using System;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;

namespace TimerApp
{
    public static class NativeMethods
    {
        [StructLayout(LayoutKind.Sequential)]
        struct LASTINPUTINFO
        {
            public static readonly int SizeOf = Marshal.SizeOf(typeof(LASTINPUTINFO));

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 cbSize;
            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dwTime;
        }

        [DllImport("user32.dll")]
        static extern bool GetLastInputInfo(ref LASTINPUTINFO plii);

        [DllImport("kernel32.dll")]
        static extern uint GetTickCount();

        /// <summary>
        /// 获取系统空闲时间（毫秒）
        /// </summary>
        /// <returns></returns>
        public static long GetIdleTime()
        {
            LASTINPUTINFO lastInputInfo = new LASTINPUTINFO
            {
                cbSize = (uint)Marshal.SizeOf<LASTINPUTINFO>(),
                dwTime = 0
            };

            if (GetLastInputInfo(ref lastInputInfo))
            {
                uint tickCount = GetTickCount();
                uint idleMs = unchecked(tickCount - lastInputInfo.dwTime);
                return idleMs;
            }

            return 0;
        }

        static NativeMethods()
        {
        }

        public static void Shutdown()
        {
        }
    }
}