require 'mega/dynamod'

module Og

# Attach list/ordering methods to the enchanted class.

module Orderable

  def self.append_dynamic_features(base, options)
    o = { 
      :position => 'position', 
      :type => Fixnum, 
    }
    o.update(options) if options

    if o[:scope].is_a?(Symbol) && o[:scope].to_s !~ /_oid$/    
      o[:scope] = "#{o[:scope]}_oid".intern 
    end

    position = o[:position]
    scope = o[:scope]

    if scope
      if scope.is_a?(Symbol)
        scope = %{(#{scope} ? "#{scope} = \#{@#{scope}}" : "#{scope} IS NULL")}
      end
    
      cond = ':condition => ' + scope
      cond_and = ':condition => ' + scope + ' + " AND " +'
    else
      cond = ':condition => nil'
      cond_and = ':condition => '
    end    

    code = %{    
      property :#{position}, #{o[:type]}

      pre "add_to_bottom", :on => :og_insert  
      pre "decrement_position_of_lower_items", :on => :og_delete
      
      def move_higher
        if higher = higher_item
          #{base}.transaction do
            higher.increment_position
            decrement_position
          end
        end
      end

      def move_lower
        if lower = lower_item
          #{base}.transaction do
            lower.decrement_position
            increment_position
          end
        end
      end

      def move_to_top
        #{base}.transaction do
          increment_position_of_higher_items
          set_top_position
        end
      end

      def move_to_bottom
        #{base}.transaction do
          decrement_position_of_lower_items
          set_bottom_position
        end                      
      end

      def move_to(dest_position)
        return if @#{position} == dest_position
        
        #{base}.transaction do
          if @#{position} < dest_position
            #{base}.update("#{position}=(#{position} - 1)", #{cond_and}"#{position} > \#\{@#{position}\} AND #{position} <= \#\{dest_position\}")
          else
            #{base}.update("#{position}=(#{position} + 1)", #{cond_and}"#{position} >= \#\{dest_position\} AND #{position} < \#\{@#{position}\} ")
          end
          @#{position} = dest_position
          update_property(:#{position})
        end
        
        self
      end

      def add_to_top
        increment_position_of_all_items
      end

      def add_to_bottom
        @#{position} = bottom_position + 1
      end

      def add_to
      end

      def higher_item
        #{base}.one(#{cond_and}"#{position}=\#\{@#{position} - 1\}")
      end
      alias_method :previous_item, :higher_item

      def lower_item
        #{base}.one(#{cond_and}"#{position}=\#\{@#{position} + 1\}")
      end
      alias_method :next_item, :lower_item

      def top_item
      end
      alias_method :first_item, :top_item

      def bottom_item
        #{base}.one(#{cond}, :order => "#{position} DESC", :limit => 1)
      end
      alias_method :last_item, :last_item

      def top?
        @#{position} == 1
      end
      alias_method :first?, :top?

      def bottom?
        @#{position} == bottom_position
      end
      alias_method :last?, :bottom?

      def increment_position
        @#{position} += 1
        update_property(:#{position})
      end
    
      def decrement_position
        @#{position} -= 1
        update_property(:#{position})
      end

      def bottom_position
        item = bottom_item
        item ? item.#{position} : 0
      end

      def set_top_position
        @#{position} = 1
        update_property(:#{position})
      end

      def set_bottom_position
        @#{position} = bottom_position + 1
        update_property(:#{position})
      end

      def increment_position_of_higher_items
        #{base}.update("#{position}=(#{position} + 1)", #{cond_and}"#{position} < \#\{@#{position}\}")
      end

      def increment_position_of_all_items
        #{base}.update("#{position}=(#{position} + 1)", #{cond})
      end
      
      def decrement_position_of_lower_items
        #{base}.update("#{position}=(#{position} - 1)", #{cond_and}"#{position} > \#\{@#{position}\}")
      end
    }    
    
    base.module_eval(code)
  end
  
end

end 

# * George Moschovitis <gm@navel.gr>