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module CollectiveIdea #:nodoc:

  module Acts #:nodoc:

    module NestedSet #:nodoc:

      def self.included(base)

        base.extend(SingletonMethods)

      end

      # This acts provides Nested Set functionality. Nested Set is a smart way to implement

      # an _ordered_ tree, with the added feature that you can select the children and all of their

      # descendants with a single query. The drawback is that insertion or move need some complex

      # sql queries. But everything is done here by this module!

      #

      # Nested sets are appropriate each time you want either an orderd tree (menus,

      # commercial categories) or an efficient way of querying big trees (threaded posts).

      #

      # == API

      #

      # Methods names are aligned with acts_as_tree as much as possible, to make replacment from one

      # by another easier, except for the creation:

      #

      # in acts_as_tree:

      #   item.children.create(:name => "child1")

      #

      # in acts_as_nested_set:

      #   # adds a new item at the "end" of the tree, i.e. with child.left = max(tree.right)+1

      #   child = MyClass.new(:name => "child1")

      #   child.save

      #   # now move the item to its right place

      #   child.move_to_child_of my_item

      #

      # You can pass an id or an object to:

      # * <tt>#move_to_child_of</tt>

      # * <tt>#move_to_right_of</tt>

      # * <tt>#move_to_left_of</tt>

      #

      module SingletonMethods

        # Configuration options are:

        #

        # * +:parent_column+ - specifies the column name to use for keeping the position integer (default: parent_id)

        # * +:left_column+ - column name for left boundry data, default "lft"

        # * +:right_column+ - column name for right boundry data, default "rgt"

        # * +:scope+ - restricts what is to be considered a list. Given a symbol, it'll attach "_id"

        #   (if it hasn't been already) and use that as the foreign key restriction. You

        #   can also pass an array to scope by multiple attributes.

        #   Example: <tt>acts_as_nested_set :scope => [:notable_id, :notable_type]</tt>

        # * +:dependent+ - behavior for cascading destroy. If set to :destroy, all the

        #   child objects are destroyed alongside this object by calling their destroy

        #   method. If set to :delete_all (default), all the child objects are deleted

        #   without calling their destroy method.

        #

        # See CollectiveIdea::Acts::NestedSet::ClassMethods for a list of class methods and

        # CollectiveIdea::Acts::NestedSet::InstanceMethods for a list of instance methods added 

        # to acts_as_nested_set models

        def acts_as_nested_set(options = {})

          options = {

            :parent_column => 'parent_id',

            :left_column => 'lft',

            :right_column => 'rgt',

            :order => 'id',

            :dependent => :delete_all, # or :destroy

          }.merge(options)

          if options[:scope].is_a?(Symbol) && options[:scope].to_s !~ /_id$/

            options[:scope] = "#{options[:scope]}_id".intern

          end

          write_inheritable_attribute :acts_as_nested_set_options, options

          class_inheritable_reader :acts_as_nested_set_options

          include Comparable

          include Columns

          include InstanceMethods

          extend Columns

          extend ClassMethods

          # no bulk assignment

          attr_protected  left_column_name.intern,

                          right_column_name.intern, 

                          parent_column_name.intern

          before_create :set_default_left_and_right

          before_destroy :prune_from_tree

          # no assignment to structure fields

          [left_column_name, right_column_name, parent_column_name].each do |column|

            module_eval <<-"end_eval", __FILE__, __LINE__

              def #{column}=(x)

                raise ActiveRecord::ActiveRecordError, "Unauthorized assignment to #{column}: it's an internal field handled by acts_as_nested_set code, use move_to_* methods instead."

              end

            end_eval

          end

          named_scope :roots, :conditions => {parent_column_name => nil}, :order => quoted_left_column_name

          named_scope :leaves, :conditions => "#{quoted_right_column_name} - #{quoted_left_column_name} = 1", :order => quoted_left_column_name

          if self.respond_to?(:define_callbacks)

            define_callbacks("before_move", "after_move")              

          end

        end

      end

      module ClassMethods

        # Returns the first root

        def root

          roots.find(:first)

        end

        def valid?

          left_and_rights_valid? && no_duplicates_for_columns? && all_roots_valid?

        end

        def left_and_rights_valid?

          count(

            :joins => "LEFT OUTER JOIN #{quoted_table_name} AS parent ON " +

              "#{quoted_table_name}.#{quoted_parent_column_name} = parent.#{primary_key}",

            :conditions =>

              "#{quoted_table_name}.#{quoted_left_column_name} IS NULL OR " +

              "#{quoted_table_name}.#{quoted_right_column_name} IS NULL OR " +

              "#{quoted_table_name}.#{quoted_left_column_name} >= " +

                "#{quoted_table_name}.#{quoted_right_column_name} OR " +

              "(#{quoted_table_name}.#{quoted_parent_column_name} IS NOT NULL AND " +

                "(#{quoted_table_name}.#{quoted_left_column_name} <= parent.#{quoted_left_column_name} OR " +

