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

namespace MoShiro.Measurement;

/// <summary>诊断采集进程所在的网络环境。宿主网络容器看到的是主机；桥接容器看到自己的网络环境。</summary>
public static class Ipv6Diagnostics
{
    public static Ipv6Diagnostic Sample(bool? listening = null, string? networkScope = null, string? hostProcRoot = null)
    {
        bool supported = Socket.OSSupportsIPv6;
        bool? address = null;
        bool? route = null;
        if (supported)
        {
            if (OperatingSystem.IsLinux())
            {
                address = ParseAddresses(Read("/proc/net/if_inet6"));
                route = ParseRoutes(Read("/proc/net/ipv6_route"));
            }
            else if (OperatingSystem.IsWindows() || OperatingSystem.IsMacOS())
            {
                try
                {
                    address = false;
                    route = false;
                    foreach (NetworkInterface adapter in NetworkInterface.GetAllNetworkInterfaces())
                    {
                        if (adapter.OperationalStatus != OperationalStatus.Up || adapter.NetworkInterfaceType == NetworkInterfaceType.Loopback)
                        {
                            continue;
                        }

                        IPInterfaceProperties properties = adapter.GetIPProperties();
                        foreach (UnicastIPAddressInformation unicast in properties.UnicastAddresses)
                        {
                            if (IsGlobal(unicast.Address))
                            {
                                address = true;
                            }
                        }

                        foreach (GatewayIPAddressInformation gateway in properties.GatewayAddresses)
                        {
                            if (gateway.Address.AddressFamily == AddressFamily.InterNetworkV6 && !gateway.Address.Equals(IPAddress.IPv6Any))
                            {
                                route = true;
                            }
                        }
                    }
                }
                catch (Exception ex) when (ex is NetworkInformationException or PlatformNotSupportedException)
                {
                    address = null;
                    route = null;
                }
            }
        }

        string scope = networkScope is "host" or "container" ? networkScope
            : File.Exists("/run/.containerenv") || File.Exists("/.dockerenv") ? "container" : "host";
        bool? hostAddress = scope == "host" ? address : null;
        bool? hostRoute = scope == "host" ? route : null;
        if (scope == "container" && OperatingSystem.IsLinux() && hostProcRoot is not null)
        {
            // /host/proc/net 通常指向当前进程的网络空间；宿主 PID 1 才是宿主网络。
            hostAddress = ParseAddresses(Read(Path.Combine(hostProcRoot, "1/net/if_inet6")));
            hostRoute = ParseRoutes(Read(Path.Combine(hostProcRoot, "1/net/ipv6_route")));
        }

        Ipv6Diagnostic result = Evaluate(supported, listening, address, route);
        result.NetworkScope = scope;
        result.HostHasGlobalAddress = hostAddress;
        result.HostHasDefaultRoute = hostRoute;
        if (scope == "container" && address == false && hostAddress == true)
        {
            result.State = "container_network_not_ready";
        }

        return result;
    }

    public static Ipv6Diagnostic Evaluate(bool supported, bool? listening, bool? address, bool? route) => new()
    {
        SocketSupported = supported,
        Listening = listening,
        HasGlobalAddress = address,
        HasDefaultRoute = route,
        State = !supported ? "unsupported" : address == false ? "no_global_address" : listening == false ? "not_listening"
            : route == false ? "no_default_route" : address is null || route is null ? "unknown" : "ready",
    };

    public static bool? ParseAddresses(string? text)
    {
        if (text is null)
        {
            return null;
        }

        foreach (string line in text.Split('\n'))
        {
            string[] fields = line.Split((char[]?)null, StringSplitOptions.RemoveEmptyEntries);
            if (fields.Length != 6 || fields[0].Length != 32 || fields[0][0] is not ('2' or '3') || fields[3] != "00")
            {
                continue;
            }

            // tentative、DAD failed 和 deprecated 地址不能作为就绪的公网地址。
            if (uint.TryParse(fields[4], NumberStyles.HexNumber, CultureInfo.InvariantCulture, out uint flags) && (flags & 0x68) == 0)
            {
                return true;
            }
        }

        return false;
    }

    public static bool? ParseRoutes(string? text)
    {
        if (text is null)
        {
            return null;
        }

        foreach (string line in text.Split('\n'))
        {
            string[] fields = line.Split((char[]?)null, StringSplitOptions.RemoveEmptyEntries);
            if (fields.Length == 10 && fields[0] == "00000000000000000000000000000000" && fields[1] == "00" && fields[9] != "lo"
                && uint.TryParse(fields[8], NumberStyles.HexNumber, CultureInfo.InvariantCulture, out uint flags) && (flags & 1) != 0 && (flags & 0x200) == 0)
            {
                return true;
            }
        }

        return false;
    }

    private static bool IsGlobal(IPAddress address) => address.AddressFamily == AddressFamily.InterNetworkV6 && (address.GetAddressBytes()[0] & 0xE0) == 0x20;

    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;
        }
    }
}