// Implementation of the Stack ADT using a linked list

// !!! DO NOT MODIFY THIS FILE !!!

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

#include "Stack.h"

typedef struct node *Node;
struct node {
    char *item;
    Node next;
};

struct stack {
    Node head;
    int size;
};

static Node newNode(char *it);

Stack StackNew(void) {
    Stack s = malloc(sizeof(*s));
    if (s == NULL) {
        fprintf(stderr, "error: out of memory\n");
        exit(EXIT_FAILURE);
    }

    s->head = NULL;
    s->size = 0;
    return s;
}

void StackFree(Stack s) {
    Node curr = s->head;
    while (curr != NULL) {
        Node temp = curr;
        curr = curr->next;
        free(temp);
    }
    free(s);
}

void StackPush(Stack s, char *it) {
    Node n = newNode(it);
    n->next = s->head;
    s->head = n;
    s->size++;
}

static Node newNode(char *it) {
    Node n = malloc(sizeof(*n));
    if (n == NULL) {
        fprintf(stderr, "error: out of memory\n");
        exit(EXIT_FAILURE);
    }

    n->item = it;
    n->next = NULL;
    return n;
}

char *StackPop(Stack s) {
    if (s->size == 0) {
        fprintf(stderr, "error: stack is empty\n");
        exit(EXIT_FAILURE);
    }

    Node oldHead = s->head;
    char *it = oldHead->item;
    s->head = oldHead->next;
    free(oldHead);
    s->size--;

    return it;
}

char *StackTop(Stack s) {
    if (s->size == 0) {
        fprintf(stderr, "error: stack is empty\n");
        exit(EXIT_FAILURE);
    }

    return s->head->item;
}

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

bool StackIsEmpty(Stack s) {
    return s->size == 0;
}

void StackShow(Stack s) {
    for (Node curr = s->head; curr != NULL; curr = curr->next) {
        printf("%s ", curr->item);
    }
    printf("\n");
}