/*
 * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
 * 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
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 */

package com.sun.tools.javac.util;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.function.Function;
import java.util.function.Predicate;

Utilities for Iterators.
 
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.
/** 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() {
            if (currentIterator == EMPTY && !hasNext()) {
                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;
        }
    };

    public static <E> Iterator<E> createFilterIterator(Iterator<E> input, Predicate<E> test) {
        return new Iterator<E>() {
            private E current = update();
            private E update () {
                while (input.hasNext()) {
                    E sym = input.next();
                    if (test.test(sym)) {
                        return sym;
                    }
                }

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

            @Override
            public E next() {
                E res = current;
                current = update();
                return res;
            }
        };
    }

}