using System;
using System.Threading;

namespace JD.Threading
{
    /// <summary>
    /// Basic read/writer lock.
    /// </summary>

    public class ReadWriterLock
    {
        #region Variables

        private readonly ReaderWriterLockSlim m_lock;
        private readonly IDisposable m_releaseWriterLock;
        private readonly IDisposable m_releaseReaderLock;

        #endregion

        #region Creation

        private ReadWriterLock(LockRecursionPolicy policy)
        {
            m_lock = new ReaderWriterLockSlim(policy);
            m_releaseWriterLock = new ExitWriteLock(m_lock);
            m_releaseReaderLock = new ExitReadLock(m_lock);
        }

        public static ReadWriterLock Create()
        {
            return new ReadWriterLock(LockRecursionPolicy.SupportsRecursion);
        }

        /// <summary>
        /// Faster but requires that no call is reentrant.
        /// </summary>
        /// <returns></returns>
        public static ReadWriterLock CreateWithoutRecursion()
        {
            return new ReadWriterLock(LockRecursionPolicy.NoRecursion);
        }

        #endregion

        #region Methods

        public IDisposable EnterWrite()
        {
            m_lock.EnterWriteLock();
            return m_releaseWriterLock;
        }

        public IDisposable EnterRead()
        {
            m_lock.EnterReadLock();
            return m_releaseReaderLock;
        }

        #endregion

        #region Nested

        private class ExitReadLock : IDisposable
        {
            private readonly ReaderWriterLockSlim m_lock;
            public ExitReadLock(ReaderWriterLockSlim @lock)
            {
                m_lock = @lock;
            }

            public void Dispose()
            {
                m_lock.ExitReadLock();
            }
        }

        private class ExitWriteLock : IDisposable
        {
            private readonly ReaderWriterLockSlim m_lock;
            public ExitWriteLock(ReaderWriterLockSlim @lock)
            {
                m_lock = @lock;
            }

            public void Dispose()
            {
                m_lock.ExitWriteLock();
            }
        }

        #endregion
    }
}