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

// LINKED LIST -- now using a compound literal to initialize the new node.

typedef struct _Node {
    int value;
    struct _Node* next;
} Node;


void append(int value, Node** a_head, Node** a_tail) {
    // Create (allocate and initialize) the new node, which will become the tail.
    //
    // Allocate space for the new node.
    Node* new_tail = malloc(sizeof(*new_tail));
    //
    // Initialize fields in the new node.
    // new_tail -> value = value;  // same as `(*new_tail).value = value`
    // new_tail -> next  = NULL;
    //
    // Initialize entire node at once using a compound literal
    *new_tail = (Node) { .value = value, .next = NULL };
    //          «TYPE» «looks like a named initializer»
//  └───────┘
//  type of *new_tail is Node.
//  type of the part on the right is also Node.
    
    if(*a_tail == NULL) {  // if list is empty
        // List is empty, so head will also be tail.
        *a_head = new_tail;
    }
    else {   // List is not empty, so connect new_tail to the old tail.
        (*a_tail) -> next = new_tail;
    }

    // Connect the tail of the list to new_tail.
    *a_tail = new_tail;

    assert(*a_head != NULL && *a_tail != NULL);  // Sanity check: list is not empty anymore
}

void destroy_list(Node** a_head, Node** a_tail) {
    while(*a_head != NULL) { // as long as list is not empty
        Node* new_head = (*a_head) -> next;
        free(*a_head);
        *a_head = new_head;  // Now head is the next node in the list.
    }
}

void print_list(Node* head) {
    // Step through the linked list, printing each value.
    for(Node* curr = head; curr != NULL; curr = curr -> next) {
        printf("[%d]→", curr -> value);
    }
    printf("NULL\n");
}

// RULE: Use a for loop to iterate through a linked list, not a while loop.

int main(int argc, char* argv[]) {
    // size==0
    Node* head = NULL;
    Node* tail = NULL;  // You don't always need to keep track of the tail.  It helps here.

    // size==1
    append(10, &head, &tail); // Pass address of head and tail so they can be modified.
    assert(head != NULL && tail != NULL); // Sanity check: list is no longer empty
    assert(head == tail);                 // Sanity check: head and tail are same (size==1)
    assert(head -> value == 10);          // Sanity check: head's value is 10
    
    // size==2
    append(11, &head, &tail);
    assert(head != tail);                 // Sanity check: head and tail are same (size==1)
    assert(head -> value == 10);          // Sanity check: head's value is 10
    assert(tail -> value == 11);          // Sanity check: tail's value is 11
    assert(tail -> next  == NULL);
    print_list(head);

    destroy_list(&head, &tail);
    
    return EXIT_SUCCESS;
}
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