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

// Pushes data as pointer onto the stack.
StackNode *push(StackNode *stack, void *data)
{
    StackNode *node = (StackNode *)malloc(sizeof(StackNode));
    if(node == NULL)
        return stack; // allocation failed -> return unchanged stack

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

// Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
// freed by caller.)
StackNode *pop(StackNode *stack)
{
    if(stack == NULL)
        return NULL;

    StackNode *next = stack->next;
    // Do NOT free stack->data here; caller owns the pointed data
    free(stack);
    return next;
}

// Returns the data of the top element.
void *top(StackNode *stack)
{
    if(stack == NULL)
        return NULL;
    return stack->data;
}

// Clears stack and releases all memory.
void clearStack(StackNode *stack)
{
    while(stack != NULL)
    {
        StackNode *next = stack->next;
        // Do NOT free stack->data here; caller owns the pointed data
        free(stack);
        stack = next;
    }
}