Chris@909: module ActiveRecord
Chris@909:   module Acts #:nodoc:
Chris@909:     module List #:nodoc:
Chris@909:       def self.included(base)
Chris@909:         base.extend(ClassMethods)
Chris@909:       end
Chris@909: 
Chris@909:       # This +acts_as+ extension provides the capabilities for sorting and reordering a number of objects in a list.
Chris@909:       # The class that has this specified needs to have a +position+ column defined as an integer on
Chris@909:       # the mapped database table.
Chris@909:       #
Chris@909:       # Todo list example:
Chris@909:       #
Chris@909:       #   class TodoList < ActiveRecord::Base
Chris@909:       #     has_many :todo_items, :order => "position"
Chris@909:       #   end
Chris@909:       #
Chris@909:       #   class TodoItem < ActiveRecord::Base
Chris@909:       #     belongs_to :todo_list
Chris@909:       #     acts_as_list :scope => :todo_list
Chris@909:       #   end
Chris@909:       #
Chris@909:       #   todo_list.first.move_to_bottom
Chris@909:       #   todo_list.last.move_higher
Chris@909:       module ClassMethods
Chris@909:         # Configuration options are:
Chris@909:         #
Chris@909:         # * +column+ - specifies the column name to use for keeping the position integer (default: +position+)
Chris@909:         # * +scope+ - restricts what is to be considered a list. Given a symbol, it'll attach <tt>_id</tt> 
Chris@909:         #   (if it hasn't already been added) and use that as the foreign key restriction. It's also possible 
Chris@909:         #   to give it an entire string that is interpolated if you need a tighter scope than just a foreign key.
Chris@909:         #   Example: <tt>acts_as_list :scope => 'todo_list_id = #{todo_list_id} AND completed = 0'</tt>
Chris@909:         def acts_as_list(options = {})
Chris@909:           configuration = { :column => "position", :scope => "1 = 1" }
Chris@909:           configuration.update(options) if options.is_a?(Hash)
Chris@909: 
Chris@909:           configuration[:scope] = "#{configuration[:scope]}_id".intern if configuration[:scope].is_a?(Symbol) && configuration[:scope].to_s !~ /_id$/
Chris@909: 
Chris@909:           if configuration[:scope].is_a?(Symbol)
Chris@909:             scope_condition_method = %(
Chris@909:               def scope_condition
Chris@909:                 if #{configuration[:scope].to_s}.nil?
Chris@909:                   "#{configuration[:scope].to_s} IS NULL"
Chris@909:                 else
Chris@909:                   "#{configuration[:scope].to_s} = \#{#{configuration[:scope].to_s}}"
Chris@909:                 end
Chris@909:               end
Chris@909:             )
Chris@909:           else
Chris@909:             scope_condition_method = "def scope_condition() \"#{configuration[:scope]}\" end"
Chris@909:           end
Chris@909: 
Chris@909:           class_eval <<-EOV
Chris@909:             include ActiveRecord::Acts::List::InstanceMethods
Chris@909: 
Chris@909:             def acts_as_list_class
Chris@909:               ::#{self.name}
Chris@909:             end
Chris@909: 
Chris@909:             def position_column
Chris@909:               '#{configuration[:column]}'
Chris@909:             end
Chris@909: 
Chris@909:             #{scope_condition_method}
Chris@909: 
Chris@909:             before_destroy :remove_from_list
Chris@909:             before_create  :add_to_list_bottom
Chris@909:           EOV
Chris@909:         end
Chris@909:       end
Chris@909: 
Chris@909:       # All the methods available to a record that has had <tt>acts_as_list</tt> specified. Each method works
Chris@909:       # by assuming the object to be the item in the list, so <tt>chapter.move_lower</tt> would move that chapter
Chris@909:       # lower in the list of all chapters. Likewise, <tt>chapter.first?</tt> would return +true+ if that chapter is
Chris@909:       # the first in the list of all chapters.
Chris@909:       module InstanceMethods
Chris@909:         # Insert the item at the given position (defaults to the top position of 1).
