Insertion sort on doubly linked list in ruby

Ruby program for Insertion sort on doubly linked list. Here problem description and other solutions.

#  Ruby program for
#  Perform insertion sort on doubly linked list
class LinkNode 
	# Define the accessor and reader of class LinkNode
	attr_reader :data, :next, :prev
	attr_accessor :data, :next, :prev
	def initialize(data) 
		self.data = data
		self.next = nil
		self.prev = nil
	end

end

class DoublyLinkedList 
	# Define the accessor and reader of class DoublyLinkedList
	attr_reader :head, :tail
	attr_accessor :head, :tail
	def initialize() 
		self.head = nil
		self.tail = nil
	end

	#  Insert new node at end position
	def insert(value) 
		#  Create a node
		node = LinkNode.new(value)
		if (self.head == nil) 
			#  Add first node
			self.head = node
			self.tail = node
			return
		end

		#  Add node at last position
		self.tail.next = node
		node.prev = self.tail
		self.tail = node
	end

	#  Display node element of doubly linked list
	def display() 
		if (self.head == nil) 
			print("Empty Linked List\n")
		else
 
			print("\nLinked List Head to Tail :")
			#  Get first node of linked list
			temp = self.head
			#  iterate linked list 
			while (temp != nil) 
				#  Display node value
				print("  ", temp.data)
				#  Visit to next node
				temp = temp.next
			end

			print("\nLinked List Tail to Head :")
			#  Get last node of linked list
			temp = self.tail
			#  iterate linked list 
			while (temp != nil) 
				#  Display node value
				print("  ", temp.data)
				#  Visit to prev node
				temp = temp.prev
			end

			print("\n")
		end

	end

	#  Swap value of given node
	def swapData(first, second) 
		value = first.data
		first.data = second.data
		second.data = value
	end

	#  Sort elements using insertion sort
	def insertionSort() 
		#  Get first node
		front = self.head
		back = nil
		while (front != nil) 
			#  Get next node
			back = front.next
			#  Update node value when consecutive nodes are not sort
			while (back != nil && 
                   back.prev != nil && 
                   back.data < back.prev.data) 
				#  Modified node data
				self.swapData(back, back.prev)
				#  Visit to previous node
				back = back.prev
			end

			#  Visit to next node
			front = front.next
		end

	end

end

def main() 
	dll = DoublyLinkedList.new()
	# Insert element of linked list
	dll.insert(25)
	dll.insert(2)
	dll.insert(6)
	dll.insert(14)
	dll.insert(12)
	dll.insert(9)
	dll.insert(16)
	dll.insert(3)
	print("\n Before Sort")
	dll.display()
	#  Display all node
	dll.insertionSort()
	print("\n After Sort")
	dll.display()
end

main()

Output

 Before Sort
Linked List Head to Tail :  25  2  6  14  12  9  16  3
Linked List Tail to Head :  3  16  9  12  14  6  2  25

 After Sort
Linked List Head to Tail :  2  3  6  9  12  14  16  25
Linked List Tail to Head :  25  16  14  12  9  6  3  2