// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;

namespace LinqToDB.Common.Internal.Cache
{
	/// <summary>
	/// Propagates notifications that a change has occurred.
	/// </summary>
	public interface IChangeToken
	{
		/// <summary>
		/// Gets a value that indicates if a change has occurred.
		/// </summary>
		bool HasChanged { get; }

		/// <summary>
		/// Indicates if this token will pro-actively raise callbacks. If <c>false</c>, the token consumer must
		/// poll <see cref="HasChanged" /> to detect changes.
		/// </summary>
		bool ActiveChangeCallbacks { get; }

		/// <summary>
		/// Registers for a callback that will be invoked when the entry has changed.
		/// <see cref="HasChanged"/> MUST be set before the callback is invoked.
		/// </summary>
		/// <param name="callback">The <see cref="Action{Object}"/> to invoke.</param>
		/// <param name="state">State to be passed into the callback.</param>
		/// <returns>An <see cref="IDisposable"/> that is used to unregister the callback.</returns>
		IDisposable RegisterChangeCallback(Action<object> callback, object state);
	}
}
