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

/* TIPS and BEST PRACTICES for linked lists
 * ∙ Avoid duplication.
 *   - Avoid needless special cases.
 * ∙ Draw box-arrow diagrams.
 *   - Write the step number on the diagram.
 * ∙ Be careful about order.
 *   - To check yourself, try drawing box-arrow diagram if you flipped two key lines.
 * ∙ Read error message.  Ask for explanation of message if needed.
 *
 * You are encouraged to post error messages on Piazza.
 */
typedef struct _Node {
    int value;
    struct _Node* next;
} Node;

void print_list(Node* head) {
    for(Node* curr = head;  curr != NULL; curr = curr -> next) {
        printf("[%d]", curr -> value);   
        if(curr -> next != NULL) { // If curr is not the tail...
            printf("→");
        }
    }
    printf("\n");
}


void _append(int value, Node** a_head, Node** a_tail) {
    // Do not copy this code (or any other code).

    // Allocate memory on heap for a new node.
    Node* new_node = malloc(sizeof(*new_node));
    
    // Initialize fields of the new node.
    *new_node = (Node) { .value = value, .next = NULL };
    //_______   _______________________________________
    // ↑                   ↑
    // Node               Node
    //
    // ⚠ Type on left and right of '=' in an assignment must be the same.
    // BAD:   new_node = (Node)  { .value = value, .next = NULL };
    // BAD:  *new_node = (Node*) { .value = value, .next = NULL };
    // BAD:   new_node = (Node*) { .value = value, .next = NULL };
    // GOOD: *new_node = (Node)  { .value = value, .next = NULL };

    // new_node -> value = value;
    // new_node -> next  = NULL;

    if(*a_head == NULL) {  // If list is empty (size=0), initialize a list of size one.
        assert(*a_tail == NULL);
        *a_head = new_node;
        *a_tail = new_node;
        assert(*a_head = *a_tail);  // Size must be 1 now.
    }
    else {
        assert(*a_head != NULL && *a_tail != NULL);
        (*a_tail) -> next = new_node;  // Connect tail to new node.
        *a_tail = new_node;            // Set tail to new node.
    }                                  // ⚠ Do not switch the order of these two steps!!!
    assert(*a_head != NULL && *a_tail != NULL);
    assert((*a_tail) -> value == value);
    assert((*a_tail) -> next  == NULL);  // Tail's '.next' field must always be NULL.
}

int main(int argc, char* argv[]) {
    Node* head = NULL;
    Node* tail = head;

    _append(5, &head, &tail);
    _append(6, &head, &tail);
    _append(7, &head, &tail);
    for(int i = 0; i < 15; i++) {
        _append(i, &head, &tail);
    }

    print_list(head);

    return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */