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

//TODO: grundlegende Stackfunktionen implementieren:
/*  * `push`: legt ein Element oben auf den Stack,
    * `pop`: entfernt das oberste Element,
    * `top`: liefert das oberste Element zurück,
    * `clearStack`: gibt den gesamten Speicher frei. */

// Pushes data as pointer onto the stack.
StackNode *push(StackNode *stack, void *data)
{
    if(!(stack)) { // check if stack is empty
        stack = malloc(sizeof(StackNode));
        if(!stack)
            return NULL;
        stack->stackData = data;
        stack->below = NULL;
        return stack;
    }

    StackNode* newStack = malloc(sizeof(StackNode));
        if(!newStack)
            return stack;
    newStack->below = stack;
    newStack->stackData = data;
    stack = newStack;
    return stack;

}

// 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) {
        StackNode* temp = stack;
        stack = stack->below;
        temp->stackData = NULL;
        free(temp);
        temp = NULL;
        return stack;
    } else {
        return NULL;
    }
}

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

}

// Clears stack and releases all memory.
void clearStack(StackNode *stack)
{
    while(stack)
        stack = pop(stack);

}