// Week 8 Thursday Lecture
// Modified as a debugging exercise 
// for Week 10 Revision
// Using search and delete approach 2

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

struct node {
    int data;
    struct node *next;
};

struct node *create_node(int data, struct node *next);
void print_list(struct node *head);
struct node *insert_at_tail(struct node *head, int data);  

//Deletion related functions
struct node *delete_first(struct node *head); 
void delete_all(struct node *head);
struct node *search_and_delete(struct node *head, int value);
struct node *search_and_delete_all(struct node *head, int value);


int main(void) {
    //create a node with data value i using function
    //add node to tail/end of list  
    struct node *head = NULL;
    printf("Search and delete empty list\n");
    head = search_and_delete(head, 0);
    print_list(head);


    for (int i = 0; i < 10; i++) {
        head = insert_at_tail(head, i);
    }
 
    print_list(head); 

    printf("Search and delete middle: 5 \n");
    head = search_and_delete(head, 5);
    print_list(head);

    printf("Search and delete value not found: 99\n");
    head = search_and_delete(head, 99);
    print_list(head);

    printf("Search and head: 0\n");
    head = search_and_delete(head, 0);
    print_list(head);

    printf("Search and tail: 9\n");
    head = search_and_delete(head, 9);
    print_list(head);

    delete_all(head);
    // check for memory leaks
    return 0;
}

// Approach 2. 
struct node *search_and_delete(struct node *head, int value) {
    if (head == NULL) {
        return head;
    }
    // Approach 2: Just use 1 pointer to traverse 
    // but check the next node
    struct node *current = head;
    if (current->data == value) {
        head = head->next;
        free(current);
        return head;
    }
    
    while (current->next != NULL && current->next->data != value) {
	    current = current->next;
    }
    struct node *temporary = current->next;
    if (temporary != NULL) {
        current->next = temporary->next;
        free(temporary);
    }
    return head;
}


struct node *create_node(int data, struct node *next) {
    struct node *new_node = malloc(sizeof(struct node));
    if (new_node == NULL) {
        return NULL;
    }
    new_node->data = data;
    new_node->next = next;
    return new_node;
}

void print_list(struct node *head) {
    printf("list:\n");
    struct node *curr = head;
    while (curr != NULL) {
        printf("%d ", curr->data);
        curr = curr->next;
    }
    printf("\n");
}

struct node *insert_at_tail(struct node *head, int data) {
    struct node *new_node = create_node(data, NULL);
    struct node *current = head;

    // Case for when the list is empty
    if (head == NULL) {
        head = new_node;
    } else {
        // Find the last node in the list
        while (current->next != NULL) {
            current = current->next;
        }
        current->next = new_node;
    }
    return head;
}

// Deletes and frees the memory of the first node in the list
// returns the head of the list
struct node *delete_first(struct node *head) {
    if (head == NULL) {
        return NULL;
    }
    struct node *tmp = head;
    head = head->next;
    free(tmp);
    return head;
}

// frees memory of all nodes in the given list
void delete_all(struct node *head) {
    struct node *current = head;
    while (current != NULL) {
        head = head->next;
        free(current);
        current = head; 
    }
}

// searches for a value in the list, deletes it and frees
// the memory.
// returns the head of the list
// Only deletes the first occurrence of a value in the list
struct node *search_and_delete1(struct node *head, int value) {
    struct node *previous = NULL;
    struct node *current = head;

    while (current != NULL && current->data != value) {
        previous = current;
        current = current->next;
    }
    // If current is NULL
    // We did not find the element 
    // (this includes the case where the list is empty)
    // so we have nothing to delete.
    if (current != NULL) {
       // If previous is NULL we are deleting first element
       if (previous == NULL) {
            head = head->next;
       } else {
            previous->next = current->next;
       }
       free(current);
    }
    return head;
}

struct node *search_and_delete_all(struct node *head, int value) {
    struct node *previous = NULL;
    struct node *current = head;

    while (current != NULL) {
        if (current->data == value) {
            if (previous == NULL) {
                head = head->next;
                free(current);
                current = head;
            } else {
                previous->next = current->next;
                free(current);
                current = previous->next;
            }
            
        } else {
            previous = current;
            current = current->next;
        }
    }
   
    return head;
}