package main

import (
	"crypto/x509"
	"encoding/json"
	"encoding/pem"
	"flag"
	"fmt"
	"io/ioutil"
	"os"
)

func main() {
	jsonOut := flag.Bool("json", false, "output JSON with all certs/fields")
	flag.Parse()
	if flag.NArg() < 1 {
		fmt.Println("usage: certinfo [--json] <foo.crt>")
		os.Exit(2)
	}
	path := flag.Arg(0)

	certs, err := ParseCertinfo(path)
	if err != nil {
		fmt.Println("parse error:", err)
		os.Exit(1)
	}
	if *jsonOut {
		jsonBytes, err := json.Marshal(certs)
		if err != nil {
			fmt.Println("marshal error:", err)
			os.Exit(1)
		}
		fmt.Println(string(jsonBytes))
		return
	}

	// Usually just the first one is interesting
	cert := certs[0]

	fmt.Println("Subject:", cert.Subject.String())
	fmt.Println("Issuer:", cert.Issuer.String())
	fmt.Println("Serial:", cert.SerialNumber.String())
	fmt.Println("NotBefore:", cert.NotBefore)
	fmt.Println("NotAfter:", cert.NotAfter)
	if len(cert.DNSNames) > 0 {
		fmt.Println("DNS SANs:", cert.DNSNames)
	}
	fmt.Println("Signature Algorithm:", cert.SignatureAlgorithm)
	fmt.Println("Public Key Algorithm:", cert.PublicKeyAlgorithm)
}

func ParseCertinfo(filename string) ([]*x509.Certificate, error) {
	data, err := ioutil.ReadFile(filename)
	if err != nil {
		return nil, err
	}

	var certs []*x509.Certificate
	for {
		var block *pem.Block
		block, data = pem.Decode(data)
		if block == nil {
			break
		}
		if block.Type != "CERTIFICATE" {
			fmt.Fprintf(os.Stderr, "warning: Ignoring block type: %s\n", block.Type)
			continue
		}
		cert, err := x509.ParseCertificate(block.Bytes)
		if err != nil {
			return nil, err
		}
		certs = append(certs, cert)
	}
	return certs, nil
}