package main

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"flag"
	"io"
	"log"
	"math/big"
	"net"
	"net/http"
	"os"
	"time"

	"fmt"
)

func exists(path string) bool {
	_, err := os.Stat(path)
	return err == nil
}

func generateCert(host string) (string, string) {
	var err error

	dir := "/tmp/https-certs/" + host + "/"
	certPath := dir + "cert.pem"
	keyPath := dir + "key.pem"

	if exists(certPath) && exists(keyPath) {
		return certPath, keyPath
	}

	log.Println("Generating new certificates...")

	priv, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		log.Fatalf("failed to generate private key: %s", err)
	}

	notBefore := time.Now()
	notAfter := notBefore.Add(365 * 24 * time.Hour)

	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		log.Fatalf("failed to generate serial number: %s", err)
	}

	template := x509.Certificate{
		IsCA: true,

		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{"Acme Co"},
		},
		NotBefore: notBefore,
		NotAfter:  notAfter,

		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	if ip := net.ParseIP(host); ip != nil {
		template.IPAddresses = append(template.IPAddresses, ip)
	} else {
		template.DNSNames = append(template.DNSNames, host)
	}

	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
	if err != nil {
		log.Fatalf("Failed to create certificate: %s", err)
	}

	err = os.MkdirAll(dir, 0700)
	if err != nil {
		log.Fatalf("Failed to write certificates: %s", err)
	}

	certOut, err := os.Create(certPath)
	if err != nil {
		log.Fatalf("failed to open cert.pem for writing: %s", err)
	}
	pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
	certOut.Close()

	keyOut, err := os.OpenFile(keyPath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		log.Fatalf("failed to open key.pem for writing: %s", err)
	}

	pem.Encode(keyOut, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)})
	keyOut.Close()
	return certPath, keyPath
}

func handleTunneling(w http.ResponseWriter, r *http.Request) {
	//conf:=&tls.Config{InsecureSkipVerify:true}
	tcpAddr, err := net.ResolveTCPAddr("tcp", r.Host)
	if err != nil {
		println("ResolveTCPAddr failed:", err.Error())
		return
	}
	//investigate why net.Dial keeps failing while DialTCP works
	dest_conn, err := net.DialTCP("tcp", nil, tcpAddr)
	if err != nil {
		fmt.Println("Connection failed to dest server")
		http.Error(w, "Cant connect to dest", http.StatusServiceUnavailable)
		return
	}
	//respond the server
	w.WriteHeader(http.StatusOK)

	//Investigate why cant create client with http.Transport with proxy
	//transport := http.Transport{
	//	Proxy:           http.ProxyURL(proxyURL),
	//	TLSClientConfig: &tls.Config{},
	//}
	//Just use http.Hijacker
	hijacker, ok := w.(http.Hijacker)
	if !ok {
		http.Error(w, "Hijacking not supported", http.StatusInternalServerError)
		return
	}
	client_conn, _, err := hijacker.Hijack()
	if err != nil {
		fmt.Println("Client ERROR")
		http.Error(w, err.Error(), http.StatusServiceUnavailable)
	}
	//Let the proxy begin
	go transfer(dest_conn, client_conn)
	go transfer(client_conn, dest_conn)
}
func transfer(destination io.WriteCloser, source io.ReadCloser) {
	defer destination.Close()
	defer source.Close()
	//Copy the data
	io.Copy(destination, source)

}

//Regular HTTP PRoxy
func handleHTTP(w http.ResponseWriter, req *http.Request) {
	resp, err := http.DefaultTransport.RoundTrip(req)
	if err != nil {
		http.Error(w, err.Error(), http.StatusServiceUnavailable)
		return
	}
	defer resp.Body.Close()
	copyHeader(w.Header(), resp.Header)
	w.WriteHeader(resp.StatusCode)
	io.Copy(w, resp.Body)
}
func copyHeader(dst, src http.Header) {
	for k, vv := range src {
		for _, v := range vv {
			dst.Add(k, v)
		}
	}
}
func main() {

	var proto string
	flag.StringVar(&proto, "proto", "http", "Proxy protocol (http or https)")
	flag.Parse()
	if proto != "http" && proto != "https" {
		log.Fatal("Protocol must be either http or https")
	}
	host := "165.227.74.36"
	cert, key := generateCert(host)

	server := &http.Server{
		Addr: ":9000",

		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			if r.Method == http.MethodConnect {
				handleTunneling(w, r)
			} else {
				handleHTTP(w, r)
			}
		}),
		// Disable HTTP/2.
		TLSNextProto: make(map[string]func(*http.Server, *tls.Conn, http.Handler)),
	}
	if proto == "http" {
		log.Fatal(server.ListenAndServe())
	} else {
		log.Fatal(server.ListenAndServeTLS(cert, key))
	}
}