package crypto

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"math/big"
	"net"
	"os"
	"time"

	log "github.com/sirupsen/logrus"
)

func GenerateKeypair(hosts []string) {
	priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		log.Fatalf("Failed to generate private key: %v", err)
	}

	keyUsage := x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment

	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: %v", err)
	}

	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{"BeryJu.org"},
		},
		NotBefore: notBefore,
		NotAfter:  notAfter,

		KeyUsage:              keyUsage,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	for _, h := range hosts {
		if ip := net.ParseIP(h); ip != nil {
			template.IPAddresses = append(template.IPAddresses, ip)
		} else {
			template.DNSNames = append(template.DNSNames, h)
		}
	}

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

	certOut, err := os.Create("cert.pem")
	if err != nil {
		log.Fatalf("Failed to open cert.pem for writing: %v", err)
	}
	if err := pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
		log.Fatalf("Failed to write data to cert.pem: %v", err)
	}
	if err := certOut.Close(); err != nil {
		log.Fatalf("Error closing cert.pem: %v", err)
	}
	log.Print("wrote cert.pem\n")

	keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		log.Fatalf("Failed to open key.pem for writing: %v", err)
		return
	}
	privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
	if err != nil {
		log.Fatalf("Unable to marshal private key: %v", err)
	}
	if err := pem.Encode(keyOut, &pem.Block{Type: "PRIVATE KEY", Bytes: privBytes}); err != nil {
		log.Fatalf("Failed to write data to key.pem: %v", err)
	}
	if err := keyOut.Close(); err != nil {
		log.Fatalf("Error closing key.pem: %v", err)
	}
	log.Print("wrote key.pem\n")
	return
}