grammar SQLOrderByClause
  include SQLPrimitives
  include SQLRowSupport
  include SQLHelpers

  rule order_by
    "ORDER" SPACE "BY" SPACE one_or_more_column_names_with_sort { 
      def eval
        OrderBy.new(one_or_more_column_names_with_sort.eval)
      end
    }
  end

  rule one_or_more_column_names_with_sort
    one_column_name_with_sort "," SPACE one_or_more_column_names_with_sort {
      def eval
        result1, result2 = one_column_name_with_sort.eval, one_or_more_column_names_with_sort.eval
        [result1, result2].flatten
      end
    }
    / 
    one_column_name_with_sort
  end

  rule one_column_name_with_sort
    one_column_name optional_sort_condition { 
      def eval
        column = one_column_name.eval
        if value = optional_sort_condition.eval
          OrderByPair.new(column, value)
        else
          OrderByPair.new(column)
        end
      end 
    }
  end

  rule optional_sort_condition
    SPACE sort_condition { def eval; sort_condition.eval; end } / EMPTY_STRING
  end

  rule sort_condition
    ascending / descending
  end

  rule ascending
    "ASC" { def eval; Guillotine::Expressions::OrderBy::ASC; end }
  end

  rule descending
    "DESC" { def eval; Guillotine::Expressions::OrderBy::DESC; end }
  end
end