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/*
 * Copyright (c) 2008-2016, 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.map.impl.eviction;

import com.hazelcast.core.EntryView;
import com.hazelcast.map.eviction.MapEvictionPolicy;
import com.hazelcast.map.impl.record.Record;
import com.hazelcast.map.impl.recordstore.LazyEntryViewFromRecord;
import com.hazelcast.map.impl.recordstore.RecordStore;
import com.hazelcast.map.impl.recordstore.Storage;
import com.hazelcast.nio.serialization.Data;
import com.hazelcast.spi.partition.IPartition;
import com.hazelcast.spi.partition.IPartitionService;
import com.hazelcast.util.Clock;

import static com.hazelcast.util.Preconditions.checkNotNull;

/**
 * Evictor helper methods.
 */
public class EvictorImpl implements Evictor {

    protected final EvictionChecker evictionChecker;
    protected final IPartitionService partitionService;
    protected final MapEvictionPolicy mapEvictionPolicy;

    public EvictorImpl(MapEvictionPolicy mapEvictionPolicy,
                       EvictionChecker evictionChecker, IPartitionService partitionService) {
        this.evictionChecker = checkNotNull(evictionChecker);
        this.partitionService = checkNotNull(partitionService);
        this.mapEvictionPolicy = checkNotNull(mapEvictionPolicy);
    }

    @Override
    public void evict(RecordStore recordStore) {
        EntryView evictableEntry = selectEvictableEntry(recordStore);
        if (evictableEntry == null) {
            return;
        }

        evictEntry(evictableEntry, recordStore);
    }

    private EntryView selectEvictableEntry(RecordStore recordStore) {
        Iterable samples = getSamples(recordStore);
        EntryView selected = null;

        for (EntryView candidate : samples) {
            if (selected == null) {
                selected = candidate;
            } else if (mapEvictionPolicy.compare(candidate, selected) < 0) {
                selected = candidate;
            }
        }

        return selected;
    }

    private void evictEntry(EntryView selectedEntry, RecordStore recordStore) {
        Record record = getRecordFromEntryView(selectedEntry);
        Data key = record.getKey();

        if (recordStore.isLocked(record.getKey())) {
            return;
        }

        boolean backup = isBackup(recordStore);
        recordStore.evict(key, backup);

        if (!backup) {
            recordStore.doPostEvictionOperations(record, backup);
        }
    }

    @Override
    public boolean checkEvictable(RecordStore recordStore) {
        return evictionChecker.checkEvictable(recordStore);
    }

    // this method is overridden in another context.
    protected Record getRecordFromEntryView(EntryView selectedEntry) {
        return ((LazyEntryViewFromRecord) selectedEntry).getRecord();
    }

    protected boolean isBackup(RecordStore recordStore) {
        int partitionId = recordStore.getPartitionId();
        IPartition partition = partitionService.getPartition(partitionId, false);
        return !partition.isLocal();
    }

    protected Iterable getSamples(RecordStore recordStore) {
        Storage storage = recordStore.getStorage();
        return (Iterable) storage.getRandomSamples(SAMPLE_COUNT);
    }

    protected static long getNow() {
        return Clock.currentTimeMillis();
    }

}