require 'digest/md5'
require 'base64'
require 'base64'
require 'digest'
require 'openssl'

module Cryptojs
  module Aes
    module Decrypt
      class Error < StandardError; end
      class << self
        def bytes_to_key(data, salt, output = 48)
          merged = data + salt
          key = Digest::MD5.digest(merged)
          final_key = key
          while final_key.length < output
            key = Digest::MD5.digest(key + merged)
            final_key += key
          end
          final_key[0..output - 1]
        end

        def aes256_cbc_decrypt(key, data, iv)
          # p key
          key = Digest::SHA256.digest(key) if key.is_a?(String) && key.bytesize != 32
          iv = Digest::MD5.digest(iv) if iv.is_a?(String) && iv.bytesize != 16
          aes = OpenSSL::Cipher.new('AES-256-CBC')
          aes.decrypt
          aes.key = key
          aes.iv = iv
          aes.update(data) + aes.final
        end

        def run(cipher, passcode)
          secret = Base64.decode64(cipher)
          unless secret[0..7] == 'Salted__'
            puts 'Invalid encrypted data'
            exit(1)
          end
          decrypt(secret, passcode)
        end

        def decrypt(secret, passcode)
          salt = secret[8..15]
          key_iv = bytes_to_key(passcode, salt, 48)
          key = key_iv[0..31]
          iv = key_iv[32..key_iv.length - 1]
          aes256_cbc_decrypt(key, secret[16..secret.length - 1], iv)
        end
      end
    end
  end
end