package server

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"regexp"
	"strings"
	"time"
	"tunnel_pls/session"
	"tunnel_pls/utils"

	"golang.org/x/crypto/ssh"
)

type Interaction interface {
	SendMessage(message string)
}

type HTTPWriter interface {
	io.Reader
	io.Writer
	SetInteraction(interaction Interaction)
	AddInteraction(interaction Interaction)
	GetRemoteAddr() net.Addr
	GetWriter() io.Writer
	AddResponseMiddleware(mw ResponseMiddleware)
	AddRequestStartMiddleware(mw RequestMiddleware)
	SetRequestHeader(header RequestHeaderManager)
	GetRequestStartMiddleware() []RequestMiddleware
}

type customWriter struct {
	remoteAddr  net.Addr
	writer      io.Writer
	reader      io.Reader
	headerBuf   []byte
	buf         []byte
	respHeader  ResponseHeaderManager
	reqHeader   RequestHeaderManager
	interaction Interaction
	respMW      []ResponseMiddleware
	reqStartMW  []RequestMiddleware
	reqEndMW    []RequestMiddleware
}

func (cw *customWriter) SetInteraction(interaction Interaction) {
	cw.interaction = interaction
}

func (cw *customWriter) GetRemoteAddr() net.Addr {
	return cw.remoteAddr
}

func (cw *customWriter) GetWriter() io.Writer {
	return cw.writer
}

func (cw *customWriter) AddResponseMiddleware(mw ResponseMiddleware) {
	cw.respMW = append(cw.respMW, mw)
}

func (cw *customWriter) AddRequestStartMiddleware(mw RequestMiddleware) {
	cw.reqStartMW = append(cw.reqStartMW, mw)
}

func (cw *customWriter) SetRequestHeader(header RequestHeaderManager) {
	cw.reqHeader = header
}

func (cw *customWriter) GetRequestStartMiddleware() []RequestMiddleware {
	return cw.reqStartMW
}

func (cw *customWriter) Read(p []byte) (int, error) {
	tmp := make([]byte, len(p))
	read, err := cw.reader.Read(tmp)
	if read == 0 && err != nil {
		return 0, err
	}

	tmp = tmp[:read]

	idx := bytes.Index(tmp, DELIMITER)
	if idx == -1 {
		copy(p, tmp)
		if err != nil {
			return read, err
		}
		return read, nil
	}

	header := tmp[:idx+len(DELIMITER)]
	body := tmp[idx+len(DELIMITER):]

	if !isHTTPHeader(header) {
		copy(p, tmp)
		return read, nil
	}

	for _, m := range cw.reqEndMW {
		err = m.HandleRequest(cw.reqHeader)
		if err != nil {
			log.Printf("Error when applying request middleware: %v", err)
			return 0, err
		}
	}

	headerReader := bufio.NewReader(bytes.NewReader(header))
	reqhf, err := NewRequestHeaderFactory(headerReader)
	if err != nil {
		return 0, err
	}

	for _, m := range cw.reqStartMW {
		if mwErr := m.HandleRequest(reqhf); mwErr != nil {
			log.Printf("Error when applying request middleware: %v", mwErr)
			return 0, mwErr
		}
	}

	cw.reqHeader = reqhf
	finalHeader := reqhf.Finalize()

	combined := append(finalHeader, body...)

	n := copy(p, combined)

	return n, nil
}

func NewCustomWriter(writer io.Writer, reader io.Reader, remoteAddr net.Addr) HTTPWriter {
	return &customWriter{
		remoteAddr:  remoteAddr,
		writer:      writer,
		reader:      reader,
		buf:         make([]byte, 0, 4096),
		interaction: nil,
	}
}

var DELIMITER = []byte{0x0D, 0x0A, 0x0D, 0x0A}
var requestLine = regexp.MustCompile(`^(GET|POST|PUT|DELETE|HEAD|OPTIONS|PATCH|TRACE|CONNECT) \S+ HTTP/\d\.\d$`)
var responseLine = regexp.MustCompile(`^HTTP/\d\.\d \d{3} .+`)

func isHTTPHeader(buf []byte) bool {
	lines := bytes.Split(buf, []byte("\r\n"))

	startLine := string(lines[0])
	if !requestLine.MatchString(startLine) && !responseLine.MatchString(startLine) {
		return false
	}

	for _, line := range lines[1:] {
		if len(line) == 0 {
			break
		}
		colonIdx := bytes.IndexByte(line, ':')
		if colonIdx <= 0 {
			return false
		}
	}
	return true
}

func (cw *customWriter) Write(p []byte) (int, error) {
	if cw.respHeader != nil && len(cw.buf) == 0 && len(p) >= 5 && string(p[0:5]) == "HTTP/" {
		cw.respHeader = nil
	}

	if cw.respHeader != nil {
		n, err := cw.writer.Write(p)
		if err != nil {
			return n, err
		}
		return n, nil
	}

	cw.buf = append(cw.buf, p...)

	idx := bytes.Index(cw.buf, DELIMITER)
	if idx == -1 {
		return len(p), nil
	}

	header := cw.buf[:idx+len(DELIMITER)]
	body := cw.buf[idx+len(DELIMITER):]

	if !isHTTPHeader(header) {
		_, err := cw.writer.Write(cw.buf)
		cw.buf = nil
		if err != nil {
			return 0, err
		}
		return len(p), nil
	}

	resphf := NewResponseHeaderFactory(header)
	for _, m := range cw.respMW {
		err := m.HandleResponse(resphf, body)
		if err != nil {
			log.Printf("Cannot apply middleware: %s\n", err)
			return 0, err
		}
	}
	header = resphf.Finalize()
	cw.respHeader = resphf

