// Copyright (c) 2014 AlphaSierraPapa for the SharpDevelop Team
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.ObjectModel;

namespace Unity.CodeEditor.Utils
{
    /// <summary>
    /// A collection where adding and removing items causes a callback.
    /// It is valid for the onAdd callback to throw an exception - this will prevent the new item from
    /// being added to the collection.
    /// </summary>
    internal sealed class ObserveAddRemoveCollection<T> : Collection<T>
    {
        private readonly Action<T> _onAdd;
        private readonly Action<T> _onRemove;

        /// <summary>
        /// Creates a new ObserveAddRemoveCollection using the specified callbacks.
        /// </summary>
        internal ObserveAddRemoveCollection(Action<T> onAdd, Action<T> onRemove)
        {
            _onAdd = onAdd ?? throw new ArgumentNullException(nameof(onAdd));
            _onRemove = onRemove ?? throw new ArgumentNullException(nameof(onRemove));
        }

        /// <inheritdoc/>
        protected override void ClearItems()
        {
            if (_onRemove != null)
            {
                foreach (T val in this)
                    _onRemove(val);
            }
            base.ClearItems();
        }

        /// <inheritdoc/>
        protected override void InsertItem(int index, T item)
        {
            _onAdd?.Invoke(item);
            base.InsertItem(index, item);
        }

        /// <inheritdoc/>
        protected override void RemoveItem(int index)
        {
            _onRemove?.Invoke(this[index]);
            base.RemoveItem(index);
        }

        /// <inheritdoc/>
        protected override void SetItem(int index, T item)
        {
            _onRemove?.Invoke(this[index]);
            try
            {
                _onAdd?.Invoke(item);
            }
            catch
            {
                // When adding the new item fails, just remove the old one
                // (we cannot keep the old item since we already successfully called onRemove for it)
                RemoveAt(index);
                throw;
            }
            base.SetItem(index, item);
        }
    }
}