/*
   Copyright (c) 2016 VMware, Inc. All Rights Reserved.
   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package utils

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha1"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"strings"

	"golang.org/x/crypto/pbkdf2"
)

// Encrypt encrypts the content with salt
func Encrypt(content string, salt string) string {
	return fmt.Sprintf("%x", pbkdf2.Key([]byte(content), []byte(salt), 4096, 16, sha1.New))
}

const (
	// EncryptHeaderV1 ...
	EncryptHeaderV1 = "<enc-v1>"
)

// ReversibleEncrypt encrypts the str with aes/base64
func ReversibleEncrypt(str, key string) (string, error) {
	keyBytes := []byte(key)
	var block cipher.Block
	var err error

	if block, err = aes.NewCipher(keyBytes); err != nil {
		return "", err
	}
	cipherText := make([]byte, aes.BlockSize+len(str))
	iv := cipherText[:aes.BlockSize]
	if _, err = io.ReadFull(rand.Reader, iv); err != nil {
		return "", err
	}

	cfb := cipher.NewCFBEncrypter(block, iv)
	cfb.XORKeyStream(cipherText[aes.BlockSize:], []byte(str))
	encrypted := EncryptHeaderV1 + base64.StdEncoding.EncodeToString(cipherText)
	return encrypted, nil
}

// ReversibleDecrypt decrypts the str with aes/base64 or base 64 depending on "header"
func ReversibleDecrypt(str, key string) (string, error) {
	if strings.HasPrefix(str, EncryptHeaderV1) {
		str = str[len(EncryptHeaderV1):]
		return decryptAES(str, key)
	}
	//fallback to base64
	return decodeB64(str)
}

func decodeB64(str string) (string, error) {
	cipherText, err := base64.StdEncoding.DecodeString(str)
	return string(cipherText), err
}

func decryptAES(str, key string) (string, error) {
	keyBytes := []byte(key)
	var block cipher.Block
	var cipherText []byte
	var err error

	if block, err = aes.NewCipher(keyBytes); err != nil {
		return "", err
	}
	if cipherText, err = base64.StdEncoding.DecodeString(str); err != nil {
		return "", err
	}
	if len(cipherText) < aes.BlockSize {
		err = errors.New("cipherText too short")
		return "", err
	}

	iv := cipherText[:aes.BlockSize]
	cipherText = cipherText[aes.BlockSize:]
	cfb := cipher.NewCFBDecrypter(block, iv)
	cfb.XORKeyStream(cipherText, cipherText)
	return string(cipherText), nil
}