using System.ComponentModel;
using System.Runtime.InteropServices;

namespace MoonlightServers.Daemon.Helpers;

public partial class SystemMetrics
{
    public record DiskInfo(
        string MountPoint,
        string Device,
        string FileSystem,
        long TotalBytes,
        long UsedBytes,
        long FreeBytes,
        double UsedPercent,
        long InodesTotal,
        long InodesUsed,
        long InodesFree,
        double InodesUsedPercent
    );

    private static readonly HashSet<string> IgnoredFileSystems = new(StringComparer.OrdinalIgnoreCase)
    {
        "overlay", "aufs", // Container image layers
        "tmpfs", "devtmpfs", "ramfs", // RAM-backed virtual filesystems
        "sysfs", "proc", "devpts", // Kernel virtual filesystems
        "cgroup", "cgroup2",
        "pstore", "securityfs", "debugfs", "tracefs",
        "mqueue", "hugetlbfs", "fusectl", "configfs",
        "binfmt_misc", "nsfs", "rpc_pipefs",
        "squashfs", // Snap package loop mounts
    };

    private static readonly string[] IgnoredMountPrefixes =
    {
        "/sys",
        "/proc",
        "/dev",
        "/run/docker",
        "/var/lib/docker",
        "/var/lib/containers",
        "/boot", "/boot/efi"
    };

    private static async Task<IReadOnlyList<DiskInfo>> ReadDisksAsync()
    {
        var lines = await File.ReadAllLinesAsync("/proc/mounts");
        var results = new List<DiskInfo>();

        foreach (var line in lines)
        {
            var parts = line.Split(' ');
            if (parts.Length < 4) continue;

            var device = parts[0];
            var mountPoint = UnescapeOctal(parts[1]);
            var fsType = parts[2];

            if (IgnoredFileSystems.Contains(fsType)) continue;
            if (IgnoredMountPrefixes.Any(p => mountPoint.StartsWith(p, StringComparison.Ordinal))) continue;
            if (device == "none" || device.StartsWith("//", StringComparison.Ordinal)) continue;

            var disk = ReadSingleDisk(device, mountPoint, fsType);
            
            if (disk is not null)
                results.Add(disk);
        }

        return results
            .GroupBy(d => d.Device)
            .Select(g => g.OrderBy(d => d.MountPoint.Length).First())
            .OrderBy(d => d.MountPoint)
            .ToList();
    }

    private static DiskInfo? ReadSingleDisk(string device, string mountPoint, string fsType)
    {
        if (NativeMethods.StatVfs(mountPoint, out var st) != 0)
        {
            var errno = Marshal.GetLastPInvokeError();
            Console.WriteLine($"statvfs({mountPoint}) failed: errno {errno} ({new Win32Exception(errno).Message})");
            return null;
        }

        var blockSize = (long)st.frsize;
        var totalBytes = (long)st.blocks * blockSize;
        var freeBytes = (long)st.bavail * blockSize;

        if (totalBytes <= 0) return null;

        var usedBytes = totalBytes - ((long)st.bfree * blockSize);
        var usedPct = Math.Round((double)usedBytes / totalBytes * 100.0, 2);

        long inodesTotal, inodesUsed, inodesFree;
        double inodePct;

        if (st.files == 0)
        {
            // Filesystem doesn't expose inode counts (FAT, exFAT, NTFS via ntfs-3g, etc.)
            inodesTotal = inodesUsed = inodesFree = -1;
            inodePct = -1.0;
        }
        else
        {
            inodesTotal = (long)st.files;
            inodesFree = (long)st.ffree;
            inodesUsed = inodesTotal - inodesFree;
            inodePct = Math.Round((double)inodesUsed / inodesTotal * 100.0, 2);
        }

        return new DiskInfo(
            MountPoint: mountPoint,
            Device: device,
            FileSystem: fsType,
            TotalBytes: totalBytes,
            UsedBytes: usedBytes,
            FreeBytes: freeBytes,
            UsedPercent: usedPct,
            InodesTotal: inodesTotal,
            InodesUsed: inodesUsed,
            InodesFree: inodesFree,
            InodesUsedPercent: inodePct
        );
    }

    private static string UnescapeOctal(string s)
    {
        if (!s.Contains('\\')) return s;

        var sb = new System.Text.StringBuilder(s.Length);
        for (var i = 0; i < s.Length; i++)
        {
            if (s[i] == '\\' && i + 3 < s.Length
                             && s[i + 1] is >= '0' and <= '7'
                             && s[i + 2] is >= '0' and <= '7'
                             && s[i + 3] is >= '0' and <= '7')
            {
                sb.Append((char)((s[i + 1] - '0') * 64 + (s[i + 2] - '0') * 8 + (s[i + 3] - '0')));
                i += 3;
            }
            else
            {
                sb.Append(s[i]);
            }
        }

        return sb.ToString();
    }
}