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

namespace DataStructures.ConcurrentHashSet
{
    [Serializable]
    public class ConcurrentHashSet<T>
    {
        private readonly ReaderWriterLockSlim _lock = new ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion);
        private readonly HashSet<T> _hashSet = new HashSet<T>();

        //TODO: implement icollection
        public bool Add(T item)
        {
            try
            {
                _lock.EnterWriteLock();
                return _hashSet.Add(item);
            }
            finally
            {
                if (_lock.IsWriteLockHeld)
                {
                    _lock.ExitWriteLock();
                }
            }
        }

        public void Clear()
        {
            try
            {
                _lock.EnterWriteLock();
                _hashSet.Clear();
            }
            finally
            {
                if (_lock.IsWriteLockHeld)
                {
                    _lock.ExitWriteLock();
                }
            }
        }

        public bool Contains(T item)
        {
            try
            {
                _lock.EnterReadLock();
                return _hashSet.Contains(item);
            }
            finally
            {
                if (_lock.IsReadLockHeld)
                {
                    _lock.ExitReadLock();
                }
            }
        }

        public bool Remove(T item)
        {
            try
            {
                _lock.EnterWriteLock();
                return _hashSet.Remove(item);
            }
            finally
            {
                if (_lock.IsWriteLockHeld)
                {
                    _lock.ExitWriteLock();
                }
            }
        }

        public int Count
        {
            get
            {
                try
                {
                    _lock.EnterReadLock();
                    return _hashSet.Count;
                }
                finally
                {
                    if (_lock.IsReadLockHeld)
                    {
                        _lock.ExitReadLock();
                    }
                }
            }
        }
    }
}