/*

         ###
#  #  #########     _______ _     _  ______ _     _
##  ######## @ ##   |______ |     | |  ____ |     |
##################  |       |_____| |_____| |_____|
##  #############      f  r  a  m  e  w  o  r  k
#  #  #########
         ###

(c) 2015 - 2017 FUGU framework project

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

*/

using System;
using System.Collections.Generic;
using System.Threading;

namespace Fugu.Async
{
    internal class ExclusiveSynchronizationContext : SynchronizationContext
    {
        private class TaskToRun
        {
            public TaskToRun(SendOrPostCallback delegateToCall, object state)
            {
                DelegateToCall = delegateToCall;
                State = state;
            }

            public SendOrPostCallback DelegateToCall { get; }

            public object State { get; }
        }

        private bool _done;

        private readonly AutoResetEvent _workItemsWaiting = new AutoResetEvent(false);

        private readonly Queue<TaskToRun> _items = new Queue<TaskToRun>();

        public Exception InnerException { get; set; }

        public override void Send(SendOrPostCallback d, object state)
        {
            throw new NotSupportedException("We cannot send to our same thread");
        }

        public override void Post(SendOrPostCallback d, object state)
        {
            lock (_items)
            {
                _items.Enqueue(new TaskToRun(d, state));
            }
            _workItemsWaiting.Set();
        }

        public void EndMessageLoop()
        {
            Post(_ => _done = true, null);
        }

        public void BeginMessageLoop()
        {
            while (!_done)
            {
                TaskToRun task = null;
                lock (_items)
                {
                    if (_items.Count > 0)
                    {
                        task = _items.Dequeue();
                    }
                }
                if (task != null)
                {
                    task.DelegateToCall(task.State);
                    if (InnerException != null) // the method threw an exeption
                    {
                        throw new AggregateException("AsyncExtensions.RunSync method threw an exception.", InnerException);
                    }
                }
                else
                {
                    _workItemsWaiting.WaitOne();
                }
            }
        }

        public override SynchronizationContext CreateCopy()
        {
            return this;
        }
    }
}