using System.Net.NetworkInformation;
using System.Runtime.InteropServices;
using System.Runtime.Versioning;

namespace MoShiro.Measurement;

/// <summary>
/// Windows 上读主机资源占用（<see cref="HostSampler"/> 在 Linux 之外的实现）：CPU 时间和物理内存用两个只读的系统调用
/// （<c>GetSystemTimes</c>、<c>GlobalMemoryStatusEx</c>），网卡流量和链路速率用 .NET 自带的 <see cref="NetworkInterface"/>。
/// 和 Linux 一样只有汇总的数字：不读网卡名、MAC、IP，也不启动任何进程。
/// </summary>
[SupportedOSPlatform("windows")]
internal static partial class WindowsHost
{
    private static readonly string[] s_virtualWords = ["Virtual", "vEthernet", "Hyper-V", "VMware", "VirtualBox", "TAP-", "Wintun", "WireGuard", "Npcap", "Bluetooth", "Loopback", "isatap", "Teredo"];

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

        public readonly long Value => (long)(((ulong)High << 32) | Low);
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct MemoryStatus
    {
        public uint Length;
        public uint MemoryLoad;
        public ulong TotalPhys;
        public ulong AvailPhys;
        public ulong TotalPageFile;
        public ulong AvailPageFile;
        public ulong TotalVirtual;
        public ulong AvailVirtual;
        public ulong AvailExtendedVirtual;
    }

    [LibraryImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static partial bool GetSystemTimes(out FileTime idle, out FileTime kernel, out FileTime user);

    [LibraryImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static partial bool GlobalMemoryStatusEx(ref MemoryStatus status);

    /// <summary>系统启动以来的 CPU 总时间和空闲时间（和 Linux 的 <c>/proc/stat</c> 第一行同一个意思：两次采样相减得到占用）。</summary>
    public static (long Total, long Idle)? Cpu()
    {
        try
        {
            if (!GetSystemTimes(out FileTime idle, out FileTime kernel, out FileTime user))
            {
                return null;
            }

            // 内核时间里已经包含了空闲时间
            return (kernel.Value + user.Value, idle.Value);
        }
        catch (Exception ex) when (ex is DllNotFoundException or EntryPointNotFoundException)
        {
            return null;
        }
    }

    /// <summary>物理内存的总量和已用（总量减去可用）。</summary>
    public static (long Total, long Used)? Memory()
    {
        try
        {
            var status = new MemoryStatus { Length = (uint)Marshal.SizeOf<MemoryStatus>() };
            if (!GlobalMemoryStatusEx(ref status) || status.TotalPhys == 0)
            {
                return null;
            }

            return ((long)status.TotalPhys, (long)(status.TotalPhys - Math.Min(status.AvailPhys, status.TotalPhys)));
        }
        catch (Exception ex) when (ex is DllNotFoundException or EntryPointNotFoundException)
        {
            return null;
        }
    }

    /// <summary>所有物理网卡（在用的，排除回环、隧道、虚拟网卡）的累计收发字节，以及链路速率之和（Mbit/s；有一块读不到速率就是 null）。</summary>
    public static (long Rx, long Tx, long? LinkMbps)? Network()
    {
        try
        {
            long rx = 0;
            long tx = 0;
            long mbps = 0;
            bool speedKnown = true;
            bool any = false;
            foreach (NetworkInterface nic in NetworkInterface.GetAllNetworkInterfaces())
            {
                if (nic.OperationalStatus != OperationalStatus.Up || nic.NetworkInterfaceType is NetworkInterfaceType.Loopback or NetworkInterfaceType.Tunnel
                    || s_virtualWords.Any(w => nic.Description.Contains(w, StringComparison.OrdinalIgnoreCase) || nic.Name.Contains(w, StringComparison.OrdinalIgnoreCase)))
                {
                    continue;
                }

                IPInterfaceStatistics stats = nic.GetIPStatistics();
                rx += stats.BytesReceived;
                tx += stats.BytesSent;
                any = true;
                if (nic.Speed > 0)
                {
                    mbps += nic.Speed / 1_000_000;
                }
                else
                {
                    speedKnown = false;
                }
            }

            return any ? (rx, tx, speedKnown && mbps > 0 ? mbps : null) : null;
        }
        catch (NetworkInformationException)
        {
            return null;
        }
    }
}