using System.Net.NetworkInformation;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Text;

namespace CertifiEd.Client;

/// <summary>
/// Computes a stable hardware fingerprint for the current machine — a SHA-256 hex
/// digest over machine name, OS description, the first stable MAC address, and the
/// platform machine id when available.
/// </summary>
public static class HwFingerprint
{
    private static string? _cached;

    /// <summary>Returns the fingerprint, computed once per process.</summary>
    public static string Get()
    {
        if (_cached is not null)
            return _cached;

        var raw = new StringBuilder()
            .Append(Environment.MachineName).Append('|')
            .Append(RuntimeInformation.OSDescription).Append('|')
            .Append(GetStableMac() ?? "no-mac");

        var platformId = GetPlatformMachineId();
        if (platformId is not null)
            raw.Append('|').Append(platformId);

        var hash = SHA256.HashData(Encoding.UTF8.GetBytes(raw.ToString()));
        _cached = Convert.ToHexStringLower(hash);
        return _cached;
    }

    private static string? GetStableMac()
    {
        try
        {
            return NetworkInterface.GetAllNetworkInterfaces()
                .Where(n => n.NetworkInterfaceType != NetworkInterfaceType.Loopback
                         && n.OperationalStatus == OperationalStatus.Up)
                .Select(n => n.GetPhysicalAddress().ToString())
                .Where(mac => mac.Length > 0)
                .Order(StringComparer.Ordinal)
                .FirstOrDefault();
        }
        catch (NetworkInformationException)
        {
            return null;
        }
    }

    private static string? GetPlatformMachineId()
    {
        if (OperatingSystem.IsWindows())
            return GetWindowsMachineGuid();

        if (OperatingSystem.IsLinux())
            return TryReadFile("/etc/machine-id") ?? TryReadFile("/var/lib/dbus/machine-id");

        if (OperatingSystem.IsMacOS())
            return GetMacSerialNumber();

        return null;
    }

    [System.Runtime.Versioning.SupportedOSPlatform("windows")]
    private static string? GetWindowsMachineGuid()
    {
        try
        {
            using var key = Microsoft.Win32.Registry.LocalMachine
                .OpenSubKey(@"SOFTWARE\Microsoft\Cryptography");
            return key?.GetValue("MachineGuid")?.ToString();
        }
        catch (Exception ex) when (ex is System.Security.SecurityException or UnauthorizedAccessException or IOException)
        {
            return null;
        }
    }

    private static string? TryReadFile(string path)
    {
        try
        {
            return File.Exists(path) ? File.ReadAllText(path).Trim() : null;
        }
        catch (IOException)
        {
            return null;
        }
        catch (UnauthorizedAccessException)
        {
            return null;
        }
    }

    private static string? GetMacSerialNumber()
    {
        try
        {
            var psi = new System.Diagnostics.ProcessStartInfo("ioreg", "-l")
            {
                RedirectStandardOutput = true,
                UseShellExecute = false,
            };
            using var process = System.Diagnostics.Process.Start(psi);
            var output = process?.StandardOutput.ReadToEnd() ?? string.Empty;
            var line = output.Split('\n').FirstOrDefault(l => l.Contains("IOPlatformSerialNumber", StringComparison.Ordinal));
            if (line is null)
                return null;

            var start = line.IndexOf('"', line.IndexOf('=', StringComparison.Ordinal) + 1);
            var end = start >= 0 ? line.IndexOf('"', start + 1) : -1;
            return start >= 0 && end > start ? line[(start + 1)..end] : null;
        }
        catch (Exception ex) when (ex is System.ComponentModel.Win32Exception or InvalidOperationException or IOException)
        {
            return null;
        }
    }
}