/*
    * 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.hadoop.hbase.codec.prefixtree.encode.other;
  
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.io.OutputStream;
  import java.util.Arrays;
  import java.util.HashSet;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.util.ArrayUtils;
  import org.apache.hadoop.hbase.util.CollectionUtils;
  import org.apache.hadoop.hbase.util.vint.UFIntTool;
  
  import com.google.common.base.Joiner;
  
  /**
   * Used to de-duplicate, sort, minimize/diff, and serialize timestamps and mvccVersions from a
   * collection of Cells.
   *
   * 1. add longs to a HashSet for fast de-duplication
   * 2. keep track of the min and max
   * 3. copy all values to a new long[]
   * 4. Collections.sort the long[]
   * 5. calculate maxDelta = max - min
   * 6. determine FInt width based on maxDelta
   * 7. PrefixTreeEncoder binary searches to find index of each value
   */
  @InterfaceAudience.Private
  public class LongEncoder {
  
    /****************** fields ****************************/
  
    protected HashSet<Long> uniqueValues;
    protected long[] sortedUniqueValues;
    protected long min, max, maxDelta;
  
    protected int bytesPerDelta;
    protected int bytesPerIndex;
    protected int totalCompressedBytes;
  
  
    /****************** construct ****************************/
  
    public LongEncoder() {
      this.uniqueValues = new HashSet<Long>();
    }
  
    public void reset() {
      uniqueValues.clear();
      sortedUniqueValues = null;
      min = Long.MAX_VALUE;
      max = Long.MIN_VALUE;
      maxDelta = Long.MIN_VALUE;
      bytesPerIndex = 0;
      bytesPerDelta = 0;
      totalCompressedBytes = 0;
    }
  
  
    /************* methods ***************************/
  
    public void add(long timestamp) {
      uniqueValues.add(timestamp);
    }
  
    public LongEncoder compile() {
      int numUnique = uniqueValues.size();
      if (numUnique == 1) {
        min = CollectionUtils.getFirst(uniqueValues);
        sortedUniqueValues = new long[] { min };
        return this;
      }
  
      sortedUniqueValues = new long[numUnique];
      int lastIndex = -1;
      for (long value : uniqueValues) {
        sortedUniqueValues[++lastIndex] = value;
      }
      Arrays.sort(sortedUniqueValues);
      min = ArrayUtils.getFirst(sortedUniqueValues);
      max = ArrayUtils.getLast(sortedUniqueValues);
     maxDelta = max - min;
     if (maxDelta > 0) {
       bytesPerDelta = UFIntTool.numBytes(maxDelta);
     } else {
       bytesPerDelta = 0;
     }
 
     int maxIndex = numUnique - 1;
     bytesPerIndex = UFIntTool.numBytes(maxIndex);
 
     totalCompressedBytes = numUnique * bytesPerDelta;
 
     return this;
   }
 
   public long getDelta(int index) {
     if (sortedUniqueValues.length == 0) {
       return 0;
     }
     return sortedUniqueValues[index] - min;
   }
 
   public int getIndex(long value) {
     // should always find an exact match
     return Arrays.binarySearch(sortedUniqueValues, value);
   }
 
   public void writeBytes(OutputStream os) throws IOException {
     for (int i = 0; i < sortedUniqueValues.length; ++i) {
       long delta = sortedUniqueValues[i] - min;
       UFIntTool.writeBytes(bytesPerDelta, delta, os);
     }
   }
 
   //convenience method for tests
   public byte[] getByteArray() throws IOException{
     ByteArrayOutputStream baos = new ByteArrayOutputStream();
     writeBytes(baos);
     return baos.toByteArray();
   }
 
   public int getOutputArrayLength() {
     return sortedUniqueValues.length * bytesPerDelta;
   }
 
   public int getNumUniqueValues() {
     return sortedUniqueValues.length;
   }
 
 
   /******************* Object methods **********************/
 
   @Override
   public String toString() {
     if (ArrayUtils.isEmpty(sortedUniqueValues)) {
       return "[]";
     }
     return "[" + Joiner.on(",").join(ArrayUtils.toList(sortedUniqueValues)) + "]";
   }
 
 
   /******************** get/set **************************/
 
   public long getMin() {
     return min;
   }
 
   public int getBytesPerDelta() {
     return bytesPerDelta;
   }
 
   public int getBytesPerIndex() {
     return bytesPerIndex;
   }
 
   public int getTotalCompressedBytes() {
     return totalCompressedBytes;
   }
 
   public long[] getSortedUniqueTimestamps() {
     return sortedUniqueValues;
   }
 
 }