package main

import (
	"context"
	"crypto"
	"crypto/rand"
	"crypto/sha1"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"flag"
	"fmt"
	"math/big"
	"os"
	"time"

	"github.com/smallstep/certificates/kms/apiv1"
	"github.com/smallstep/certificates/kms/awskms"
	"go.step.sm/cli-utils/fileutil"
	"go.step.sm/cli-utils/ui"
	"go.step.sm/crypto/pemutil"
	"golang.org/x/crypto/ssh"
)

func main() {
	var credentialsFile, region string
	var ssh bool
	flag.StringVar(&credentialsFile, "credentials-file", "", "Path to the `file` containing the AWS KMS credentials.")
	flag.StringVar(&region, "region", "", "AWS KMS region name.")
	flag.BoolVar(&ssh, "ssh", false, "Create SSH keys.")
	flag.Usage = usage
	flag.Parse()

	c, err := awskms.New(context.Background(), apiv1.Options{
		Type:            string(apiv1.AmazonKMS),
		Region:          region,
		CredentialsFile: credentialsFile,
	})
	if err != nil {
		fatal(err)
	}

	if err := createX509(c); err != nil {
		fatal(err)
	}

	if ssh {
		ui.Println()
		if err := createSSH(c); err != nil {
			fatal(err)
		}
	}
}

func fatal(err error) {
	fmt.Fprintln(os.Stderr, err)
	os.Exit(1)
}

func usage() {
	fmt.Fprintln(os.Stderr, "Usage: step-awskms-init")
	fmt.Fprintln(os.Stderr, `
The step-awskms-init command initializes a public key infrastructure (PKI)
to be used by step-ca.

This tool is experimental and in the future it will be integrated in step cli.

OPTIONS`)
	fmt.Fprintln(os.Stderr)
	flag.PrintDefaults()
	fmt.Fprintln(os.Stderr, `
COPYRIGHT

  (c) 2018-2020 Smallstep Labs, Inc.`)
	os.Exit(1)
}

func createX509(c *awskms.KMS) error {
	ui.Println("Creating X.509 PKI ...")

	// Root Certificate
	resp, err := c.CreateKey(&apiv1.CreateKeyRequest{
		Name:               "root",
		SignatureAlgorithm: apiv1.ECDSAWithSHA256,
	})
	if err != nil {
		return err
	}

	signer, err := c.CreateSigner(&resp.CreateSignerRequest)
	if err != nil {
		return err
	}

	now := time.Now()
	root := &x509.Certificate{
		IsCA:                  true,
		NotBefore:             now,
		NotAfter:              now.Add(time.Hour * 24 * 365 * 10),
		KeyUsage:              x509.KeyUsageCertSign | x509.KeyUsageCRLSign,
		BasicConstraintsValid: true,
		MaxPathLen:            1,
		MaxPathLenZero:        false,
		Issuer:                pkix.Name{CommonName: "Smallstep Root"},
		Subject:               pkix.Name{CommonName: "Smallstep Root"},
		SerialNumber:          mustSerialNumber(),
		SubjectKeyId:          mustSubjectKeyID(resp.PublicKey),
		AuthorityKeyId:        mustSubjectKeyID(resp.PublicKey),
	}

	b, err := x509.CreateCertificate(rand.Reader, root, root, resp.PublicKey, signer)
	if err != nil {
		return err
	}

	if err = fileutil.WriteFile("root_ca.crt", pem.EncodeToMemory(&pem.Block{
		Type:  "CERTIFICATE",
		Bytes: b,
	}), 0600); err != nil {
		return err
	}

	ui.PrintSelected("Root Key", resp.Name)
	ui.PrintSelected("Root Certificate", "root_ca.crt")

	root, err = pemutil.ReadCertificate("root_ca.crt")
	if err != nil {
		return err
	}

	// Intermediate Certificate
	resp, err = c.CreateKey(&apiv1.CreateKeyRequest{
		Name:               "intermediate",
		SignatureAlgorithm: apiv1.ECDSAWithSHA256,
	})
	if err != nil {
		return err
	}

	intermediate := &x509.Certificate{
		IsCA:                  true,
		NotBefore:             now,
		NotAfter:              now.Add(time.Hour * 24 * 365 * 10),
		KeyUsage:              x509.KeyUsageCertSign | x509.KeyUsageCRLSign,
		BasicConstraintsValid: true,
		MaxPathLen:            0,
		MaxPathLenZero:        true,
		Issuer:                root.Subject,
		Subject:               pkix.Name{CommonName: "Smallstep Intermediate"},
		SerialNumber:          mustSerialNumber(),
		SubjectKeyId:          mustSubjectKeyID(resp.PublicKey),
	}

	b, err = x509.CreateCertificate(rand.Reader, intermediate, root, resp.PublicKey, signer)
	if err != nil {
		return err
	}

	if err = fileutil.WriteFile("intermediate_ca.crt", pem.EncodeToMemory(&pem.Block{
		Type:  "CERTIFICATE",
		Bytes: b,
	}), 0600); err != nil {
		return err
	}

	ui.PrintSelected("Intermediate Key", resp.Name)
	ui.PrintSelected("Intermediate Certificate", "intermediate_ca.crt")

	return nil
}

func createSSH(c *awskms.KMS) error {
	ui.Println("Creating SSH Keys ...")

	// User Key
	resp, err := c.CreateKey(&apiv1.CreateKeyRequest{
		Name:               "ssh-user-key",
		SignatureAlgorithm: apiv1.ECDSAWithSHA256,
	})
	if err != nil {
		return err
	}

	key, err := ssh.NewPublicKey(resp.PublicKey)
	if err != nil {
		return err
	}

	if err = fileutil.WriteFile("ssh_user_ca_key.pub", ssh.MarshalAuthorizedKey(key), 0600); err != nil {
		return err
	}

	ui.PrintSelected("SSH User Public Key", "ssh_user_ca_key.pub")
	ui.PrintSelected("SSH User Private Key", resp.Name)

	// Host Key
	resp, err = c.CreateKey(&apiv1.CreateKeyRequest{
		Name:               "ssh-host-key",
		SignatureAlgorithm: apiv1.ECDSAWithSHA256,
	})
	if err != nil {
		return err
	}

	key, err = ssh.NewPublicKey(resp.PublicKey)
	if err != nil {
		return err
	}

	if err = fileutil.WriteFile("ssh_host_ca_key.pub", ssh.MarshalAuthorizedKey(key), 0600); err != nil {
		return err
	}

	ui.PrintSelected("SSH Host Public Key", "ssh_host_ca_key.pub")
	ui.PrintSelected("SSH Host Private Key", resp.Name)

	return nil
}

func mustSerialNumber() *big.Int {
	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	sn, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		panic(err)
	}
	return sn
}

func mustSubjectKeyID(key crypto.PublicKey) []byte {
	b, err := x509.MarshalPKIXPublicKey(key)
	if err != nil {
		panic(err)
	}
	hash := sha1.Sum(b)
	return hash[:]
}