                "#{quoted_table_name}.#{quoted_right_column_name} >= parent.#{quoted_right_column_name}))"

          ) == 0

        end

        def no_duplicates_for_columns?

          scope_string = Array(acts_as_nested_set_options[:scope]).map do |c|

            connection.quote_column_name(c)

          end.push(nil).join(", ")

          [quoted_left_column_name, quoted_right_column_name].all? do |column|

            # No duplicates

            find(:first, 

              :select => "#{scope_string}#{column}, COUNT(#{column})", 

              :group => "#{scope_string}#{column} 

                HAVING COUNT(#{column}) > 1").nil?

          end

        end

        # Wrapper for each_root_valid? that can deal with scope.

        def all_roots_valid?

          if acts_as_nested_set_options[:scope]

            roots(:group => scope_column_names).group_by{|record| scope_column_names.collect{|col| record.send(col.to_sym)}}.all? do |scope, grouped_roots|

              each_root_valid?(grouped_roots)

            end

          else

            each_root_valid?(roots)

          end

        end

        def each_root_valid?(roots_to_validate)

          left = right = 0

          roots_to_validate.all? do |root|

            (root.left > left && root.right > right).tap do

              left = root.left

              right = root.right

            end

          end

        end

        # Rebuilds the left & rights if unset or invalid.  Also very useful for converting from acts_as_tree.

        def rebuild!(force=false)

          # Don't rebuild a valid tree.

          # valid? doesn't strictly validate the tree

          return true if !force && valid?

          scope = lambda{|node|}

          if acts_as_nested_set_options[:scope]

            scope = lambda{|node| 

              scope_column_names.inject(""){|str, column_name|

                str << "AND #{connection.quote_column_name(column_name)} = #{connection.quote(node.send(column_name.to_sym))} "

              }

            }

          end

          indices = {}

          set_left_and_rights = lambda do |node|

            # set left

            node[left_column_name] = indices[scope.call(node)] += 1

            # find

            find(:all, :conditions => ["#{quoted_parent_column_name} = ? #{scope.call(node)}", node], :order => "#{quoted_left_column_name}, #{quoted_right_column_name}, #{acts_as_nested_set_options[:order]}").each{|n| set_left_and_rights.call(n) }

            # set right

            node[right_column_name] = indices[scope.call(node)] += 1    

            node.save!    

          end

          # Find root node(s)

          root_nodes = find(:all, :conditions => "#{quoted_parent_column_name} IS NULL", :order => "#{quoted_left_column_name}, #{quoted_right_column_name}, #{acts_as_nested_set_options[:order]}").each do |root_node|

            # setup index for this scope

            indices[scope.call(root_node)] ||= 0

            set_left_and_rights.call(root_node)

          end

        end

      end

      # Mixed into both classes and instances to provide easy access to the column names

      module Columns

        def left_column_name

          acts_as_nested_set_options[:left_column]

        end

        def right_column_name

          acts_as_nested_set_options[:right_column]

        end

        def parent_column_name

          acts_as_nested_set_options[:parent_column]

        end

        def scope_column_names

          Array(acts_as_nested_set_options[:scope])

        end

        def quoted_left_column_name

          connection.quote_column_name(left_column_name)

        end

        def quoted_right_column_name

          connection.quote_column_name(right_column_name)

        end

        def quoted_parent_column_name

          connection.quote_column_name(parent_column_name)

        end

        def quoted_scope_column_names

          scope_column_names.collect {|column_name| connection.quote_column_name(column_name) }

        end

      end

      # Any instance method that returns a collection makes use of Rails 2.1's named_scope (which is bundled for Rails 2.0), so it can be treated as a finder.

      #

      #   category.self_and_descendants.count

      #   category.ancestors.find(:all, :conditions => "name like '%foo%'")

      module InstanceMethods

        # Value of the parent column

        def parent_id

          self[parent_column_name]

        end

        # Value of the left column

        def left

          self[left_column_name]

        end

        # Value of the right column

        def right

          self[right_column_name]

        end

        # Returns true if this is a root node.

        def root?

          parent_id.nil?

        end

        def leaf?

          new_record? || (right - left == 1)

        end

        # Returns true is this is a child node

        def child?

