package acme

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"math/big"
	"time"
)

func generatePrivateKey(keyLength int) (*rsa.PrivateKey, error) {
	return rsa.GenerateKey(rand.Reader, keyLength)
}

func generateCsr(privateKey *rsa.PrivateKey, domain string) ([]byte, error) {
	template := x509.CertificateRequest{
		Subject: pkix.Name{
			CommonName: domain,
		},
	}

	return x509.CreateCertificateRequest(rand.Reader, &template, privateKey)
}

func pemEncode(data interface{}) []byte {
	var pemBlock *pem.Block
	switch key := data.(type) {
	case *rsa.PrivateKey:
		pemBlock = &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(key)}
	}

	return pem.EncodeToMemory(pemBlock)
}

// GetCertExpiration returns the "NotAfter" date of a DER encoded certificate.
func GetCertExpiration(cert []byte) (time.Time, error) {
	pCert, err := x509.ParseCertificate(cert)
	if err != nil {
		return time.Time{}, err
	}

	return pCert.NotAfter, 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
	}

	zero := time.Time{}
	if expiration == zero {
		expiration = time.Now().Add(365)
	}

	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			CommonName: "ACME Challenge TEMP",
		},
		NotBefore: time.Now(),
		NotAfter:  expiration,

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

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