Enhanced Simple Table for ActiveAdmin + Arbre

simple_table.rb

module ActiveAdmin
  module Views
    ##
    # Exposes Arbre's table support as a simple control for use in ActiveAdmin.
    #
    # Example usage:
    # ```
    # simple_table [ [ "User count", User.count ],
    #                [ "Item count", Item.count ],
    #                [ "Total Wishes", Wish.count ],
    #                [ "Available Items", Item.available.count ] ]
    # ```
    #
    # Based on the following source (released into the public domain):
    # http://rubyglasses.blogspot.com.br/2015/02/activeadmin-simpletable.html
    #
    class SimpleTable < ::Arbre::HTML::Table
      builder_method :simple_table

      def build(collection)
        ensure_uniform_columns(collection)

        collection.each do |row|
          tr do
            row.each do |col|
              td col, style: style_for(col)
            end
          end
        end
      end

      ##
      # Ensures that this control renders as a table.
      #
      # (This prevents the default Arbre behavior of trying to render a
      # "<simpletable>" tag instead).
      def tag_name
        'table'
      end

      private

      ##
      # Ensures every row within the given two-dimensional array has the same
      # number of columns.
      #
      # @param [Array<Array<Object>>]
      #   A two-dimensional array of values, in which the first dimension is
      #   rows, and the second dimension is columns.
      #
      def ensure_uniform_columns(values)
        return if values.empty?

        distinct_column_lengths = values.map(&:length).uniq

        unless distinct_column_lengths.length == 1
          raise ArgumentError,
                "Not all columns are the same length (got column lengths of "\
                "#{distinct_column_lengths})."
        end
      end

      ##
      # Obtains the appropriate inline style for the specified column value.
      #
      # @param [Object] col
      #   The value being displayed in the column.
      #
      def style_for(col)
        if col.is_a? Numeric
          'text-align: right;'
        else
          ''
        end
      end
    end
  end
end