import java.util.Iterator;

/**
 * Created by manykey on 28.11.14.
 */
public class Filter<T> implements Iterable<T> {

    public static <T> Iterable<T> by(Predicate<T> predicate, Iterable<T> sequence) {
        return new Filter<>(sequence, predicate);
    }

    public interface Predicate<T>{
        public boolean apply(T t);
    }

    public Filter(Iterable<T> original, Predicate<T> predicate) {
        this.original = original;
        this.predicate = predicate;
    }

    class FilterIterator implements Iterator<T> {

        FilterIterator(Iterator<T> originalIterator) {
            this.originalIterator = originalIterator;
            this.item = null;
        }

        @Override
        public boolean hasNext() {
            updateIfNeeded();
            return item != null;
        }

        @Override
        public T next() {
            updateIfNeeded();
            return extractItem();
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException("FilterIterator.remove");
        }

        private T extractItem() {
            T t = item;
            item = null;
            return t;
        }

        private void updateIfNeeded() {
            if (item != null) {
                return;
            }
            while (originalIterator.hasNext()) {
                T temp = originalIterator.next();
                if (predicate.apply(temp)) {
                    item = temp;
                    break;
                }
            }
        }

        private T item;
        private Iterator<T> originalIterator;
    }

    @Override
    public Iterator<T> iterator() {
        return null;
    }

    private Iterable<T> original;
    private Predicate<T> predicate;
}