/*
 * 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;


import java.io.Closeable;
import java.io.IOException;

import org.apache.lucene.index.PostingsEnum;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.ImpactsEnum;
import org.apache.lucene.index.SegmentReadState;
import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.IndexInput;
import org.apache.lucene.util.Accountable;

/** The core terms dictionaries (BlockTermsReader,
 *  BlockTreeTermsReader) interact with a single instance
 *  of this class to manage creation of {@link org.apache.lucene.index.PostingsEnum} and
 *  {@link org.apache.lucene.index.PostingsEnum} instances.  It provides an
 *  IndexInput (termsIn) where this class may read any
 *  previously stored data that it had written in its
 *  corresponding {@link PostingsWriterBase} at indexing
 *  time. 
 *  @lucene.experimental */

// TODO: maybe move under blocktree?  but it's used by other terms dicts (e.g. Block)

// TODO: find a better name; this defines the API that the
// terms dict impls use to talk to a postings impl.
// TermsDict + PostingsReader/WriterBase == PostingsConsumer/Producer
public abstract class PostingsReaderBase implements Closeable, Accountable {

  /** Sole constructor. (For invocation by subclass 
   *  constructors, typically implicit.) */
  protected PostingsReaderBase() {
  }

  /** Performs any initialization, such as reading and
   *  verifying the header from the provided terms
   *  dictionary {@link IndexInput}. */
  public abstract void init(IndexInput termsIn, SegmentReadState state) throws IOException;

  /** Return a newly created empty TermState */
  public abstract BlockTermState newTermState() throws IOException;

  /** Actually decode metadata for next term 
   *  @see PostingsWriterBase#encodeTerm 
   */
  public abstract void decodeTerm(DataInput in, FieldInfo fieldInfo, BlockTermState state, boolean absolute) throws IOException;

  /** Must fully consume state, since after this call that
   *  TermState may be reused. */
  public abstract PostingsEnum postings(FieldInfo fieldInfo, BlockTermState state, PostingsEnum reuse, int flags) throws IOException;

  /**
   * Return a {@link ImpactsEnum} that computes impacts with {@code scorer}.
   * @see #postings(FieldInfo, BlockTermState, PostingsEnum, int)
   */
  public abstract ImpactsEnum impacts(FieldInfo fieldInfo, BlockTermState state, int flags) throws IOException;

  /** 
   * Checks consistency of this reader.
   * <p>
   * Note that this may be costly in terms of I/O, e.g. 
   * may involve computing a checksum value against large data files.
   * @lucene.internal
   */
  public abstract void checkIntegrity() throws IOException;

  @Override
  public abstract void close() throws IOException;
}
