/*
支援轉址與壓縮
自動處理 301 / 302 轉址
自動解壓縮 gzip / deflate 壓縮的內容
保持使用 Socket + (SslStream)，不依賴 HttpClient 或 WebRequest

usage1:
string html = WebClientSocket.Request("httpbin.org", "/gzip", "GET", true);
Console.WriteLine(html);


usage2:
string html = WebClientSocket.Request("http://google.com", "/", "GET", false);
Console.WriteLine(html); // 會自動跳轉到 https://www.google.com


功能	支援
HTTP / HTTPS	✅
GET / POST	✅
自訂 headers	✅
表單 / JSON body	✅
301 / 302 跳轉	✅ 自動
gzip / deflate	✅ 自動解壓縮
純 Socket + SslStream	✅

如果你有要包成 reusable class（例如像 SimpleHttpClient），我也可以幫你整理成更乾淨的封裝版本，要嗎？
*/

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.IO;
using System.IO.Compression;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.Collections.Generic;

public class WebClientSocket
{
    private const int MaxRedirects = 5;

    public static string Request(
        string host,
        string path = "/",
        string method = "GET",
        bool useHttps = true,
        Dictionary<string, string> headers = null,
        string postData = null,
        int redirectCount = 0)
    {
        if (redirectCount > MaxRedirects)
            throw new Exception("Too many redirects.");

        int port = useHttps ? 443 : 80;
        IPAddress ipAddress = Dns.GetHostEntry(host).AddressList[0];
        IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);

        using (Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
        {
            socket.Connect(remoteEP);

            Stream netStream;
            if (useHttps)
            {
                var sslStream = new SslStream(new NetworkStream(socket), false,
                    new RemoteCertificateValidationCallback((sender, cert, chain, sslErrors) => true));
                sslStream.AuthenticateAsClient(host);
                netStream = sslStream;
            }
            else
            {
                netStream = new NetworkStream(socket);
            }

            var requestBuilder = new StringBuilder();
            requestBuilder.AppendLine($"{method} {path} HTTP/1.1");
            requestBuilder.AppendLine($"Host: {host}");
            requestBuilder.AppendLine("Connection: Close");
            requestBuilder.AppendLine("User-Agent: CustomSocketClient/1.0");
            requestBuilder.AppendLine("Accept-Encoding: gzip, deflate");

            if (headers != null)
            {
                foreach (var header in headers)
                    requestBuilder.AppendLine($"{header.Key}: {header.Value}");
            }

            if (!string.IsNullOrEmpty(postData))
            {
                var postBytes = Encoding.UTF8.GetBytes(postData);
                requestBuilder.AppendLine($"Content-Length: {postBytes.Length}");
                requestBuilder.AppendLine("Content-Type: application/x-www-form-urlencoded");
                requestBuilder.AppendLine();
                requestBuilder.Append(postData);
            }
            else
            {
                requestBuilder.AppendLine();
            }

            byte[] requestBytes = Encoding.UTF8.GetBytes(requestBuilder.ToString());
            netStream.Write(requestBytes, 0, requestBytes.Length);

            using (var memoryStream = new MemoryStream())
            {
                byte[] buffer = new byte[4096];
                int bytesRead;
                while ((bytesRead = netStream.Read(buffer, 0, buffer.Length)) > 0)
                    memoryStream.Write(buffer, 0, bytesRead);

                string fullResponse = Encoding.UTF8.GetString(memoryStream.ToArray());

                // 拆解 headers 和 body
                int headerEndIndex = fullResponse.IndexOf("\r\n\r\n", StringComparison.Ordinal);
                if (headerEndIndex < 0)
                    return fullResponse;

                string headerPart = fullResponse.Substring(0, headerEndIndex);
                byte[] bodyBytes = memoryStream.ToArray()[headerEndIndex + 4..];

                // 檢查是否是轉址
                string[] lines = headerPart.Split("\r\n");
                string statusLine = lines[0];
                if (statusLine.Contains(" 301 ") || statusLine.Contains(" 302 "))
                {
                    foreach (var line in lines)
                    {
                        if (line.StartsWith("Location:", StringComparison.OrdinalIgnoreCase))
                        {
                            string newUrl = line.Substring(9).Trim();
                            Uri uri = new Uri(newUrl);

                            return Request(
                                uri.Host,
                                uri.PathAndQuery,
                                method,
                                uri.Scheme == "https",
                                headers,
                                postData,
                                redirectCount + 1
                            );
                        }
                    }
                }

                // 處理壓縮內容
                string contentEncoding = "";
                foreach (var line in lines)
                {
                    if (line.StartsWith("Content-Encoding:", StringComparison.OrdinalIgnoreCase))
                    {
                        contentEncoding = line.Substring(18).Trim().ToLower();
                        break;
                    }
                }

                Stream bodyStream = new MemoryStream(bodyBytes);
                if (contentEncoding == "gzip")
                {
                    using var gzip = new GZipStream(bodyStream, CompressionMode.Decompress);
                    using var reader = new StreamReader(gzip, Encoding.UTF8);
                    return reader.ReadToEnd();
                }
                else if (contentEncoding == "deflate")
                {
                    using var deflate = new DeflateStream(bodyStream, CompressionMode.Decompress);
                    using var reader = new StreamReader(deflate, Encoding.UTF8);
                    return reader.ReadToEnd();
                }
                else
                {
                    return Encoding.UTF8.GetString(bodyBytes);
                }
            }
        }
    }
}