using System;
using System.Collections.Generic;
using System.Linq;

namespace YourNamespace
{
    /// <summary>A disposable collection of disposables.</summary>
    /// <seealso cref="System.IDisposable" />
    public class DisposableBag : IDisposable
    {
        private object _lock = new object();
        private List<IDisposable> _bag = new List<IDisposable>();
        private bool _disposed = false;

        /// <summary>Creates disposable collection of disposables.</summary>
        /// <returns>New disposable collection of disposables</returns>
        public static DisposableBag Create()
        {
            return new DisposableBag();
        }

        /// <summary>Creates disposable collection of disposables starting with provided ones.</summary>
        /// <param name="disposables">The disposables.</param>
        /// <returns>New disposable collection of disposables.</returns>
        public static DisposableBag Create(IEnumerable<IDisposable> disposables)
        {
            return new DisposableBag(disposables);
        }

        /// <summary>Creates disposable collection of disposables.</summary>
        /// <param name="disposables">The disposables.</param>
        /// <returns>New disposable collection of disposables.</returns>
        public static DisposableBag Create(params IDisposable[] disposables)
        {
            return new DisposableBag(disposables);
        }

        /// <summary>Initializes a new instance of the <see cref="DisposableBag"/> class.</summary>
        public DisposableBag()
        {
        }

        /// <summary>Initializes a new instance of the <see cref="DisposableBag"/> class.</summary>
        /// <param name="disposables">The disposables.</param>
        public DisposableBag(IEnumerable<IDisposable> disposables)
        {
            lock (_lock)
            {
                AddMany(disposables);
            }
        }

        /// <summary>Adds many disposables.</summary>
        /// <param name="disposables">The disposables.</param>
        public void AddMany(IEnumerable<IDisposable> disposables)
        {
            lock (_lock)
            {
                if (_disposed)
                {
                    DisposeMany(disposables.ToArray());
                }
                else
                {
                    _bag.AddRange(disposables);
                }
            }
        }

        /// <summary>Disposes items.</summary>
        /// <param name="disposables">The disposables.</param>
        /// <exception cref="AggregateException">Combines exceptions thrown when disposing items.</exception>
        private static void DisposeMany(IDisposable[] disposables)
        {
            IList<Exception> exceptions = null;
            foreach (var disposable in disposables)
            {
                try
                {
                    disposable.Dispose();
                }
                catch (Exception e)
                {
                    (exceptions = exceptions ?? new List<Exception>()).Add(e);
                }
            }

            if (exceptions != null)
                throw new AggregateException(exceptions);
        }

        /// <summary>Adds disposable.</summary>
        /// <typeparam name="T">Type of object.</typeparam>
        /// <param name="item">The disposable item.</param>
        /// <returns>Same item for further processing.</returns>
        public T Add<T>(T item) where T : IDisposable
        {
            if (item == null)
                return item;

            lock (_lock)
            {
                if (_disposed)
                {
                    item.Dispose();
                }
                else
                {
                    _bag.Add(item);
                }
                return item;
            }
        }

        /// <summary>Performs application-defined tasks associated with
        /// freeing, releasing, or resetting unmanaged resources.</summary>
        public void Dispose()
        {
            lock (_lock)
            {
                _disposed = true;
                var disposables = _bag.ToArray();
                _bag.Clear();
                DisposeMany(disposables);
            }
        }
    }
}