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.sasi.disk;
  
  import java.nio.ByteBuffer;
  
  import org.apache.cassandra.index.sasi.Term;
  import org.apache.cassandra.index.sasi.utils.MappedBuffer;
  import org.apache.cassandra.db.marshal.AbstractType;
  
  public abstract class OnDiskBlock<T extends Term>
  {
      public enum BlockType
      {
          POINTER, DATA
      }
  
      // this contains offsets of the terms and term data
      protected final MappedBuffer blockIndex;
      protected final int blockIndexSize;
  
      protected final boolean hasCombinedIndex;
      protected final TokenTree combinedIndex;
  
      public OnDiskBlock(Descriptor descriptor, MappedBuffer block, BlockType blockType)
      {
          blockIndex = block;
  
          if (blockType == BlockType.POINTER)
          {
              hasCombinedIndex = false;
              combinedIndex = null;
              blockIndexSize = block.getInt() << 1; // num terms * sizeof(short)
              return;
          }
  
          long blockOffset = block.position();
          int combinedIndexOffset = block.getInt(blockOffset + OnDiskIndexBuilder.BLOCK_SIZE);
  
          hasCombinedIndex = (combinedIndexOffset >= 0);
          long blockIndexOffset = blockOffset + OnDiskIndexBuilder.BLOCK_SIZE + 4 + combinedIndexOffset;
  
          combinedIndex = hasCombinedIndex ? new TokenTree(descriptor, blockIndex.duplicate().position(blockIndexOffset)) : null;
          blockIndexSize = block.getInt() * 2;
      }
  
      public SearchResult<T> search(AbstractType<?> comparator, ByteBuffer query)
      {
          int cmp = -1, start = 0, end = termCount() - 1, middle = 0;
  
          T element = null;
          while (start <= end)
          {
              middle = start + ((end - start) >> 1);
              element = getTerm(middle);
  
              cmp = element.compareTo(comparator, query);
              if (cmp == 0)
                  return new SearchResult<>(element, cmp, middle);
              else if (cmp < 0)
                  start = middle + 1;
              else
                  end = middle - 1;
          }
  
          return new SearchResult<>(element, cmp, middle);
      }
  
      protected T getTerm(int index)
      {
          MappedBuffer dup = blockIndex.duplicate();
          long startsAt = getTermPosition(index);
          if (termCount() - 1 == index) // last element
              dup.position(startsAt);
          else
              dup.position(startsAt).limit(getTermPosition(index + 1));
  
          return cast(dup);
      }
  
      protected long getTermPosition(int idx)
      {
          return getTermPosition(blockIndex, idx, blockIndexSize);
      }
  
      protected int termCount()
      {
          return blockIndexSize >> 1;
      }
  
      protected abstract T cast(MappedBuffer data);
  
      static long getTermPosition(MappedBuffer data, int idx, int indexSize)
      {
          idx <<= 1;
          assert idx < indexSize;
          return data.position() + indexSize + data.getShort(data.position() + idx);
      }
  
      public TokenTree getBlockIndex()
      {
          return combinedIndex;
      }
  
      public int minOffset(OnDiskIndex.IteratorOrder order)
      {
          return order == OnDiskIndex.IteratorOrder.DESC ? 0 : termCount() - 1;
      }
  
      public int maxOffset(OnDiskIndex.IteratorOrder order)
      {
          return minOffset(order) == 0 ? termCount() - 1 : 0;
      }
  
      public static class SearchResult<T>
      {
          public final T result;
          public final int index, cmp;
  
          public SearchResult(T result, int cmp, int index)
          {
              this.result = result;
              this.index = index;
              this.cmp = cmp;
          }
      }
  }
  