Chris@909:         def insert_at(position = 1)
Chris@909:           insert_at_position(position)
Chris@909:         end
Chris@909: 
Chris@909:         # Swap positions with the next lower item, if one exists.
Chris@909:         def move_lower
Chris@909:           return unless lower_item
Chris@909: 
Chris@909:           acts_as_list_class.transaction do
Chris@909:             lower_item.decrement_position
Chris@909:             increment_position
Chris@909:           end
Chris@909:         end
Chris@909: 
Chris@909:         # Swap positions with the next higher item, if one exists.
Chris@909:         def move_higher
Chris@909:           return unless higher_item
Chris@909: 
Chris@909:           acts_as_list_class.transaction do
Chris@909:             higher_item.increment_position
Chris@909:             decrement_position
Chris@909:           end
Chris@909:         end
Chris@909: 
Chris@909:         # Move to the bottom of the list. If the item is already in the list, the items below it have their
Chris@909:         # position adjusted accordingly.
Chris@909:         def move_to_bottom
Chris@909:           return unless in_list?
Chris@909:           acts_as_list_class.transaction do
Chris@909:             decrement_positions_on_lower_items
Chris@909:             assume_bottom_position
Chris@909:           end
Chris@909:         end
Chris@909: 
Chris@909:         # Move to the top of the list. If the item is already in the list, the items above it have their
Chris@909:         # position adjusted accordingly.
Chris@909:         def move_to_top
Chris@909:           return unless in_list?
Chris@909:           acts_as_list_class.transaction do
Chris@909:             increment_positions_on_higher_items
Chris@909:             assume_top_position
Chris@909:           end
Chris@909:         end
Chris@909:         
Chris@909:         # Move to the given position
Chris@909:         def move_to=(pos)
Chris@909:           case pos.to_s
Chris@909:           when 'highest'
Chris@909:             move_to_top
Chris@909:           when 'higher'
Chris@909:             move_higher
Chris@909:           when 'lower'
Chris@909:             move_lower
Chris@909:           when 'lowest'
Chris@909:             move_to_bottom
Chris@909:           end
Chris@909:         end
Chris@909: 
Chris@909:         # Removes the item from the list.
Chris@909:         def remove_from_list
Chris@909:           if in_list?
Chris@909:             decrement_positions_on_lower_items
Chris@909:             update_attribute position_column, nil
Chris@909:           end
Chris@909:         end
Chris@909: 
Chris@909:         # Increase the position of this item without adjusting the rest of the list.
Chris@909:         def increment_position
Chris@909:           return unless in_list?
Chris@909:           update_attribute position_column, self.send(position_column).to_i + 1
Chris@909:         end
Chris@909: 
Chris@909:         # Decrease the position of this item without adjusting the rest of the list.
Chris@909:         def decrement_position
Chris@909:           return unless in_list?
Chris@909:           update_attribute position_column, self.send(position_column).to_i - 1
Chris@909:         end
Chris@909: 
Chris@909:         # Return +true+ if this object is the first in the list.
Chris@909:         def first?
Chris@909:           return false unless in_list?
Chris@909:           self.send(position_column) == 1
Chris@909:         end
Chris@909: 
Chris@909:         # Return +true+ if this object is the last in the list.
Chris@909:         def last?
Chris@909:           return false unless in_list?
Chris@909:           self.send(position_column) == bottom_position_in_list
Chris@909:         end
Chris@909: 
Chris@909:         # Return the next higher item in the list.
Chris@909:         def higher_item
Chris@909:           return nil unless in_list?
Chris@909:           acts_as_list_class.find(:first, :conditions =>
Chris@909:             "#{scope_condition} AND #{position_column} = #{(send(position_column).to_i - 1).to_s}"
Chris@909:           )
Chris@909:         end
Chris@909: 
Chris@909:         # Return the next lower item in the list.
Chris@909:         def lower_item
Chris@909:           return nil unless in_list?
Chris@909:           acts_as_list_class.find(:first, :conditions =>
Chris@909:             "#{scope_condition} AND #{position_column} = #{(send(position_column).to_i + 1).to_s}"
Chris@909:           )
Chris@909:         end
Chris@909: 
Chris@909:         # Test if this record is in a list
Chris@909:         def in_list?
