/*
Copyright (C) 2021 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3 of the License.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package main

import (
	"bytes"
	"context"
	"crypto"
	"crypto/sha256"
	"crypto/tls"
	"crypto/x509"
	"encoding/hex"
	"flag"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"os/exec"
	"strings"
	"sync"
	"time"

	"github.com/dustin/go-humanize"
	"go.cypherpunks.ru/ucspi"
)

var (
	tlsNextProtoS = make(map[string]func(*http.Server, *tls.Conn, http.Handler))
	tlsNextProtoC = make(map[string]func(string, *tls.Conn) http.RoundTripper)
	caCert        *x509.Certificate
	caPrv         crypto.PrivateKey
	certs         *string
	dnsSrv        *string
	transport     = http.Transport{
		ForceAttemptHTTP2:   false,
		DisableKeepAlives:   true,
		MaxIdleConnsPerHost: 2,
		TLSNextProto:        tlsNextProtoC,
		DialTLSContext:      dialTLS,
	}

	accepted  = make(map[string]string)
	acceptedM sync.RWMutex
	rejected  = make(map[string]string)
	rejectedM sync.RWMutex
)

func spkiHash(cert *x509.Certificate) string {
	hsh := sha256.Sum256(cert.RawSubjectPublicKeyInfo)
	return hex.EncodeToString(hsh[:])
}

func certInfo(certRaw []byte) string {
	cmd := exec.Command("certtool", "--certificate-info", "--inder")
	cmd.Stdin = bytes.NewReader(certRaw)
	out, err := cmd.Output()
	if err == nil {
		return string(out)
	}
	return err.Error()
}

func acceptedAdd(addr, h string) {
	acceptedM.Lock()
	accepted[addr] = h
	acceptedM.Unlock()
}

func rejectedAdd(addr, h string) {
	rejectedM.Lock()
	rejected[addr] = h
	rejectedM.Unlock()
}

type ErrRejected struct {
	addr string
}

func (err ErrRejected) Error() string { return err.addr + " was rejected" }

func dialTLS(ctx context.Context, network, addr string) (net.Conn, error) {
	host := strings.TrimSuffix(addr, ":443")
	cfg := tls.Config{
		VerifyPeerCertificate: func(
			rawCerts [][]byte,
			verifiedChains [][]*x509.Certificate,
		) error {
			return verifyCert(host, nil, rawCerts, verifiedChains)
		},
	}
	conn, dialErr := tls.Dial(network, addr, &cfg)
	if dialErr != nil {
		if _, ok := dialErr.(ErrRejected); ok {
			return nil, dialErr
		}
		cfg.InsecureSkipVerify = true
		cfg.VerifyPeerCertificate = func(
			rawCerts [][]byte,
			verifiedChains [][]*x509.Certificate,
		) error {
			return verifyCert(host, dialErr, rawCerts, verifiedChains)
		}
		var err error
		conn, err = tls.Dial(network, addr, &cfg)
		if err != nil {
			sinkErr <- fmt.Sprintf("%s\t%s", addr, dialErr.Error())
			return nil, err
		}
	}
	connState := conn.ConnectionState()
	sinkTLS <- fmt.Sprintf(
		"%s\t%s %s\t%s",
		strings.TrimSuffix(addr, ":443"),
		ucspi.TLSVersion(connState.Version),
		tls.CipherSuiteName(connState.CipherSuite),
		spkiHash(connState.PeerCertificates[0]),
	)
	return conn, nil
}

