// http proxy
// NOTE: never keep-alive so the implementation can be much easier.

package http

import (
	"bufio"
	"bytes"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"net"
	"net/textproto"
	"net/url"
	"strings"
	"time"

	"github.com/nadoo/glider/common/conn"
	"github.com/nadoo/glider/common/log"
	"github.com/nadoo/glider/proxy"
)

// HTTP struct
type HTTP struct {
	dialer             proxy.Dialer
	addr               string
	user               string
	password           string
	pretendAsWebServer bool
}

func init() {
	proxy.RegisterDialer("http", NewHTTPDialer)
	proxy.RegisterServer("http", NewHTTPServer)
}

// NewHTTP returns a http proxy
func NewHTTP(s string, dialer proxy.Dialer) (*HTTP, error) {
	u, err := url.Parse(s)
	if err != nil {
		log.F("parse err: %s", err)
		return nil, err
	}

	addr := u.Host
	user := u.User.Username()
	pass, _ := u.User.Password()

	h := &HTTP{
		dialer:             dialer,
		addr:               addr,
		user:               user,
		password:           pass,
		pretendAsWebServer: false,
	}

	pretend := u.Query().Get("pretend")
	if pretend == "true" {
		h.pretendAsWebServer = true
	}

	return h, nil
}

// NewHTTPDialer returns a http proxy dialer
func NewHTTPDialer(s string, dialer proxy.Dialer) (proxy.Dialer, error) {
	return NewHTTP(s, dialer)
}

// NewHTTPServer returns a http proxy server
func NewHTTPServer(s string, dialer proxy.Dialer) (proxy.Server, error) {
	return NewHTTP(s, dialer)
}

// ListenAndServe .
func (s *HTTP) ListenAndServe() {
	l, err := net.Listen("tcp", s.addr)
	if err != nil {
		log.F("[http] failed to listen on %s: %v", s.addr, err)
		return
	}
	defer l.Close()

	log.F("[http] listening TCP on %s", s.addr)

	for {
		c, err := l.Accept()
		if err != nil {
			log.F("[http] failed to accept: %v", err)
			continue
		}

		go s.Serve(c)
	}
}

// Serve .
func (s *HTTP) Serve(c net.Conn) {
	defer c.Close()

	if c, ok := c.(*net.TCPConn); ok {
		c.SetKeepAlive(true)
	}

	reqR := bufio.NewReader(c)
	reqTP := textproto.NewReader(reqR)
	method, requestURI, proto, ok := parseFirstLine(reqTP)
	if !ok {
		return
	}

	if s.pretendAsWebServer {
		fmt.Fprintf(c, "%s 404 Not Found\r\nServer: nginx\r\n\r\n404 Not Found\r\n", proto)
		log.F("[http pretender] being accessed as web server from %s", c.RemoteAddr().String())
		return
	}

	if method == "CONNECT" {
		s.servHTTPS(method, requestURI, proto, c)
		return
	}

	reqHeader, err := reqTP.ReadMIMEHeader()
	if err != nil {
		log.F("[http] read header error:%s", err)
		return
	}
	cleanHeaders(reqHeader)

	// tell the remote server not to keep alive
	reqHeader.Set("Connection", "close")

	u, err := url.ParseRequestURI(requestURI)
	if err != nil {
		log.F("[http] parse request url error: %s", err)
		return
	}

	var tgt = u.Host
	if !strings.Contains(u.Host, ":") {
		tgt += ":80"
	}

	rc, p, err := s.dialer.Dial("tcp", tgt)
	if err != nil {
		fmt.Fprintf(c, "%s 502 ERROR\r\n\r\n", proto)
		log.F("[http] %s <-> %s, %s, error in dial: %v", c.RemoteAddr(), tgt, err, p)
		return
	}
	defer rc.Close()

	// GET http://example.com/a/index.htm HTTP/1.1 -->
	// GET /a/index.htm HTTP/1.1
	u.Scheme = ""
	u.Host = ""
	uri := u.String()

	var reqBuf bytes.Buffer
	writeFirstLine(&reqBuf, method, uri, proto)
	writeHeaders(&reqBuf, reqHeader)

	// send request to remote server
	rc.Write(reqBuf.Bytes())

	// copy the left request bytes to remote server. eg. length specificed or chunked body.
	go func() {
		if _, err := reqR.Peek(1); err == nil {
			io.Copy(rc, reqR)
			rc.SetDeadline(time.Now())
			c.SetDeadline(time.Now())
		}
	}()

	respR := bufio.NewReader(rc)
	respTP := textproto.NewReader(respR)
	proto, code, status, ok := parseFirstLine(respTP)
	if !ok {
		return
	}

	respHeader, err := respTP.ReadMIMEHeader()
	if err != nil {
		log.F("[http] read header error:%s", err)
		return
	}

	respHeader.Set("Proxy-Connection", "close")
	respHeader.Set("Connection", "close")

	var respBuf bytes.Buffer
	writeFirstLine(&respBuf, proto, code, status)
	writeHeaders(&respBuf, respHeader)

	log.F("[http] %s <-> %s, %s", c.RemoteAddr(), tgt, p)
	c.Write(respBuf.Bytes())

	io.Copy(c, respR)

