using System;

namespace ConsoleApplication1
{
    public delegate void SmartAction<T>(SmartAction<T> self, T data);

    class EventSource<T>
    {
        private event SmartAction<T> actions;

        public void AddListener(SmartAction<T> eventHandler)
        {
            actions += eventHandler;
        }

        public void RemoveListener(SmartAction<T> eventHandler)
        {
            actions -= eventHandler;
        }

        public void Fire(T eventData)
        {
            if (actions == null)
            {
                return;
            }
            Delegate[] delegates = actions.GetInvocationList();
            for (int i = delegates.Length - 1; i >= 0; --i)
            {
                var action = (SmartAction<T>) delegates[i];
                action(action, eventData);
            }
        }
    }

    internal class Program
    {
        public event SmartAction<int> ProgressChanged;

        public static event Action EventA;
        public static event Action EventB;

        public static void Main(string[] args)
        {
            new Program().TestSequence();
        }

        public void TestSequence()
        {
            EventB += () => Console.WriteLine("b");

            EventB();
            SmartActionExt.Copy2(out EventB);
            EventB();
        }

        public void TestFirst()
        {
            Action a = () => Console.WriteLine("a");

            EventA += a.First();

            EventA();
            EventA();
            EventA();
        }

        public void TestUntilEvent()
        {
            Action a = () => Console.WriteLine("a");
            Action b = () => Console.WriteLine("b");

            EventA += a.Until(ref EventB);

            EventA();
            EventA();
            EventB();
            EventA();
        }

        public void TestConcurentModification()
        {
            // no exception
            Action b = () =>
            {
                Console.WriteLine("b");
            };
            Action a = () =>
            {
                Console.WriteLine("a");
                b();
            };
            Action c = () =>
            {
                Console.WriteLine("c");
                b();
            };

            a = (a + c).Until(ref b);

            a();
            b();
            a();
        }

        public void TestUntil()
        {
            // result is b
            Action b = () => Console.WriteLine("b");
            Action a = () => Console.WriteLine("a");

            a = a.Until(ref b);

            a();
            b();
            a();
        }

        public void Test3()
        {
            EventA += () => Console.WriteLine("a");
            Action b = () => Console.WriteLine("b");
            Action c = () => Console.WriteLine("c");

            EventA += (b + c);
            EventA();
        }

        public void Test1()
        {
            var source = new EventSource<int>();
            source.AddListener((self, n) =>
            {
                source.RemoveListener(self);
                Console.WriteLine(n);
            });
            source.Fire(5);
            source.Fire(25);
        }

        public void DoSome()
        {
            ProgressChanged += (self, progress) => { ProgressChanged -= self; };
        }
    }

    public static class SmartActionExt
    {
        public static void DoNothing() {}

        public static Action First(this Action a)
        {
            Action sub = null;
            sub = () =>
            {
                sub = DoNothing;
                a();
            };
            return () => sub();
        }

        // TODO CombineEventSource.FromSequence(ref eventA, ref eventB)
        // pass to Until as second param. Via overload of Until (CombineEventSource must implement += operator)
        public static Action Until(this Action a, ref Action b)
        {
            Action sub = () => a();
            Action result = () => sub();
            b += () =>
            {
                sub = DoNothing;
            };
            return result;
        }

        public static Action Copy(ref Action a)
        {
            return a;
        }

        public static void Copy2(out Action a)
        {
            a = null;
        }

       /* public static Action Sequence(ref Action event1, ref Action event2)
        {

            return a += b;
        }*/
    }
}