chief/acts_as_defaultable

require 'active_support/concern'

module ActsAsDefaultable
  extend ActiveSupport::Concern

  included do
    def self.acts_as_defaultable(*options)

      after_save :set_unique_default

      if options.size > 1
        column = options.first
        relation = options.second[:relation]
      elsif options.first.is_a?(Hash)
        relation = options.first[:relation]
      else
        column = options.first
      end

      column ||= :default
      column = column.to_s
      relation = relation.to_s
      relation_column = column + '_' + relation

      puts "acts_as_defaultable: Specify a column #{column} in #{self}" unless column_names.include?(column)
      if !relation.blank? && !column_names.include?(relation_column)
         puts "acts_as_defaultable: Specify a column #{relation_column} in #{self}"
      end

      if column_names.include?(column)
        positive_value =
          case columns_hash[column].type
          when :integer
            1
          when :boolean
            true
          when :string
            "'on'"
          end

        negative_value =
          case columns_hash[column].type
          when :integer
            0
          when :boolean
            false
          when :string
            "'off'"
          end
      end

      class_methods = %(
        def self.default_column
          "#{column}"
        end

        def self.default_relation_column
          "#{relation_column}"
        end

        def self.default_positive_value
          #{positive_value}
        end

        def self.default_negative_value
          #{negative_value}
        end
      )

      class_eval <<-EOF

        #{class_methods}

        def self.default
          all_defaults.first
        end

        def self.all_defaults
          where(default_column => default_positive_value)
        end

        def set_unique_default
          if send(self.class.default_column) == self.class.default_positive_value
            self.class.all_defaults.reject{ |x| x == self }.each do |obj|
              obj.update_attribute self.class.default_column, self.class.default_negative_value
            end
          end
        end

        def #{relation_column}
         Object.const_get("#{relation.classify}").find_by_id(read_attribute(self.class.default_relation_column))
        end

        def #{relation_column}=(obj)
         default_relation_id = obj.instance_of?(#{relation.classify}) ? obj.id : 0
         write_attribute(self.class.default_relation_column, default_relation_id)
        end

        def after_destroy(record)
          self.class.where(self.class.default_relation_column => record.id).update_all(self.class.default_relation_column => 0)
        end

      EOF

    end
  end

end

ActiveRecord::Base.send :include, ActsAsDefaultable