package tls

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"log"
	"math/big"
	"net"
	"time"
)

func pemBlockForKey(priv interface{}) *pem.Block {
	switch k := priv.(type) {
	case *ecdsa.PrivateKey:
		b, err := x509.MarshalECPrivateKey(k)
		if err != nil {
			log.Fatal(err)
		}
		return &pem.Block{Type: "EC PRIVATE KEY", Bytes: b}
	default:
		return nil
	}
}

func generate() ([]byte, crypto.PrivateKey, error) {
	hosts := []string{"localhost"}

	var err error
	privateKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to generate private key: %s", err)
	}

	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 {
		return nil, nil, fmt.Errorf("failed to generate serial number: %s", err)
	}

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

		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		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)
		}
	}

	certBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &privateKey.PublicKey, privateKey)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to create certificate: %s", err)
	}
	return certBytes, privateKey, nil
}

// generatePEM generates a new certificate and key and returns it as PEM encoded bytes
func generatePEM() ([]byte, []byte, error) {
	certBytes, privateKey, err := generate()
	if err != nil {
		return nil, nil, err
	}
	certpem := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certBytes})
	keypem := pem.EncodeToMemory(pemBlockForKey(privateKey))
	return certpem, keypem, nil
}

// GenerateX509KeyPair generates a X509 key pair
func GenerateX509KeyPair() (*tls.Certificate, error) {
	certpem, keypem, err := generatePEM()
	if err != nil {
		return nil, err
	}
	cert, err := tls.X509KeyPair(certpem, keypem)
	if err != nil {
		return nil, err
	}
	return &cert, nil
}

func certTemplate(org string, hosts []string, notAfter time.Time) (*x509.Certificate, error) {
	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		return nil, fmt.Errorf("failed to generate serial number, %w", err)
	}
	return &x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{org},
		},
		SignatureAlgorithm:    x509.SHA256WithRSA,
		NotBefore:             time.Now(),
		NotAfter:              notAfter,
		BasicConstraintsValid: true,
		DNSNames:              hosts,
	}, nil
}

func createCACertTemplate(org string, hosts []string, notAfter time.Time) (*x509.Certificate, error) {
	rootCert, err := certTemplate(org, hosts, notAfter)
	if err != nil {
		return nil, err
	}
	rootCert.IsCA = true
	rootCert.KeyUsage = x509.KeyUsageCertSign | x509.KeyUsageDigitalSignature
	rootCert.ExtKeyUsage = []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth}
	return rootCert, nil
}

// Sign the cert
func createCert(template, parent *x509.Certificate, pub, parentPriv interface{}) (
	cert *x509.Certificate, certPEM []byte, err error) {
	certDER, err := x509.CreateCertificate(rand.Reader, template, parent, pub, parentPriv)
	if err != nil {
		return
	}
	cert, err = x509.ParseCertificate(certDER)
	if err != nil {
		return
	}
	b := pem.Block{Type: "CERTIFICATE", Bytes: certDER}
	certPEM = pem.EncodeToMemory(&b)
	return
}

func createCA(org string, hosts []string, notAfter time.Time) (*rsa.PrivateKey, *x509.Certificate, []byte, error) {
	rootKey, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return nil, nil, nil, fmt.Errorf("failed to generate random key, %w", err)
	}

	rootCertTmpl, err := createCACertTemplate(org, hosts, notAfter)
	if err != nil {
		return nil, nil, nil, fmt.Errorf("failed to generate CA cert, %w", err)
	}

	rootCert, rootCertPEM, err := createCert(rootCertTmpl, rootCertTmpl, &rootKey.PublicKey, rootKey)
	if err != nil {
		return nil, nil, nil, fmt.Errorf("failed to sign CA cert, %w", err)
	}
	return rootKey, rootCert, rootCertPEM, nil
}

// CreateCerts creates and returns a CA certificate and certificate and key
// if server==true, generate these for a server
// if client==true, generate these for a client
// can generate for both server and client but at least one must be specified
func CreateCerts(org string, hosts []string, notAfter time.Time, server bool, client bool) (serverKey, serverCert, caCert []byte, err error) {
	if !server && !client {
		return nil, nil, nil, fmt.Errorf("CreateCerts() must specify either server or client")
	}

	// Create a CA certificate and private key
	caKey, caCertificate, caCertificatePEM, err := createCA(org, hosts, notAfter)
	if err != nil {
		return nil, nil, nil, err
	}

	// Create the private key
	privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return nil, nil, nil, fmt.Errorf("failed to generate random key, %w", err)
	}
	var cert *x509.Certificate

	cert, err = certTemplate(org, hosts, notAfter)
	if err != nil {
		return nil, nil, nil, err
	}
	cert.KeyUsage = x509.KeyUsageDigitalSignature
	if server {
		cert.ExtKeyUsage = append(cert.ExtKeyUsage, x509.ExtKeyUsageServerAuth)
	}
	if client {
		cert.ExtKeyUsage = append(cert.ExtKeyUsage, x509.ExtKeyUsageClientAuth)
	}

	// create a certificate wrapping the public key, sign it with the CA private key
	_, certPEM, err := createCert(cert, caCertificate, &privateKey.PublicKey, caKey)
	if err != nil {
		return nil, nil, nil, fmt.Errorf("failed to sign server cert, %w", err)
	}
	privateKeyPEM := pem.EncodeToMemory(&pem.Block{
		Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(privateKey),
	})
	return privateKeyPEM, certPEM, caCertificatePEM, nil
}
