def pre_parse
      @file_reader.read
      metadata = Metadata.new(MetadataParser.new(@file_reader.first_line).parse)
      if metadata.valid?
        @metadata = metadata
        @alias_registry = AliasRegistry.new(@metadata.their_screen_name)
        @my_aliases.each do |my_alias|
          @alias_registry[my_alias] = @metadata.my_screen_name
        end
      end
    end
def pre_parse
      @file_reader.read
      metadata = Metadata.new(MetadataParser.new(@file_reader.first_line).parse)
      if metadata.valid?
        @metadata = metadata
        @alias_registry = AliasRegistry.new(@metadata.their_screen_name)
        @my_aliases.each do |my_alias|
          @alias_registry[my_alias] = @metadata.my_screen_name
        end
      end
    end
Extract required data from the file. Run by parse.