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/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.solr.search;

import org.apache.solr.common.SolrException;
import org.apache.solr.common.util.NamedList;
import org.apache.solr.common.util.SimpleOrderedMap;
import org.apache.solr.core.SolrCore;

import java.util.*;
import java.util.concurrent.atomic.AtomicLong;
import java.io.IOException;
import java.net.URL;


/**
 * @version $Id: LRUCache.java 681440 2008-07-31 18:59:52Z yonik $
 */
public class LRUCache implements SolrCache {

  /* An instance of this class will be shared across multiple instances
   * of an LRUCache at the same time.  Make sure everything is thread safe.
   */
  private static class CumulativeStats {
    AtomicLong lookups = new AtomicLong();
    AtomicLong hits = new AtomicLong();
    AtomicLong inserts = new AtomicLong();
    AtomicLong evictions = new AtomicLong();
  }

  private CumulativeStats stats;

  // per instance stats.  The synchronization used for the map will also be
  // used for updating these statistics (and hence they are not AtomicLongs
  private long lookups;
  private long hits;
  private long inserts;
  private long evictions;

  private long warmupTime = 0;

  private Map map;
  private String name;
  private int autowarmCount;
  private State state;
  private CacheRegenerator regenerator;
  private String description="LRU Cache";

  public Object init(Map args, Object persistence, CacheRegenerator regenerator) {
    state=State.CREATED;
    this.regenerator = regenerator;
    name = (String)args.get("name");
    String str = (String)args.get("size");
    final int limit = str==null ? 1024 : Integer.parseInt(str);
    str = (String)args.get("initialSize");
    final int initialSize = Math.min(str==null ? 1024 : Integer.parseInt(str), limit);
    str = (String)args.get("autowarmCount");
    autowarmCount = str==null ? 0 : Integer.parseInt(str);

    description = "LRU Cache(maxSize=" + limit + ", initialSize=" + initialSize;
    if (autowarmCount>0) {
      description += ", autowarmCount=" + autowarmCount
              + ", regenerator=" + regenerator;
    }
    description += ')';

    map = new LinkedHashMap(initialSize, 0.75f, true) {
        protected boolean removeEldestEntry(Map.Entry eldest) {
          if (size() > limit) {
            // increment evictions regardless of state.
            // this doesn't need to be synchronized because it will
            // only be called in the context of a higher level synchronized block.
            evictions++;
            stats.evictions.incrementAndGet();
            return true;
          }
          return false;
        }
      };

    if (persistence==null) {
      // must be the first time a cache of this type is being created
      persistence = new CumulativeStats();
    }

    stats = (CumulativeStats)persistence;

    return persistence;
  }

  public String name() {
    return name;
  }

  public int size() {
    synchronized(map) {
      return map.size();
    }
  }

  public Object put(Object key, Object value) {
    synchronized (map) {
      if (state == State.LIVE) {
        stats.inserts.incrementAndGet();
      }

      // increment local inserts regardless of state???
      // it does make it more consistent with the current size...
      inserts++;
      return map.put(key,value);
    }
  }

  public Object get(Object key) {
    synchronized (map) {
      Object val = map.get(key);
      if (state == State.LIVE) {
        // only increment lookups and hits if we are live.
        lookups++;
        stats.lookups.incrementAndGet();
        if (val!=null) {
          hits++;
          stats.hits.incrementAndGet();
        }
      }
      return val;
    }
  }

  public void clear() {
    synchronized(map) {
      map.clear();
    }
  }

  public void setState(State state) {
    this.state = state;
  }

  public State getState() {
    return state;
  }

  public void warm(SolrIndexSearcher searcher, SolrCache old) throws IOException {
    if (regenerator==null) return;
    long warmingStartTime = System.currentTimeMillis();
    LRUCache other = (LRUCache)old;

    // warm entries
    if (autowarmCount != 0) {
      Object[] keys,vals = null;

      // Don't do the autowarming in the synchronized block, just pull out the keys and values.
      synchronized (other.map) {
        int sz = other.map.size();
        if (autowarmCount!=-1) sz = Math.min(sz,autowarmCount);
        keys = new Object[sz];
        vals = new Object[sz];

        Iterator iter = other.map.entrySet().iterator();

        // iteration goes from oldest (least recently used) to most recently used,
        // so we need to skip over the oldest entries.
        int skip = other.map.size() - sz;
        for (int i=0; i