using System.Diagnostics;

namespace System.Threading
{
	[DebuggerDisplay("IsCancellationRequested = {IsCancellationRequested}")]
	public struct CancellationToken
	{
		private readonly CancellationTokenSource source;

		public static CancellationToken None => default(CancellationToken);

		public bool CanBeCanceled => source != null;

		public bool IsCancellationRequested => Source.IsCancellationRequested;

		public WaitHandle WaitHandle => Source.WaitHandle;

		private CancellationTokenSource Source => source ?? CancellationTokenSource.NoneSource;

		public CancellationToken(bool canceled)
			: this(canceled ? CancellationTokenSource.CanceledSource : null)
		{
		}

		internal CancellationToken(CancellationTokenSource source)
		{
			this.source = source;
		}

		public CancellationTokenRegistration Register(Action callback)
		{
			return Register(callback, useSynchronizationContext: false);
		}

		public CancellationTokenRegistration Register(Action callback, bool useSynchronizationContext)
		{
			if (callback == null)
			{
				throw new ArgumentNullException("callback");
			}
			return Source.Register(callback, useSynchronizationContext);
		}

		public CancellationTokenRegistration Register(Action<object> callback, object state)
		{
			return Register(callback, state, useSynchronizationContext: false);
		}

		public CancellationTokenRegistration Register(Action<object> callback, object state, bool useSynchronizationContext)
		{
			if (callback == null)
			{
				throw new ArgumentNullException("callback");
			}
			return Register(delegate
			{
				callback(state);
			}, useSynchronizationContext);
		}

		public void ThrowIfCancellationRequested()
		{
			if (Source.IsCancellationRequested)
			{
				throw new OperationCanceledException();
			}
		}

		public bool Equals(CancellationToken other)
		{
			return Source == other.Source;
		}

		public override bool Equals(object other)
		{
			if (!(other is CancellationToken))
			{
				return false;
			}
			return Equals((CancellationToken)other);
		}

		public override int GetHashCode()
		{
			return Source.GetHashCode();
		}

		public static bool operator ==(CancellationToken left, CancellationToken right)
		{
			return left.Equals(right);
		}

		public static bool operator !=(CancellationToken left, CancellationToken right)
		{
			return !left.Equals(right);
		}
	}
}