/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package com.sun.tools.javac.util;

import java.util.Iterator;

import java.util.NoSuchElementException;

import java.util.function.Function;

/** Utilities for Iterators.

 *

 *  <p><b>This is NOT part of any supported API.

 *  If you write code that depends on this, you do so at your own risk.

 *  This code and its internal interfaces are subject to change or

 *  deletion without notice.</b>

 */

public class Iterators {

    public static <I, O> Iterator<O> createCompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {

        return new CompoundIterator<>(inputs, convertor);

    }

    private static class CompoundIterator<I, O> implements Iterator<O> {

        private final Iterator<I> inputs;

        private final Function<I, Iterator<O>> convertor;

        @SuppressWarnings("unchecked")

        private Iterator<O> currentIterator = EMPTY;

        public CompoundIterator(Iterable<I> inputs, Function<I, Iterator<O>> convertor) {

            this.inputs = inputs.iterator();

            this.convertor = convertor;

        }

        public boolean hasNext() {

            if (currentIterator != null && !currentIterator.hasNext()) {

                update();

            }

            return currentIterator != null;

        }

        public O next() {

                throw new NoSuchElementException();

            return currentIterator.next();

        }

        public void remove() {

            throw new UnsupportedOperationException();

        }

        private void update() {

            while (inputs.hasNext()) {

                currentIterator = convertor.apply(inputs.next());

                if (currentIterator.hasNext()) return;

            }

            currentIterator = null;

        }

    }

    @SuppressWarnings("rawtypes")

    private final static Iterator EMPTY = new Iterator() {

        public boolean hasNext() {

            return false;

        }

        @Override

        public Object next() {

            return null;

        }

    };

}