package sqlite

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"fmt"
)

var iv = []byte{10, 22, 13, 79, 05, 8, 52, 91, 87, 98, 88, 98, 35, 25, 13, 05}

type FieldEncrypt struct {
	block cipher.Block
}

func GenerateKey() (string, error) {
	key := make([]byte, 32)
	_, err := rand.Read(key)
	if err != nil {
		return "", err
	}
	readableKey := base64.StdEncoding.EncodeToString(key)
	return readableKey, nil
}

func NewFieldEncrypt(key string) (*FieldEncrypt, error) {
	binKey, err := base64.StdEncoding.DecodeString(key)
	if err != nil {
		return nil, err
	}

	block, err := aes.NewCipher(binKey)
	if err != nil {
		return nil, err
	}
	ec := &FieldEncrypt{
		block: block,
	}

	return ec, nil
}

func (ec *FieldEncrypt) Encrypt(payload string) string {
	plainText := pkcs5Padding([]byte(payload))
	cipherText := make([]byte, len(plainText))
	cbc := cipher.NewCBCEncrypter(ec.block, iv)
	cbc.CryptBlocks(cipherText, plainText)
	return base64.StdEncoding.EncodeToString(cipherText)
}

func (ec *FieldEncrypt) Decrypt(data string) (string, error) {
	cipherText, err := base64.StdEncoding.DecodeString(data)
	if err != nil {
		return "", err
	}
	cbc := cipher.NewCBCDecrypter(ec.block, iv)
	cbc.CryptBlocks(cipherText, cipherText)
	payload, err := pkcs5UnPadding(cipherText)
	if err != nil {
		return "", err
	}

	return string(payload), nil
}

func pkcs5Padding(ciphertext []byte) []byte {
	padding := aes.BlockSize - len(ciphertext)%aes.BlockSize
	padText := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(ciphertext, padText...)
}

func pkcs5UnPadding(src []byte) ([]byte, error) {
	srcLen := len(src)
	paddingLen := int(src[srcLen-1])
	if paddingLen >= srcLen || paddingLen > aes.BlockSize {
		return nil, fmt.Errorf("padding size error")
	}
	return src[:srcLen-paddingLen], nil
}