// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.md in the project root for license information.

using System.Collections.Generic;

namespace Microsoft.AspNet.SignalR.Infrastructure
{
    internal class DiffSet<T>
    {
        private readonly HashSet<T> _items;
        private readonly HashSet<T> _addedItems;
        private readonly HashSet<T> _removedItems;

        public DiffSet(IEnumerable<T> items)
        {
            _addedItems = new HashSet<T>();
            _removedItems = new HashSet<T>();

            _items = new HashSet<T>(items);
        }

        public bool Add(T item)
        {
            if (_items.Add(item))
            {
                if (!_removedItems.Remove(item))
                {
                    _addedItems.Add(item);
                }
                return true;
            }
            return false;
        }

        public bool Remove(T item)
        {
            if (_items.Remove(item))
            {
                if (!_addedItems.Remove(item))
                {
                    _removedItems.Add(item);
                }
                return true;
            }
            return false;
        }

        public bool Contains(T item)
        {
            return _items.Contains(item);
        }

        public ICollection<T> GetSnapshot()
        {
            return _items;
        }

        public bool DetectChanges()
        {
            bool anyChanges = _addedItems.Count > 0 || _removedItems.Count > 0;
            _addedItems.Clear();
            _removedItems.Clear();
            return anyChanges;
        }
    }
}