//This is the implementation file
// It implements the functions in the header file

#include <stdio.h>
#include <stdlib.h>
#include "linked_list.h"

//Define a node 
struct node {
    int data;
    struct node *next;
};

//Function that creates a node
struct node *create_node(int data, struct node *next) {
    //create a pointer to a node of type struct node 
    //by using malloc to allocate memory
  
    struct node *new_node = malloc(sizeof(struct node)); 
    
    //Initialise the data by setting it to the given int

    new_node->data = data;
    
    //Initialise next pointer to point to the next node given

    new_node->next = next;
    
    return new_node;
}

//Function that prints a list
void print_list(struct node *head) {
    //create a way to keep track of where we are in the list
    struct node *current = head;
    while (current != NULL) {
        printf("%d -> ", current->data);
        current = current->next;
    }
    printf("X\n");
}

void print_list_recursive(struct node *head) {
//STOPPING CASE
//RECURSIVE CASE
    if (head == NULL) {
        printf("X\n");
    } else {
        printf("%d -> ", head->data);
        print_list_recursive(head->next);
    }
}

struct node *insert_endnode(int data, struct node *head) {
    //create a pointer and point it to the head of the list
    //that will keep track of where you are
    struct node *current = head;
    //create the new node that you want to insert by using 
    //the create_node function we wrote last week
    struct node *new_node = create_node(data, NULL);
    //Loop through until you get to the last node in the list
    //You want to stop at the last node and not go past it
    while (current->next != NULL) {
        current = current->next;
    }
    //Set the new node as the last node, but pointing the current node to it
    current->next = new_node;
    new_node->next = NULL;
    
    return head;  
}

//Function that adds node at the end of the list
struct node *insert_end(struct node *head, int data) {

//STOPPING CASE
    if (head == NULL) {
        return create_node(data, NULL);
    }
//RECURSIVE CASE
    head->next = insert_end(head->next, data);
    return head;
}



//Function to sum up the nodes of a linked list
int sum_list(struct node *head) {
    int sum = 0;
    struct node *current = head;
    
    while (current != NULL) {
        sum = sum + current->data;
        current = current->next;
    }
    return sum;
}

int sum_list_recursive(struct node *head) {

//1. Stopping case? head == NULL
//2. Recursive case? ??? sum = head->data + head->next->data
    if (head == NULL) { //STOPPING CASE
        return 0;
    } else {        //RECURSIVE CASE 
        int sum = head->data + sum_list_recursive(head->next);
        return sum;
    }
}