package cn.home1.oss.lib.common.crypto;
   
   import static java.nio.charset.StandardCharsets.UTF_8;
   import static java.util.Arrays.copyOfRange;
   import static javax.crypto.Cipher.DECRYPT_MODE;
   
   import lombok.Getter;
   import lombok.SneakyThrows;
   
  import java.nio.charset.Charset;
  import java.security.Provider;
  
  import javax.crypto.BadPaddingException;
  import javax.crypto.Cipher;
  import javax.crypto.IllegalBlockSizeException;
  
  import cn.home1.oss.lib.common.CodecUtils;
  
  /**
   * Created by zhanghaolun on 16/11/17.
   */
  public class AesDecryptor implements EncodeDecryptor {
  
    @Getter
    private final Charset charset;
    private final Provider provider;
    private final AesCbcKey key;
  
    public AesDecryptor(final Provider provider, final KeyExpression keyExpression) {
      this.charset = UTF_8;
      this.provider = provider;
      this.key = new AesCbcKey(keyExpression);
    }
  
    @Override
    public String decrypt(final String encryptedAndEncoded) {
      return new String(this.decryptBytes(encryptedAndEncoded), this.charset);
    }
  
    public byte[] decryptBytes(final String encryptedAndEncoded) {
      final byte[] unencrypted;
      try {
        // 使用BASE64对密文进行解码
        final byte[] decoded = CodecUtils.decodeBase64(encryptedAndEncoded);
        // 解密
        unencrypted = this.decryptCipher().doFinal(decoded);
      } catch (final IllegalBlockSizeException | BadPaddingException | IllegalArgumentException cause) {
        throw new AesException(AesException.AesError.DECRYPT_AES_ERROR, cause);
      }
      try {
        // 去除补位字符
        final byte[] unpad = Pkcs7Encoder.PKCS7_UTF8_BLOCK32.decode(unencrypted);
        return copyOfRange(unpad, 16, unpad.length);
      } catch (final IllegalArgumentException cause) {
        throw new AesException(AesException.AesError.ILLEGAL_BUFFER, cause);
      }
    }
  
    @SneakyThrows
    Cipher decryptCipher() {
      final Cipher cipher = Cipher.getInstance(CryptoConstants.AES_CBC_NOPADDING, this.provider);// 设置解密模式为AES的CBC模式
      cipher.init(DECRYPT_MODE, this.key.getKeySpec(), this.key.getCbcIv());
      return cipher;
    }
  }