func roundTrip(w http.ResponseWriter, req *http.Request) {
	if req.Method == http.MethodHead {
		http.Error(w, "go away", http.StatusMethodNotAllowed)
		return
	}
	sinkReq <- fmt.Sprintf("%s %s", req.Method, req.URL.String())
	host := strings.TrimSuffix(req.URL.Host, ":443")
	for _, spy := range SpyDomains {
		if strings.HasSuffix(host, spy) {
			http.NotFound(w, req)
			sinkOther <- fmt.Sprintf(
				"%s %s\t%d\tspy one",
				req.Method,
				req.URL.String(),
				http.StatusNotFound,
			)
			return
		}
	}
	if strings.HasPrefix(req.URL.Host, "www.reddit.com") {
		req.URL.Host = "old.reddit.com"
		http.Redirect(w, req, req.URL.String(), http.StatusMovedPermanently)
		return
	}
	resp, err := transport.RoundTrip(req)
	if err != nil {
		sinkErr <- fmt.Sprintf("%s\t%s", req.URL.Host, err.Error())
		w.WriteHeader(http.StatusBadGateway)
		w.Write([]byte(err.Error()))
		return
	}
	for k, vs := range resp.Header {
		if k == "Location" || k == "Content-Type" || k == "Content-Length" {
			continue
		}
		for _, v := range vs {
			w.Header().Add(k, v)
		}
	}
	if req.Method == http.MethodGet {
		var redirType string
		switch resp.StatusCode {
		case http.StatusMovedPermanently, http.StatusPermanentRedirect:
			redirType = "permanent"
			goto Redir
		case http.StatusFound, http.StatusSeeOther, http.StatusTemporaryRedirect:
			if strings.Contains(req.Header.Get("User-Agent"), "newsboat/") {
				goto NoRedir
			}
			redirType = "temporary"
		default:
			goto NoRedir
		}
	Redir:
		resp.Body.Close()
		w.Header().Add("Content-Type", "text/html")
		w.WriteHeader(http.StatusOK)
		location := resp.Header.Get("Location")
		w.Write([]byte(
			fmt.Sprintf(
				`<html>
<head><title>%d %s: %s redirection</title></head>
<body>Redirection to <a href="%s">%s</a>
</body></html>`,
				resp.StatusCode, http.StatusText(resp.StatusCode),
				redirType, location, location,
			)))
		sinkRedir <- fmt.Sprintf(
			"%s %s\t%s\t%s", req.Method, resp.Status, req.URL.String(), location,
		)
		return
	}
NoRedir:
	for _, h := range []string{"Location", "Content-Type", "Content-Length"} {
		if v := resp.Header.Get(h); v != "" {
			w.Header().Add(h, v)
		}
	}
	w.WriteHeader(resp.StatusCode)
	n, err := io.Copy(w, resp.Body)
	if err != nil {
		log.Printf("Error during %s: %+v\n", req.URL, err)
	}
	resp.Body.Close()
	msg := fmt.Sprintf(
		"%s %s\t%s\t%s\t%s",
		req.Method,
		req.URL.String(),
		resp.Status,
		resp.Header.Get("Content-Type"),
		humanize.IBytes(uint64(n)),
	)
	if resp.StatusCode == http.StatusOK {
		sinkOK <- msg
	} else {
		sinkOther <- msg
	}
}

type Handler struct{}

func (h *Handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	if req.Method != http.MethodConnect {
		roundTrip(w, req)
		return
	}
	hj, ok := w.(http.Hijacker)
	if !ok {
		log.Fatalln("no hijacking")
	}
	conn, _, err := hj.Hijack()
	if err != nil {
		log.Fatalln(err)
	}
	defer conn.Close()
	conn.Write([]byte(fmt.Sprintf(
		"%s %d %s\r\n\r\n",
		req.Proto,
		http.StatusOK, http.StatusText(http.StatusOK),
	)))
	host := strings.Split(req.Host, ":")[0]
	hostCertsM.Lock()
	keypair, ok := hostCerts[host]
	if !ok || !keypair.cert.NotAfter.After(time.Now().Add(time.Hour)) {
		keypair = newKeypair(host, caCert, caPrv)
		hostCerts[host] = keypair
	}
	hostCertsM.Unlock()
	tlsConn := tls.Server(conn, &tls.Config{
		Certificates: []tls.Certificate{{
			Certificate: [][]byte{keypair.cert.Raw},
			PrivateKey:  keypair.prv,
		}},
	})
	if err = tlsConn.Handshake(); err != nil {
		log.Printf("TLS error %s: %+v\n", host, err)
		return
	}
	srv := http.Server{
		Handler:      &HTTPSHandler{host: req.Host},
		TLSNextProto: tlsNextProtoS,
	}
	err = srv.Serve(&SingleListener{conn: tlsConn})
	if err != nil {
		if _, ok := err.(AlreadyAccepted); !ok {
			log.Printf("TLS serve error %s: %+v\n", host, err)
			return
		}
	}
}

type HTTPSHandler struct {
	host string
}

func (h *HTTPSHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	req.URL.Scheme = "https"
	req.URL.Host = h.host
	roundTrip(w, req)
}

func main() {
	crtPath := flag.String("cert", "cert.pem", "Path to server X.509 certificate")
	prvPath := flag.String("key", "prv.pem", "Path to server PKCS#8 private key")
	bind := flag.String("bind", "[::1]:8080", "Bind address")
	certs = flag.String("certs", "certs", "Directory with pinned certificates")
	dnsSrv = flag.String("dns", "[::1]:53", "DNS server")
	fifos = flag.String("fifos", "fifos", "Directory with FIFOs")
	notai = flag.Bool("notai", false, "Do not prepend TAI64N to logs")
	flag.Parse()
	log.SetFlags(log.Lshortfile)
	fifoInit()

	var err error
	_, caCert, err = ucspi.CertificateFromFile(*crtPath)
	if err != nil {
		log.Fatalln(err)
	}
	caPrv, err = ucspi.PrivateKeyFromFile(*prvPath)
	if err != nil {
		log.Fatalln(err)
	}

	ln, err := net.Listen("tcp", *bind)
	if err != nil {
		log.Fatalln(err)
	}
	srv := http.Server{
		Handler:      &Handler{},
		TLSNextProto: tlsNextProtoS,
	}
	srv.SetKeepAlivesEnabled(false)
	log.Println("listening:", *bind)
	if err := srv.Serve(ln); err != nil {
		log.Fatalln(err)
	}
}