package acme

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/hex"
	"encoding/pem"
	"fmt"
	"math/big"
	"time"
)

func generateDefaultCertificate() (*tls.Certificate, error) {
	rsaPrivKey, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return nil, err
	}
	rsaPrivPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(rsaPrivKey)})

	randomBytes := make([]byte, 100)
	_, err = rand.Read(randomBytes)
	if err != nil {
		return nil, err
	}
	zBytes := sha256.Sum256(randomBytes)
	z := hex.EncodeToString(zBytes[:sha256.Size])
	domain := fmt.Sprintf("%s.%s.traefik.default", z[:32], z[32:])
	tempCertPEM, err := generatePemCert(rsaPrivKey, domain)
	if err != nil {
		return nil, err
	}

	certificate, err := tls.X509KeyPair(tempCertPEM, rsaPrivPEM)
	if err != nil {
		return nil, err
	}

	return &certificate, nil
}
func generatePemCert(privKey *rsa.PrivateKey, domain string) ([]byte, error) {
	derBytes, err := generateDerCert(privKey, time.Time{}, domain)
	if err != nil {
		return nil, err
	}

	return pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes}), nil
}

func generateDerCert(privKey *rsa.PrivateKey, expiration time.Time, domain string) ([]byte, error) {
	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		return nil, err
	}

	if expiration.IsZero() {
		expiration = time.Now().Add(365)
	}

	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			CommonName: "TRAEFIK DEFAULT CERT",
		},
		NotBefore: time.Now(),
		NotAfter:  expiration,

		KeyUsage:              x509.KeyUsageKeyEncipherment,
		BasicConstraintsValid: true,
		DNSNames:              []string{domain},
	}

	return x509.CreateCertificate(rand.Reader, &template, &template, &privKey.PublicKey, privKey)
}