package com.malk.rjk.util;

import com.google.common.base.CharMatcher;
import com.google.common.io.BaseEncoding;
import org.apache.commons.codec.binary.Base64;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;

public class CryptUtil {
    protected byte[] aesKey;

    public CryptUtil(String encodingAesKey) {
        this.aesKey = BaseEncoding.base64().decode(CharMatcher.whitespace().removeFrom(encodingAesKey));
    }

    public String decrypt(String encryptedText) {
        byte[] original;
        try {
            // 设置解密模式为AES的CBC模式
            Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
            SecretKeySpec keySpec = new SecretKeySpec(this.aesKey, "AES");
            IvParameterSpec iv = new IvParameterSpec(Arrays.copyOfRange(this.aesKey, 0, 16));
            cipher.init(Cipher.DECRYPT_MODE, keySpec, iv);
            // 使用BASE64对密文进行解码
            byte[] encrypted = Base64.decodeBase64(encryptedText);
            // 解密
            original = cipher.doFinal(encrypted);
        } catch (Exception e) {
            return null;
        }
        String trueContent;
        try {
            // 去除补位字符
            byte[] bytes = decode(original);
            // 分离16位随机字符串,网络字节序
            byte[] networkOrder = Arrays.copyOfRange(bytes, 16, 20);
            int contentLength = bytesNetworkOrder2Number(networkOrder);
            trueContent = new String(Arrays.copyOfRange(bytes, 20, 20 + contentLength), StandardCharsets.UTF_8);
        } catch (Exception e) {
            return null;
        }
        return trueContent;
    }

    public static byte[] decode(byte[] decrypted) {
        int pad = decrypted[decrypted.length - 1];
        if (pad < 1 || pad > 32) {
            pad = 0;
        }
        return Arrays.copyOfRange(decrypted, 0, decrypted.length - pad);
    }

    /**
     * 4个字节的网络字节序bytes数组还原成一个数字.
     */
    private static int bytesNetworkOrder2Number(byte[] bytesInNetworkOrder) {
        int sourceNumber = 0;
        for (int i = 0; i < 4; i++) {
            sourceNumber <<= 8;
            sourceNumber |= bytesInNetworkOrder[i] & 0xff;
        }
        return sourceNumber;
    }
}