}

func (s *HTTP) servHTTPS(method, requestURI, proto string, c net.Conn) {
	rc, p, err := s.dialer.Dial("tcp", requestURI)
	if err != nil {
		c.Write([]byte(proto))
		c.Write([]byte(" 502 ERROR\r\n\r\n"))
		log.F("[http] %s <-> %s [c], error in dial: %v", c.RemoteAddr(), requestURI, err)
		return
	}

	c.Write([]byte("HTTP/1.1 200 Connection established\r\n\r\n"))

	log.F("[http] %s <-> %s [c], %s", c.RemoteAddr(), requestURI, p)

	_, _, err = conn.Relay(c, rc)
	if err != nil {
		if err, ok := err.(net.Error); ok && err.Timeout() {
			return // ignore i/o timeout
		}
		log.F("relay error: %v", err)
	}
}

// Addr returns forwarder's address
func (s *HTTP) Addr() string {
	if s.addr == "" {
		return s.dialer.Addr()
	}
	return s.addr
}

// NextDialer returns the next dialer
func (s *HTTP) NextDialer(dstAddr string) proxy.Dialer { return s.dialer.NextDialer(dstAddr) }

// Dial connects to the address addr on the network net via the proxy
func (s *HTTP) Dial(network, addr string) (net.Conn, string, error) {
	rc, p, err := s.dialer.Dial(network, s.addr)
	if err != nil {
		log.F("[http] dial to %s error: %s", s.addr, err)
		return nil, p, err
	}

	var buf bytes.Buffer
	buf.Write([]byte("CONNECT " + addr + " HTTP/1.1\r\n"))
	// TODO: add host header for compatibility?
	buf.Write([]byte("Proxy-Connection: Keep-Alive\r\n"))

	if s.user != "" && s.password != "" {
		auth := s.user + ":" + s.password
		buf.Write([]byte("Proxy-Authorization: Basic " + base64.StdEncoding.EncodeToString([]byte(auth)) + "\r\n"))
	}

	// header ended
	buf.Write([]byte("\r\n"))
	_, err = rc.Write(buf.Bytes())
	if err != nil {
		return nil, p, err
	}

	c := conn.NewConn(rc)
	tpr := textproto.NewReader(c.Reader())
	_, code, _, ok := parseFirstLine(tpr)
	if ok && code == "200" {
		tpr.ReadMIMEHeader()
		return c, p, err
	}

	if code == "407" {
		log.F("[http] authencation needed by proxy %s", s.addr)
	} else if code == "405" {
		log.F("[http] 'CONNECT' method not allowed by proxy %s", s.addr)
	}

	return nil, p, errors.New("[http] can not connect remote address: " + addr + ". error code: " + code)
}

// DialUDP connects to the given address via the proxy
func (s *HTTP) DialUDP(network, addr string) (pc net.PacketConn, writeTo net.Addr, err error) {
	return nil, nil, errors.New("http client does not support udp")
}

// parseFirstLine parses "GET /foo HTTP/1.1" OR "HTTP/1.1 200 OK" into its three parts
func parseFirstLine(tp *textproto.Reader) (r1, r2, r3 string, ok bool) {
	line, err := tp.ReadLine()
	if err != nil {
		return
	}

	s1 := strings.Index(line, " ")
	s2 := strings.Index(line[s1+1:], " ")
	if s1 < 0 || s2 < 0 {
		return
	}
	s2 += s1 + 1
	return line[:s1], line[s1+1 : s2], line[s2+1:], true
}

func cleanHeaders(header textproto.MIMEHeader) {
	header.Del("Proxy-Connection")
	header.Del("Connection")
	header.Del("Keep-Alive")
	header.Del("Proxy-Authenticate")
	header.Del("Proxy-Authorization")
	header.Del("TE")
	header.Del("Trailers")
	header.Del("Transfer-Encoding")
	header.Del("Upgrade")
}

func writeFirstLine(buf *bytes.Buffer, s1, s2, s3 string) {
	buf.WriteString(s1 + " " + s2 + " " + s3 + "\r\n")
}

func writeHeaders(buf *bytes.Buffer, header textproto.MIMEHeader) {
	for key, values := range header {
		for _, v := range values {
			buf.WriteString(key + ": " + v + "\r\n")
		}
	}
	buf.WriteString("\r\n")
}