package encryption_decryption

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

// 必须16字节
var key = "fusen20230405145"

// 加密(key必须16字节),前端加解密需要先把base64转字符串再取前16字节作为iv
func CBCEncrypt(data string) (string, error) {
	defer func() {
		if err := recover(); err != nil {
			fmt.Println("cbc decrypt err:", err)
		}
	}()
	block, err := aes.NewCipher([]byte(key))
	if err != nil {
		return "", err
	}
	blockSize := len(key)
	padding := blockSize - len(data)%blockSize // 填充字节
	if padding == 0 {
		padding = blockSize
	}
	// 填充 padding 个 byte(padding) 到 data
	data += string(bytes.Repeat([]byte{byte(padding)}, padding))
	ciphertext := make([]byte, aes.BlockSize+len(data))
	iv := ciphertext[:aes.BlockSize]
	if _, err = rand.Read(iv); err != nil { // 将同时写到 ciphertext 的开头
		return "", err
	}
	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(ciphertext[aes.BlockSize:], []byte(data))
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

// 解密(key必须16字节)
func CBCDecrypt(src string) (string, error) {
	defer func() {
		if err := recover(); err != nil {
			fmt.Println("cbc decrypt err:", err)
		}
	}()
	block, err := aes.NewCipher([]byte(key))
	if err != nil {
		return "", err
	}
	ciphercode, err := base64.StdEncoding.DecodeString(src)
	if err != nil {
		return "", err
	}
	iv := ciphercode[:aes.BlockSize]        // 密文的前 16 个字节为 iv
	ciphercode = ciphercode[aes.BlockSize:] // 正式密文
	mode := cipher.NewCBCDecrypter(block, iv)
	mode.CryptBlocks(ciphercode, ciphercode)
	plaintext := string(ciphercode) // ↓ 减去 padding
	return plaintext[:len(plaintext)-int(plaintext[len(plaintext)-1])], nil
}