/*
 * 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 org.apache.lucene.codecs.blocktree.BlockTreeTermsWriter;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.SegmentWriteState;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.store.IndexOutput;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.FixedBitSet;

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

Class that plugs into term dictionaries, such as BlockTreeTermsWriter, and handles writing postings. 
See Also:
PostingsReaderBase
@lucene.experimental
/**
 * Class that plugs into term dictionaries, such as {@link
 * BlockTreeTermsWriter}, and handles writing postings.
 * 
 * @see PostingsReaderBase
 * @lucene.experimental
 */
// TODO: find a better name; this defines the API that the
// terms dict impls use to talk to a postings impl.
// TermsDict + PostingsReader/WriterBase == FieldsProducer/Consumer
public abstract class PostingsWriterBase implements Closeable {

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

  
Called once after startup, before any terms have been added. Implementations typically write a header to the provided termsOut. /** Called once after startup, before any terms have been
   *  added.  Implementations typically write a header to
   *  the provided {@code termsOut}. */
  public abstract void init(IndexOutput termsOut, SegmentWriteState state) throws IOException;

  
Write all postings for one term; use the provided TermsEnum to pull a PostingsEnum. This method should not re-position the TermsEnum! It is already positioned on the term that should be written. This method must set the bit in the provided FixedBitSet for every docID written. If no docs were written, this method should return null, and the terms dict will skip the term. /** Write all postings for one term; use the provided
   *  {@link TermsEnum} to pull a {@link org.apache.lucene.index.PostingsEnum}.
   *  This method should not
   *  re-position the {@code TermsEnum}!  It is already
   *  positioned on the term that should be written.  This
   *  method must set the bit in the provided {@link
   *  FixedBitSet} for every docID written.  If no docs
   *  were written, this method should return null, and the
   *  terms dict will skip the term. */
  public abstract BlockTermState writeTerm(BytesRef term, TermsEnum termsEnum, FixedBitSet docsSeen, NormsProducer norms) throws IOException;

  
Encode metadata as long[] and byte[]. absolute controls whether current term is delta encoded according to latest term. Usually elements in longs are file pointers, so each one always increases when a new term is consumed. out is used to write generic bytes, which are not monotonic. NOTE: sometimes long[] might contain "don't care" values that are unused, e.g. the pointer to postings list may not be defined for some terms but is defined for others, if it is designed to inline some postings data in term dictionary. In this case, the postings writer should always use the last value, so that each element in metadata long[] remains monotonic. /**
   * Encode metadata as long[] and byte[]. {@code absolute} controls whether 
   * current term is delta encoded according to latest term. 
   * Usually elements in {@code longs} are file pointers, so each one always 
   * increases when a new term is consumed. {@code out} is used to write generic
   * bytes, which are not monotonic.
   *
   * NOTE: sometimes long[] might contain "don't care" values that are unused, e.g. 
   * the pointer to postings list may not be defined for some terms but is defined
   * for others, if it is designed to inline  some postings data in term dictionary.
   * In this case, the postings writer should always use the last value, so that each
   * element in metadata long[] remains monotonic.
   */
  public abstract void encodeTerm(long[] longs, DataOutput out, FieldInfo fieldInfo, BlockTermState state, boolean absolute) throws IOException;

  
Sets the current field for writing, and returns the
fixed length of long[] metadata (which is fixed per
field), called when the writing switches to another field. /** 
   * Sets the current field for writing, and returns the
   * fixed length of long[] metadata (which is fixed per
   * field), called when the writing switches to another field. */
  // TODO: better name?
  public abstract int setField(FieldInfo fieldInfo);

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