package main

import (
	"crypto/rand"
	"crypto/tls"
	"crypto/x509"
	"encoding/base64"
	"encoding/pem"
	"fmt"
	"io/ioutil"
	"net/http"
	"os"
	"os/signal"
	"strings"
	"syscall"
	"time"

	"github.com/BurntSushi/toml"
	"github.com/gorilla/csrf"
	"github.com/nicksnyder/go-i18n/v2/i18n"
	log "github.com/sirupsen/logrus"
	"golang.org/x/text/language"

	"git.dittberner.info/jan/browser_csr_generation/handlers"
)

func main() {
	tlsConfig := &tls.Config{
		CipherSuites: []uint16{
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
		},
		NextProtos:               []string{"h2"},
		PreferServerCipherSuites: true,
		MinVersion:               tls.VersionTLS12,
	}

	bundle := loadI18nBundle()
	mux := http.NewServeMux()

	csrfKey := initCSRFKey()

	signingRequestRegistry := handlers.NewSigningRequestRegistry(loadCACertificates())
	mux.Handle("/sign/", handlers.NewCertificateSigningHandler(signingRequestRegistry))
	mux.Handle("/", handlers.NewIndexHandler(bundle))
	fileServer := http.FileServer(http.Dir("./public"))
	mux.Handle("/css/", fileServer)
	mux.Handle("/js/", fileServer)
	mux.Handle("/locales/", handlers.NewJSLocalesHandler(bundle))
	mux.Handle("/ws/", handlers.NewWebSocketHandler(signingRequestRegistry))
	server := http.Server{
		Addr:              ":8000",
		Handler:           csrf.Protect(csrfKey, csrf.FieldName("csrfToken"), csrf.RequestHeader("X-CSRF-Token"))(mux),
		TLSConfig:         tlsConfig,
		ReadTimeout:       20 * time.Second,
		ReadHeaderTimeout: 5 * time.Second,
		WriteTimeout:      30 * time.Second,
		IdleTimeout:       30 * time.Second,
	}
	go func() {
		err := server.ListenAndServeTLS("server.crt.pem", "server.key.pem")
		if err != nil {
			log.Fatal(err)
		}
	}()
	var hostPort string
	if strings.HasPrefix(server.Addr, ":") {
		hostPort = fmt.Sprintf("localhost%s", server.Addr)
	} else {
		hostPort = server.Addr
	}
	log.Infof("started web server on https://%s/", hostPort)
	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
	s := <-c
	log.Infof("received %s, shutting down", s)
	_ = server.Close()
}

func loadI18nBundle() *i18n.Bundle {
	bundle := i18n.NewBundle(language.English)
	bundle.RegisterUnmarshalFunc("toml", toml.Unmarshal)
	for _, lang := range []string{"en-US", "de-DE"} {
		if _, err := bundle.LoadMessageFile(fmt.Sprintf("active.%s.toml", lang)); err != nil {
			log.Panic(err)
		}
	}
	return bundle
}

func initCSRFKey() []byte {
	var csrfKey []byte = nil

	if csrfB64, exists := os.LookupEnv("CSRF_KEY"); exists {
		csrfKey, _ = base64.RawStdEncoding.DecodeString(csrfB64)
		log.Info("read CSRF key from environment variable")
	}
	if csrfKey == nil {
		csrfKey = generateRandomBytes(32)
		log.Infof(
			"generated new random CSRF key, set environment variable CSRF_KEY to %s to "+
				"keep the same key for new sessions",
			base64.RawStdEncoding.EncodeToString(csrfKey))
	}
	return csrfKey
}

func generateRandomBytes(count int) []byte {
	randomBytes := make([]byte, count)

	_, err := rand.Read(randomBytes)
	if err != nil {
		log.Fatalf("could not read random bytes: %v", err)
		return nil
	}

	return randomBytes
}

func loadCACertificates() (caCertificates []*x509.Certificate) {
	var err error
	caCertificates = make([]*x509.Certificate, 2)
	for index, certFile := range []string{"example_ca/sub/ca.crt.pem", "example_ca/root/ca.crt.pem"} {
		var certBytes []byte
		if certBytes, err = ioutil.ReadFile(certFile); err != nil {
			log.Panic(err)
		}
		var block *pem.Block
		if block, _ = pem.Decode(certBytes); block == nil {
			log.Panicf("no PEM data found in %s", certFile)
			return
		}
		if caCertificates[index], err = x509.ParseCertificate(block.Bytes); err != nil {
			log.Panic(err)
		}
	}
	log.Infof("read %d CA certificates", len(caCertificates))
	return
}