require "rexml/child"

module REXML
	# A parent has children, and has methods for accessing them.  The Parent
  # class is never encountered except as the superclass for some other
  # object.
	class Parent < Child
		include Enumerable

		# Constructor
		# @param parent if supplied, will be set as the parent of this object
		def initialize parent=nil
			super(parent)
			@children = []
		end

		def add( object )
			begin
				object.parent = self
				@children << object
			rescue Exception
				raise "#{$!.message}: only Child-ren can be added to a Parent"
			end
			object
		end

		alias :push :add
		alias :<< :push

		def unshift( object )
			object.parent = self
			@children.unshift object
		end

		def delete( object )
			return unless @children.include? object
			@children.delete object
			object.parent = nil
		end

		def each(&block)
			@children.each(&block)
		end

		def delete_if( &block )
			@children.delete_if(&block)
		end

		def delete_at( index )
			@children.delete_at index
		end

		def each_index( &block )
			@children.each_index(&block)
		end

		# Fetches a child at a given index
		# @param index the Integer index of the child to fetch
		def []( index )
			@children[index]
		end

		alias :each_child :each



		# Set an index entry.  See Array.[]=
		# @param index the index of the element to set
		# @param opt either the object to set, or an Integer length
		# @param child if opt is an Integer, this is the child to set
		# @return the parent (self)
		def []=( *args )
			args[-1].parent = self
			@children[*args[0..-2]] = args[-1]
		end

		# Inserts an child before another child
		# @param child1 this is either an xpath or an Element.  If an Element,
		# child2 will be inserted before child1 in the child list of the parent.
		# If an xpath, child2 will be inserted before the first child to match
		# the xpath.
		# @param child2 the child to insert
		# @return the parent (self)
		def insert_before( child1, child2 )
			if child1.kind_of? String
				child1 = XPath.first( self, child1 )
				child1.parent.insert_before child1, child2
			else
				ind = index(child1)
				@children[ind,0] = child2
				child2.parent = self
			end
			self
		end

		# Inserts an child after another child
		# @param child1 this is either an xpath or an Element.  If an Element,
		# child2 will be inserted after child1 in the child list of the parent.
		# If an xpath, child2 will be inserted after the first child to match
		# the xpath.
		# @param child2 the child to insert
		# @return the parent (self)
		def insert_after( child1, child2 )
			if child1.kind_of? String
				child1 = XPath.first( self, child1 )
				child1.parent.insert_after child1, child2
			else
				ind = index(child1)+1
				@children[ind,0] = child2
				child2.parent = self
			end
			self
		end

		def to_a
			@children.dup
		end

		# Fetches the index of a given child
		# @param child the child to get the index of
		# @return the index of the child, or nil if the object is not a child
		# of this parent.
		def index( child )
			count = -1
			@children.find { |i| count += 1 ; i.hash == child.hash }
			count
		end

		# @return the number of children of this parent
		def size
			@children.size
		end

		# Replaces one child with another, making sure the nodelist is correct
		# @param to_replace the child to replace (must be a Child)
		# @param replacement the child to insert into the nodelist (must be a 
		# Child)
		def replace_child( to_replace, replacement )
			ind = @children.index( to_replace )
			to_replace.parent = nil
			to_replace.remove
			@children[ind] = replacement
			replacement.parent = self
		end

	end
end
