module ActiveRecord
  module ConnectionAdapters
    module MySQL
      class ExplainPrettyPrinter # :nodoc:
        # Pretty prints the result of an EXPLAIN in a way that resembles the output of the
        # MySQL shell:
        #
        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
        #   | id | select_type | table | type  | possible_keys | key     | key_len | ref   | rows | Extra       |
        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
        #   |  1 | SIMPLE      | users | const | PRIMARY       | PRIMARY | 4       | const |    1 |             |
        #   |  1 | SIMPLE      | posts | ALL   | NULL          | NULL    | NULL    | NULL  |    1 | Using where |
        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
        #   2 rows in set (0.00 sec)
        #
        # This is an exercise in Ruby hyperrealism :).
        def pp(result, elapsed)
          widths    = compute_column_widths(result)
          separator = build_separator(widths)

          pp = []

          pp << separator
          pp << build_cells(result.columns, widths)
          pp << separator

          result.rows.each do |row|
            pp << build_cells(row, widths)
          end

          pp << separator
          pp << build_footer(result.rows.length, elapsed)

          pp.join("\n") + "\n"
        end

        private

        def compute_column_widths(result)
          [].tap do |widths|
            result.columns.each_with_index do |column, i|
              cells_in_column = [column] + result.rows.map {|r| r[i].nil? ? 'NULL' : r[i].to_s}
              widths << cells_in_column.map(&:length).max
            end
          end
        end

        def build_separator(widths)
          padding = 1
          '+' + widths.map {|w| '-' * (w + (padding*2))}.join('+') + '+'
        end

        def build_cells(items, widths)
          cells = []
          items.each_with_index do |item, i|
            item = 'NULL' if item.nil?
            justifier = item.is_a?(Numeric) ? 'rjust' : 'ljust'
            cells << item.to_s.send(justifier, widths[i])
          end
          '| ' + cells.join(' | ') + ' |'
        end

        def build_footer(nrows, elapsed)
          rows_label = nrows == 1 ? 'row' : 'rows'
          "#{nrows} #{rows_label} in set (%.2f sec)" % elapsed
        end
      end
    end
  end
end