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package au.id.zancanaro;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Optional;
import java.util.function.Function;
import java.util.function.Predicate;
public final class Iterators {
public static <T> RangeIterator<T> rangeIterator(int countTo, Function<Integer,T> fn) {
return new RangeIterator<T>(countTo, fn);
}
private static class RangeIterator<T> implements Iterator<T> {
private final Function<Integer, T> action;
private final int countTo;
private int index = 0;
public RangeIterator(int countTo, Function<Integer, T> action) {
this.countTo = countTo;
this.action = action;
}
@Override
public boolean hasNext() {
return index < countTo;
}
@Override
public T next() {
return action.apply(index++);
}
}
public static <T> FlattenIterator<T> flatten(Iterator<Iterator<T>> iterators) {
return new FlattenIterator<>(iterators);
}
public static class FlattenIterator<T> implements Iterator<T> {
private Iterator<T> current;
private Iterator<Iterator<T>> iterators;
public FlattenIterator(Iterator<Iterator<T>> iterators) {
this.current = Iterators.emptyIterator();
this.iterators = iterators;
}
private Iterator<T> getCurrent() {
while (!current.hasNext() && iterators.hasNext()) {
current = iterators.next();
}
return current;
}
@Override
public boolean hasNext() {
return getCurrent().hasNext();
}
@Override
public T next() {
return getCurrent().next();
}
}
public static <T> ConcatIterator<T> concat(Iterator<T> left, Iterator<T> right) {
return new ConcatIterator<>(left, right);
}
public static class ConcatIterator<T> implements Iterator<T> {
private final Iterator<T> left;
private final Iterator<T> right;
public ConcatIterator(Iterator<T> left, Iterator<T> right) {
this.left = left;
this.right = right;
}
@Override
public boolean hasNext() {
return left.hasNext() || right.hasNext();
}
@Override
public T next() {
if (left.hasNext()) {
return left.next();
} else {
return right.next();
}
}
}
public static <T> EmptyIterator<T> emptyIterator() {
return new EmptyIterator<>();
}
public static class EmptyIterator<T> implements Iterator<T> {
@Override
public boolean hasNext() {
return false;
}
@Override
public T next() {
return null;
}
}
public static <T,R> MappingIterator<T,R> mappingIterator(Function<T,R> f, Iterator<T> iterator) {
return new MappingIterator<>(f, iterator);
}
private static class MappingIterator<T, R> implements Iterator<R> {
private final Function<T, R> mapping;
private final Iterator<T> iterator;
public MappingIterator(Function<T, R> mapping, Iterator<T> iterator) {
this.mapping = mapping;
this.iterator = iterator;
}
@Override
public boolean hasNext() {
return iterator.hasNext();
}
@Override
public R next() {
return mapping.apply(iterator.next());
}
}
public static <T> FilteringIterator<T> filteringIterator(Predicate<T> pred, Iterator<T> iterator) {
return new FilteringIterator<>(pred, iterator);
}
private static class FilteringIterator<T> implements Iterator<T> {
private final Predicate<T> predicate;
private final Iterator<T> iterator;
private List<T> nextValue;
public FilteringIterator(Predicate<T> pred, Iterator<T> iterator) {
this.predicate = pred;
this.iterator = iterator;
this.nextValue = null;
}
private void populateNext() {
while (nextValue == null && iterator.hasNext()) {
T value = iterator.next();
if (predicate.test(value)) {
nextValue = Collections.singletonList(value);
} else {
nextValue = null;
}
}
}
@Override
public boolean hasNext() {
populateNext();
return nextValue != null;
}
@Override
public T next() {
populateNext();
T result = nextValue.get(0);
nextValue = null;
return result;
}
}
}
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