#region CPL License
/*
Nuclex Framework
Copyright (C) 2002-2010 Nuclex Development Labs

This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.

You should have received a copy of the IBM Common Public
License along with this library
*/
#endregion

using System;
using System.Collections.Generic;
using System.Threading;

namespace Nuclex.Support.Scheduling {

  /// <summary>Provides time measurement and change notification services</summary>
  public interface ITimeSource {

    /// <summary>Called when the system date/time are adjusted</summary>
    /// <remarks>
    ///   An adjustment is a change out of the ordinary, eg. when a time synchronization
    ///   alters the current system time, when daylight saving time takes effect or
    ///   when the user manually adjusts the system date/time.
    /// </remarks>
    event EventHandler DateTimeAdjusted;

    /// <summary>Waits for an AutoResetEvent to become signalled</summary>
    /// <param name="waitHandle">WaitHandle the method will wait for</param>
    /// <param name="ticks">Number of ticks to wait</param>
    /// <returns>
    ///   True if the WaitHandle was signalled, false if the timeout was reached
    ///   or the time source thinks its time to recheck the system date/time.
    /// </returns>
    /// <remarks>
    ///   Depending on whether the system will provide notifications when date/time
    ///   is adjusted, the time source will be forced to let this method block for
    ///   less than the indicated time before returning a timeout in order to give
    ///   the caller a chance to recheck the system time.
    /// </remarks>
    bool WaitOne(AutoResetEvent waitHandle, long ticks);

    /// <summary>Current system time in UTC format</summary>
    DateTime CurrentUtcTime { get; }

    /// <summary>How long the time source has been running</summary>
    /// <remarks>
    ///   There is no guarantee this value starts at zero (or anywhere near it) when
    ///   the time source is created. The only requirement for this value is that it
    ///   keeps increasing with the passing of time and that it stays unaffected
    ///   (eg. doesn't skip or jump back) when the system date/time are changed.
    /// </remarks>
    long Ticks { get; }

  }

} // namespace Nuclex.Support.Scheduling