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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.lucene.analysis.ja.dict;


import java.io.IOException;

import org.apache.lucene.util.fst.FST.Arc;
import org.apache.lucene.util.fst.FST;

Thin wrapper around an FST with root-arc caching for Japanese.

Depending upon fasterButMoreRam, either just kana (191 arcs),
or kana and han (28,607 arcs) are cached. The latter offers
additional performance at the cost of more RAM.
/**
 * Thin wrapper around an FST with root-arc caching for Japanese.
 * <p>
 * Depending upon fasterButMoreRam, either just kana (191 arcs),
 * or kana and han (28,607 arcs) are cached. The latter offers
 * additional performance at the cost of more RAM.
 */
public final class TokenInfoFST {
  private final FST<Long> fst;

  // depending upon fasterButMoreRam, we cache root arcs for either 
  // kana (0x3040-0x30FF) or kana + han (0x3040-0x9FFF)
  // false: 191 arcs
  // true:  28,607 arcs (costs ~1.5MB)
  private final int cacheCeiling;
  private final FST.Arc<Long> rootCache[];
  
  public final Long NO_OUTPUT;

  public TokenInfoFST(FST<Long> fst, boolean fasterButMoreRam) throws IOException {
    this.fst = fst;
    this.cacheCeiling = fasterButMoreRam ? 0x9FFF : 0x30FF;
    NO_OUTPUT = fst.outputs.getNoOutput();
    rootCache = cacheRootArcs();
  }
  
  @SuppressWarnings({"rawtypes","unchecked"})
  private FST.Arc<Long>[] cacheRootArcs() throws IOException {
    FST.Arc<Long> rootCache[] = new FST.Arc[1+(cacheCeiling-0x3040)];
    FST.Arc<Long> firstArc = new FST.Arc<>();
    fst.getFirstArc(firstArc);
    FST.Arc<Long> arc = new FST.Arc<>();
    final FST.BytesReader fstReader = fst.getBytesReader();
    // TODO: jump to 3040, readNextRealArc to ceiling? (just be careful we don't add bugs)
    for (int i = 0; i < rootCache.length; i++) {
      if (fst.findTargetArc(0x3040 + i, firstArc, arc, fstReader) != null) {
        rootCache[i] = new FST.Arc<Long>().copyFrom(arc);
      }
    }
    return rootCache;
  }
  
  public FST.Arc<Long> findTargetArc(int ch, FST.Arc<Long> follow, FST.Arc<Long> arc, boolean useCache, FST.BytesReader fstReader) throws IOException {
    if (useCache && ch >= 0x3040 && ch <= cacheCeiling) {
      assert ch != FST.END_LABEL;
      final Arc<Long> result = rootCache[ch - 0x3040];
      if (result == null) {
        return null;
      } else {
        arc.copyFrom(result);
        return arc;
      }
    } else {
      return fst.findTargetArc(ch, follow, arc, fstReader);
    }
  }
  
  public Arc<Long> getFirstArc(FST.Arc<Long> arc) {
    return fst.getFirstArc(arc);
  }

  public FST.BytesReader getBytesReader() {
    return fst.getBytesReader();
  }
  
  
@lucene.internal
for testing only/** @lucene.internal for testing only */
  FST<Long> getInternalFST() {
    return fst;
  }
}