/*
    * 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.giraph.mapping;
  
  import org.apache.hadoop.io.LongWritable;
  
  /**
   * MappingStoreOps implementation used to embed target information into
   * vertex id. Stores information in the higher order bits of the long id
   */
  public class DefaultEmbeddedLongByteOps extends AbstractLongByteOps {
    /** Bit mask for first 9 bits in a long */
    private static final long MASK = ((long) 0x1FF) << 55;
    /** Inverse of MASK */
    private static final long IMASK = ~ MASK;
  
    /**
     * Default constructor (do not use)
     */
    public DefaultEmbeddedLongByteOps() {
    }
  
    @Override
    public boolean hasEmbedding() {
      return true;
    }
  
    @Override
    public void embedTargetInfo(LongWritable id) {
      if ((id.get() & MASK) != 0) {
        throw new IllegalStateException("Expected first 9 bits of long " +
            " to be empty");
      }
      byte target = mappingStore.getByteTarget(id);
      // first bit = 0 & rest 8 bits set to target
      // add 1 to distinguish between not set and assignment to worker-0
      // (prefix bits = 0 can mean one of two things :
      // no entry in the mapping, in which case target = -1, so -1 + 1 = 0
      // vertex is created later during computation, so prefix bits are 0 anyway)
      long maskValue = ((1L + target) & 0xFF) << 55;
      id.set(id.get() | maskValue);
    }
  
    @Override
    public void removeTargetInfo(LongWritable id) {
      id.set(id.get() & IMASK);
    }
  
    @Override
    public int getPartition(LongWritable id, int partitionCount,
      int workerCount) {
      // extract last 8 bits
      // subtract 1 since added 1 during embedInfo (unset = -1)
      byte target = (byte) (((id.get() >>> 55) & 0xFF) - 1);
      return computePartition(id, partitionCount, workerCount, target);
    }
  }