from __future__ import print_function
from linked_list import LinkedList
from linked_list_node import LinkedListNode
from linked_list_reversal import reverse_linked_list
from print_list import print_list_with_forward_arrow

def reverse_k_groups(head, k):

    # Create a dummy node and set its next pointer to the head
    dummy = LinkedListNode(0)
    dummy.next = head
    ptr = dummy
 
    while(ptr != None):

        print("\tIdentifying a group of", k, "nodes:")
        print("\t\tptr:", ptr.data)

        # Keep track of the current position
        tracker = ptr

        print("\t\tCurrent group: ", end = "")

        # Traverse k nodes to check if there are enough nodes to reverse
        for i in range(k):

            # If there are not enough nodes to reverse, break out of the loop
            if tracker == None:
                break
       
            tracker = tracker.next
            print(tracker.data, end = " ") if tracker else print("", end = "")

        if tracker == None:
            print("\n\t\tThe above group contains less than", k, "nodes, so we can't reverse it.\n")
            break
    
        # Reverse the current group of k nodes
        print("\n\t\tThe above group of",k,"nodes can be reversed.\n")
        print("\tReversing the current group of", k, "nodes:")
        previous, current = reverse_linked_list(ptr.next, k)
        print("\t\tReversed group: ", end = "")
        print_list_with_forward_arrow(previous)

        # Connect the reversed group to the rest of the linked list
        print("\n\n\tRe-attatching the reversed group to the rest of the linked list:")
        last_node_of_reversed_group = ptr.next
        last_node_of_reversed_group.next = current
        ptr.next = previous
        ptr = last_node_of_reversed_group
        print("\t\t", end = "")
        print_list_with_forward_arrow(dummy.next)

        break

# Driver code    
def main():
    input_list = [1, 2, 3, 4, 5, 6, 7, 8]
    k = 3
    input_linked_list = LinkedList()
    input_linked_list.create_linked_list(input_list)

    print("Linked list: ", end=" ")
    print_list_with_forward_arrow(input_linked_list.head)
    print('\n')
    result = reverse_k_groups(input_linked_list.head, k)

if __name__ == '__main__':
    main()