import com.google.common.collect.Maps;
import lombok.SneakyThrows;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.codec.binary.Base64;
import javax.crypto.Cipher;
import java.io.ByteArrayOutputStream;
import java.nio.charset.StandardCharsets;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Map;
import java.util.UUID;

/** 
  * RSA plus decryption tool class 
  * 
  * @Author Wangqinglong01 
  */
@Slf4j
public class RSAUtil {
    

    private static final String RSA = "RSA";
    private static final String PRIVATE_KEY = "privateKey";
    private static final String PUBLIC_KEY = "publicKey";
    private static final String ALGORITHM = "MD5withRSA";

    private static final int ZERO = 0;

    /** 
      * RSA's maximum encryption text size 
      */
    private static final int MAX_ENCRYPT_BLOCK = 117;

    /** 
      * RSA's maximum decryption ciphertext size 
      */
    private static final int MAX_DECRYPT_BLOCK = 128;

    /** 
      * Public key and private key used for packaging randomly 
      */
    private final static Map<String, String> KEY_MAP = Maps.newHashMap();


    /** 
      * Get the public key 
      */
    public static String getPublicKey() {
    
        if (KEY_MAP.size() == ZERO) {
    
            genKeyPair();
        }
        return KEY_MAP.get(PUBLIC_KEY);
    }

    /** 
      * Get private key 
      */
    public static String getPriKey() {
    
        if (KEY_MAP.size() == ZERO) {
    
            genKeyPair();
        }
        return KEY_MAP.get(PRIVATE_KEY);
    }


    @SneakyThrows
    public static void genKeyPair() {
    
        // keypairgenrator class is used to generate public key and private key pairs, based on the RSA algorithm generation object
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(RSA);
        // Initialize the key-generator, the key size is 96-1024 bits
        keyPairGen.initialize(1024, new SecureRandom());
        // generate a key pair, store in keypair
        KeyPair keyPair = keyPairGen.generateKeyPair();
        // get the private key
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
        // Get the public key
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        String publicKeyString = new String(Base64.encodeBase64(publicKey.getEncoded()));
        // Get the private key string
        String privateKeyString = new String(Base64.encodeBase64((privateKey.getEncoded())));
        // Save the public key and private key to MAP
        // 0 means the public key
        KEY_MAP.put(PUBLIC_KEY, publicKeyString);
        // 1 means private key
        KEY_MAP.put(PRIVATE_KEY, privateKeyString);
    }

    /** 
      * RSA public key encryption (field length cannot exceed 117 bytes) 
      * 
      * @param Str encrypted string 
      * @param PublicKey Public Key 
      * @Return ciphertext 
      * @throws Exception in the process of encryption process 
      */
    public static String encrypt(String str, String publicKey) throws Exception {
    
        // base64 encoding public key
        byte[] decoded = Base64.decodeBase64(publicKey);
        RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance(RSA).generatePublic(new X509EncodedKeySpec(decoded));
        // RSA encryption
        Cipher cipher = Cipher.getInstance(RSA);
        cipher.init(Cipher.ENCRYPT_MODE, pubKey);
        return Base64.encodeBase64String(cipher.doFinal(str.getBytes(StandardCharsets.UTF_8)));
    }


    /** 
      * RSA private key decryption (field length cannot exceed 128 bytes) 
      * 
      * @param Str encrypted string 
      * @param PrivateKey private key 
      * @Return inscription 
      * @throws Exception Decrypting Disciplinary Information 
      */
    public static String decrypt(String str, String privateKey) throws Exception {
    
        // 64 -bit decoding and encrypted string
        byte[] inputByte = Base64.decodeBase64(str.getBytes(StandardCharsets.UTF_8));
        // base64 encoding private key
        byte[] decoded = Base64.decodeBase64(privateKey);
        RSAPrivateKey priKey = (RSAPrivateKey) KeyFactory.getInstance(RSA).generatePrivate(new PKCS8EncodedKeySpec(decoded));
        // RSA decryption
        Cipher cipher = Cipher.getInstance(RSA);
        cipher.init(Cipher.DECRYPT_MODE, priKey);
        return new String(cipher.doFinal(inputByte));
    }



    /*=========================================== ========================*/

    /** 
      * RSA encryption (segment) 
      * 
      * @param Data to be encrypted data 
      * @param PubKey Public Key 
      * @Return encrypted data 
      */
    public static String encryptSegment(String data, String pubKey) throws Exception {
    