Chris@909:           !send(position_column).nil?
Chris@909:         end
Chris@909: 
Chris@909:         private
Chris@909:           def add_to_list_top
Chris@909:             increment_positions_on_all_items
Chris@909:           end
Chris@909: 
Chris@909:           def add_to_list_bottom
Chris@909:             self[position_column] = bottom_position_in_list.to_i + 1
Chris@909:           end
Chris@909: 
Chris@909:           # Overwrite this method to define the scope of the list changes
Chris@909:           def scope_condition() "1" end
Chris@909: 
Chris@909:           # Returns the bottom position number in the list.
Chris@909:           #   bottom_position_in_list    # => 2
Chris@909:           def bottom_position_in_list(except = nil)
Chris@909:             item = bottom_item(except)
Chris@909:             item ? item.send(position_column) : 0
Chris@909:           end
Chris@909: 
Chris@909:           # Returns the bottom item
Chris@909:           def bottom_item(except = nil)
Chris@909:             conditions = scope_condition
Chris@909:             conditions = "#{conditions} AND #{self.class.primary_key} != #{except.id}" if except
Chris@909:             acts_as_list_class.find(:first, :conditions => conditions, :order => "#{position_column} DESC")
Chris@909:           end
Chris@909: 
Chris@909:           # Forces item to assume the bottom position in the list.
Chris@909:           def assume_bottom_position
Chris@909:             update_attribute(position_column, bottom_position_in_list(self).to_i + 1)
Chris@909:           end
Chris@909: 
Chris@909:           # Forces item to assume the top position in the list.
Chris@909:           def assume_top_position
Chris@909:             update_attribute(position_column, 1)
Chris@909:           end
Chris@909: 
Chris@909:           # This has the effect of moving all the higher items up one.
Chris@909:           def decrement_positions_on_higher_items(position)
Chris@909:             acts_as_list_class.update_all(
Chris@909:               "#{position_column} = (#{position_column} - 1)", "#{scope_condition} AND #{position_column} <= #{position}"
Chris@909:             )
Chris@909:           end
Chris@909: 
Chris@909:           # This has the effect of moving all the lower items up one.
Chris@909:           def decrement_positions_on_lower_items
Chris@909:             return unless in_list?
Chris@909:             acts_as_list_class.update_all(
Chris@909:               "#{position_column} = (#{position_column} - 1)", "#{scope_condition} AND #{position_column} > #{send(position_column).to_i}"
Chris@909:             )
Chris@909:           end
Chris@909: 
Chris@909:           # This has the effect of moving all the higher items down one.
Chris@909:           def increment_positions_on_higher_items
Chris@909:             return unless in_list?
Chris@909:             acts_as_list_class.update_all(
Chris@909:               "#{position_column} = (#{position_column} + 1)", "#{scope_condition} AND #{position_column} < #{send(position_column).to_i}"
Chris@909:             )
Chris@909:           end
Chris@909: 
Chris@909:           # This has the effect of moving all the lower items down one.
Chris@909:           def increment_positions_on_lower_items(position)
Chris@909:             acts_as_list_class.update_all(
Chris@909:               "#{position_column} = (#{position_column} + 1)", "#{scope_condition} AND #{position_column} >= #{position}"
Chris@909:            )
Chris@909:           end
Chris@909: 
Chris@909:           # Increments position (<tt>position_column</tt>) of all items in the list.
Chris@909:           def increment_positions_on_all_items
Chris@909:             acts_as_list_class.update_all(
Chris@909:               "#{position_column} = (#{position_column} + 1)",  "#{scope_condition}"
Chris@909:             )
Chris@909:           end
Chris@909: 
Chris@909:           def insert_at_position(position)
Chris@909:             remove_from_list
Chris@909:             increment_positions_on_lower_items(position)
Chris@909:             self.update_attribute(position_column, position)
Chris@909:           end
Chris@909:       end 
Chris@909:     end
Chris@909:   end
Chris@909: end