          !parent_id.nil?

        end

        # order by left column

        def <=>(x)

          left <=> x.left

        end

        # Redefine to act like active record

        def ==(comparison_object)

          comparison_object.equal?(self) ||

            (comparison_object.instance_of?(self.class) &&

              comparison_object.id == id &&

              !comparison_object.new_record?)

        end

        # Returns root

        def root

          self_and_ancestors.find(:first)

        end

        # Returns the immediate parent

        def parent

          nested_set_scope.find_by_id(parent_id) if parent_id

        end

        # Returns the array of all parents and self

        def self_and_ancestors

          nested_set_scope.scoped :conditions => [

            "#{self.class.table_name}.#{quoted_left_column_name} <= ? AND #{self.class.table_name}.#{quoted_right_column_name} >= ?", left, right

          ]

        end

        # Returns an array of all parents

        def ancestors

          without_self self_and_ancestors

        end

        # Returns the array of all children of the parent, including self

        def self_and_siblings

          nested_set_scope.scoped :conditions => {parent_column_name => parent_id}

        end

        # Returns the array of all children of the parent, except self

        def siblings

          without_self self_and_siblings

        end

        # Returns a set of all of its nested children which do not have children  

        def leaves

          descendants.scoped :conditions => "#{self.class.table_name}.#{quoted_right_column_name} - #{self.class.table_name}.#{quoted_left_column_name} = 1"

        end    

        # Returns the level of this object in the tree

        # root level is 0

        def level

          parent_id.nil? ? 0 : ancestors.count

        end

        # Returns a set of itself and all of its nested children

        def self_and_descendants

          nested_set_scope.scoped :conditions => [

            "#{self.class.table_name}.#{quoted_left_column_name} >= ? AND #{self.class.table_name}.#{quoted_right_column_name} <= ?", left, right

          ]

        end

        # Returns a set of all of its children and nested children

        def descendants

          without_self self_and_descendants

        end

        # Returns a set of only this entry's immediate children

        def children

          nested_set_scope.scoped :conditions => {parent_column_name => self}

        end

        def is_descendant_of?(other)

          other.left < self.left && self.left < other.right && same_scope?(other)

        end

        def is_or_is_descendant_of?(other)

          other.left <= self.left && self.left < other.right && same_scope?(other)

        end

        def is_ancestor_of?(other)

          self.left < other.left && other.left < self.right && same_scope?(other)

        end

        def is_or_is_ancestor_of?(other)

          self.left <= other.left && other.left < self.right && same_scope?(other)

        end

        # Check if other model is in the same scope

        def same_scope?(other)

          Array(acts_as_nested_set_options[:scope]).all? do |attr|

            self.send(attr) == other.send(attr)

          end

        end

        # Find the first sibling to the left

        def left_sibling

          siblings.find(:first, :conditions => ["#{self.class.table_name}.#{quoted_left_column_name} < ?", left],

            :order => "#{self.class.table_name}.#{quoted_left_column_name} DESC")

        end

        # Find the first sibling to the right

        def right_sibling

          siblings.find(:first, :conditions => ["#{self.class.table_name}.#{quoted_left_column_name} > ?", left])

        end

        # Shorthand method for finding the left sibling and moving to the left of it.

        def move_left

          move_to_left_of left_sibling

        end

        # Shorthand method for finding the right sibling and moving to the right of it.

        def move_right

          move_to_right_of right_sibling

        end

        # Move the node to the left of another node (you can pass id only)

        def move_to_left_of(node)

          move_to node, :left

        end

        # Move the node to the left of another node (you can pass id only)

        def move_to_right_of(node)

          move_to node, :right

        end

        # Move the node to the child of another node (you can pass id only)

        def move_to_child_of(node)

          move_to node, :child

        end

        # Move the node to root nodes

        def move_to_root

          move_to nil, :root

        end

        def move_possible?(target)

          self != target && # Can't target self

          same_scope?(target) && # can't be in different scopes

          # !(left..right).include?(target.left..target.right) # this needs tested more

          # detect impossible move

          !((left <= target.left && right >= target.left) or (left <= target.right && right >= target.right))

        end

        def to_text

          self_and_descendants.map do |node|

            "#{'*'*(node.level+1)} #{node.id} #{node.to_s} (#{node.parent_id}, #{node.left}, #{node.right})"

          end.join("\n")

        end

      protected

        def without_self(scope)

          scope.scoped :conditions => ["#{self.class.table_name}.#{self.class.primary_key} != ?", self]

        end

        # All nested set queries should use this nested_set_scope, which performs finds on

        # the base ActiveRecord class, using the :scope declared in the acts_as_nested_set

        # declaration.

        def nested_set_scope

          options = {:order => "#{self.class.table_name}.#{quoted_left_column_name}"}

          scopes = Array(acts_as_nested_set_options[:scope])

          options[:conditions] = scopes.inject({}) do |conditions,attr|

            conditions.merge attr => self[attr]

          end unless scopes.empty?

