/*
 * 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.lucene.facet.taxonomy.writercache;

import org.apache.lucene.facet.taxonomy.FacetLabel;

LRU TaxonomyWriterCache - good choice for huge taxonomies. 
@lucene.experimental
/**
 * LRU {@link TaxonomyWriterCache} - good choice for huge taxonomies.
 * 
 * @lucene.experimental
 */
public class LruTaxonomyWriterCache implements TaxonomyWriterCache {

  
Determines cache type.
For guaranteed correctness - not relying on no-collisions in the hash
function, LRU_STRING should be used.
/**
   * Determines cache type.
   * For guaranteed correctness - not relying on no-collisions in the hash
   * function, LRU_STRING should be used.
   */
  public enum LRUType {
    
Use only the label's 64 bit longHashCode as the hash key. Do not
 check equals, unlike most hash maps.
 Note that while these hashes are very likely to be unique, the chance
 of a collision is still greater than zero. If such an unlikely event
 occurs, your document will get an incorrect facet.
/** Use only the label's 64 bit longHashCode as the hash key. Do not
     *  check equals, unlike most hash maps.
     *  Note that while these hashes are very likely to be unique, the chance
     *  of a collision is still greater than zero. If such an unlikely event
     *  occurs, your document will get an incorrect facet.
     */
    LRU_HASHED,

    
Use the label as the hash key; this is always
 correct but will usually use more RAM. /** Use the label as the hash key; this is always
     *  correct but will usually use more RAM. */
    LRU_STRING
  }

  private NameIntCacheLRU cache;

  
Creates this with LRUType.LRU_STRING method. /** Creates this with {@link LRUType#LRU_STRING} method. */
  public LruTaxonomyWriterCache(int cacheSize) {
    // TODO (Facet): choose between NameHashIntCacheLRU and NameIntCacheLRU.
    // For guaranteed correctness - not relying on no-collisions in the hash
    // function, NameIntCacheLRU should be used:
    // On the other hand, NameHashIntCacheLRU takes less RAM but if there
    // are collisions two different paths would be mapped to the same
    // ordinal...
    this(cacheSize, LRUType.LRU_STRING);
  }

  
Creates this with the specified method. /** Creates this with the specified method. */
  public LruTaxonomyWriterCache(int cacheSize, LRUType lruType) {
    // TODO (Facet): choose between NameHashIntCacheLRU and NameIntCacheLRU.
    // For guaranteed correctness - not relying on no-collisions in the hash
    // function, NameIntCacheLRU should be used:
    // On the other hand, NameHashIntCacheLRU takes less RAM but if there
    // are collisions two different paths would be mapped to the same
    // ordinal...
    if (lruType == LRUType.LRU_HASHED) {
      this.cache = new NameHashIntCacheLRU(cacheSize);
    } else {
      this.cache = new NameIntCacheLRU(cacheSize);
    }
  }

  @Override
  public synchronized boolean isFull() {
    return cache.getSize() == cache.getMaxSize();
  }

  @Override
  public synchronized void clear() {
    cache.clear();
  }
  
  @Override
  public synchronized void close() {
    cache.clear();
    cache = null;
  }

  @Override
  public int size() {
    return cache.getSize();
  }
  
  @Override
  public synchronized int get(FacetLabel categoryPath) {
    Integer res = cache.get(categoryPath);
    if (res == null) {
      return -1;
    }

    return res.intValue();
  }

  @Override
  public synchronized boolean put(FacetLabel categoryPath, int ordinal) {
    boolean ret = cache.put(categoryPath, ordinal);
    // If the cache is full, we need to clear one or more old entries
    // from the cache. However, if we delete from the cache a recent
    // addition that isn't yet in our reader, for this entry to be
    // visible to us we need to make sure that the changes have been
    // committed and we reopen the reader. Because this is a slow
    // operation, we don't delete entries one-by-one but rather in bulk
    // (put() removes the 1/3rd oldest entries).
    if (ret) {
      cache.makeRoomLRU();
    }
    return ret;
  }

}