);
            //Changing the value so that the event is triggered.
            //Put a breakpoint and step into the code (F11)
            snc.SpecialNumber = 40;
            Console.ReadLine();
        }
    }
}