var crypto = require('crypto');
var CIPHER_ALGORITHM = 'aes-256-ctr';

function decrypt(key, encrypted) {
    if (typeof key !== 'string' || !key) {
      throw new TypeError('Provided "key" must be a non-empty string');
    }

    var isString = typeof encrypted === 'string';
    var isBuffer = Buffer.isBuffer(encrypted);
    if (!(isString || isBuffer) || (isString && !encrypted) || (isBuffer && !Buffer.byteLength(encrypted))) {
      throw new TypeError('Provided "encrypted" must be a non-empty string or buffer');
    }

    var sha256 = crypto.createHash('sha256');
    sha256.update(key);

    var input = encrypted;
    if (isString) {
      input = Buffer.from(encrypted, 'base64');

      if (input.length < 17) {
        throw new TypeError('Provided "encrypted" must decrypt to a non-empty string or buffer');
      }
    } else {
      if (Buffer.byteLength(encrypted) < 17) {
        throw new TypeError('Provided "encrypted" must decrypt to a non-empty string or buffer');
      }
    }

    // Initialization Vector
    var iv = input.slice(0, 16);
    var decipher = crypto.createDecipheriv(CIPHER_ALGORITHM, sha256.digest(), iv);

    var ciphertext = input.slice(16);

    var output;
    if (isString) {
      output = decipher.update(ciphertext) + decipher.final();
    } else {
      output = Buffer.concat([decipher.update(ciphertext), decipher.final()]);
    }

    return output;
  }