package kademlia

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Generate a self-signed X.509 certificate for a TLS server. Outputs to
// 'cert.pem' and 'key.pem' and will overwrite existing files.

import (
	"crypto/ecdsa"
	"crypto/ed25519"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"flag"
	"log"
	"math/big"
	"net"
	"os"
	"strings"
	"time"
)

func publicKey(priv any) any {
	switch k := priv.(type) {
	case *rsa.PrivateKey:
		return &k.PublicKey
	case *ecdsa.PrivateKey:
		return &k.PublicKey
	case ed25519.PrivateKey:
		return k.Public().(ed25519.PublicKey)
	default:
		return nil
	}
}

func GenerateCert(host, certOutFile, keyOutFile string) {
	flag.Parse()

	if len(host) == 0 {
		log.Fatalf("Missing required --host parameter")
	}

	var priv any
	var err error
	priv, err = ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		log.Fatalf("Failed to generate private key: %v", err)
	}

	// ECDSA, ED25519 and RSA subject keys should have the DigitalSignature
	// KeyUsage bits set in the x509.Certificate template
	keyUsage := x509.KeyUsageDigitalSignature

	var notBefore time.Time
	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{"DHT inc"},
		},
		NotBefore: notBefore,
		NotAfter:  notAfter,

		KeyUsage:              keyUsage,
		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)
		}
	}

	template.IsCA = true
	template.KeyUsage |= x509.KeyUsageCertSign

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

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

	keyOut, err := os.OpenFile(keyOutFile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		log.Fatalf("Failed to open %s for writing: %v", keyOutFile, err)
	}
	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 %s: %v", keyOutFile, err)
	}
	if err := keyOut.Close(); err != nil {
		log.Fatalf("Error closing %s: %v", keyOutFile, err)
	}

}