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/*
 * Copyright (C) 2015-2022 Igor A. Maznitsa
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.igormaznitsa.mindmap.swing.panel.utils;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.SecretKeySpec;

public final class CryptoUtils {
  private CryptoUtils() {

  }

  public static byte[] sha256(final byte[] data) {
    try {
      return MessageDigest.getInstance("SHA-256").digest(data);
    } catch (NoSuchAlgorithmException ex) {
      throw new IllegalStateException(ex);
    }
  }

  public static String encrypt(final String pass, final String text) {
    if (pass == null || pass.isEmpty()) {
      return text;
    }
    try {
      final byte[] textBytes = text.getBytes(StandardCharsets.UTF_8);
      final byte[] textHash = sha256(textBytes);

      final ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
      outputStream.write(textHash);
      outputStream.write(textBytes);

      final byte[] originalData = outputStream.toByteArray();

      final byte[] key = sha256(pass.getBytes(StandardCharsets.UTF_8));
      Key aesKey = new SecretKeySpec(key, "AES");
      Cipher cipher = Cipher.getInstance("AES");
      cipher.init(Cipher.ENCRYPT_MODE, aesKey);
      final byte[] encodedData = cipher.doFinal(originalData);
      if (Arrays.equals(originalData, encodedData)) {
        throw new IllegalStateException(
            "Data can't be encrypted! Check encryption provider and settings!");
      }
      return Utils.base64encode(encodedData);
    } catch (NoSuchPaddingException | InvalidKeyException | NoSuchAlgorithmException |
             IllegalBlockSizeException | BadPaddingException | IOException ex) {
      throw new RuntimeException(ex);
    }
  }

  public static boolean decrypt(final String pass, final String text,
                                final StringBuilder output) {
    try {
      final byte[] key = sha256(pass.getBytes(StandardCharsets.UTF_8));
      final Key aesKey = new SecretKeySpec(key, "AES");
      Cipher cipher = Cipher.getInstance("AES");
      cipher.init(Cipher.DECRYPT_MODE, aesKey);
      final byte[] decrypted = cipher.doFinal(Utils.base64decode(text));
      if (decrypted.length < 32) {
        return false;
      }
      final byte[] sha256data = Arrays.copyOfRange(decrypted, 0, 32);
      final byte[] textPart = Arrays.copyOfRange(decrypted, 32, decrypted.length);
      final byte[] calculatedHash = sha256(textPart);
      if (!Arrays.equals(sha256data, calculatedHash)) {
        return false;
      }
      output.append(new String(textPart, StandardCharsets.UTF_8));
      return true;
    } catch (BadPaddingException ex) {
      return false;
    } catch (NoSuchPaddingException | InvalidKeyException | NoSuchAlgorithmException | IllegalBlockSizeException ex) {
      throw new RuntimeException(ex);
    }
  }

}