package main

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"log"
	"math/big"
	"net"
	"os"
	"strings"
	"time"
)

func GenerateCert(host string, validFrom string, validFor time.Duration, isCA bool, rsaBits int) {
	if len(host) == 0 {
		log.Fatalf("Missing required -host parameter")
	}

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

	var notBefore time.Time
	if len(validFrom) == 0 {
		notBefore = time.Now()
	} else {
		notBefore, err = time.Parse("Jan 2 15:04:05 2006", validFrom)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Failed to parse creation date: %s\n", err)
			return
		}
	}

	notAfter := notBefore.Add(validFor)

	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)
		return
	}

	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{"I2P"},
		},
		NotBefore: notBefore,
		NotAfter:  notAfter,

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

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

	if isCA {
		template.IsCA = true
		template.KeyUsage |= x509.KeyUsageCertSign
	}

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

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

	keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		log.Print("failed to open key.pem for writing:", err)
		return
	}
	pem.Encode(keyOut, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)})
	keyOut.Close()
	log.Print("written key.pem\n")
}