package org.apache.lucene.codecs.lucene46;

/*
 * 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.
 */

import java.io.IOException;

import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.DocValuesFormat;
import org.apache.lucene.codecs.FieldInfosFormat;
import org.apache.lucene.codecs.FieldInfosReader;
import org.apache.lucene.codecs.FieldInfosWriter;
import org.apache.lucene.index.FieldInfo.DocValuesType;
import org.apache.lucene.store.DataOutput;

/**
 * Lucene 4.6 Field Infos format.
 * <p>
 * <p>Field names are stored in the field info file, with suffix <tt>.fnm</tt>.</p>
 * <p>FieldInfos (.fnm) --&gt; Header,FieldsCount, &lt;FieldName,FieldNumber,
 * FieldBits,DocValuesBits,DocValuesGen,Attributes&gt; <sup>FieldsCount</sup>,Footer</p>
 * <p>Data types:
 * <ul>
 *   <li>Header --&gt; {@link CodecUtil#checkHeader CodecHeader}</li>
 *   <li>FieldsCount --&gt; {@link DataOutput#writeVInt VInt}</li>
 *   <li>FieldName --&gt; {@link DataOutput#writeString String}</li>
 *   <li>FieldBits, DocValuesBits --&gt; {@link DataOutput#writeByte Byte}</li>
 *   <li>FieldNumber --&gt; {@link DataOutput#writeInt VInt}</li>
 *   <li>Attributes --&gt; {@link DataOutput#writeStringStringMap Map&lt;String,String&gt;}</li>
 *   <li>DocValuesGen --&gt; {@link DataOutput#writeLong(long) Int64}</li>
 *   <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}</li>
 * </ul>
 * </p>
 * Field Descriptions:
 * <ul>
 *   <li>FieldsCount: the number of fields in this file.</li>
 *   <li>FieldName: name of the field as a UTF-8 String.</li>
 *   <li>FieldNumber: the field's number. Note that unlike previous versions of
 *       Lucene, the fields are not numbered implicitly by their order in the
 *       file, instead explicitly.</li>
 *   <li>FieldBits: a byte containing field options.
 *       <ul>
 *         <li>The low-order bit is one for indexed fields, and zero for non-indexed
 *             fields.</li>
 *         <li>The second lowest-order bit is one for fields that have term vectors
 *             stored, and zero for fields without term vectors.</li>
 *         <li>If the third lowest order-bit is set (0x4), offsets are stored into
 *             the postings list in addition to positions.</li>
 *         <li>Fourth bit is unused.</li>
 *         <li>If the fifth lowest-order bit is set (0x10), norms are omitted for the
 *             indexed field.</li>
 *         <li>If the sixth lowest-order bit is set (0x20), payloads are stored for the
 *             indexed field.</li>
 *         <li>If the seventh lowest-order bit is set (0x40), term frequencies and
 *             positions omitted for the indexed field.</li>
 *         <li>If the eighth lowest-order bit is set (0x80), positions are omitted for the
 *             indexed field.</li>
 *       </ul>
 *    </li>
 *    <li>DocValuesBits: a byte containing per-document value types. The type
 *        recorded as two four-bit integers, with the high-order bits representing
 *        <code>norms</code> options, and the low-order bits representing 
 *        {@code DocValues} options. Each four-bit integer can be decoded as such:
 *        <ul>
 *          <li>0: no DocValues for this field.</li>
 *          <li>1: NumericDocValues. ({@link DocValuesType#NUMERIC})</li>
 *          <li>2: BinaryDocValues. ({@code DocValuesType#BINARY})</li>
 *          <li>3: SortedDocValues. ({@code DocValuesType#SORTED})</li>
 *        </ul>
 *    </li>
 *    <li>DocValuesGen is the generation count of the field's DocValues. If this is -1,
 *        there are no DocValues updates to that field. Anything above zero means there 
 *        are updates stored by {@link DocValuesFormat}.</li>
 *    <li>Attributes: a key-value map of codec-private attributes.</li>
 * </ul>
 *
 * @lucene.experimental
 */
public final class Lucene46FieldInfosFormat extends FieldInfosFormat {
  private final FieldInfosReader reader = new Lucene46FieldInfosReader();
  private final FieldInfosWriter writer = new Lucene46FieldInfosWriter();
  
  /** Sole constructor. */
  public Lucene46FieldInfosFormat() {
  }

  @Override
  public FieldInfosReader getFieldInfosReader() throws IOException {
    return reader;
  }

  @Override
  public FieldInfosWriter getFieldInfosWriter() throws IOException {
    return writer;
  }
  
  /** Extension of field infos */
  static final String EXTENSION = "fnm";
  
  // Codec header
  static final String CODEC_NAME = "Lucene46FieldInfos";
  static final int FORMAT_START = 0;
  static final int FORMAT_CHECKSUM = 1;
  static final int FORMAT_CURRENT = FORMAT_CHECKSUM;
  
  // Field flags
  static final byte IS_INDEXED = 0x1;
  static final byte STORE_TERMVECTOR = 0x2;
  static final byte STORE_OFFSETS_IN_POSTINGS = 0x4;
  static final byte OMIT_NORMS = 0x10;
  static final byte STORE_PAYLOADS = 0x20;
  static final byte OMIT_TERM_FREQ_AND_POSITIONS = 0x40;
  static final byte OMIT_POSITIONS = -128;
}
