package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"os"

	survey "github.com/AlecAivazis/survey/v2" // survey package
)

// admin need set env: ENCRYPTION_KEY
// the default value: ")ZLxR6X@h5tYGhkwin<j"
var EncryptionKey = ")ZLxR6X@h5tYGhkwin<j"

func main() {
	// command usage
	flag.Usage = func() {
		fmt.Fprintln(os.Stderr, `
        Usage: crypter -action=<enc|dec> [options]

        Options:
            -action    enc|dec
            -password  password (if empty, will be prompted)
        `)
	}

	action := flag.String("action", "", "action to perform: enc or dec")
	password := flag.String("password", "", "password")

	flag.Parse()

	if *action != "enc" && *action != "dec" {
		fmt.Println("Invalid action. Use -action=enc or -action=dec")
		os.Exit(1)
	}

	// use survey to prompt for missing values
	var inputPassword string
	if *password == "" {
		survey.AskOne(&survey.Password{Message: "Enter password:\n"}, password)
		inputPassword = *password
	}
	inputPassword = *password

	if *action == "enc" {
		encryptedPassword, err := Encrypt(inputPassword, "")
		if err != nil {
			log.Fatalf("Failed to encrypt password: %v", err)
		}
		fmt.Println(encryptedPassword)
	}

	if *action == "dec" {
		realPassword, err := Decrypt(inputPassword, "")
		if err != nil {
			log.Fatalf("Failed to decrypt password: %v", err)
		}
		fmt.Println(realPassword)
	}
}

// use sha256 to get 32 bytes key
func getAESKey(key string) []byte {
	selfSecretKey := os.Getenv("ENCRYPTION_KEY")
	if selfSecretKey != "" {
		key = selfSecretKey
	} else {
		key = EncryptionKey
	}
	hash := sha256.Sum256([]byte(key))
	return hash[:]
}

func Encrypt(plaintext, secret string) (string, error) {
	key := getAESKey(secret)
	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}
	ciphertext := make([]byte, aes.BlockSize+len(plaintext))
	iv := ciphertext[:aes.BlockSize]
	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
		return "", err
	}

	stream := cipher.NewCFBEncrypter(block, iv)
	stream.XORKeyStream(ciphertext[aes.BlockSize:], []byte(plaintext))
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

func Decrypt(encryptedText, secret string) (string, error) {
	key := getAESKey(secret)
	ciphertext, err := base64.StdEncoding.DecodeString(encryptedText)
	if err != nil {
		return "", err
	}
	if len(ciphertext) < aes.BlockSize {
		return "", errors.New("the ciphertext is too short")
	}
	iv := ciphertext[:aes.BlockSize]
	ciphertext = ciphertext[aes.BlockSize:]
	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}
	stream := cipher.NewCFBDecrypter(block, iv)
	stream.XORKeyStream(ciphertext, ciphertext)
	return string(ciphertext), nil
}