/*
 * 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.backward_codecs.lucene50.compressing;

import java.io.IOException;
import org.apache.lucene.backward_codecs.compressing.CompressionMode;
import org.apache.lucene.backward_codecs.packed.LegacyDirectMonotonicWriter;
import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.StoredFieldsFormat;
import org.apache.lucene.codecs.StoredFieldsReader;
import org.apache.lucene.codecs.StoredFieldsWriter;
import org.apache.lucene.index.FieldInfos;
import org.apache.lucene.index.MergePolicy;
import org.apache.lucene.index.SegmentInfo;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.IOContext;

/**
 * A {@link StoredFieldsFormat} that compresses documents in chunks in order to improve the
 * compression ratio.
 *
 * <p>For a chunk size of <var>chunkSize</var> bytes, this {@link StoredFieldsFormat} does not
 * support documents larger than (<code>2<sup>31</sup> - chunkSize</code>) bytes.
 *
 * <p>For optimal performance, you should use a {@link MergePolicy} that returns segments that have
 * the biggest byte size first.
 *
 * @lucene.experimental
 */
public class Lucene50CompressingStoredFieldsFormat extends StoredFieldsFormat {

  /** format name */
  protected final String formatName;

  /** segment suffix */
  protected final String segmentSuffix;

  /** compression mode */
  protected final CompressionMode compressionMode;

  /** chunk size */
  protected final int chunkSize;

  /** max docs per chunk */
  protected final int maxDocsPerChunk;

  /** block shift */
  protected final int blockShift;

  /**
   * Create a new {@link Lucene50CompressingStoredFieldsFormat} with an empty segment suffix.
   *
   * @see Lucene50CompressingStoredFieldsFormat#Lucene50CompressingStoredFieldsFormat(String,
   *     String, CompressionMode, int, int, int)
   */
  public Lucene50CompressingStoredFieldsFormat(
      String formatName,
      CompressionMode compressionMode,
      int chunkSize,
      int maxDocsPerChunk,
      int blockShift) {
    this(formatName, "", compressionMode, chunkSize, maxDocsPerChunk, blockShift);
  }

  /**
   * Create a new {@link Lucene50CompressingStoredFieldsFormat}.
   *
   * <p><code>formatName</code> is the name of the format. This name will be used in the file
   * formats to perform {@link CodecUtil#checkIndexHeader codec header checks}.
   *
   * <p><code>segmentSuffix</code> is the segment suffix. This suffix is added to the result file
   * name only if it's not the empty string.
   *
   * <p>The <code>compressionMode</code> parameter allows you to choose between compression
   * algorithms that have various compression and decompression speeds so that you can pick the one
   * that best fits your indexing and searching throughput. You should never instantiate two {@link
   * Lucene50CompressingStoredFieldsFormat}s that have the same name but different {@link
   * CompressionMode}s.
   *
   * <p><code>chunkSize</code> is the minimum byte size of a chunk of documents. A value of <code>1
   * </code> can make sense if there is redundancy across fields. <code>maxDocsPerChunk</code> is an
   * upperbound on how many docs may be stored in a single chunk. This is to bound the cpu costs for
   * highly compressible data.
   *
   * <p>Higher values of <code>chunkSize</code> should improve the compression ratio but will
   * require more memory at indexing time and might make document loading a little slower (depending
   * on the size of your OS cache compared to the size of your index).
   *
   * @param formatName the name of the {@link StoredFieldsFormat}
   * @param compressionMode the {@link CompressionMode} to use
   * @param chunkSize the minimum number of bytes of a single chunk of stored documents
   * @param maxDocsPerChunk the maximum number of documents in a single chunk
   * @param blockShift the log in base 2 of number of chunks to store in an index block
   * @see CompressionMode
   */
  public Lucene50CompressingStoredFieldsFormat(
      String formatName,
      String segmentSuffix,
      CompressionMode compressionMode,
      int chunkSize,
      int maxDocsPerChunk,
      int blockShift) {
    this.formatName = formatName;
    this.segmentSuffix = segmentSuffix;
    this.compressionMode = compressionMode;
    if (chunkSize < 1) {
      throw new IllegalArgumentException("chunkSize must be >= 1");
    }
    this.chunkSize = chunkSize;
    if (maxDocsPerChunk < 1) {
      throw new IllegalArgumentException("maxDocsPerChunk must be >= 1");
    }
    this.maxDocsPerChunk = maxDocsPerChunk;
    if (blockShift < LegacyDirectMonotonicWriter.MIN_BLOCK_SHIFT
        || blockShift > LegacyDirectMonotonicWriter.MAX_BLOCK_SHIFT) {
      throw new IllegalArgumentException(
          "blockSize must be in "
              + LegacyDirectMonotonicWriter.MIN_BLOCK_SHIFT
              + "-"
              + LegacyDirectMonotonicWriter.MAX_BLOCK_SHIFT
              + ", got "
              + blockShift);
    }
    this.blockShift = blockShift;
  }

  @Override
  public StoredFieldsReader fieldsReader(
      Directory directory, SegmentInfo si, FieldInfos fn, IOContext context) throws IOException {
    return new Lucene50CompressingStoredFieldsReader(
        directory, si, segmentSuffix, fn, context, formatName, compressionMode);
  }

  @Override
  public StoredFieldsWriter fieldsWriter(Directory directory, SegmentInfo si, IOContext context)
      throws IOException {
    throw new UnsupportedOperationException("Old formats can't be used for writing");
  }

  @Override
  public String toString() {
    return getClass().getSimpleName()
        + "(compressionMode="
        + compressionMode
        + ", chunkSize="
        + chunkSize
        + ", maxDocsPerChunk="
        + maxDocsPerChunk
        + ", blockShift="
        + blockShift
        + ")";
  }
}
