using System.Globalization;
using System.Net;
using System.Net.NetworkInformation;
using System.Net.Sockets;
using MoShiro.Protocol;

namespace MoShiro.Measurement;

/// <summary>
/// 本机的公网地址：Agent 注册之后在 hello 里上报，面板用它自动填 <c>public_host</c> 和 <c>ipv6_host</c>，不需要管理员手填。
/// 只列出「别人能拨进来」的地址：IPv4 要排除私网、CGNAT、回环、链路本地；IPv6 只要全球单播（2000::/3），
/// 并且排除临时地址、tentative、deprecated 和文档/6to4/Teredo 段。读不到网卡信息时返回空，面板退回到管理员手填或观察到的来源地址。
/// </summary>
public static class LocalAddresses
{
    public static IReadOnlyList<string> Sample()
    {
        var result = new List<string>();
        HashSet<string> unusable = OperatingSystem.IsLinux() ? UnusableIpv6(Read("/proc/net/if_inet6")) : [];
        try
        {
            foreach (NetworkInterface adapter in NetworkInterface.GetAllNetworkInterfaces())
            {
                if (adapter.OperationalStatus != OperationalStatus.Up || adapter.NetworkInterfaceType is NetworkInterfaceType.Loopback or NetworkInterfaceType.Tunnel)
                {
                    continue;
                }

                foreach (UnicastIPAddressInformation unicast in adapter.GetIPProperties().UnicastAddresses)
                {
                    IPAddress address = unicast.Address;
                    bool usable = address.AddressFamily == AddressFamily.InterNetwork
                        ? PublicAddress.IsPublicIpv4(address)
                        : PublicAddress.IsGlobalIpv6(address) && !unusable.Contains(address.ToString()) && !IsTemporary(unicast);
                    if (usable && !result.Contains(address.ToString()))
                    {
                        result.Add(address.ToString());
                    }
                }
            }
        }
        catch (Exception ex) when (ex is NetworkInformationException or PlatformNotSupportedException)
        {
            return [];
        }

        // 稳定顺序：同一台机器每次上报的顺序一样，面板不会因为顺序变化而改地址
        result.Sort(StringComparer.Ordinal);
        return result;
    }

    /// <summary>Linux 的 <c>/proc/net/if_inet6</c>：临时（0x01）、dadfailed（0x08）、deprecated（0x20）、tentative（0x40）的地址不能当作对外地址。</summary>
    public static HashSet<string> UnusableIpv6(string? procNetIfInet6)
    {
        var result = new HashSet<string>(StringComparer.Ordinal);
        if (procNetIfInet6 is null)
        {
            return result;
        }

        foreach (string line in procNetIfInet6.Split('\n'))
        {
            string[] fields = line.Split((char[]?)null, StringSplitOptions.RemoveEmptyEntries);
            if (fields.Length != 6 || fields[0].Length != 32 || !uint.TryParse(fields[4], NumberStyles.HexNumber, CultureInfo.InvariantCulture, out uint flags) || (flags & 0x69) == 0)
            {
                continue;
            }

            var bytes = new byte[16];
            for (int i = 0; i < 16; i++)
            {
                bytes[i] = byte.Parse(fields[0].AsSpan(i * 2, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture);
            }

            result.Add(new IPAddress(bytes).ToString());
        }

        return result;
    }

    // Windows 和 macOS：随机后缀就是隐私（临时）地址
    private static bool IsTemporary(UnicastIPAddressInformation unicast)
    {
        try
        {
            return OperatingSystem.IsWindows()
                && (unicast.SuffixOrigin == SuffixOrigin.Random || unicast.DuplicateAddressDetectionState is DuplicateAddressDetectionState.Tentative or DuplicateAddressDetectionState.Duplicate);
        }
        catch (PlatformNotSupportedException)
        {
            return false;
        }
    }

    private static string? Read(string path)
    {
        try
        {
            return File.Exists(path) ? File.ReadAllText(path) : null;
        }
        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
        {
            return null;
        }
    }
}