          self.class.base_class.scoped options

        end

        # on creation, set automatically lft and rgt to the end of the tree

        def set_default_left_and_right

          maxright = nested_set_scope.maximum(right_column_name) || 0

          # adds the new node to the right of all existing nodes

          self[left_column_name] = maxright + 1

          self[right_column_name] = maxright + 2

        end

        # Prunes a branch off of the tree, shifting all of the elements on the right

        # back to the left so the counts still work.

        def prune_from_tree

          return if right.nil? || left.nil? || !self.class.exists?(id)

          self.class.base_class.transaction do

            reload_nested_set

            if acts_as_nested_set_options[:dependent] == :destroy

              children.each(&:destroy)

            else

              nested_set_scope.send(:delete_all,

                ["#{quoted_left_column_name} > ? AND #{quoted_right_column_name} < ?",

                  left, right]

              )

            end

            reload_nested_set

            diff = right - left + 1

            nested_set_scope.update_all(

              ["#{quoted_left_column_name} = (#{quoted_left_column_name} - ?)", diff],

              ["#{quoted_left_column_name} >= ?", right]

            )

            nested_set_scope.update_all(

              ["#{quoted_right_column_name} = (#{quoted_right_column_name} - ?)", diff],

              ["#{quoted_right_column_name} >= ?", right]

            )

          end

          # Reload is needed because children may have updated their parent (self) during deletion.

          reload

        end

        # reload left, right, and parent

        def reload_nested_set

          reload(:select => "#{quoted_left_column_name}, " +

            "#{quoted_right_column_name}, #{quoted_parent_column_name}")

        end

        def move_to(target, position)

          raise ActiveRecord::ActiveRecordError, "You cannot move a new node" if self.new_record?

          return if callback(:before_move) == false

          transaction do

            if target.is_a? self.class.base_class

              target.reload_nested_set

            elsif position != :root

              # load object if node is not an object

              target = nested_set_scope.find(target)

            end

            self.reload_nested_set

            unless position == :root || move_possible?(target)

              raise ActiveRecord::ActiveRecordError, "Impossible move, target node cannot be inside moved tree."

            end

            bound = case position

              when :child;  target[right_column_name]

              when :left;   target[left_column_name]

              when :right;  target[right_column_name] + 1

              when :root;   1

              else raise ActiveRecord::ActiveRecordError, "Position should be :child, :left, :right or :root ('#{position}' received)."

            end

            if bound > self[right_column_name]

              bound = bound - 1

              other_bound = self[right_column_name] + 1

            else

              other_bound = self[left_column_name] - 1

            end

            # there would be no change

            return if bound == self[right_column_name] || bound == self[left_column_name]

            # we have defined the boundaries of two non-overlapping intervals, 

            # so sorting puts both the intervals and their boundaries in order

            a, b, c, d = [self[left_column_name], self[right_column_name], bound, other_bound].sort

            new_parent = case position

              when :child;  target.id

              when :root;   nil

              else          target[parent_column_name]

            end

            self.class.base_class.update_all([

              "#{quoted_left_column_name} = CASE " +

                "WHEN #{quoted_left_column_name} BETWEEN :a AND :b " +

                  "THEN #{quoted_left_column_name} + :d - :b " +

                "WHEN #{quoted_left_column_name} BETWEEN :c AND :d " +

                  "THEN #{quoted_left_column_name} + :a - :c " +

                "ELSE #{quoted_left_column_name} END, " +

              "#{quoted_right_column_name} = CASE " +

                "WHEN #{quoted_right_column_name} BETWEEN :a AND :b " +

                  "THEN #{quoted_right_column_name} + :d - :b " +

                "WHEN #{quoted_right_column_name} BETWEEN :c AND :d " +

                  "THEN #{quoted_right_column_name} + :a - :c " +

                "ELSE #{quoted_right_column_name} END, " +

              "#{quoted_parent_column_name} = CASE " +

                "WHEN #{self.class.base_class.primary_key} = :id THEN :new_parent " +

                "ELSE #{quoted_parent_column_name} END",

              {:a => a, :b => b, :c => c, :d => d, :id => self.id, :new_parent => new_parent}

            ], nested_set_scope.proxy_options[:conditions])

          end

          target.reload_nested_set if target

          self.reload_nested_set

          callback(:after_move)

        end

      end

    end

  end

end