package main

import (
	"bytes"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"flag"
	"fmt"
	"math/big"
	"net/http"
	"os"
	"os/signal"
	"regexp"
	"runtime"
	"strings"
	"time"

	"git.sati.ac/sati.ac/bridge/api"
	"git.sati.ac/sati.ac/bridge/config"
	"git.sati.ac/sati.ac/sati-go"
	"github.com/sirupsen/logrus"
)

type bridge struct {
	config *config.Config
}

func issueCACert(certPath string, keyPath string) error {
	cert := &x509.Certificate{
		SerialNumber: big.NewInt(0),
		Subject: pkix.Name{
			CommonName:   "Bridge CA",
			Country:      []string{"VA"},
			Organization: []string{"sati.ac"},
			Locality:     []string{"Everywhere"},
		},
		NotBefore:             time.Now(),
		NotAfter:              time.Now().AddDate(100, 0, 0),
		IsCA:                  true,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
		BasicConstraintsValid: true,
	}
	keys, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return err
	}

	der, err := x509.CreateCertificate(rand.Reader, cert, cert, &keys.PublicKey, keys)
	if err != nil {
		return err
	}

	certFile, err := os.OpenFile(certPath, os.O_CREATE|os.O_WRONLY, 0600)
	if err != nil {
		return err
	}
	defer certFile.Close()

	if err := pem.Encode(certFile, &pem.Block{
		Type:  "CERTIFICATE",
		Bytes: der,
	}); err != nil {
		return err
	}

	keyFile, err := os.OpenFile(keyPath, os.O_CREATE|os.O_WRONLY, 0600)
	if err != nil {
		return err
	}
	defer keyFile.Close()

	if err := pem.Encode(keyFile, &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(keys),
	}); err != nil {
		return err
	}

	return nil
}

func issueCert(domains []string, caCertPath string, caKeyPath string) (string, string, error) {
	cert := &x509.Certificate{
		SerialNumber: big.NewInt(time.Now().Unix()),
		Subject: pkix.Name{
			Country:            []string{"VA"},
			Organization:       []string{"sati.ac"},
			OrganizationalUnit: []string{"Bridge ephemeral certificate"},
			Locality:           []string{"Everywhere"},
		},
		DNSNames:     domains,
		NotBefore:    time.Now(),
		NotAfter:     time.Now().AddDate(100, 0, 0),
		SubjectKeyId: []byte{0},
		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth, x509.ExtKeyUsageServerAuth},
		KeyUsage:     x509.KeyUsageDigitalSignature,
	}

	keys, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return "", "", err
	}

	caCertPem, err := os.ReadFile(caCertPath)
	if err != nil {
		return "", "", err
	}
	block, _ := pem.Decode(caCertPem)
	if block == nil || block.Type != "CERTIFICATE" {
		return "", "", fmt.Errorf(`certificate: bad pem block "%s"`, block.Type)
	}
	caCert, err := x509.ParseCertificate(block.Bytes)
	if err != nil {
		return "", "", err
	}

	caKeyPem, err := os.ReadFile(caKeyPath)
	if err != nil {
		return "", "", err
	}
	block, _ = pem.Decode(caKeyPem)
	if block == nil || block.Type != "RSA PRIVATE KEY" {
		return "", "", fmt.Errorf(`key: bad pem block "%s"`, block.Type)
	}
	caKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
	if err != nil {
		return "", "", err
	}

	der, err := x509.CreateCertificate(rand.Reader, cert, caCert, &keys.PublicKey, caKey)
	if err != nil {
		return "", "", err
	}

	certFile, err := os.CreateTemp("", "bridge*.crt")
	if err != nil {
		return "", "", err
	}
	defer certFile.Close()
	keyFile, err := os.CreateTemp("", "bridge*.key")
	if err != nil {
		return "", "", err
	}
	defer keyFile.Close()

	if err := pem.Encode(certFile, &pem.Block{
		Type:  "CERTIFICATE",
		Bytes: der,
	}); err != nil {
		return "", "", err
	}

	if err := pem.Encode(keyFile, &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(keys),
	}); err != nil {
		return "", "", err
	}

	return certFile.Name(), keyFile.Name(), nil
}

func getHostsPath() (string, error) {
	switch runtime.GOOS {
	case "freebsd":
		fallthrough
	case "openbsd":
		fallthrough
	case "dragonfly":
		fallthrough
	case "netbsd":
		fallthrough
	case "darwin":
		fallthrough
	case "android":
		fallthrough
	case "linux":
		return "/etc/hosts", nil
	case "windows":
		return `C:\Windows\System32\drivers\etc\hosts`, nil
	}

