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

namespace Matteopic
{
    class AsyncTask<Result>
    {
        private Action preExecute;
        private Action<Result> postExecute;
        private Action<Exception> onException;
        private Func<Result> function;

        public AsyncTask<Result> OnException(Action<Exception> action)
        {
            this.onException = action;
            return this;
        }

	// Run the Action in the GUI Thread
        public AsyncTask<Result> OnPreExecute(Action action) {
            this.preExecute = action;
            return this;
        }

	// Run the Action in the GUI Thread
        public AsyncTask<Result> OnPostExecute(Action<Result> action)
        {
            this.postExecute = action;
            return this;
        }

	// Run the Action in a separated Thread
        public AsyncTask<Result> DoInBackground(Func<Result> function)
        {
            this.function = function;
            return this;
        }

        public void Start()
        {
		//Console.WriteLine("Execute");
		/**
		.NET 4.0
		Task.Factory.StartNew((Action)(() =>{}
                App.Current.Dispatcher.Invoke((Action)(() =>
                {
                    //Console.WriteLine("Starting PreExecute");
                    if (preExecute != null) preExecute.Invoke();
                }));
		), CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
		*/

		//.NET 4.5
            Task.Run((Action)(() =>
            {
                App.Current.Dispatcher.Invoke((Action)(() =>
                {
                    //Console.WriteLine("Starting PreExecute");
                    if (preExecute != null) preExecute.Invoke();
                }));
            }))

            .ContinueWith((Func<Task, Result>)((Task t) =>
            {
                try
                {
                    //Console.WriteLine("Starting Background ");
                    return function.Invoke();
                }catch(Exception ex){
                    //Console.WriteLine("Starting Exception ");
                    if (onException != null) onException.Invoke(ex);
                    return default(Result);
                }
            }))

            .ContinueWith((Action<Task<Result>>)((Task<Result> t) =>
            {
                App.Current.Dispatcher.Invoke((Action)(() =>
                {
                    //Console.WriteLine("Starting PostExecute");
                    Result res = t.Result;
                    if (postExecute != null) postExecute.Invoke(res);
                }));
            }));
            //Console.WriteLine("/Execute");
        }

    }

}