/* SPDX-License-Identifier: MIT */
/*
 * Author: Jianhui Zhao <zhaojh329@gmail.com>
 */

package main

import (
	"bufio"
	"bytes"
	"context"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"net"
	"net/http"
	"net/url"
	"strconv"
	"sync"
	"sync/atomic"
	"time"

	"github.com/zhaojh329/rtty-go/proto"
	"github.com/zhaojh329/rttys/v5/utils"

	"github.com/gin-gonic/gin"
	"github.com/rs/zerolog/log"
	"github.com/valyala/bytebufferpool"
)

type HttpProxySession struct {
	expire   atomic.Int64
	ctx      context.Context
	cancel   context.CancelFunc
	devid    string
	group    string
	destaddr string
	https    bool
}

var httpProxySessions = sync.Map{}

const httpProxySessionsExpire = 15 * time.Minute

func (ses *HttpProxySession) Expire() {
	ses.expire.Store(time.Now().Add(httpProxySessionsExpire).Unix())
}

func (ses *HttpProxySession) String() string {
	return fmt.Sprintf("{devid: %s, group: %s, destaddr: %s, https: %v}",
		ses.devid, ses.group, ses.destaddr, ses.https)
}

func (srv *RttyServer) ListenHttpProxy() {
	cfg := &srv.cfg

	if cfg.AddrHttpProxy != "" {
		addr, err := net.ResolveTCPAddr("tcp", cfg.AddrHttpProxy)
		if err != nil {
			log.Warn().Msg("invalid http proxy addr: " + err.Error())
		} else {
			srv.httpProxyPort = addr.Port
		}
	}

	ln, err := net.Listen("tcp", cfg.AddrHttpProxy)
	if err != nil {
		log.Fatal().Msg(err.Error())
	}
	defer ln.Close()

	srv.httpProxyPort = ln.Addr().(*net.TCPAddr).Port

	log.Info().Msgf("Listen http proxy on: %s", ln.Addr().(*net.TCPAddr))

	go httpProxySessionsClean()

	for {
		c, err := ln.Accept()
		if err != nil {
			log.Error().Msg(err.Error())
			continue
		}

		go doHttpProxy(srv, c)
	}
}

func httpProxySessionsClean() {
	for {
		time.Sleep(time.Second * 30)

		httpProxySessions.Range(func(key, value any) bool {
			ses := value.(*HttpProxySession)
			if time.Now().Unix() > ses.expire.Load() {
				log.Debug().Msgf("Http proxy session '%s' expired", key)
				ses.cancel()
				httpProxySessions.Delete(key)
			}
			return true
		})
	}
}

func doHttpProxy(srv *RttyServer, c net.Conn) {
	defer logPanic()
	defer c.Close()

	br := bufio.NewReader(c)

	req, err := http.ReadRequest(br)
	if err != nil {
		return
	}

	cookie, err := req.Cookie("rtty-http-sid")
	if err != nil {
		log.Debug().Msgf(`not found cookie "rtty-http-sid"`)
		sendHTTPErrorResponse(c, "invalid")
		return
	}
	sid := cookie.Value

	sesVal, ok := httpProxySessions.Load(sid)
	if !ok {
		log.Debug().Msgf(`not found httpProxySession "%s"`, sid)
		sendHTTPErrorResponse(c, "unauthorized")
		return
	}

	ses := sesVal.(*HttpProxySession)

	dev := srv.GetDevice(ses.group, ses.devid)
	if dev == nil {
		log.Debug().Msgf(`device "%s" group "%s" offline`, ses.devid, ses.group)
		sendHTTPErrorResponse(c, "offline")
		return
	}

	hostHeaderRewrite := ses.destaddr

	destAddr := genDestAddr(hostHeaderRewrite)

	hpw := &HttpProxyWriter{
		destAddr:          destAddr,
		hostHeaderRewrite: hostHeaderRewrite,
		dev:               dev,
		https:             ses.https,
	}

	tcpAddr2Bytes(c.RemoteAddr().(*net.TCPAddr), hpw.srcAddr[:])

	ctx, cancel := context.WithCancel(ses.ctx)
	defer cancel()

	go func() {
		<-ctx.Done()
		c.Close()
		log.Debug().Msgf("http proxy conn closed: %s", ses)
		dev.https.Delete(hpw.srcAddr)
	}()

	log.Debug().Msgf("new http proxy conn: %s", ses)

	dev.https.Store(hpw.srcAddr, c)

	req.Host = hostHeaderRewrite
	hpw.WriteRequest(req)

	if req.Header.Get("Upgrade") == "websocket" {
		b := make([]byte, 4096)

		for {
			n, err := c.Read(b)
			if err != nil {
				return
			}
			sendHttpReq(dev, ses.https, hpw.srcAddr[:], destAddr, b[:n])
			ses.Expire()
		}
	} else {
		for {
			req, err := http.ReadRequest(br)
			if err != nil {
				return
			}
			hpw.WriteRequest(req)
			ses.Expire()
		}
	}
}

func httpProxyRedirect(a *APIServer, c *gin.Context, group string) {
	srv := a.srv
	cfg := &srv.cfg

	devid := c.Param("devid")
	proto := c.Param("proto")
	addr := c.Param("addr")
	rawPath := c.Param("path")

	if !a.callUserHookUrl(c) {
		c.Status(http.StatusForbidden)
		return
	}

	log.Debug().Msgf("httpProxyRedirect devid: %s, proto: %s, addr: %s, path: %s", devid, proto, addr, rawPath)

