package tls

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

func CreateCertificate() (*tls.Certificate, error) {
	// 1. Generate an RSA private key
	privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return nil, err
	}

	// 2. Define the certificate template
	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{"home"},
			CommonName:   "localhost",
		},
		NotBefore: time.Now(),
		NotAfter:  time.Now().Add(365 * 24 * time.Hour), // Valid for 1 year

		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,

		// Add localhost as a valid IP and DNS name
		IPAddresses: []net.IP{[]byte{127, 0, 0, 1}},
		DNSNames:    []string{"localhost"},
	}

	// 3. Create a self-signed certificate
	// The parent is the template itself, and we use the generated public and private keys.
	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &privateKey.PublicKey, privateKey)
	if err != nil {
		return nil, err
	}

	derBytes = pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
	keyBytes := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(privateKey)})

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

	return &cert, nil
}