package cz.cvut.k36.pr2.hw.hw06.impl;

import cz.cvut.k36.pr2.hw.hw06.Function;
import cz.cvut.k36.pr2.hw.hw06.Pr2List;
import cz.cvut.k36.pr2.hw.hw06.Predicate;

/**
 *
 * @author Lukas
 */
public class FilterView<T> extends View<T> {

    Pr2List<T> source;
    final Predicate<T> predicate;
    Boolean isEmpty;

    public FilterView(Pr2List<T> source, Predicate<T> predicate) {
        this.source = source;
        this.predicate = predicate;
    }

    @Override
    public T head() {
        if (isEmpty())
            throw new UnsupportedOperationException("Prázdný list.");
        return source.head();
    }

    @Override
    public Pr2List<T> tail() {
        if (isEmpty())
            throw new UnsupportedOperationException("Prázdný list.");
        return new FilterView(source.tail(), predicate);
    }

    @Override
    public boolean isEmpty() {
        if(isEmpty != null) return isEmpty;
        if(source.isEmpty()) return isEmpty = true;

        if(predicate.apply(source.head())) return isEmpty = false;

        source = source.tail();
        return isEmpty();
    }

    @Override
    public int size() {
        if(source.isEmpty()) return 0;

        if(predicate.apply(source.head()))
            return 1 + new FilterView(source.tail(), predicate).size();

        source = source.tail();
        return size();
    }

}