module Carrierwave
  module Base64
    class Base64StringIO < StringIO
      class ArgumentError < StandardError; end

      attr_accessor :file_extension, :file_name

      def initialize(encoded_file, file_name_proc_or_string)
        description, encoded_bytes = encoded_file.split(',')

        raise ArgumentError unless encoded_bytes
        raise ArgumentError if encoded_bytes.eql?('(null)')

        @file_name = extract_file_name(file_name_proc_or_string)
        @file_extension = get_file_extension description
        bytes = ::Base64.decode64 encoded_bytes

        super bytes
      end

      def original_filename
        File.basename("#{@file_name}.#{@file_extension}")
      end

      private

      def get_file_extension(description)
        content_type = description.split(';base64').first
        mime_type = MIME::Types[content_type].first
        unless mime_type
          raise ArgumentError, "Unknown MIME type: #{content_type}"
        end
        mime_type.preferred_extension
      end

      def extract_file_name(proc_or_string)
        if proc_or_string.is_a?(Proc)
          proc_or_string.call
        else
          warn(
            '[Deprecation warning] Setting `file_name` option to a string is '\
            'deprecated and will be removed in 3.0.0. If you want to keep the '\
            'existing behaviour, wrap the string in a Proc'
          )
          proc_or_string
        end
      end
    end
  end
end