	_, err := cw.writer.Write(header)
	if err != nil {
		return 0, err
	}
	if len(body) > 0 {
		_, err = cw.writer.Write(body)
		if err != nil {
			return 0, err
		}
	}
	cw.buf = nil
	return len(p), nil
}

func (cw *customWriter) AddInteraction(interaction Interaction) {
	cw.interaction = interaction
}

var redirectTLS = false

func NewHTTPServer() error {
	httpPort := utils.Getenv("HTTP_PORT", "8080")
	listener, err := net.Listen("tcp", ":"+httpPort)
	if err != nil {
		return errors.New("Error listening: " + err.Error())
	}
	if utils.Getenv("TLS_ENABLED", "false") == "true" && utils.Getenv("TLS_REDIRECT", "false") == "true" {
		redirectTLS = true
	}
	go func() {
		for {
			var conn net.Conn
			conn, err = listener.Accept()
			if err != nil {
				if errors.Is(err, net.ErrClosed) {
					return
				}
				log.Printf("Error accepting connection: %v", err)
				continue
			}

			go Handler(conn)
		}
	}()
	return nil
}

func Handler(conn net.Conn) {
	defer func() {
		err := conn.Close()
		if err != nil && !errors.Is(err, net.ErrClosed) {
			log.Printf("Error closing connection: %v", err)
			return
		}
		return
	}()

	dstReader := bufio.NewReader(conn)
	reqhf, err := NewRequestHeaderFactory(dstReader)
	if err != nil {
		log.Printf("Error creating request header: %v", err)
		return
	}

	host := strings.Split(reqhf.Get("Host"), ".")
	if len(host) < 1 {
		_, err := conn.Write([]byte("HTTP/1.1 400 Bad Request\r\n\r\n"))
		if err != nil {
			log.Println("Failed to write 400 Bad Request:", err)
			return
		}
		return
	}

	slug := host[0]

	if redirectTLS {
		_, err = conn.Write([]byte("HTTP/1.1 301 Moved Permanently\r\n" +
			fmt.Sprintf("Location: https://%s.%s/\r\n", slug, utils.Getenv("DOMAIN", "localhost")) +
			"Content-Length: 0\r\n" +
			"Connection: close\r\n" +
			"\r\n"))
		if err != nil {
			log.Println("Failed to write 301 Moved Permanently:", err)
			return
		}
		return
	}

	if slug == "ping" {
		_, err = conn.Write([]byte(
			"HTTP/1.1 200 OK\r\n" +
				"Content-Length: 0\r\n" +
				"Connection: close\r\n" +
				"Access-Control-Allow-Origin: *\r\n" +
				"Access-Control-Allow-Methods: GET, HEAD, OPTIONS\r\n" +
				"Access-Control-Allow-Headers: *\r\n" +
				"\r\n",
		))
		if err != nil {
			log.Println("Failed to write 200 OK:", err)
			return
		}
		return
	}

	sshSession, ok := session.Clients[slug]
	if !ok {
		_, err = conn.Write([]byte("HTTP/1.1 301 Moved Permanently\r\n" +
			fmt.Sprintf("Location: https://tunnl.live/tunnel-not-found?slug=%s\r\n", slug) +
			"Content-Length: 0\r\n" +
			"Connection: close\r\n" +
			"\r\n"))
		if err != nil {
			log.Println("Failed to write 301 Moved Permanently:", err)
			return
		}
		return
	}
	cw := NewCustomWriter(conn, dstReader, conn.RemoteAddr())
	forwardRequest(cw, reqhf, sshSession)
	return
}

func forwardRequest(cw HTTPWriter, initialRequest RequestHeaderManager, sshSession *session.SSHSession) {
	payload := sshSession.GetForwarder().CreateForwardedTCPIPPayload(cw.GetRemoteAddr())

	type channelResult struct {
		channel ssh.Channel
		reqs    <-chan *ssh.Request
		err     error
	}
	resultChan := make(chan channelResult, 1)

	go func() {
		channel, reqs, err := sshSession.GetLifecycle().GetConnection().OpenChannel("forwarded-tcpip", payload)
		resultChan <- channelResult{channel, reqs, err}
	}()

	var channel ssh.Channel
	var reqs <-chan *ssh.Request

	select {
	case result := <-resultChan:
		if result.err != nil {
			log.Printf("Failed to open forwarded-tcpip channel: %v", result.err)
			sshSession.GetForwarder().WriteBadGatewayResponse(cw.GetWriter())
			return
		}
		channel = result.channel
		reqs = result.reqs
	case <-time.After(5 * time.Second):
		log.Printf("Timeout opening forwarded-tcpip channel")
		sshSession.GetForwarder().WriteBadGatewayResponse(cw.GetWriter())
		return
	}

	go ssh.DiscardRequests(reqs)

	fingerprintMiddleware := NewTunnelFingerprint()
	forwardedForMiddleware := NewForwardedFor(cw.GetRemoteAddr())

	cw.AddResponseMiddleware(fingerprintMiddleware)
	cw.AddRequestStartMiddleware(forwardedForMiddleware)
	cw.SetRequestHeader(initialRequest)

	for _, m := range cw.GetRequestStartMiddleware() {
		if err := m.HandleRequest(initialRequest); err != nil {
			log.Printf("Error handling request: %v", err)
			return
		}
	}

	_, err := channel.Write(initialRequest.Finalize())
	if err != nil {
		log.Printf("Failed to forward request: %v", err)
		return
	}

	sshSession.GetForwarder().HandleConnection(cw, channel, cw.GetRemoteAddr())
	return
}