/*
 * 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.lucene50;


import java.io.IOException;

import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.CompoundFormat;
import org.apache.lucene.index.IndexFileNames;
import org.apache.lucene.index.SegmentInfo;
import org.apache.lucene.store.ChecksumIndexInput;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.IOContext;
import org.apache.lucene.store.IndexOutput;
import org.apache.lucene.util.StringHelper;

/**
 * Lucene 5.0 compound file format
 * <p>
 * Files:
 * <ul>
 *    <li><tt>.cfs</tt>: An optional "virtual" file consisting of all the other 
 *    index files for systems that frequently run out of file handles.
 *    <li><tt>.cfe</tt>: The "virtual" compound file's entry table holding all 
 *    entries in the corresponding .cfs file.
 * </ul>
 * <p>Description:</p>
 * <ul>
 *   <li>Compound (.cfs) --> Header, FileData <sup>FileCount</sup>, Footer</li>
 *   <li>Compound Entry Table (.cfe) --> Header, FileCount, <FileName,
 *       DataOffset, DataLength> <sup>FileCount</sup></li>
 *   <li>Header --> {@link CodecUtil#writeIndexHeader IndexHeader}</li>
 *   <li>FileCount --> {@link DataOutput#writeVInt VInt}</li>
 *   <li>DataOffset,DataLength,Checksum --> {@link DataOutput#writeLong UInt64}</li>
 *   <li>FileName --> {@link DataOutput#writeString String}</li>
 *   <li>FileData --> raw file data</li>
 *   <li>Footer --> {@link CodecUtil#writeFooter CodecFooter}</li>
 * </ul>
 * <p>Notes:</p>
 * <ul>
 *   <li>FileCount indicates how many files are contained in this compound file. 
 *       The entry table that follows has that many entries. 
 *   <li>Each directory entry contains a long pointer to the start of this file's data
 *       section, the files length, and a String with that file's name.
 * </ul>
 */
public final class Lucene50CompoundFormat extends CompoundFormat {

  /** Sole constructor. */
  public Lucene50CompoundFormat() {
  }
  
  @Override
  public Directory getCompoundReader(Directory dir, SegmentInfo si, IOContext context) throws IOException {
    return new Lucene50CompoundReader(dir, si, context);
  }

  @Override
  public void write(Directory dir, SegmentInfo si, IOContext context) throws IOException {
    String dataFile = IndexFileNames.segmentFileName(si.name, "", DATA_EXTENSION);
    String entriesFile = IndexFileNames.segmentFileName(si.name, "", ENTRIES_EXTENSION);
    
    byte[] expectedID = si.getId();
    byte[] id = new byte[StringHelper.ID_LENGTH];

    try (IndexOutput data =    dir.createOutput(dataFile, context);
         IndexOutput entries = dir.createOutput(entriesFile, context)) {
      CodecUtil.writeIndexHeader(data,    DATA_CODEC, VERSION_CURRENT, si.getId(), "");
      CodecUtil.writeIndexHeader(entries, ENTRY_CODEC, VERSION_CURRENT, si.getId(), "");
      
      // write number of files
      entries.writeVInt(si.files().size());
      for (String file : si.files()) {
        
        // write bytes for file
        long startOffset = data.getFilePointer();
        try (ChecksumIndexInput in = dir.openChecksumInput(file, IOContext.READONCE)) {

          // just copies the index header, verifying that its id matches what we expect
          CodecUtil.verifyAndCopyIndexHeader(in, data, si.getId());
          
          // copy all bytes except the footer
          long numBytesToCopy = in.length() - CodecUtil.footerLength() - in.getFilePointer();
          data.copyBytes(in, numBytesToCopy);

          // verify footer (checksum) matches for the incoming file we are copying
          long checksum = CodecUtil.checkFooter(in);

          // this is poached from CodecUtil.writeFooter, but we need to use our own checksum, not data.getChecksum(), but I think
          // adding a public method to CodecUtil to do that is somewhat dangerous:
          data.writeInt(CodecUtil.FOOTER_MAGIC);
          data.writeInt(0);
          data.writeLong(checksum);
        }
        long endOffset = data.getFilePointer();
        
        long length = endOffset - startOffset;
        
        // write entry for file
        entries.writeString(IndexFileNames.stripSegmentName(file));
        entries.writeLong(startOffset);
        entries.writeLong(length);
      }
      
      CodecUtil.writeFooter(data);
      CodecUtil.writeFooter(entries);
    }
  }

  /** Extension of compound file */
  static final String DATA_EXTENSION = "cfs";
  /** Extension of compound file entries */
  static final String ENTRIES_EXTENSION = "cfe";
  static final String DATA_CODEC = "Lucene50CompoundData";
  static final String ENTRY_CODEC = "Lucene50CompoundEntries";
  static final int VERSION_START = 0;
  static final int VERSION_CURRENT = VERSION_START;
}