#include <stdlib.h>
#include "stack.h"

// Pushes data onto the stack and returns new stack top
StackNode *push(StackNode *stack, void *data) {
    StackNode *node = malloc(sizeof(StackNode));
    if (!node) return stack;  // allocation failed → leave stack unchanged

    node->data = data;
    node->next = stack;

    return node; // new top
}

// Removes the top element, frees node (NOT data), returns new top
StackNode *pop(StackNode *stack) {
    if (stack == NULL) return NULL;

    StackNode *next = stack->next;
    free(stack);

    return next; // new top
}

// Returns data of top node or NULL
void *top(StackNode *stack) {
    if (!stack) return NULL;
    return stack->data;
}

// Frees entire stack (NOT data!)
void clearStack(StackNode *stack) {
    while (stack != NULL) {
        StackNode *next = stack->next;
        free(stack);
        stack = next;
    }
}