/*

SimpleHttpClient class — 支援 HTTP/HTTPS、GET/POST、自動轉址、gzip/deflate 解壓
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: 
建立實例與 GET 請求：
var client = new SimpleHttpClient();
string html = client.Get("https://example.com");
Console.WriteLine(html);


usage2:
POST 請求（form）：
string response = client.Post("https://httpbin.org/post", "username=test&password=1234");
Console.WriteLine(response);

usage3:
POST 請求（JSON）：
client.DefaultHeaders["Accept"] = "application/json";

string json = "{\"name\":\"ChatGPT\",\"job\":\"assistant\"}";
string response = client.Post("https://httpbin.org/post", json, "application/json");
Console.WriteLine(response);


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	✅

接下來可擴充的方向（可選）：
支援 cookie 管理
支援 chunked 讀取（Transfer-Encoding: chunked）
支援 keep-alive 串流持續連線

*/

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

public class SimpleHttpClient
{
    private const int MaxRedirects = 5;

    public string UserAgent { get; set; } = "SimpleHttpClient/1.0";
    public Dictionary<string, string> DefaultHeaders { get; set; } = new();

    public string Get(string url) => SendRequest(url, "GET", null);
    public string Post(string url, string body, string contentType = "application/x-www-form-urlencoded") =>
        SendRequest(url, "POST", body, contentType);

    private string SendRequest(string url, string method, string body = null, string contentType = null, int redirectCount = 0)
    {
        if (redirectCount > MaxRedirects)
            throw new Exception("Too many redirects.");

        Uri uri = new Uri(url);
        string host = uri.Host;
        string path = string.IsNullOrEmpty(uri.PathAndQuery) ? "/" : uri.PathAndQuery;
        bool useHttps = uri.Scheme == "https";
        int port = uri.Port;

        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 = useHttps
                ? new SslStream(new NetworkStream(socket), false, (_, __, ___, ____) => true)
                : new NetworkStream(socket);

            if (useHttps)
                ((SslStream)netStream).AuthenticateAsClient(host);

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

            foreach (var header in DefaultHeaders)
                requestBuilder.AppendLine($"{header.Key}: {header.Value}");

            if (!string.IsNullOrEmpty(body))
            {
                byte[] bodyBytes = Encoding.UTF8.GetBytes(body);
                requestBuilder.AppendLine($"Content-Length: {bodyBytes.Length}");
                requestBuilder.AppendLine($"Content-Type: {contentType ?? "application/x-www-form-urlencoded"}");
                requestBuilder.AppendLine();
                requestBuilder.Append(body);
            }
            else
            {
                requestBuilder.AppendLine();
            }

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

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

            string fullResponse = Encoding.UTF8.GetString(responseStream.ToArray());
            int headerEndIndex = fullResponse.IndexOf("\r\n\r\n", StringComparison.Ordinal);
            if (headerEndIndex < 0)
                return fullResponse;

            string headerPart = fullResponse[..headerEndIndex];
            byte[] bodyBytes = responseStream.ToArray()[headerEndIndex + 4..];

            // Redirect
            string[] headers = headerPart.Split("\r\n");
            string statusLine = headers[0];
            if (statusLine.Contains(" 301 ") || statusLine.Contains(" 302 "))
            {
                foreach (var line in headers)
                {
                    if (line.StartsWith("Location:", StringComparison.OrdinalIgnoreCase))
                    {
                        string newUrl = line[9..].Trim();
                        return SendRequest(newUrl, method, body, contentType, redirectCount + 1);
                    }
                }
            }

            // Decompress if needed
            string encoding = "";
            foreach (var line in headers)
            {
                if (line.StartsWith("Content-Encoding:", StringComparison.OrdinalIgnoreCase))
                {
                    encoding = line[18..].Trim().ToLower();
                    break;
                }
            }

            Stream decompressed = new MemoryStream(bodyBytes);
            if (encoding == "gzip")
                decompressed = new GZipStream(decompressed, CompressionMode.Decompress);
            else if (encoding == "deflate")
                decompressed = new DeflateStream(decompressed, CompressionMode.Decompress);

            using StreamReader reader = new StreamReader(decompressed, Encoding.UTF8);
            return reader.ReadToEnd();
        }
    }
}