package ph.edu.dlsu.datsral;

import java.util.NoSuchElementException;

public class MyStack<T> {

    private static final int INITIAL_CAPACITY = 4;
    private GenericArray<T> data;
    private int capacity;
    private int count;

    public MyStack() {
        capacity = INITIAL_CAPACITY;
        data = new GenericArray<T>(capacity);
        count = 0;
    }

    public T top() {
        if (empty()) throw new NoSuchElementException("Stack is Empty (Underflow)");
        return data.get(count - 1);
    }

    public void push(T value) {
        if (count == capacity) {
            ensureCapacity();
        }
        data.set(count++, value);
    }

    T pop(){
        if (empty()) throw new NoSuchElementException("Stack is Empty (Underflow)");
        return data.get(--count);
    }

    private void ensureCapacity() {
        System.out.println("Resizing...");
        capacity *= 2;
        GenericArray<T> newArray = new GenericArray<T>(capacity);
        for (int i = 0; i < count; i++) {
            newArray.set(i, data.get(i));
        }
        data = newArray;
    }

    public int size() {
        return count;
    }

    public boolean empty() {
        return count == 0;
    }

    class GenericArray<T> {

        private Object[] data;

        public GenericArray(int n) {
            data = new Object[n];
        }

        public int size() {
            return data.length;
        }

        public T get(int idx) {
            return (T) data[idx];
        }

        public void set(int idx, T item) {
            data[idx] = item;
        }
    }
}