/*
 * 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.lucene90;

import java.io.IOException;
import java.util.Map;
import java.util.Set;
import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.SegmentInfoFormat;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.IndexFileNames;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.SegmentInfo;
import org.apache.lucene.index.SegmentInfos;
import org.apache.lucene.index.SortFieldProvider;
import org.apache.lucene.search.Sort;
import org.apache.lucene.search.SortField;
import org.apache.lucene.store.ChecksumIndexInput;
import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.IOContext;
import org.apache.lucene.util.Version;

/**
 * Lucene 9.0 Segment info format.
 *
 * <p>Files:
 *
 * <ul>
 *   <li><code>.si</code>: Header, SegVersion, SegSize, IsCompoundFile, Diagnostics, Files,
 *       Attributes, IndexSort, Footer
 * </ul>
 *
 * Data types:
 *
 * <ul>
 *   <li>Header --&gt; {@link CodecUtil#writeIndexHeader IndexHeader}
 *   <li>SegSize --&gt; {@link DataOutput#writeInt Int32}
 *   <li>SegVersion --&gt; {@link DataOutput#writeString String}
 *   <li>SegMinVersion --&gt; {@link DataOutput#writeString String}
 *   <li>Files --&gt; {@link DataOutput#writeSetOfStrings Set&lt;String&gt;}
 *   <li>Diagnostics,Attributes --&gt; {@link DataOutput#writeMapOfStrings Map&lt;String,String&gt;}
 *   <li>IsCompoundFile --&gt; {@link DataOutput#writeByte Int8}
 *   <li>IndexSort --&gt; {@link DataOutput#writeVInt Int32} count, followed by {@code count}
 *       SortField
 *   <li>SortField --&gt; {@link DataOutput#writeString String} sort class, followed by a per-sort
 *       bytestream (see {@link SortFieldProvider#readSortField(DataInput)})
 *   <li>Footer --&gt; {@link CodecUtil#writeFooter CodecFooter}
 * </ul>
 *
 * Field Descriptions:
 *
 * <ul>
 *   <li>SegVersion is the code version that created the segment.
 *   <li>SegMinVersion is the minimum code version that contributed documents to the segment.
 *   <li>SegSize is the number of documents contained in the segment index.
 *   <li>IsCompoundFile records whether the segment is written as a compound file or not. If this is
 *       -1, the segment is not a compound file. If it is 1, the segment is a compound file.
 *   <li>The Diagnostics Map is privately written by {@link IndexWriter}, as a debugging aid, for
 *       each segment it creates. It includes metadata like the current Lucene version, OS, Java
 *       version, why the segment was created (merge, flush, addIndexes), etc.
 *   <li>Files is a list of files referred to by this segment.
 * </ul>
 *
 * @see SegmentInfos
 * @lucene.experimental
 */
public class Lucene90SegmentInfoFormat extends SegmentInfoFormat {

  /** File extension used to store {@link SegmentInfo}. */
  public static final String SI_EXTENSION = "si";

  static final String CODEC_NAME = "Lucene90SegmentInfo";
  static final int VERSION_START = 0;
  static final int VERSION_CURRENT = VERSION_START;

  /** Sole constructor. */
  public Lucene90SegmentInfoFormat() {}

  @Override
  public SegmentInfo read(Directory dir, String segment, byte[] segmentID, IOContext context)
      throws IOException {
    final String fileName = IndexFileNames.segmentFileName(segment, "", SI_EXTENSION);
    try (ChecksumIndexInput input = dir.openChecksumInput(fileName)) {
      Throwable priorE = null;
      SegmentInfo si = null;
      try {
        CodecUtil.checkIndexHeader(
            input, CODEC_NAME, VERSION_START, VERSION_CURRENT, segmentID, "");
        si = parseSegmentInfo(dir, input, segment, segmentID);
      } catch (Throwable exception) {
        priorE = exception;
      } finally {
        CodecUtil.checkFooter(input, priorE);
      }
      return si;
    }
  }

  private SegmentInfo parseSegmentInfo(
      Directory dir, DataInput input, String segment, byte[] segmentID) throws IOException {
    final Version version = Version.fromBits(input.readInt(), input.readInt(), input.readInt());
    byte hasMinVersion = input.readByte();
    final Version minVersion;
    switch (hasMinVersion) {
      case 0:
        minVersion = null;
        break;
      case 1:
        minVersion = Version.fromBits(input.readInt(), input.readInt(), input.readInt());
        break;
      default:
        throw new CorruptIndexException("Illegal boolean value " + hasMinVersion, input);
    }

    final int docCount = input.readInt();
    if (docCount < 0) {
      throw new CorruptIndexException("invalid docCount: " + docCount, input);
    }
    final boolean isCompoundFile = input.readByte() == SegmentInfo.YES;

    final Map<String, String> diagnostics = input.readMapOfStrings();
    final Set<String> files = input.readSetOfStrings();
    final Map<String, String> attributes = input.readMapOfStrings();

    int numSortFields = input.readVInt();
    Sort indexSort;
    if (numSortFields > 0) {
      SortField[] sortFields = new SortField[numSortFields];
      for (int i = 0; i < numSortFields; i++) {
        String name = input.readString();
        sortFields[i] = SortFieldProvider.forName(name).readSortField(input);
      }
      indexSort = new Sort(sortFields);
    } else if (numSortFields < 0) {
      throw new CorruptIndexException("invalid index sort field count: " + numSortFields, input);
    } else {
      indexSort = null;
    }

    SegmentInfo si =
        new SegmentInfo(
            dir,
            version,
            minVersion,
            segment,
            docCount,
            isCompoundFile,
            false,
            null,
            diagnostics,
            segmentID,
            attributes,
            indexSort);
    si.setFiles(files);
    return si;
  }

  @Override
  public void write(Directory dir, SegmentInfo si, IOContext ioContext) throws IOException {
    throw new UnsupportedOperationException("Old formats can't be used for writing");
  }
}
