using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Net;
using System.Net.Http;
using System.Net.Security;
using System.Net.Sockets;
using System.Text;
using System.Text.Json;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using Newtonsoft.Json.Linq;

namespace DnsClient
{
    class DnsClientTool
    {
        public async Task<string> GetNotices(string domain)
        {
            var dohServers = new List<string>
            {
                "https://cloudflare-dns.com/dns-query",
                "https://dns.cloudflare.com/dns-query",
                "https://1.1.1.1/dns-query",
                "https://1.0.0.1/dns-query",
                "https://dns.google/resolve",
                "https://sm2.doh.pub/dns-query",
                "https://doh.pub/dns-query",
                "https://dns.alidns.com/resolve",
                "https://223.5.5.5/resolve",
                "https://223.6.6.6/resolve",
                "https://doh.360.cn/resolve"
            };

            var dotServers = new List<NameServer>
            {
                new NameServer(IPAddress.Parse("101.226.4.6"), 853),
                new NameServer(IPAddress.Parse("223.5.5.5"), 853),
                new NameServer(IPAddress.Parse("223.6.6.6"), 853),
                new NameServer(IPAddress.Parse("1.12.12.12"), 853),
                new NameServer(IPAddress.Parse("1.1.1.1"), 853),
                new NameServer(IPAddress.Parse("1.0.0.1"), 853),
                new NameServer(IPAddress.Parse("8.8.8.8"), 853),
                new NameServer(IPAddress.Parse("8.8.4.4"), 853),
                new NameServer(IPAddress.Parse("9.9.9.9"), 853),
                new NameServer(IPAddress.Parse("149.112.112.112"), 853)
            };

            var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));

            var results = new List<string>();

            var dohTasks = dohServers.Select(server =>
                QueryDohAsync(server, domain, cts.Token));
            var dotTasks = dotServers.Select(server =>
                QueryDotAsync(server, domain, cts.Token));
            var dohResults = await Task.WhenAll(dohTasks);
            var dotResults = await Task.WhenAll(dotTasks);

            foreach (var list in dohResults.Concat(dotResults))
            {
                results.AddRange(list);
            }
            var recordCounts = results.GroupBy(x => x).ToDictionary(g => g.Key, g => g.Count());
            var mostFrequentRecord = recordCounts.OrderByDescending(x => x.Value).FirstOrDefault();
            return mostFrequentRecord.Key ?? "没有 TXT 记录";
        }

        private async Task<List<string>> QueryDohAsync(string server, string domain, CancellationToken token)
        {
            var stopwatch = System.Diagnostics.Stopwatch.StartNew();
            List<string> results = new List<string>();
            try
            {
                var httpClient = new HttpClient();
                httpClient.Timeout = TimeSpan.FromSeconds(5);
                httpClient.DefaultRequestHeaders.Add("Accept", "application/dns-json");
                var response = await httpClient.GetAsync($"{server}?name={domain}&type=16", token);
                response.EnsureSuccessStatusCode();
                var responseString = await response.Content.ReadAsStringAsync();
                var json = JsonDocument.Parse(responseString);
                stopwatch.Stop();
                var elapsedMs = (int)stopwatch.ElapsedMilliseconds;

                if (json.RootElement.TryGetProperty("Answer", out var answers))
                {
                    foreach (var answer in answers.EnumerateArray())
                    {
                        string txtData = NormalizeResult(answer.GetProperty("data").GetString());
                        results.Add(txtData);
                    }
                }
            }
            catch (Exception ex)
            {
                stopwatch.Stop();
            }
            return results;
        }

        private async Task<List<string>> QueryDotAsync(NameServer server, string domain, CancellationToken token)
        {
            var results = new List<string>();
            TcpClient tcpClient = null;
            SslStream sslStream = null;

            try
            {
                tcpClient = new TcpClient();
                var cts = CancellationTokenSource.CreateLinkedTokenSource(token);
                cts.CancelAfter(TimeSpan.FromSeconds(5));

                await ConnectWithTimeoutAsync(tcpClient, server.Address.ToString(), server.Port, cts.Token);

                sslStream = new SslStream(tcpClient.GetStream(), false, (sender, certificate, chain, errors) => true);
                await sslStream.AuthenticateAsClientAsync(server.Address.ToString());

