module Dingtalk
  module Prpcrypt
    extend self

    # 对密文进行解密.
    # text 需要解密的密文
    def decrypt(aes_key, text, corpid)
      status = 200
      text        = Base64.decode64(text)
      text        = handle_cipher(:decrypt, aes_key, text)
      result      = PKCS7Encoder.decode(text)
      content     = result[16...result.length]
      len_list    = content[0...4].unpack("N")
      xml_len     = len_list[0]
      xml_content = content[4...4 + xml_len]
      from_corpid = content[xml_len+4...content.size]
      # TODO: refactor
      if corpid != from_corpid
        Rails.logger.debug("#{__FILE__}:#{__LINE__} Failure because #{corpid} != #{from_corpid}")
        status = 401
      end
      [xml_content, status]
    end

    # 加密
    def encrypt(aes_key, text, corpid)
      text    = text.force_encoding("ASCII-8BIT")
      random  = SecureRandom.hex(8)
      msg_len = [text.length].pack("N")
      text    = "#{random}#{msg_len}#{text}#{corpid}"
      text    = PKCS7Encoder.encode(text)
      text    = handle_cipher(:encrypt, aes_key, text)
      Base64.encode64(text)
    end

    private
      def handle_cipher(action, aes_key, text)
        cipher = OpenSSL::Cipher.new('AES-256-CBC')
        cipher.send(action)
        cipher.padding = 0
        cipher.key     = aes_key
        cipher.iv      = aes_key[0...16]
        cipher.update(text) + cipher.final
      end
  end
end