package pki

import (
	"crypto/rand"
	"crypto/x509"
	"encoding/pem"
	"errors"
	"fmt"
	"math"
	"math/big"
	"os"
)

// Generates a cyrptographically randon number to be used as a cert serial number.
func NewCertSerialNumber() *big.Int {
	sn, err := rand.Int(rand.Reader, big.NewInt(math.MaxInt64))
	if err != nil {
		panic(errors.New("Could not generate a serial number"))
	}
	return sn
}

// ParseCertFromFile retrieves a certificate stored in PEM format from a file.
func ParseCertFromFile(fn string) (*x509.Certificate, error) {
	pemBytes, err := os.ReadFile(fn)
	if err != nil {
		return nil, err
	}
	certBlock, _ := pem.Decode(pemBytes)
	if certBlock == nil || certBlock.Type != PEMTypeCertificate {
		return nil, fmt.Errorf("file was not PEM or first block wasn't %s", PEMTypeCertificate)
	}

	cert, err := x509.ParseCertificate(certBlock.Bytes)
	if err != nil {
		return nil, err
	}

	return cert, nil
}