package com.xjrsoft.common.utils;

import org.apache.commons.io.IOUtils;
import org.springframework.core.io.ClassPathResource;
import org.springframework.util.ResourceUtils;

import javax.crypto.Cipher;
import java.io.BufferedWriter;
import java.io.ByteArrayOutputStream;
import java.io.FileWriter;
import java.io.InputStream;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;

/**
 * RSA加解密
 */
public class RSAUtil {
    public static final String KEY_ALGORITHM = "RSA";
    public static final String PUBLIC_KEY = "RSAPublicKey";
    public static final String PRIVATE_KEY = "RSAPrivateKey";
    public static final String SIGNATURE_ALGORITHM = "MD5withRSA";

    public static final  String DefaultPrivateKeyFileName = "rsa_private_key.pem";

    public static final  String DefaultPublicKeyFileName = "rsa_public_key.pem";

    /**
     * RSA最大加密明文大小
     */
    private static final int MAX_ENCRYPT_BLOCK = 117;

    /**
     * RSA最大解密密文大小
     */
    private static final int MAX_DECRYPT_BLOCK = 128;

    /**
     * 获取密钥对
     */
    public static KeyPair getKeyPair() throws Exception {
        KeyPairGenerator generator = KeyPairGenerator.getInstance(KEY_ALGORITHM);
        generator.initialize(1024);
        return generator.generateKeyPair();
    }

    /**
     * 生成秘钥到资源文件中
     */
    public static void generateKeyPairResources() throws Exception {
        String basePath = ResourceUtils.getURL("classpath:").getPath();
        KeyPair keyPair = getKeyPair();

        String privateKey = Base64.getEncoder().encodeToString(keyPair.getPrivate().getEncoded());
        String publicKey = Base64.getEncoder().encodeToString(keyPair.getPublic().getEncoded());

        Path priPath = Paths.get(basePath, "rsa_private_key.pem");
        Path pubPath = Paths.get(basePath, "rsa_public_key.pem");

        // 将密钥对写入到文件
        try (
                FileWriter prifw = new FileWriter(priPath.toFile());
                BufferedWriter pribw = new BufferedWriter(prifw);

                FileWriter pubfw = new FileWriter(pubPath.toFile());
                BufferedWriter pubbw = new BufferedWriter(pubfw);
        ) {
            pribw.write(privateKey);
            pubbw.write(publicKey);
        }
    }

    /**
     * 获取私钥
     */
    public static PrivateKey getPrivateKey(String privateKey) throws Exception {
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        byte[] decodedKey = Base64.getDecoder().decode(privateKey.getBytes());
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(decodedKey);
        return keyFactory.generatePrivate(keySpec);
    }

    /**
     * 获取公钥
     *
     * @param publicKey 公钥字符串
     * @param publicKey
     */
    public static PublicKey getPublicKey(String publicKey) throws Exception {
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        byte[] decodedKey = Base64.getDecoder().decode(publicKey.getBytes());
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(decodedKey);
        return keyFactory.generatePublic(keySpec);
    }

    /**
     * RSA加密
     *
     * @param data      待加密数据
     * @param publicKey 公钥
     * @return java.lang.String
     */
    public static String encrypt(String data, PublicKey publicKey) throws Exception {
        Cipher cipher = Cipher.getInstance(KEY_ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        int inputLen = data.getBytes().length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offset = 0;
        byte[] cache;
        int i = 0;
        // 对数据分段加密
        while (inputLen - offset > 0) {
            if (inputLen - offset > MAX_ENCRYPT_BLOCK) {
                cache = cipher.doFinal(data.getBytes(), offset, MAX_ENCRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(data.getBytes(), offset, inputLen - offset);
            }
            out.write(cache, 0, cache.length);
            i++;
            offset = i * MAX_ENCRYPT_BLOCK;
        }
        byte[] encryptedData = out.toByteArray();
        out.close();
        // 获取加密内容使用base64进行编码,并以UTF-8为标准转化成字符串
        // 加密后的字符串
        return Base64.getEncoder().encodeToString(encryptedData);
    }

    /**
     * RSA加密
     *
     * @param data      待加密数据
     * @return java.lang.String
     */
    public static String encrypt(String data) throws Exception {
        ClassPathResource classPathResource = new ClassPathResource(DefaultPublicKeyFileName);
        InputStream inputStream = classPathResource.getInputStream();
        String Key = new String(IOUtils.toByteArray(inputStream));
        return encrypt(data,RSAUtil.getPublicKey(Key));
    }

    /**
     * RSA解密
     *
     * @param data       待解密数据
     * @param privateKey 私钥
     * @return java.lang.String
     */
    public static String decrypt(String data, PrivateKey privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance(KEY_ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        byte[] dataBytes = Base64.getDecoder().decode(data);
        int inputLen = dataBytes.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offset = 0;
        byte[] cache;
        int i = 0;
        //对数据分段解密
        while (inputLen - offset > 0) {
            if (inputLen - offset > MAX_DECRYPT_BLOCK) {
                cache = cipher.doFinal(dataBytes, offset, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(dataBytes, offset, inputLen - offset);
            }
            out.write(cache, 0, cache.length);
            i++;
            offset = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        // 解密后的内容
        return new String(decryptedData, "UTF-8");
    }

    /**
     * RSA解密
     *
     * @param data       待解密数据
     * @return java.lang.String
     */
    public static String decrypt(String data) throws Exception {
        ClassPathResource classPathResource = new ClassPathResource(DefaultPrivateKeyFileName);
        InputStream inputStream = classPathResource.getInputStream();
        String Key = new String(IOUtils.toByteArray(inputStream));
        return decrypt(data,RSAUtil.getPrivateKey(Key));
    }

    /**
     * 签名
     *
     * @param data       待签名数据
     * @param privateKey 私钥
     * @return java.lang.String
     */
    public static String sign(String data, PrivateKey privateKey) throws Exception {
        byte[] keyBytes = privateKey.getEncoded();
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        PrivateKey key = keyFactory.generatePrivate(keySpec);
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initSign(key);
        signature.update(data.getBytes());
        return Base64.getEncoder().encodeToString(signature.sign());
    }

    /**
     * 验签
     *
     * @param srcData   原始字符串
     * @param publicKey 公钥
     * @param sign      签名
     * @return boolean
     */
    public static boolean verify(String srcData, PublicKey publicKey, String sign) throws Exception {
        byte[] keyBytes = publicKey.getEncoded();
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        PublicKey key = keyFactory.generatePublic(keySpec);
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initVerify(key);
        signature.update(srcData.getBytes());
        return signature.verify(Base64.getDecoder().decode(sign.getBytes()));
    }
}