	_, _, err := httpProxyVaildAddr(addr)
	if err != nil {
		log.Debug().Msgf("invalid addr: %s", addr)
		c.Status(http.StatusBadRequest)
		return
	}

	path, err := url.Parse(rawPath)
	if err != nil {
		log.Debug().Msgf("invalid path: %s", rawPath)
		c.Status(http.StatusBadRequest)
		return
	}

	dev := srv.GetDevice(group, devid)
	if dev == nil {
		c.Redirect(http.StatusFound, "/error/offline")
		return
	}

	location := c.Request.Header.Get("HttpProxyRedir")
	if location == "" {
		location = cfg.HttpProxyRedirURL
		if location != "" {
			log.Debug().Msgf("use HttpProxyRedirURL from config: %s, devid: %s", location, devid)
		}
	} else {
		log.Debug().Msgf("use HttpProxyRedir from HTTP header: %s, devid: %s", location, devid)
	}

	if location == "" {
		host, _, err := net.SplitHostPort(c.Request.Host)
		if err != nil {
			host = c.Request.Host
		}

		location = "http://" + host

		if srv.httpProxyPort != 80 {
			location += fmt.Sprintf(":%d", srv.httpProxyPort)
		}
	}

	location += path.Path

	location += fmt.Sprintf("?_=%d", time.Now().Unix())

	if path.RawQuery != "" {
		location += "&" + path.RawQuery
	}

	sid, err := c.Cookie("rtty-http-sid")
	if err == nil {
		if v, loaded := httpProxySessions.LoadAndDelete(sid); loaded {
			s := v.(*HttpProxySession)
			s.cancel()
			log.Debug().Msgf(`del old httpProxySession "%s" for device "%s"`, sid, devid)
		}
	}

	sid = utils.GenUniqueID()

	ctx, cancel := context.WithCancel(dev.ctx)

	ses := &HttpProxySession{
		ctx:      ctx,
		cancel:   cancel,
		devid:    devid,
		group:    group,
		destaddr: addr,
		https:    proto == "https",
	}
	ses.Expire()
	httpProxySessions.Store(sid, ses)

	log.Debug().Msgf(`new httpProxySession "%s" for device "%s"`, sid, devid)

	domain := c.Request.Header.Get("HttpProxyRedirDomain")
	if domain == "" {
		domain = cfg.HttpProxyRedirDomain
		if domain != "" {
			log.Debug().Msgf("set cookie domain from config: %s, devid: %s", domain, devid)
		}
	} else {
		log.Debug().Msgf("set cookie domain from HTTP header: %s, devid: %s", domain, devid)
	}

	c.SetCookie("rtty-http-sid", sid, 0, "", domain, false, true)
	c.Redirect(http.StatusFound, location)
}

func sendHttpReq(dev *Device, https bool, srcAddr []byte, destAddr []byte, data []byte) {
	bb := bytebufferpool.Get()
	defer bytebufferpool.Put(bb)

	if dev.proto > 3 {
		if https {
			bb.WriteByte(1)
		} else {
			bb.WriteByte(0)
		}
	}

	bb.Write(srcAddr)
	bb.Write(destAddr)
	bb.Write(data)

	dev.WriteMsg(proto.MsgTypeHttp, bb)
}

func genDestAddr(addr string) []byte {
	destIP, destPort, err := httpProxyVaildAddr(addr)
	if err != nil {
		return nil
	}

	b := make([]byte, 6)
	copy(b, destIP)

	binary.BigEndian.PutUint16(b[4:], destPort)

	return b
}

func tcpAddr2Bytes(addr *net.TCPAddr, b []byte) {
	binary.BigEndian.PutUint16(b[:2], uint16(addr.Port))
	copy(b[2:], addr.IP)
}

func httpProxyVaildAddr(addr string) (net.IP, uint16, error) {
	ips, ports, err := net.SplitHostPort(addr)
	if err != nil {
		ips = addr
		ports = "80"
	}

	ip := net.ParseIP(ips)
	if ip == nil {
		return nil, 0, errors.New("invalid IPv4 Addr")
	}

	ip = ip.To4()
	if ip == nil {
		return nil, 0, errors.New("invalid IPv4 Addr")
	}

	port, _ := strconv.Atoi(ports)

	return ip, uint16(port), nil
}

type HttpProxyWriter struct {
	destAddr          []byte
	srcAddr           [18]byte
	hostHeaderRewrite string
	dev               *Device
	https             bool
}

func (rw *HttpProxyWriter) Write(p []byte) (n int, err error) {
	sendHttpReq(rw.dev, rw.https, rw.srcAddr[:], rw.destAddr, p)
	return len(p), nil
}

func (rw *HttpProxyWriter) WriteRequest(req *http.Request) {
	req.Host = rw.hostHeaderRewrite
	req.Write(rw)
}

func sendHTTPErrorResponse(conn net.Conn, errorType string) {
	fs, _ := fs.Sub(staticFs, "assets")

	f, err := fs.Open("http-proxy-err.html")
	if err != nil {
		fmt.Println(err)
		return
	}
	defer f.Close()

	content, err := io.ReadAll(f)
	if err != nil {
		fmt.Println(err)
		return
	}

	content = bytes.ReplaceAll(content, []byte("{{.}}"), []byte(errorType))

	response := "HTTP/1.1 200 OK\r\n"
	response += "Content-Type: text/html; charset=utf-8\r\n"
	response += fmt.Sprintf("Content-Length: %d\r\n", len(content))
	response += "Connection: close\r\n"
	response += "\r\n"

	conn.Write([]byte(response))
	conn.Write(content)
}