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!
          # Don't rebuild a valid tree.
          return true if 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? || leaf? || !self.class.exists?(id)

          delete_method = acts_as_nested_set_options[:dependent] == :destroy ?
            :destroy_all : :delete_all

          # TODO: should destroy children (not descendants) when deleted_method is :destroy_all
          self.class.base_class.transaction do
            reload_nested_set
            nested_set_scope.send(delete_method,
              ["#{quoted_left_column_name} > ? AND #{quoted_right_column_name} < ?",
                left, right]
            )
            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
