package com.foxinmy.weixin4j.wxa;
   
   import java.nio.charset.Charset;
   
   import org.apache.commons.codec.binary.Base64;
   
   import com.alibaba.fastjson.JSON;
   import com.alibaba.fastjson.JSONObject;
   
  /**
   * 对微信小程序用户加密数据的解密。
   *
   * @since 1.8
   * @see <a href="https://developers.weixin.qq.com/miniprogram/dev/framework/open-ability/signature.html">开放数据校验与解密</a>
   */
  public class WXBizDataCrypt {
  
  	private final String appId;
  
  	private final String sessionKey;
  
  	public WXBizDataCrypt(String appId, String sessionKey) {
  		this.appId = appId;
  		this.sessionKey = sessionKey;
  	}
  
  	/**
  	 * 解密微信小程序用户加密数据.
  	 *
  	 * @param encryptedData 加密的用户数据.
  	 * @param iv 与用户数据一同返回的初始向量.
  	 * @return 解密后的原文.
  	 */
  	public JSONObject decryptData(final String encryptedData, final String iv) {
  		final byte[] aesKey = Base64.decodeBase64(sessionKey);
  		final byte[] aesCipher = Base64.decodeBase64(encryptedData);
  		final byte[] aesIV = Base64.decodeBase64(iv);
  
  		final byte[] decryptedBytes = AESUtils.decrypt(aesCipher, aesKey, aesIV);
  		final String decryptedText = new String(decryptedBytes, Charset.forName("UTF-8"));
  		final JSONObject decrypted = JSON.parseObject(decryptedText);
  
  		final String watermarkAppId = decrypted.getJSONObject("watermark").getString("appid");
  		if (!watermarkAppId.equals(this.appId)) {
  			throw new IllegalArgumentException("Invalid Buffer");
  		}
  
  		return decrypted;
  	}
  
  }