	return "", fmt.Errorf("unknown os: %s", runtime.GOOS)
}

var hostsModRE = regexp.MustCompile("(?:\n|\r\n|\r)#sati-bridge start, DO NOT MODIFY(?:\n|\r\n|\r)[^#]*(?:\n|\r\n|\r)#sati-bridge end")

var configPath = flag.String("config", "./data/config.json", "config path")

func addDomainsToHosts(ctx *api.ApiContext) error {
	ctx.Logger.Info("adding domains to hosts")
	path, err := getHostsPath()
	if err != nil {
		ctx.Logger.WithError(err).Warn("unable to get hosts path")
		return err
	}

	hosts, err := os.ReadFile(path)
	if err != nil {
		ctx.Logger.WithError(err).Warn("unable to read hosts file")
		return err
	}

	hosts = hostsModRE.ReplaceAll(hosts, []byte{}) // remove old entries

	hostIp := "127.0.0.1"
	suffix := "\r\n#sati-bridge start, DO NOT MODIFY\r\n"
	for _, domain := range ctx.Server.GetDomains() {
		suffix += hostIp + " " + domain + "\r\n"
	}
	suffix += "#sati-bridge end\r\n"
	hosts = []byte(strings.TrimRight(string(hosts), "\r\n\t ") + suffix)

	err = os.WriteFile(path, hosts, 0644)
	if err != nil {
		ctx.Logger.WithError(err).Warn("unable to write hosts file")
	}

	return err
}

func removeDomainsFromHosts(ctx *api.ApiContext) error {
	ctx.Logger.Info("removing domains from hosts")
	path, err := getHostsPath()
	if err != nil {
		ctx.Logger.WithError(err).Warn("unable to get hosts path")
		return err
	}

	hosts, err := os.ReadFile(path)
	if err != nil {
		ctx.Logger.WithError(err).Warn("unable to read hosts file")
		return err
	}

	hosts = hostsModRE.ReplaceAll(hosts, []byte{})
	hosts = bytes.TrimRight(hosts, "\r\n\t ")

	err = os.WriteFile(path, hosts, 0644)
	if err != nil {
		ctx.Logger.WithError(err).Warn("unable to write hosts file")
	}

	return err
}

func main() {
	logger := logrus.New()
	logger.Info("starting")

	cfg := config.Default()
	cfg.Path = *configPath
	if err := cfg.Load(); err != nil {
		logger.Info("failed to load config: ", err.Error(), ". attempting to create new")
		if err := cfg.Save(); err != nil {
			logger.Panic("failed to create config: ", err.Error())
		}
	}

	if cfg.Debug {
		logger.SetLevel(logrus.DebugLevel)
	} else {
		logger.SetLevel(logrus.InfoLevel)
	}

	_, certReadErr := os.Stat(cfg.TlsCertPath)
	_, keyReadErr := os.Stat(cfg.TlsKeyPath)
	if certReadErr != nil || keyReadErr != nil {
		logger.Info("CA certificate or key not found, issuing new")
		err := issueCACert(cfg.TlsCertPath, cfg.TlsKeyPath)
		if err != nil {
			logger.Panic("failed to issue CA certificate: ", err.Error())
		}
	}

	if cfg.Token == "" {
		logger.Fatal("api token not specified, get it at https://sati.ac/dashboard")
	}

	if strings.HasPrefix(cfg.Host, "0.0.0.0:") || strings.HasPrefix(cfg.TlsHost, "0.0.0.0:") {
		logger.Warn("you are trying to listen on all interfaces, THIS IS INSECURE")
	}

	satiConfig := sati.NewConfig(cfg.Token)
	satiConfig.Debug = cfg.Debug
	satiApi := sati.NewApi(satiConfig)

	registry := api.NewTaskRegistry(satiApi, time.Minute)

	ctx := api.ApiContext{
		Config:   cfg,
		Api:      satiApi,
		Registry: registry,
		Logger:   logger,
	}

	server := api.NewApiServer(&ctx)
	ctx.Logger.WithFields(logrus.Fields{
		"domains": server.GetDomains(),
	}).Debug("api server created")

	logger.Info("issuing ephemeral certificate")
	certFile, keyFile, err := issueCert(server.GetDomains(), cfg.TlsCertPath, cfg.TlsKeyPath)
	if err != nil {
		logger.Panic(err)
	}
	defer os.Remove(certFile)
	defer os.Remove(keyFile)

	if addDomainsToHosts(&ctx) == nil {
		defer removeDomainsFromHosts(&ctx)
	}

	logger.Info("starting api server")

	terminator := make(chan error)
	go func() { terminator <- http.ListenAndServe(cfg.Host, server) }()
	go func() { terminator <- http.ListenAndServeTLS(cfg.TlsHost, certFile, keyFile, server) }()

	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt)
	go func() {
		<-c
		terminator <- fmt.Errorf("interrupted")
	}()

	logger.Error(<-terminator)
}