namespace SmartCoalApplication.SystemLayer
{
    /// <summary>
    /// Methods for keeping track of time in a high precision manner.
    /// </summary>
    /// <remarks>
    /// This class provides precision and accuracy of 1 millisecond.
    /// </remarks>
    public sealed class Timing
    {
        private ulong countsPerMs;
        private double countsPerMsDouble;
        private ulong birthTick;

        /// <summary>
        /// The number of milliseconds that elapsed between system startup
        /// and creation of this instance of Timing.
        /// </summary>
        public ulong BirthTick
        {
            get
            {
                return birthTick;
            }
        }

        /// <summary>
        /// Returns the number of milliseconds that have elapsed since
        /// system startup.
        /// </summary>
        public ulong GetTickCount()
        {
            ulong tick;
            SafeNativeMethods.QueryPerformanceCounter(out tick);
            return tick / countsPerMs;
        }

        /// <summary>
        /// Returns the number of milliseconds that have elapsed since
        /// system startup.
        /// </summary>
        public double GetTickCountDouble()
        {
            ulong tick;
            SafeNativeMethods.QueryPerformanceCounter(out tick);
            return (double)tick / countsPerMsDouble;
        }

        /// <summary>
        /// Constructs an instance of the Timing class.
        /// </summary>
        public Timing()
        {
            ulong frequency;

            if (!SafeNativeMethods.QueryPerformanceFrequency(out frequency))
            {
                NativeMethods.ThrowOnWin32Error("QueryPerformanceFrequency returned false");
            }

            countsPerMs = frequency / 1000;
            countsPerMsDouble = (double)frequency / 1000.0;
            birthTick = GetTickCount();
        }
    }
}