///////////////////////////////////////////////////////////////////////////
//  Copyright (C) Wizardry and Steamworks 2013 - License: GNU GPLv3      //
//  Please see: http://www.gnu.org/licenses/gpl.html for legal details,  //
//  rights of fair usage, the disclaimer and warranty conditions.        //
///////////////////////////////////////////////////////////////////////////
// Based on work by Ben Mosher

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

namespace wasSharp.Collections.Specialized
{
    public static class ConcurrentHashSetExtensions
    {
        public static ConcurrentHashSet<T> ToConcurrentHashSet<T>(this IEnumerable<T> enumerable)
        {
            return new ConcurrentHashSet<T>(enumerable);
        }
    }

    public class ConcurrentHashSet<T> : IDisposable, ISet<T>
    {
        private readonly ReaderWriterLockSlim _lock = new ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion);
        private readonly HashSet<T> _hashSet;

        public ConcurrentHashSet()
        {
            _lock.EnterWriteLock();
            try
            {
                _hashSet = new HashSet<T>();
            }
            finally
            {
                if (_lock.IsWriteLockHeld) _lock.ExitWriteLock();
            }
        }

        public ConcurrentHashSet(IEqualityComparer<T> stringComparer)
        {
            _lock.EnterWriteLock();
            try
            {
                _hashSet = new HashSet<T>(stringComparer);
            }
            finally
            {
                if (_lock.IsWriteLockHeld) _lock.ExitWriteLock();
            }
        }

        public ConcurrentHashSet(IEnumerable<T> enumerable)
        {
            _lock.EnterWriteLock();
            try
            {
                _hashSet = new HashSet<T>();
                foreach (var i in enumerable)
                {
                    _hashSet.Add(i);
                }
            }
            finally
            {
                if (_lock.IsWriteLockHeld) _lock.ExitWriteLock();
            }
        }

        #region Implementation of ICollection<T>

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

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

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

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

        public int RemoveWhere(Predicate<T> match)
        {
            _lock.EnterWriteLock();
            try
            {
                return _hashSet.RemoveWhere(match);
            }
            finally
            {
                if (_lock.IsWriteLockHeld) _lock.ExitWriteLock();
            }
        }

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

        void ICollection<T>.Add(T item)
        {
            _lock.EnterWriteLock();
            try
            {
                _hashSet.Add(item);
            }
            finally
            {
                if (_lock.IsWriteLockHeld) _lock.ExitWriteLock();
            }
        }

        public void CopyTo(T[] array, int arrayIndex)
        {
            _lock.EnterReadLock();
            try
            {
                _hashSet.CopyTo(array, arrayIndex);
            }
            finally
            {
                if (_lock.IsReadLockHeld) _lock.ExitReadLock();
            }
        }

        public IEnumerator<T> GetEnumerator()
        {
            _lock.EnterReadLock();
            try
            {
                using (var enumerator = _hashSet.GetEnumerator())
                {
                    while (enumerator.MoveNext())
                        yield return enumerator.Current;
                }
            }
            finally
            {
                if (_lock.IsReadLockHeld) _lock.ExitReadLock();
            }
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            _lock.EnterReadLock();
            try
            {
                using (var enumerator = _hashSet.GetEnumerator())
                {
                    while (enumerator.MoveNext())
                        yield return enumerator.Current;
                }
            }
            finally
            {
                if (_lock.IsReadLockHeld) _lock.ExitReadLock();
            }
        }

        public bool IsReadOnly => ((ICollection<T>)_hashSet).IsReadOnly;

        #endregion Implementation of ICollection<T>

        #region Dispose

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        protected virtual void Dispose(bool disposing)
        {
            if (!disposing) return;
            _lock?.Dispose();
            _hashSet.Clear();
        }

        ~ConcurrentHashSet()
        {
            Dispose(false);
        }

        #endregion Dispose

        #region Implementation of ISet<T>

        public void ExceptWith(IEnumerable<T> other)
        {
            _lock.EnterWriteLock();
            try
            {
                _hashSet.ExceptWith(other);
            }
            finally
            {
                if (_lock.IsWriteLockHeld) _lock.ExitWriteLock();
            }
        }

        public void IntersectWith(IEnumerable<T> other)
        {
            _lock.EnterWriteLock();
            try
            {
                _hashSet.IntersectWith(other);
            }
            finally
            {
                if (_lock.IsWriteLockHeld) _lock.ExitWriteLock();
            }
        }

        public bool IsProperSubsetOf(IEnumerable<T> other)
        {
            _lock.EnterReadLock();
            try
            {
                return _hashSet.IsProperSubsetOf(other);
            }
            finally
            {
                if (_lock.IsReadLockHeld) _lock.ExitReadLock();
            }
        }

        public bool IsProperSupersetOf(IEnumerable<T> other)
        {
            _lock.EnterReadLock();
            try
            {
                return _hashSet.IsProperSupersetOf(other);
            }
            finally
            {
                if (_lock.IsReadLockHeld) _lock.ExitReadLock();
            }
        }

        public bool IsSubsetOf(IEnumerable<T> other)
        {
            _lock.EnterReadLock();
            try
            {
                return _hashSet.IsSubsetOf(other);
            }
            finally
            {
                if (_lock.IsReadLockHeld) _lock.ExitReadLock();
            }
        }

        public bool IsSupersetOf(IEnumerable<T> other)
        {
            _lock.EnterReadLock();
            try
            {
                return _hashSet.IsSupersetOf(other);
            }
            finally
            {
                if (_lock.IsReadLockHeld) _lock.ExitReadLock();
            }
        }

        public bool Overlaps(IEnumerable<T> other)
        {
            _lock.EnterReadLock();
            try
            {
                return _hashSet.Overlaps(other);
            }
            finally
            {
                if (_lock.IsReadLockHeld) _lock.ExitReadLock();
            }
        }

        public bool SetEquals(IEnumerable<T> other)
        {
            _lock.EnterReadLock();
            try
            {
                return _hashSet.SetEquals(other);
            }
            finally
            {
                if (_lock.IsReadLockHeld) _lock.ExitReadLock();
            }
        }

        public void SymmetricExceptWith(IEnumerable<T> other)
        {
            _lock.EnterWriteLock();
            try
            {
                _hashSet.SymmetricExceptWith(other);
            }
            finally
            {
                if (_lock.IsWriteLockHeld) _lock.ExitWriteLock();
            }
        }

        public void UnionWith(IEnumerable<T> other)
        {
            _lock.EnterWriteLock();
            try
            {
                _hashSet.UnionWith(other);
            }
            finally
            {
                if (_lock.IsWriteLockHeld) _lock.ExitWriteLock();
            }
        }

        #endregion Implementation of ISet<T>
    }
}