package certificates

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

func GenerateKeyPair(host string) (*rsa.PrivateKey, []byte, error) {
	priv, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return &rsa.PrivateKey{}, []byte{}, err
	}
	keyUsage := x509.KeyUsageDigitalSignature
	notBefore := time.Now()
	notAfter := notBefore.Add(time.Hour * 24 * 365 * 5) // five yearss
	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		return &rsa.PrivateKey{}, []byte{}, err
	}

	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{"Castor Server"},
		},
		NotBefore:             notBefore,
		NotAfter:              notAfter,
		KeyUsage:              keyUsage,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	hosts := strings.Split(host, ",")
	for _, h := range hosts {
		if ip := net.ParseIP(h); ip != nil {
			template.IPAddresses = append(template.IPAddresses, ip)
		} else {
			template.DNSNames = append(template.DNSNames, h)
		}
	}

	bytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
	if err != nil {
		return &rsa.PrivateKey{}, []byte{}, err
	}
	return priv, bytes, nil
}

func TestCertificateExists(certname, keyname string) error {
	_, err := os.Stat(certname)
	if err != nil {
		return fmt.Errorf("Could not open %s; %w", certname, err)
	}
	_, err = os.Stat(keyname)
	if err != nil {
		return fmt.Errorf("Could not open %s; %w", keyname, err)
	}
	return nil
}

func WriteCertsToFile(certname, keyname string, cert []byte, privkey *rsa.PrivateKey) error {
	certOut, err := os.Create(certname)
	if err != nil {
		return fmt.Errorf("Failed to open %s for writing: %w", certname, err)
	}
	if err := pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: cert}); err != nil {
		return fmt.Errorf("Failed to write data to %s: %w", certname, err)
	}
	if err := certOut.Close(); err != nil {
		return fmt.Errorf("Error closing %s: %w", certname, err)
	}
	keyOut, err := os.OpenFile(keyname, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		return fmt.Errorf("Failed to open %s for writing: %w", keyname, err)
	}
	privBytes, err := x509.MarshalPKCS8PrivateKey(privkey)
	if err != nil {
		return fmt.Errorf("Unable to marshal private key: %v", err)
	}
	if err := pem.Encode(keyOut, &pem.Block{Type: "PRIVATE KEY", Bytes: privBytes}); err != nil {
		return fmt.Errorf("Failed to write data to %s: %v", keyname, err)
	}
	if err := keyOut.Close(); err != nil {
		return fmt.Errorf("Error closing %s: %v", keyname, err)
	}
	return nil
}