content: /*
   * 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.cassandra.index.sai.disk.v1.bitpack;
  
  import java.io.IOException;
  
  import org.apache.cassandra.index.sai.disk.ResettableByteBuffersIndexOutput;
  import org.apache.lucene.store.IndexOutput;
  import org.apache.lucene.util.packed.DirectWriter;
  
  import static org.apache.cassandra.index.sai.disk.v1.SAICodecUtils.checkBlockSize;
  
  /**
   * Modified copy of {@code org.apache.lucene.util.packed.AbstractBlockPackedWriter} to use {@link DirectWriter} for
   * optimised reads that doesn't require seeking through the whole file to open a thread-exclusive reader.
   */
  public abstract class AbstractBlockPackedWriter
  {
      static final int MIN_BLOCK_SIZE = 64;
      static final int MAX_BLOCK_SIZE = 1 << (30 - 3);
  
      protected final IndexOutput indexOutput;
      protected final long[] blockValues;
      // This collects metadata specific to the block packed writer being used during the
      // writing of the block packed data. This cached metadata is then written to the end
      // of the data file when the block packed writer is finished.
      protected final ResettableByteBuffersIndexOutput blockMetaWriter;
  
      protected int blockIndex;
      protected boolean finished;
  
      AbstractBlockPackedWriter(IndexOutput indexOutput, int blockSize)
      {
          checkBlockSize(blockSize, MIN_BLOCK_SIZE, MAX_BLOCK_SIZE);
          this.indexOutput = indexOutput;
          this.blockMetaWriter = new ResettableByteBuffersIndexOutput(blockSize, "BlockPackedMeta");
          blockValues = new long[blockSize];
      }
  
  
      /**
       * Append a new long.
       */
      public void add(long l) throws IOException
      {
          checkNotFinished();
          if (blockIndex == blockValues.length)
          {
              flush();
          }
          blockValues[blockIndex++] = l;
      }
  
      /**
       * Flush all buffered data to disk. This instance is not usable anymore
       * after this method has been called.
       *
       * @return a file offset to the block metadata
       */
      public long finish() throws IOException
      {
          checkNotFinished();
          if (blockIndex > 0)
          {
              flush();
          }
          final long fp = indexOutput.getFilePointer();
          blockMetaWriter.copyTo(indexOutput);
          finished = true;
          return fp;
      }
  
      protected abstract void flushBlock() throws IOException;
  
      void writeValues(int numValues, int bitsPerValue) throws IOException
      {
          final DirectWriter writer = DirectWriter.getInstance(indexOutput, numValues, bitsPerValue);
          for (int i = 0; i < numValues; ++i)
          {
              writer.add(blockValues[i]);
          }
          writer.finish();
      }
  
      void writeVLong(IndexOutput out, long i) throws IOException
      {
          int k = 0;
          while ((i & ~0x7FL) != 0L && k++ < 8)
          {
              out.writeByte((byte) ((i & 0x7FL) | 0x80L));
              i >>>= 7;
          }
          out.writeByte((byte) i);
      }
  
      private void flush() throws IOException
      {
          flushBlock();
          blockIndex = 0;
      }
  
      private void checkNotFinished()
      {
          if (finished)
          {
              throw new IllegalStateException(String.format("[%s] Writer already finished!", indexOutput.getName()));
          }
      }
  }
  