                byte[] query = BuildDnsQuery(domain);
                byte[] lengthPrefixed = new byte[query.Length + 2];
                lengthPrefixed[0] = (byte)(query.Length >> 8);
                lengthPrefixed[1] = (byte)(query.Length & 0xFF);
                Buffer.BlockCopy(query, 0, lengthPrefixed, 2, query.Length);

                await sslStream.WriteAsync(lengthPrefixed, 0, lengthPrefixed.Length, cts.Token);

                byte[] lengthBytes = new byte[2];
                await sslStream.ReadAsync(lengthBytes, 0, 2, cts.Token);
                int responseLength = (lengthBytes[0] << 8) | lengthBytes[1];

                byte[] response = new byte[responseLength];
                int totalRead = 0;
                while (totalRead < responseLength)
                {
                    int read = await sslStream.ReadAsync(response, totalRead, responseLength - totalRead, cts.Token);
                    if (read == 0) break;
                    totalRead += read;
                }

                results.AddRange(ParseTxtRecordsFromResponse(response));
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error occurred while querying DoT server: {ex.Message}");
            }
            finally
            {
                sslStream?.Dispose();
                tcpClient?.Close();
            }

            return results;
        }

        private byte[] BuildDnsQuery(string domain)
        {
            var rnd = new Random();
            var id = (ushort)rnd.Next(0, ushort.MaxValue);

            var message = new List<byte>();
            message.AddRange(BitConverter.GetBytes((ushort)IPAddress.HostToNetworkOrder((short)id))); // Transaction ID
            message.AddRange(new byte[] { 0x01, 0x00 });
            message.AddRange(new byte[] { 0x00, 0x01 });
            message.AddRange(new byte[] { 0x00, 0x00 });
            message.AddRange(new byte[] { 0x00, 0x00 });
            message.AddRange(new byte[] { 0x00, 0x00 });

            foreach (var label in domain.Split('.'))
            {
                message.Add((byte)label.Length);
                message.AddRange(Encoding.ASCII.GetBytes(label));
            }
            message.Add(0);

            message.AddRange(new byte[] { 0x00, 0x10 });
            message.AddRange(new byte[] { 0x00, 0x01 });

            return message.ToArray();
        }

        private List<string> ParseTxtRecordsFromResponse(byte[] response)
        {
            var results = new List<string>();

            int answerCount = (response[6] << 8) | response[7];

            int position = 12;
            while (response[position] != 0)
            {
                position += response[position] + 1;
            }
            position += 5;

            for (int i = 0; i < answerCount; i++)
            {
                position += 2;
                ushort type = (ushort)((response[position] << 8) | response[position + 1]);
                position += 8;
                ushort rdLength = (ushort)((response[position] << 8) | response[position + 1]);
                position += 2;
                if (type == 16)
                {
                    int txtLength = response[position];
                    var txt = NormalizeResult(Encoding.UTF8.GetString(response, position + 1, txtLength));
                    results.Add(txt);
                }
                position += rdLength;
            }

            return results;
        }

        private async Task ConnectWithTimeoutAsync(TcpClient client, string address, int port, CancellationToken token)
        {
            var connectTask = client.ConnectAsync(address, port);
            var timeoutTask = Task.Delay(Timeout.InfiniteTimeSpan, token);

            var completedTask = await Task.WhenAny(connectTask, timeoutTask);
            if (completedTask == timeoutTask)
            {
                client?.Close();
                throw new TimeoutException("TCP 连接超时或已取消。");
            }

            await connectTask;
        }

        public static string DecodeByteValuesToUtf8(string input)
        {
            string pattern = @"\\(\d{1,3})";

            string decodedString = Regex.Replace(input, pattern, match =>
            {
                byte byteValue = byte.Parse(match.Groups[1].Value);
                return ((char)byteValue).ToString();
            });

            byte[] byteArray = new byte[decodedString.Length];
            for (int i = 0; i < decodedString.Length; i++)
            {
                byteArray[i] = (byte)decodedString[i];
            }

            return Encoding.UTF8.GetString(byteArray);
        }

        public static string NormalizeResult(string input)
        {
            if (!Regex.IsMatch(input, @"\\\d{1,3}"))
            {
                return input;
            }

            string decodedBytes = DecodeByteValuesToUtf8(input);

            return decodedBytes.Trim();
        }

    }
}