hazelcast-master/hazelcast/src/main/java/com/hazelcast/replicatedmap/impl/record/KeySetIteratorFactory.java
/*
 * Copyright (c) 2008-2023, Hazelcast, Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.hazelcast.replicatedmap.impl.record;

import com.hazelcast.replicatedmap.impl.record.LazySet.IteratorFactory;

import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;

class KeySetIteratorFactory<K, V> implements IteratorFactory<K, V, K> {

    private final ReplicatedRecordStore recordStore;

    KeySetIteratorFactory(ReplicatedRecordStore recordStore) {
        this.recordStore = recordStore;
    }

    @Override
    public Iterator<K> create(Iterator<Map.Entry<K, ReplicatedRecord<K, V>>> iterator) {
        return new KeySetIterator(iterator);
    }

    private final class KeySetIterator implements Iterator<K> {

        private final Iterator<Map.Entry<K, ReplicatedRecord<K, V>>> iterator;

        private Map.Entry<K, ReplicatedRecord<K, V>> nextEntry;

        private KeySetIterator(Iterator<Map.Entry<K, ReplicatedRecord<K, V>>> iterator) {
            this.iterator = iterator;
        }

        @Override
        public boolean hasNext() {
            while (iterator.hasNext()) {
                Map.Entry<K, ReplicatedRecord<K, V>> entry = iterator.next();
                if (testEntry(entry)) {
                    nextEntry = entry;
                    return true;
                }
            }
            return false;
        }

        @Override
        public K next() {
            Map.Entry<K, ReplicatedRecord<K, V>> entry = nextEntry;
            Object key = entry != null ? entry.getKey() : null;

            while (entry == null) {
                entry = findNextEntry();

                key = entry.getKey();
                if (key != null) {
                    break;
                }
            }

            nextEntry = null;
            if (key == null) {
                throw new NoSuchElementException();
            }

            //noinspection unchecked
            return (K) recordStore.unmarshall(key);
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException("Lazy structures are not modifiable");
        }

        private boolean testEntry(Map.Entry<K, ReplicatedRecord<K, V>> entry) {
            return entry.getKey() != null && entry.getValue() != null;
        }

        private Map.Entry<K, ReplicatedRecord<K, V>> findNextEntry() {
            Map.Entry<K, ReplicatedRecord<K, V>> entry = null;
            while (iterator.hasNext()) {
                entry = iterator.next();
                if (testEntry(entry)) {
                    break;
                }
                entry = null;
            }
            if (entry == null) {
                throw new NoSuchElementException();
            }
            return entry;
        }
    }
}
