Get Windows User idle time and correcting for 32 bit API uptime rollover

LastInputHelper.cs

static class LastInputHelper
{
    /// <remarks>http://www.pinvoke.net/default.aspx/user32.GetLastInputInfo</remarks>
    [DllImport("User32.dll")]
    static extern bool GetLastInputInfo(ref LASTINPUTINFO plii);

    struct LASTINPUTINFO
    {
        public uint cbSize;
        public uint dwTime;
    }

    public static TimeSpan GetIdleTime()
    {
        var plii = new LASTINPUTINFO { cbSize = (uint)Marshal.SizeOf(typeof(LASTINPUTINFO)) };

        if (!GetLastInputInfo(ref plii)) return TimeSpan.Zero;

        long up = (uint)Environment.TickCount;
        long last = plii.dwTime;
        var idle = up - last;

        // if idle is negative, it means uptime rolled over and dwTime did not and we need to adjust
        if (idle < 0) idle += uint.MaxValue;

        return TimeSpan.FromMilliseconds(idle);
    }
}