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/**
 * Copyright 2000-2024 Vaadin Ltd.
 *
 * This program is available under Vaadin Commercial License and Service Terms.
 *
 * See {@literal } for the full
 * license.
 */
package com.vaadin.flow.component.spreadsheet;

import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.NoSuchElementException;
import java.util.Queue;

@SuppressWarnings("serial")
class IteratorChain implements Iterator, Serializable {

    private static class EmptyIterator implements Iterator, Serializable {
        @Override
        public boolean hasNext() {
            return false;
        }

        @Override
        public E next() {
            throw new NoSuchElementException();
        }

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

    private final Queue> iteratorChain = new LinkedList>();
    private Iterator currentIterator = null;

    public IteratorChain(Collection> iterators) {
        iteratorChain.addAll(iterators);
    }

    private void updateCurrentIterator() {
        if (currentIterator == null) {
            if (iteratorChain.isEmpty()) {
                currentIterator = new EmptyIterator();
            } else {
                currentIterator = iteratorChain.remove();
            }
        }

        while (currentIterator.hasNext() == false && !iteratorChain.isEmpty()) {
            currentIterator = iteratorChain.remove();
        }
    }

    @Override
    public boolean hasNext() {
        updateCurrentIterator();
        return currentIterator.hasNext();
    }

    @Override
    public E next() {
        updateCurrentIterator();
        return currentIterator.next();
    }

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