// Written in 2521 24T2 lecture by Sim Mautner

#include "Stack.h"

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

#define START_SIZE 100

// from .h file: typedef struct stack * Stack;

struct stack {
    Item *items;
    int size;
    int capacity;
};

// same as: struct stack * StackNew(void) {
Stack StackNew(void) {
    Stack new_stack = malloc(sizeof(struct stack));
    if (new_stack == NULL) {
		fprintf(stderr, "error: out of memory\n");
		exit(EXIT_FAILURE);
	}

    // same as: struct stack * new_stack = malloc(sizeof(struct stack));
    new_stack->items = malloc(sizeof(Item) * START_SIZE);
    if (new_stack->items == NULL) {
		fprintf(stderr, "error: out of memory\n");
		exit(EXIT_FAILURE);
	}

    new_stack->size = 0;
    new_stack->capacity = START_SIZE;
    return new_stack;
}

void StackFree(Stack s) {
    // Step 1: Free all pointers within the struct
    free(s->items);
    // Step 2: Free main struct
    free(s);
}

void StackPush(Stack s, Item it) {
    // 1. If our array isn't big enough for more items, grow it
    if (s->size >= s->capacity) {
        s->items = realloc(s->items, s->capacity*2);
        if (s->items == NULL) {
            fprintf(stderr, "error: out of memory\n");
            exit(EXIT_FAILURE);
        }
        s->capacity = s->capacity*2;
    }


    // 2. Put item into stack
    s->items[s->size] = it;
    s->size++;
}

Item StackPop(Stack s) {
    // Check there is something to pop (Should always be the case if the user is using the ADT as specified in .h file)
    assert(s->size > 0);
    // Pop item
    s->size--;
    return s->items[s->size];
}

int StackSize(Stack s) {
    return s->size;
}

Item StackPeek(Stack s) {
    assert(s->size > 0);
    return s->items[s->size-1];
}