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

namespace DelegateEvent
{
    public class AsyncLock
    {
        private readonly AsyncSemaphore m_semaphore;
        private readonly Task<Releaser> m_releaser;

        public AsyncLock()
        {
            m_semaphore = new AsyncSemaphore(1);
            m_releaser = Task.FromResult(new Releaser(this));
        }
        public Task<Releaser> LockAsync()
        {
            var wait = m_semaphore.WaitAsync();
            return wait.IsCompleted ? m_releaser : wait.ContinueWith((_, state) => new Releaser((AsyncLock)state), this, CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
        }

        public struct Releaser : IDisposable
        {
            private readonly AsyncLock m_toRelease;
            internal Releaser(AsyncLock toRelease) { m_toRelease = toRelease; }
            public void Dispose()
            {
                if (m_toRelease != null)
                {
                    m_toRelease.m_semaphore.Release();
                }
            }
        }
    }
}