package selfcert

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

func NewTLSConfig(hosts []string) (*tls.Config, error) {
	priv, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return nil, err
	}

	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)

	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		return nil, err
	}

	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{"Acme Co"},
		},
		NotBefore:             time.Now(),
		NotAfter:              time.Now().Add(10 * 365 * 24 * time.Hour),
		KeyUsage:              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, &priv.PublicKey, priv)
	if err != nil {
		return nil, err
	}

	certPem := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certBytes})

	keyBytes, err := x509.MarshalPKCS8PrivateKey(priv)
	if err != nil {
		return nil, err
	}

	keyPem := pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: keyBytes})

	cert, err := tls.X509KeyPair(certPem, keyPem)
	if err != nil {
		return nil, err
	}

	conf := &tls.Config{
		Certificates: []tls.Certificate{cert},
		MinVersion:   tls.VersionTLS13,
		NextProtos:   []string{"h2"},
	}

	return conf, nil
}

func NewTLSConfigFromHostPort(hostport string) (*tls.Config, error) {
	host, _, err := net.SplitHostPort(hostport)
	if err != nil {
		return nil, err
	}

	return NewTLSConfig([]string{host})
}