        KeyFactory keyFactory = KeyFactory.getInstance(RSA);
        byte[] decodedKey = Base64.decodeBase64(pubKey.getBytes());
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(decodedKey);
        PublicKey publicKey = keyFactory.generatePublic(keySpec);
        Cipher cipher = Cipher.getInstance(RSA);
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        int inputLen = data.getBytes().length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offset = ZERO;
        byte[] cache;
        int i = ZERO;
        // Encryption of data segments
        while (inputLen - offset > ZERO) {
    
            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, ZERO, cache.length);
            i++;
            offset = i * MAX_ENCRYPT_BLOCK;
        }
        byte[] encryptedData = out.toByteArray();
        out.close();
        // Get the encrypted content and use Base64 to encode it, and use UTF-8 as the standard to be transformed into a string
        // The encrypted string
        return Base64.encodeBase64String(encryptedData);
    }

    /** 
      * RSA decryption (segment) 
      * 
      * @param Data to be deprived of the secret data 
      * @param prikey private key 
      * @Return Decodily data 
      */
    public static String decryptSegment(String data, String priKey) throws Exception {
    
        KeyFactory keyFactory = KeyFactory.getInstance(RSA);
        byte[] decodedKey = Base64.decodeBase64(priKey.getBytes());
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(decodedKey);
        PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
        Cipher cipher = Cipher.getInstance(RSA);
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        byte[] dataBytes = Base64.decodeBase64(data);
        int inputLen = dataBytes.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offset = ZERO;
        byte[] cache;
        int i = ZERO;
        // Decrypt the data segmentation
        while (inputLen - offset > ZERO) {
    
            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, ZERO, cache.length);
            i++;
            offset = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        // The content after decryption
        return new String(decryptedData, StandardCharsets.UTF_8);
    }



    /*========================================== =======================*/

    /** 
      * sign 
      * 
      * @param Data to be signed data 
      * @param PrivateKey private key 
      * @Return signature 
      */
    public static String sign(String data, PrivateKey privateKey) throws Exception {
    
        byte[] keyBytes = privateKey.getEncoded();
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(RSA);
        PrivateKey key = keyFactory.generatePrivate(keySpec);
        Signature signature = Signature.getInstance(ALGORITHM);
        signature.initSign(key);
        signature.update(data.getBytes());
        return new String(Base64.encodeBase64(signature.sign()));
    }

    /** 
      * Check 
      * 
      * @param srcdata raw string 
      * @param PublicKey Public Key 
      * @param Sign signature 
      * @Return Whether to check the visa 
      */
    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(RSA);
        PublicKey key = keyFactory.generatePublic(keySpec);
        Signature signature = Signature.getInstance(ALGORITHM);
        signature.initVerify(key);
        signature.update(srcData.getBytes());
        return signature.verify(Base64.decodeBase64(sign.getBytes()));
    }







    public static void main(String[] args) {
    
        try {
    
           // Generate key pair
            genKeyPair();
            // RSA encryption
            StringBuilder builder = new StringBuilder();
            do {
    
                builder.append(UUID.randomUUID().toString());
            } while (builder.toString().length() <= 100);
            String data = builder.toString();
            System.out.println("Data length:" + data.length());

            // ======================= Use segments plus decryption ============ =========
            String encryptSegment = encryptSegment(data, getPublicKey());
            System.out.println("Cousin after encryption:" + encryptSegment);
            System.out.println("After encrypted content length:" + encryptSegment.length());
            // RSA decryption
            String decryptSegment = decryptSegment(encryptSegment, getPriKey());
            System.out.println("After decryption, the content:" + decryptSegment);
            System.out.println("The content length after decryption:" + decryptSegment.length());

            // ======================= Use conventional decryption ============= =========

            String encrypt = encrypt(data, getPublicKey());
            System.out.println("Cousin after encryption:" + encrypt);
            System.out.println("After encrypted content length:" + encrypt.length());
            // RSA decryption
            String decrypt = decrypt(encrypt, getPriKey());
            System.out.println("After decryption, the content:" + decrypt);
            System.out.println("The content length after decryption:" + decrypt.length());


        } catch (Exception e) {
    
            e.printStackTrace();
            System.out.print("Adding Deconsion Abnormal");
        }
    }
}