/**
 *  Cryptography Functions
 *
 *  Forked from AndiDittrich/AesUtil.js
 *  https://gist.github.com/AndiDittrich/4629e7db04819244e843
 */

import crypto, { CipherGCM, CipherGCMTypes, DecipherGCM } from 'crypto';
import { Password } from './types';

/**
 * Get encryption/decryption algorithm
 */
function getAlgorithm(): CipherGCMTypes {
   return 'aes-256-gcm';
}

/**
 * Get encrypted string prefix
 */
function getEncryptedPrefix(): string {
   return 'enc::';
}

/**
 * Derive 256 bit encryption key from password, using salt and iterations -> 32 bytes
 * @param password
 * @param salt
 * @param iterations
 */
function deriveKeyFromPassword(password: Password, salt: Buffer, iterations: number): Buffer {
   return crypto.pbkdf2Sync(password, salt, iterations, 32, 'sha512');
}

/**
 * Encrypt AES 256 GCM
 * @param plainText
 * @param password
 */
export function encryptAesGcm(plainText: string | object, password: Password): string | undefined {
   try {
      if (typeof plainText === 'object') {
         plainText = JSON.stringify(plainText);
      } else {
         plainText = String(plainText);
      }

      const algorithm: CipherGCMTypes = getAlgorithm();

      // Generate random salt -> 64 bytes
      const salt = crypto.randomBytes(64);

      // Generate random initialization vector -> 16 bytes
      const iv = crypto.randomBytes(16);

      // Generate random count of iterations between 10.000 - 99.999 -> 5 bytes
      const iterations = Math.floor(Math.random() * (99999 - 10000 + 1)) + 10000;

      // Derive encryption key
      const encryptionKey = deriveKeyFromPassword(password, salt, Math.floor(iterations * 0.47 + 1337));

      // Create cipher
      // @ts-ignore: TS expects the wrong createCipher return type here
      const cipher: CipherGCM = crypto.createCipheriv(algorithm, encryptionKey, iv);

      // Update the cipher with data to be encrypted and close cipher
      const encryptedData = Buffer.concat([cipher.update(plainText, 'utf8'), cipher.final()]);

      // Get authTag from cipher for decryption // 16 bytes
      const authTag = cipher.getAuthTag();

      // Join all data into single string, include requirements for decryption
      const output = Buffer.concat([salt, iv, authTag, Buffer.from(iterations.toString()), encryptedData]).toString('hex');

      return getEncryptedPrefix() + output;
   } catch (error) {
      console.error('Encryption failed!');
      console.error(error);
      return void 0;
   }
}

/**
 * Decrypt AES 256 GCM
 * @param cipherText
 * @param password
 */
export function decryptAesGcm(cipherText: string, password: Password): string | undefined {
   try {
      const algorithm: CipherGCMTypes = getAlgorithm();

      const cipherTextParts = cipherText.split(getEncryptedPrefix());

      // If it's not encrypted by this, reject with undefined
      if (cipherTextParts.length !== 2) {
         console.error('Could not determine the beginning of the cipherText. Maybe not encrypted by this method.');
         return void 0;
      } else {
         cipherText = cipherTextParts[1];
      }

      const inputData: Buffer = Buffer.from(cipherText, 'hex');

      // Split cipherText into partials
      const salt: Buffer = inputData.slice(0, 64);
      const iv: Buffer = inputData.slice(64, 80);
      const authTag: Buffer = inputData.slice(80, 96);
      const iterations: number = parseInt(inputData.slice(96, 101).toString('utf-8'), 10);
      const encryptedData: Buffer = inputData.slice(101);

      // Derive key
      const decryptionKey = deriveKeyFromPassword(password, salt, Math.floor(iterations * 0.47 + 1337));

      // Create decipher
      // @ts-ignore: TS expects the wrong createDecipher return type here
      const decipher: DecipherGCM = crypto.createDecipheriv(algorithm, decryptionKey, iv);
      decipher.setAuthTag(authTag);

      // Decrypt data
      // @ts-ignore: TS expects the wrong createDecipher return type here
      const decrypted = decipher.update(encryptedData, 'binary', 'utf-8') + decipher.final('utf-8');

      try {
         return JSON.parse(decrypted);
      } catch (error) {
         return decrypted;
      }
   } catch (error) {
      console.error('Decryption failed!');
      console.error(error);
      return void 0;
   }
}