package yapingtech

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

// PKCS7Padding pads the input text according to the PKCS7 standard.
func PKCS7Padding(data []byte, blockSize int) []byte {
	padding := blockSize - len(data)%blockSize
	padText := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(data, padText...)
}

// Encrypt encrypts the given plaintext using AES-256-ECB.
func Encrypt(plaintext, key string) (string, error) {
	// Truncate the key to 32 bytes
	truncatedKey := []byte(key)[:32]
	block, err := aes.NewCipher(truncatedKey)
	if err != nil {
		return "", err
	}
	paddedText := PKCS7Padding([]byte(plaintext), aes.BlockSize)
	cipherText := make([]byte, len(paddedText))
	mode := NewECBEncrypter(block)
	mode.CryptBlocks(cipherText, paddedText)
	return base64.StdEncoding.EncodeToString(cipherText), nil
}

// ecbEncrypter is a custom implementation of ECB encryption mode.
type ecbEncrypter struct {
	b         cipher.Block
	blockSize int
}

func NewECBEncrypter(b cipher.Block) cipher.BlockMode {
	return &ecbEncrypter{
		b:         b,
		blockSize: b.BlockSize(),
	}
}
func (x *ecbEncrypter) BlockSize() int { return x.blockSize }

func (x *ecbEncrypter) CryptBlocks(dst, src []byte) {
	if len(src)%x.blockSize != 0 {
		panic("crypto/cipher: input not full blocks")
	}
	if len(dst) < len(src) {
		panic("crypto/cipher: output smaller than input")
	}
	for len(src) > 0 {
		x.b.Encrypt(dst, src[:x.blockSize])
		src = src[x.blockSize:]
		dst = dst[x.blockSize:]
	}
}