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.asterix.external.util;
  
  import java.nio.ByteBuffer;
  import java.util.BitSet;
  import java.util.Random;
  
  import org.apache.hyracks.api.comm.IFrame;
  import org.apache.hyracks.api.comm.VSizeFrame;
  import org.apache.hyracks.api.context.IHyracksTaskContext;
  import org.apache.hyracks.api.exceptions.HyracksDataException;
  import org.apache.hyracks.dataflow.common.comm.io.FrameTupleAccessor;
  import org.apache.hyracks.dataflow.common.comm.io.FrameTupleAppender;
  
  public class FeedFrameUtil {
      public static ByteBuffer removeBadTuple(IHyracksTaskContext ctx, int tupleIndex, FrameTupleAccessor fta)
              throws HyracksDataException {
          FrameTupleAppender appender = new FrameTupleAppender();
          IFrame slicedFrame = new VSizeFrame(ctx);
          appender.reset(slicedFrame, true);
          int totalTuples = fta.getTupleCount();
          for (int ti = 0; ti < totalTuples; ti++) {
              if (ti != tupleIndex) {
                  appender.append(fta, ti);
              }
          }
          return slicedFrame.getBuffer();
      }
  
      public static ByteBuffer getSampledFrame(IHyracksTaskContext ctx, FrameTupleAccessor fta, int sampleSize)
              throws HyracksDataException {
          NChooseKIterator it = new NChooseKIterator(fta.getTupleCount(), sampleSize);
          FrameTupleAppender appender = new FrameTupleAppender();
          IFrame sampledFrame = new VSizeFrame(ctx);
          appender.reset(sampledFrame, true);
          int nextTupleIndex = 0;
          while (it.hasNext()) {
              nextTupleIndex = it.next();
              appender.append(fta, nextTupleIndex);
          }
          return sampledFrame.getBuffer();
      }
  
      private static class NChooseKIterator {
  
          private final int n;
          private final int k;
          private final BitSet bSet;
          private final Random random;
  
          private int traversed = 0;
  
          public NChooseKIterator(int n, int k) {
              this.n = n;
              this.k = k;
              this.bSet = new BitSet(n);
              bSet.set(0, n - 1);
              this.random = new Random();
          }
  
          public boolean hasNext() {
              return traversed < k;
          }
  
          public int next() {
              if (hasNext()) {
                  traversed++;
                  int startOffset = random.nextInt(n);
                  int pos = -1;
                  while (pos < 0) {
                      pos = bSet.nextSetBit(startOffset);
                      if (pos < 0) {
                          startOffset = 0;
                      }
                  }
                  bSet.clear(pos);
                  return pos;
              } else {
                  return -1;
              }
          }
  
      }
  
  }
  