using System.IO;
using System.Runtime.InteropServices;

namespace AxCopilot.Services;

internal sealed class PerformanceMonitorService
{
    public static readonly PerformanceMonitorService Instance = new();

    [StructLayout(LayoutKind.Sequential)]
    private struct FILETIME
    {
        public uint Low;
        public uint High;
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    private struct MEMORYSTATUSEX
    {
        public uint dwLength;
        public uint dwMemoryLoad;
        public ulong ullTotalPhys;
        public ulong ullAvailPhys;
        public ulong ullTotalPageFile;
        public ulong ullAvailPageFile;
        public ulong ullTotalVirtual;
        public ulong ullAvailVirtual;
        public ulong ullAvailExtendedVirtual;
    }

    [DllImport("kernel32.dll", SetLastError = true)]
    private static extern bool GetSystemTimes(out FILETIME idle, out FILETIME kernel, out FILETIME user);

    [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern bool GlobalMemoryStatusEx(ref MEMORYSTATUSEX lpBuffer);

    public double CpuPercent { get; private set; }
    public double RamPercent { get; private set; }
    public string RamText { get; private set; } = "";
    public double DiskCPercent { get; private set; }
    public string DiskCText { get; private set; } = "";

    private System.Threading.Timer? _timer;
    private FILETIME _prevIdle;
    private FILETIME _prevKernel;
    private FILETIME _prevUser;
    private bool _hasPrev;

    private PerformanceMonitorService() { }

    public void StartPolling()
    {
        if (_timer != null)
            return;

        _timer = new System.Threading.Timer(_ => Sample(), null, 0, 2000);
    }

    public void StopPolling()
    {
        _timer?.Dispose();
        _timer = null;
        _hasPrev = false;
    }

    private void Sample()
    {
        SampleCpu();
        SampleRam();
        SampleDisk();
    }

    private void SampleCpu()
    {
        try
        {
            if (!GetSystemTimes(out var idle, out var kernel, out var user))
                return;

            if (_hasPrev)
            {
                var idleDelta = ToUlong(idle) - ToUlong(_prevIdle);
                var kernelDelta = ToUlong(kernel) - ToUlong(_prevKernel);
                var userDelta = ToUlong(user) - ToUlong(_prevUser);
                var total = kernelDelta + userDelta;
                var busy = total - idleDelta;
                CpuPercent = total > 0 ? Math.Clamp(100.0 * busy / total, 0, 100) : 0;
            }

            _prevIdle = idle;
            _prevKernel = kernel;
            _prevUser = user;
            _hasPrev = true;
        }
        catch { }
    }

    private void SampleRam()
    {
        try
        {
            var mem = new MEMORYSTATUSEX { dwLength = (uint)Marshal.SizeOf<MEMORYSTATUSEX>() };
            if (!GlobalMemoryStatusEx(ref mem))
                return;

            RamPercent = mem.dwMemoryLoad;
            var usedGb = (mem.ullTotalPhys - mem.ullAvailPhys) / (1024.0 * 1024 * 1024);
            var totalGb = mem.ullTotalPhys / (1024.0 * 1024 * 1024);
            RamText = $"{usedGb:F1}/{totalGb:F0}GB";
        }
        catch { }
    }

    private void SampleDisk()
    {
        try
        {
            var drive = DriveInfo.GetDrives()
                .FirstOrDefault(d => d.IsReady && d.Name.StartsWith("C", StringComparison.OrdinalIgnoreCase));
            if (drive == null)
                return;

            var usedBytes = drive.TotalSize - drive.AvailableFreeSpace;
            DiskCPercent = 100.0 * usedBytes / drive.TotalSize;
            var usedGb = usedBytes / (1024.0 * 1024 * 1024);
            var totalGb = drive.TotalSize / (1024.0 * 1024 * 1024);
            DiskCText = $"C:{usedGb:F0}/{totalGb:F0}GB";
        }
        catch { }
    }

    private static ulong ToUlong(FILETIME ft) => ((ulong)ft.High << 32) | ft.Low;
}