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


void print_list(Node* head, void(*print_one_element_fn)(void*)) {
    // print_one_element_fn(…) is a function
    for(Node* curr = head;  curr != NULL; curr = curr -> next) {
        printf("[");
        print_one_element_fn(curr -> a_value);  // print this element
        printf("]");
        if(curr -> next != NULL) { // If curr is not the tail...
            printf("→");
        }
    }
    printf("\n");
}

void append(void* a_value, Node** a_head, Node** a_tail) {
    // Do not copy this code (or any other code).  Default is always no copying.

    // Allocate memory on heap for a new node.
    Node* new_node = malloc(sizeof(*new_node));
    
    // Initialize fields of the new node using a COMPOUND LITERAL.
    *new_node = (Node) { .a_value = a_value, .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;
    }
    else {
        assert(*a_head != NULL && *a_tail != NULL);  // List not empty «before» appending new node
        (*a_tail) -> next = new_node;  // Connect tail to new node.
    }                                  // ⚠ Do not switch the order of these two steps!!!

    *a_tail = new_node;     // Set tail to new node.

    assert(*a_head != NULL && *a_tail != NULL);  // List not «after» before appending new node
    assert((*a_tail) -> a_value == a_value);
    assert((*a_tail) -> next  == NULL);  // Tail's '.next' field must always be NULL.
}

void free_list(Node** a_head, Node** a_tail, void(*free_value_fn)(void*)) {
    // Convenience variables
    Node* head = *a_head;

    while(head != NULL) { // While the list is not empty
        Node* old_head = head; // Don't lose your head.
        head = head -> next;   // Second node becomes the new of the list.
        free_value_fn(old_head -> a_value);  // Destroy (free) value the old_head refers to
        free(old_head);        // Free your mind.
    }

    // Set the head and tail in the caller's stack frame to NULL.
    *a_head = NULL;
    *a_tail = NULL;
}


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