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

typedef struct _Node {   // always called Node or ▒Node in ECE 26400
    int value;           // usually called 'value'                //  4 bytes¹ for int
    struct _Node* next;  // address of the next node in the list  //  8 bytes¹ for ▒▒▒▒▒*
} Node;                  // Think of .next as your link to the next node.
// ¹ Disclaimer:  On our platform; sizes on other platforms may vary.
// 
// This type has two names:  'struct _Node' and 'Node'.  They are interchageable. \
// 'Node' is a shortcut name or alias created with typedef.  See the reference sheet.

void append(int value, Node** a_head, Node** a_tail) {
    // Allocate space on the heap sufficient to store one new Node.
    Node* new_tail = malloc(sizeof(*new_tail));

    // This version of the append(…) function uses a COMPOUND LITERAL to initialize the
    // the 
    
    // Initialize the .value field to 'value' and the .next field to NULL.
    // new_tail -> value = value;  // same as (*new_tail).value = value … but please use <-
    // new_tail -> next  = NULL;   // same as (*new_tail).next  = next  … but please use <-
    *new_tail = (Node) { .value = value, .next = NULL };  // Better: Use COMPOUND LITERAL
//  ↑
//  CAUTION:  Left side type should be Node, not Node*.  Don't forget the '*'.

    // new_tail = (Node) { .value = value, .next = NULL };  // WRONG
    // GCC: "error: incompatible types when assigning to type ‘Node *’"

    if(*a_head == NULL) {  // If list is empty
        *a_head = new_tail;  // store the address of the new tail at address a_head.
    }
    else {
        (*a_tail) -> next = new_tail;  // append to end of list
    }

    *a_tail = new_tail;
}

void print_list(Node* head) {
    for(Node* curr = head; curr != NULL; curr = curr -> next) {
        log_int(curr -> value);
    }
}

// WARNING:  YOU CANNOT ACCESS MEMORY AFTER IT HAS BEEN FREED.

void destroy_list(Node** a_head, Node** a_tail) {
    // While the list is not empty…  (Note: This ensures that we do not for an empty list.)
    while(*a_head != NULL) {

        // Save the new head
        Node* new_head = (*a_head) -> next;  // Save the address of second node in list.

        // Free the old head
        free(*a_head);
        
        // Set 'head' to the address of new head
        *a_head = new_head;  // Set the head to what was previously the SECOND node in list.
        // If we didn't save the address of the second node, we wouldn't be able to access
        // it now.
    }

    // At this point, for our [10| ]>[11| ]→NULL example, we will have
    // *a_head == NULL
    // *a_tail == «address of the 11 node»  // 412 on our memory form

    *a_tail = NULL;
    
    // NOTE: *a_head and *a_tail will be NULL at the end so we can't accidentally access.
}
// OKAY to copy/adapt COMMENTS from this file and use general outline.  (Don't copy code.)

int main(int argc, char* argv[]) {
    // size==0  - empty list
    Node* head = NULL;   // first node in the list is always called 'head'
    Node* tail = NULL;   // last  node in the list is always called 'tail'
    append(10, &head, &tail);
    append(11, &head, &tail);

    print_list(head);

    // [ 10 | → ] → [ 11 | → ] → NULL
    
    destroy_list(&head, &tail);  // &head refers to the 10 node.
                                 // &tail refers to the 11 node.
                                 // Inside destroy_list(…) when it first begins,
                                 // *a_head will refer to the 10 node, and
                                 // *a_tail will refer to the 11 node.
    
    // After destroy_list(…) we will have
    // head == NULL and tail == NULL
    return EXIT_SUCCESS;
}
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