/*
 * 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.codecs.blockterms;

import java.io.Closeable;
import java.io.IOException;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.BytesRef;

// TODO
//   - allow for non-regular index intervals?  eg with a
//     long string of rare terms, you don't need such
//     frequent indexing

/**
 * {@link BlockTermsReader} interacts with an instance of this class to manage its terms index. The
 * writer must accept indexed terms (many pairs of BytesRef text + long fileOffset), and then this
 * reader must be able to retrieve the nearest index term to a provided term text.
 *
 * @lucene.experimental
 */
public abstract class TermsIndexReaderBase implements Closeable, Accountable {

  public abstract FieldIndexEnum getFieldEnum(FieldInfo fieldInfo);

  @Override
  public abstract void close() throws IOException;

  public abstract boolean supportsOrd();

  /**
   * Similar to TermsEnum, except, the only "metadata" it reports for a given indexed term is the
   * long fileOffset into the main terms dictionary file.
   */
  public abstract static class FieldIndexEnum {

    /**
     * Seeks to "largest" indexed term that's &lt;= term; returns file pointer index (into the main
     * terms index file) for that term
     */
    public abstract long seek(BytesRef term) throws IOException;

    /** Returns -1 at end */
    public abstract long next() throws IOException;

    public abstract BytesRef term();

    /** Only implemented if {@link TermsIndexReaderBase#supportsOrd()} returns true. */
    public abstract long seek(long ord) throws IOException;

    /** Only implemented if {@link TermsIndexReaderBase#supportsOrd()} returns true. */
    public abstract long ord();
  }
}