package cmd

import (
	"crypto/rand"
	"encoding/base64"
	"fmt"
	"github.com/spf13/cobra"
	"golang.org/x/crypto/curve25519"
)

var x25519Command = cobra.Command{
	Use:   "x25519",
	Short: "Generate key pair for x25519 key exchange",
	Run: func(cmd *cobra.Command, args []string) {
		executeX25519()
	},
}

func init() {
	command.AddCommand(&x25519Command)
}

func executeX25519() {
	var output string
	var err error
	var privateKey []byte
	var publicKey []byte

	privateKey = make([]byte, curve25519.ScalarSize)
	if _, err = rand.Read(privateKey); err != nil {
		output = err.Error()
		goto out
	}

	// Modify random bytes using algorithm described at:
	// https://cr.yp.to/ecdh.html.
	privateKey[0] &= 248
	privateKey[31] &= 127
	privateKey[31] |= 64

	if publicKey, err = curve25519.X25519(privateKey, curve25519.Basepoint); err != nil {
		output = err.Error()
		goto out
	}

	output = fmt.Sprintf("Private key: %v\nPublic key: %v",
		base64.RawURLEncoding.EncodeToString(privateKey),
		base64.RawURLEncoding.EncodeToString(publicKey))

out:
	fmt.Println(output)
}