Tree with apples

tree.rb

module Tree
  # Returns list of ancestors, starting from parent until root.
  #
  #   subchild1.ancestors # => [child1, root]
  def ancestors
    node, nodes = self, []
    nodes << node = node.parent while node.parent
    nodes
  end

  # Returns list of descendants, starting from current node, not including current node.
  #
  #   root.descendants # => [child1, child2, subchild1, subchild2, subchild3, subchild4]
  def descendants
    children.each_with_object(children.to_a) {|child, arr|
      arr.concat child.descendants
    }.uniq
  end

  # Returns list of descendants, starting from current node, including current node.
  #
  #   root.self_and_descendants # => [root, child1, child2, subchild1, subchild2, subchild3, subchild4]
  def self_and_descendants
    [self] + descendants
  end

  # Returns the root node of the tree.
  def root
    node = self
    node = node.parent while node.parent
    node
  end

  # Returns all siblings of the current node.
  #
  #   subchild1.siblings # => [subchild2]
  def siblings
    self_and_siblings - [self]
  end

  # Returns all siblings and a reference to the current node.
  #
  #   subchild1.self_and_siblings # => [subchild1, subchild2]
  def self_and_siblings
    parent ? parent.children : self.class.roots
  end

  # Returns all the nodes at the same level in the tree as the current node.
  #
  #  root1child1.generation # => [root1child2, root2child1, root2child2]
  def generation
    self_and_generation - [self]
  end

  # Returns a reference to the current node and all the nodes at the same level as it in the tree.
  #
  #  root1child1.self_and_generation # => [root1child1, root1child2, root2child1, root2child2]
  def self_and_generation
    self.class.select {|node| node.tree_level == self.tree_level }
  end

  # Returns the level (depth) of the current node
  #
  #  root1child1.tree_level # => 1
  def tree_level
    self.ancestors.size
  end

  # Returns the level (depth) of the current node unless level is a column on the node.
  # Allows backwards compatibility with older versions of the gem.
  # Allows integration with apps using level as a column name.
  #
  #  root1child1.level # => 1
  def level
    if self.class.column_names.include?('level')
      super
    else
      tree_level
    end
  end

  # Returns children (without subchildren) and current node itself.
  #
  #   root.self_and_children # => [root, child1]
  def self_and_children
    [self] + self.children
  end

  # Returns ancestors and current node itself.
  #
  #   subchild1.self_and_ancestors # => [subchild1, child1, root]
  def self_and_ancestors
    [self] + self.ancestors
  end

  # Returns true if node has no parent, false otherwise
  #
  #   subchild1.root? # => false
  #   root.root?      # => true
  def root?
    parent.nil?
  end

  # Returns true if node has no children, false otherwise
  #
  #   subchild1.leaf? # => true
  #   child1.leaf?    # => false
  def leaf?
    children.size.zero?
  end
end