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.vector;
  
  import java.io.IOException;
  import java.util.HashSet;
  import java.util.Set;
  
  import com.google.common.base.Preconditions;
  
  import io.github.jbellis.jvector.util.Bits;
  import org.apache.cassandra.io.util.FileHandle;
  import org.apache.cassandra.io.util.RandomAccessReader;
  
  public class OnDiskOrdinalsMap implements AutoCloseable
  {
      private final FileHandle fh;
      private final long ordToRowOffset;
      private final long segmentEnd;
      private final int size;
      // the offset where we switch from recording ordinal -> rows, to row -> ordinal
      private final long rowOrdinalOffset;
      private final Set<Integer> deletedOrdinals;
  
      public OnDiskOrdinalsMap(FileHandle fh, long segmentOffset, long segmentLength)
      {
          deletedOrdinals = new HashSet<>();
  
          this.segmentEnd = segmentOffset + segmentLength;
          this.fh = fh;
          try (var reader = fh.createReader())
          {
              reader.seek(segmentOffset);
              int deletedCount = reader.readInt();
              for (int i = 0; i < deletedCount; i++)
              {
                  deletedOrdinals.add(reader.readInt());
              }
  
              this.ordToRowOffset = reader.getFilePointer();
              this.size = reader.readInt();
              reader.seek(segmentEnd - 8);
              this.rowOrdinalOffset = reader.readLong();
              assert rowOrdinalOffset < segmentEnd : "rowOrdinalOffset " + rowOrdinalOffset + " is not less than segmentEnd " + segmentEnd;
          }
          catch (Exception e)
          {
              throw new RuntimeException("Error initializing OnDiskOrdinalsMap at segment " + segmentOffset, e);
          }
      }
  
      public RowIdsView getRowIdsView()
      {
          return new RowIdsView();
      }
  
      public Bits ignoringDeleted(Bits acceptBits)
      {
          return BitsUtil.bitsIgnoringDeleted(acceptBits, deletedOrdinals);
      }
  
      public class RowIdsView implements AutoCloseable
      {
          final RandomAccessReader reader = fh.createReader();
  
          public int[] getSegmentRowIdsMatching(int vectorOrdinal) throws IOException
          {
              Preconditions.checkArgument(vectorOrdinal < size, "vectorOrdinal %s is out of bounds %s", vectorOrdinal, size);
  
              // read index entry
              try
              {
                  reader.seek(ordToRowOffset + 4L + vectorOrdinal * 8L);
              }
              catch (Exception e)
              {
                  throw new RuntimeException(String.format("Error seeking to index offset for ordinal %d with ordToRowOffset %d",
                                                           vectorOrdinal, ordToRowOffset), e);
              }
              long offset = reader.readLong();
              // seek to and read rowIds
              try
              {
                  reader.seek(offset);
              }
              catch (Exception e)
              {
                  throw new RuntimeException(String.format("Error seeking to rowIds offset for ordinal %d with ordToRowOffset %d",
                                                           vectorOrdinal, ordToRowOffset), e);
              }
              int postingsSize = reader.readInt();
              int[] rowIds = new int[postingsSize];
              for (int i = 0; i < rowIds.length; i++)
              {
                  rowIds[i] = reader.readInt();
              }
              return rowIds;
          }
  
          @Override
          public void close()
          {
              reader.close();
          }
      }
  
      public OrdinalsView getOrdinalsView()
      {
          return new OrdinalsView();
      }
  
      public class OrdinalsView implements AutoCloseable
      {
          final RandomAccessReader reader = fh.createReader();
          private final long high = (segmentEnd - 8 - rowOrdinalOffset) / 8;
  
          /**
           * @return order if given row id is found; otherwise return -1
           */
          public int getOrdinalForRowId(int rowId) throws IOException
          {
              // Compute the offset of the start of the rowId to vectorOrdinal mapping
              long index = DiskBinarySearch.searchInt(0, Math.toIntExact(high), rowId, i -> {
                  try
                  {
                      long offset = rowOrdinalOffset + i * 8;
                      reader.seek(offset);
                      return reader.readInt();
                  }
                  catch (IOException e)
                  {
                      throw new RuntimeException(e);
                  }
              });
  
              // not found
              if (index < 0)
                  return -1;
  
              return reader.readInt();
          }
  
          @Override
          public void close()
          {
              reader.close();
          }
      }
  
      @Override
      public void close()
      {
          fh.close();
      }
  }
  