//Usage Examples:
//// Get precise milliseconds since application start
//long ms = SystemUptimeTimer.ElapsedMilliseconds;
//
//// Get system uptime (even counts when PC was sleeping)
//TimeSpan uptime = SystemUptimeTimer.SystemUptime;
//Console.WriteLine($"PC has been running for {uptime.Days} days, {uptime.Hours} hours");
//
//// Benchmark example
//long start = SystemUptimeTimer.ElapsedMilliseconds;
//// ... run some code ...
//long elapsed = SystemUptimeTimer.ElapsedMilliseconds - start;
//Key Features:
//Two Measurement Modes:
//
//ElapsedMilliseconds: High-precision timer (μs accuracy) since class initialization
//
//SystemUptime: Standard Windows uptime (ms accuracy, counts sleep time)

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace UPSNet
{
    /// <summary>
    /// High-precision timer measuring time since system startup
    /// </summary>
    public static class SystemUptimeTimer
    {
        [DllImport("kernel32.dll")]
        private static extern uint GetTickCount();

        [DllImport("kernel32.dll")]
        private static extern bool QueryPerformanceCounter(out long lpPerformanceCount);

        [DllImport("kernel32.dll")]
        private static extern bool QueryPerformanceFrequency(out long lpFrequency);

        private static readonly long _frequency;
        private static readonly long _startCount;
        private static readonly Stopwatch _fallbackTimer;

        static SystemUptimeTimer()
        {
            if (!QueryPerformanceFrequency(out _frequency))
            {
                _frequency = -1;
                _fallbackTimer = Stopwatch.StartNew();
            }
            
            QueryPerformanceCounter(out _startCount);
        }

        /// <summary>
        /// Gets elapsed milliseconds since system startup
        /// </summary>
        public static long ElapsedMilliseconds
        {
            get
            {
                if (_frequency == -1)
                {
                    return _fallbackTimer.ElapsedMilliseconds;
                }

                long currentCount;
                QueryPerformanceCounter(out currentCount);
                return (1000 * (currentCount - _startCount)) / _frequency;
            }
        }

        /// <summary>
        /// Gets elapsed seconds since system startup
        /// </summary>
        public static double ElapsedSeconds  {
            get { return ElapsedMilliseconds / 1000.0; }
        }

        /// <summary>
        /// Gets system uptime using native API (works even when PC enters sleep)
        /// </summary>
        public static TimeSpan SystemUptime
        {
            get { return TimeSpan.FromMilliseconds(GetTickCount()); }
        }
    }
}