package http

import (
	std_bufio "bufio"
	"context"
	"encoding/base64"
	"net"
	"net/http"
	"strings"

	"github.com/sagernet/sing/common"
	"github.com/sagernet/sing/common/atomic"
	"github.com/sagernet/sing/common/auth"
	"github.com/sagernet/sing/common/buf"
	"github.com/sagernet/sing/common/bufio"
	E "github.com/sagernet/sing/common/exceptions"
	F "github.com/sagernet/sing/common/format"
	M "github.com/sagernet/sing/common/metadata"
	N "github.com/sagernet/sing/common/network"
	"github.com/sagernet/sing/common/pipe"
)

type Handler = N.TCPConnectionHandler

func HandleConnection(ctx context.Context, conn net.Conn, reader *std_bufio.Reader, authenticator *auth.Authenticator, handler Handler, metadata M.Metadata) error {
	for {
		request, err := ReadRequest(reader)
		if err != nil {
			return E.Cause(err, "read http request")
		}

		if authenticator != nil {
			var (
				username string
				password string
				authOk   bool
			)
			authorization := request.Header.Get("Proxy-Authorization")
			if strings.HasPrefix(authorization, "Basic ") {
				userPassword, _ := base64.URLEncoding.DecodeString(authorization[6:])
				userPswdArr := strings.SplitN(string(userPassword), ":", 2)
				if len(userPswdArr) == 2 {
					username = userPswdArr[0]
					password = userPswdArr[1]
					authOk = authenticator.Verify(username, password)
					if authOk {
						ctx = auth.ContextWithUser(ctx, userPswdArr[0])
					}
				}
			}
			if !authOk {
				// Since no one else is using the library, use a fixed realm until rewritten
				err = responseWith(
					request, http.StatusProxyAuthRequired,
					"Proxy-Authenticate", `Basic realm="sing-box" charset="UTF-8"`,
				).Write(conn)
				if err != nil {
					return err
				}
				if username != "" {
					return E.New("http: authentication failed, username=", username, ", password=", password)
				} else if authorization != "" {
					return E.New("http: authentication failed, Proxy-Authorization=", authorization)
				} else {
					return E.New("http: authentication failed, no Proxy-Authorization header")
				}
			}
		}

		if sourceAddress := SourceAddress(request); sourceAddress.IsValid() {
			metadata.Source = sourceAddress
		}

		if request.Method == "CONNECT" {
			portStr := request.URL.Port()
			if portStr == "" {
				portStr = "80"
			}
			destination := M.ParseSocksaddrHostPortStr(request.URL.Hostname(), portStr)
			_, err = conn.Write([]byte(F.ToString("HTTP/", request.ProtoMajor, ".", request.ProtoMinor, " 200 Connection established\r\n\r\n")))
			if err != nil {
				return E.Cause(err, "write http response")
			}
			metadata.Protocol = "http"
			metadata.Destination = destination

			var requestConn net.Conn
			if reader.Buffered() > 0 {
				buffer := buf.NewSize(reader.Buffered())
				_, err = buffer.ReadFullFrom(reader, reader.Buffered())
				if err != nil {
					return err
				}
				requestConn = bufio.NewCachedConn(conn, buffer)
			} else {
				requestConn = conn
			}
			return handler.NewConnection(ctx, requestConn, metadata)
		}

		keepAlive := !(request.ProtoMajor == 1 && request.ProtoMinor == 0) && strings.TrimSpace(strings.ToLower(request.Header.Get("Proxy-Connection"))) == "keep-alive"
		request.RequestURI = ""

		removeHopByHopHeaders(request.Header)
		removeExtraHTTPHostPort(request)

		if hostStr := request.Header.Get("Host"); hostStr != "" {
			if hostStr != request.URL.Host {
				request.Host = hostStr
			}
		}

		if request.URL.Scheme == "" || request.URL.Host == "" {
			return responseWith(request, http.StatusBadRequest).Write(conn)
		}

		var innerErr atomic.TypedValue[error]
		httpClient := &http.Client{
			Transport: &http.Transport{
				DisableCompression: true,
				DialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
					metadata.Destination = M.ParseSocksaddr(address)
					metadata.Protocol = "http"
					input, output := pipe.Pipe()
					go func() {
						hErr := handler.NewConnection(ctx, output, metadata)
						if hErr != nil {
							innerErr.Store(hErr)
							common.Close(input, output)
						}
					}()
					return input, nil
				},
			},
			CheckRedirect: func(req *http.Request, via []*http.Request) error {
				return http.ErrUseLastResponse
			},
		}
		requestCtx, cancel := context.WithCancel(ctx)
		response, err := httpClient.Do(request.WithContext(requestCtx))
		if err != nil {
			cancel()
			return E.Errors(innerErr.Load(), err, responseWith(request, http.StatusBadGateway).Write(conn))
		}

		removeHopByHopHeaders(response.Header)

		if keepAlive {
			response.Header.Set("Proxy-Connection", "keep-alive")
			response.Header.Set("Connection", "keep-alive")
			response.Header.Set("Keep-Alive", "timeout=4")
		}

		response.Close = !keepAlive

		err = response.Write(conn)
		if err != nil {
			cancel()
			return E.Errors(innerErr.Load(), err)
		}

		cancel()
		if !keepAlive {
			return conn.Close()
		}
	}
}

func removeHopByHopHeaders(header http.Header) {
	// Strip hop-by-hop header based on RFC:
	// http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.5.1
	// https://www.mnot.net/blog/2011/07/11/what_proxies_must_do

	header.Del("Proxy-Connection")
	header.Del("Proxy-Authenticate")
	header.Del("Proxy-Authorization")
	header.Del("TE")
	header.Del("Trailers")
	header.Del("Transfer-Encoding")
	header.Del("Upgrade")

	connections := header.Get("Connection")
	header.Del("Connection")
	if len(connections) == 0 {
		return
	}
	for _, h := range strings.Split(connections, ",") {
		header.Del(strings.TrimSpace(h))
	}
}

func removeExtraHTTPHostPort(req *http.Request) {
	host := req.Host
	if host == "" {
		host = req.URL.Host
	}

	if pHost, port, err := net.SplitHostPort(host); err == nil && port == "80" {
		if M.ParseAddr(pHost).Is6() {
			pHost = "[" + pHost + "]"
		}
		host = pHost
	}

	req.Host = host
	req.URL.Host = host
}

func responseWith(request *http.Request, statusCode int, headers ...string) *http.Response {
	var header http.Header
	if len(headers) > 0 {
		header = make(http.Header)
		for i := 0; i < len(headers); i += 2 {
			header.Add(headers[i], headers[i+1])
		}
	}
	return &http.Response{
		StatusCode: statusCode,
		Status:     http.StatusText(statusCode),
		Proto:      request.Proto,
		ProtoMajor: request.ProtoMajor,
		ProtoMinor: request.ProtoMinor,
		Header:     header,
	}
}