using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Transactions;

namespace AsyncTest
{
    /// <summary>Provides a SynchronizationContext that's single-threaded.</summary>
    public class SingleThreadSynchronizationContext : SynchronizationContext
    {
        /// <summary>The queue of work items.</summary>
        private readonly BlockingCollection<KeyValuePair<SendOrPostCallback, object>> m_queue =
            new BlockingCollection<KeyValuePair<SendOrPostCallback, object>>();
        /// <summary>The processing thread.</summary>
        private readonly Thread m_thread = Thread.CurrentThread;

        /// <summary>Dispatches an asynchronous message to the synchronization context.</summary>
        /// <param name="d">The System.Threading.SendOrPostCallback delegate to call.</param>
        /// <param name="state">The object passed to the delegate.</param>
        public override void Post(SendOrPostCallback d, object state)
        {
            if (d == null) throw new ArgumentNullException("d");
            m_queue.Add(new KeyValuePair<SendOrPostCallback, object>(d, state));
        }

        /// <summary>Not supported.</summary>
        public override void Send(SendOrPostCallback d, object state)
        {
            throw new NotSupportedException("Synchronously sending is not supported.");
        }

        /// <summary>Runs an loop to process all queued work items.</summary>
        public void RunOnCurrentThread()
        {
            foreach (var workItem in m_queue.GetConsumingEnumerable())
                workItem.Key(workItem.Value);
        }

        /// <summary>Notifies the context that no more work will arrive.</summary>
        public void Complete() { m_queue.CompleteAdding(); }
    }

    class Program
    {
        public static void Run(Func<Task> func)
        {
            var prevCtx = SynchronizationContext.Current;
            try
            {
                var syncCtx = new SingleThreadSynchronizationContext();
                //var syncCtx = new System.Windows.Threading.DispatcherSynchronizationContext();
                SynchronizationContext.SetSynchronizationContext(syncCtx);

                var t = func();
                t.ContinueWith(
                    delegate { syncCtx.Complete(); }, TaskScheduler.Default);

                syncCtx.RunOnCurrentThread();
                //var frame = new System.Windows.Threading.DispatcherFrame();
                //t.ContinueWith(_ => { frame.Continue = false; },
                //    TaskScheduler.Default);
                //System.Windows.Threading.Dispatcher.PushFrame(frame); 

                t.GetAwaiter().GetResult();
            }
            finally { SynchronizationContext.SetSynchronizationContext(prevCtx); }
        }

        static async Task TestStuff(int nb)
        {
            Console.WriteLine("Entering teststuff " + Thread.CurrentThread.ManagedThreadId);
            using (var scope = new TransactionScope())
            {
                int wait = 1000 + nb;
                await Task.Delay(wait);
                scope.Complete();
            }
            
            Console.WriteLine("Leaving teststuff " + Thread.CurrentThread.ManagedThreadId);
        }

        static void Main(string[] args)
        {
            Run(async delegate
            {
                var tasks = new Task[10];
                for (int i = 0; i < 10; i++)
                {
                    tasks[i] = TestStuff(i);
                }
                await Task.WhenAll(tasks);
            });
            Console.ReadLine();
        }
    }
}