/*
    * 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.hbase.codec.prefixtree.decode;
  
  import org.apache.hadoop.classification.InterfaceAudience;
  import org.apache.hbase.Cell;
  import org.apache.hbase.cell.CellScannerPosition;
  import org.apache.hbase.cell.CellTool;
  import org.apache.hbase.codec.prefixtree.PrefixTreeBlockMeta;
  import org.apache.hbase.codec.prefixtree.scanner.CellSearcher;
  
  import com.google.common.primitives.UnsignedBytes;
  
  /**
   * Searcher extends the capabilities of the Scanner + ReversibleScanner to add the ability to
   * position itself on a requested Cell without scanning through cells before it. The PrefixTree is
   * set up to be a Trie of rows, so finding a particular row is extremely cheap.
   * <p/>
   * Once it finds the row, it does a binary search through the cells inside the row, which is not as
   * fast as the trie search, but faster than iterating through every cell like existing block formats
   * do. For this reason, this implementation is targeted towards schemas where rows are narrow enough
   * to have several or many per block, and where you are generally looking for the entire row or the
   * first cell. It will still be fast for wide rows or point queries, but could be improved upon.
   */
  @InterfaceAudience.Private
  public class PrefixTreeArraySearcher extends PrefixTreeArrayReversibleScanner implements
      CellSearcher {
  
    /*************** construct ******************************/
  
    public PrefixTreeArraySearcher(PrefixTreeBlockMeta blockMeta, int rowTreeDepth,
        int rowBufferLength, int qualifierBufferLength) {
      super(blockMeta, rowTreeDepth, rowBufferLength, qualifierBufferLength);
    }
  
  
    /********************* CellSearcher methods *******************/
  
    @Override
    public boolean positionAt(Cell key) {
      return CellScannerPosition.AT == positionAtOrAfter(key);
    }
  
    @Override
    public CellScannerPosition positionAtOrBefore(Cell key) {
      reInitFirstNode();
      int fanIndex = -1;
  
      while(true){
        //detect row mismatch.  break loop if mismatch
        int currentNodeDepth = rowLength;
        int rowTokenComparison = compareToCurrentToken(key);
        if(rowTokenComparison != 0){
          return fixRowTokenMissReverse(rowTokenComparison);
        }
  
        //exact row found, move on to qualifier & ts
        if(rowMatchesAfterCurrentPosition(key)){
          return positionAtQualifierTimestamp(key, true);
        }
  
        //detect dead end (no fan to descend into)
        if(!currentRowNode.hasFan()){
          if(hasOccurrences()){//must be leaf or nub
            populateLastNonRowFields();
            return CellScannerPosition.BEFORE;
          }else{
            //TODO i don't think this case is exercised by any tests
            return fixRowFanMissReverse(0);
          }
        }
  
        //keep hunting for the rest of the row
        byte searchForByte = CellTool.getRowByte(key, currentNodeDepth);
        fanIndex = currentRowNode.whichFanNode(searchForByte);
        if(fanIndex < 0){//no matching row.  return early
          int insertionPoint = -fanIndex;
          return fixRowFanMissReverse(insertionPoint);
        }
        //found a match, so dig deeper into the tree
        followFan(fanIndex);
      }
    }
 
   /**
    * Identical workflow as positionAtOrBefore, but split them to avoid having ~10 extra
    * if-statements. Priority on readability and debugability.
    */
   @Override
   public CellScannerPosition positionAtOrAfter(Cell key) {
     reInitFirstNode();
     int fanIndex = -1;
 
     while(true){
       //detect row mismatch.  break loop if mismatch
       int currentNodeDepth = rowLength;
       int rowTokenComparison = compareToCurrentToken(key);
       if(rowTokenComparison != 0){
         return fixRowTokenMissForward(rowTokenComparison);
       }
 
       //exact row found, move on to qualifier & ts
       if(rowMatchesAfterCurrentPosition(key)){
         return positionAtQualifierTimestamp(key, false);
       }
 
       //detect dead end (no fan to descend into)
       if(!currentRowNode.hasFan()){
         if(hasOccurrences()){
           populateFirstNonRowFields();
           return CellScannerPosition.AFTER;
         }else{
           //TODO i don't think this case is exercised by any tests
           return fixRowFanMissForward(0);
         }
       }
 
       //keep hunting for the rest of the row
       byte searchForByte = CellTool.getRowByte(key, currentNodeDepth);
       fanIndex = currentRowNode.whichFanNode(searchForByte);
       if(fanIndex < 0){//no matching row.  return early
         int insertionPoint = -fanIndex;
         return fixRowFanMissForward(insertionPoint);
       }
       //found a match, so dig deeper into the tree
       followFan(fanIndex);
     }
   }
 
   @Override
   public boolean seekForwardTo(Cell key) {
     if(currentPositionIsAfter(key)){
       //our position is after the requested key, so can't do anything
       return false;
     }
     return positionAt(key);
   }
 
   @Override
   public CellScannerPosition seekForwardToOrBefore(Cell key) {
     //Do we even need this check or should upper layers avoid this situation.  It's relatively
     //expensive compared to the rest of the seek operation.
     if(currentPositionIsAfter(key)){
       //our position is after the requested key, so can't do anything
       return CellScannerPosition.AFTER;
     }
 
     return positionAtOrBefore(key);
   }
 
   @Override
   public CellScannerPosition seekForwardToOrAfter(Cell key) {
     //Do we even need this check or should upper layers avoid this situation.  It's relatively
     //expensive compared to the rest of the seek operation.
     if(currentPositionIsAfter(key)){
       //our position is after the requested key, so can't do anything
       return CellScannerPosition.AFTER;
     }
 
     return positionAtOrAfter(key);
   }
 
   /**
    * The content of the buffers doesn't matter here, only that afterLast=true and beforeFirst=false
    */
   @Override
   public void positionAfterLastCell() {
     resetToBeforeFirstEntry();
     beforeFirst = false;
     afterLast = true;
   }
 
 
   /***************** Object methods ***************************/
 
   @Override
   public boolean equals(Object obj) {
     //trivial override to confirm intent (findbugs)
     return super.equals(obj);
   }
 
 
   /****************** internal methods ************************/
 
   protected boolean currentPositionIsAfter(Cell cell){
     return compareTo(cell) > 0;
   }
 
   protected CellScannerPosition positionAtQualifierTimestamp(Cell key, boolean beforeOnMiss) {
     int minIndex = 0;
     int maxIndex = currentRowNode.getLastCellIndex();
     int diff;
     while (true) {
       int midIndex = (maxIndex + minIndex) / 2;//don't worry about overflow
       diff = populateNonRowFieldsAndCompareTo(midIndex, key);
 
       if (diff == 0) {// found exact match
         return CellScannerPosition.AT;
       } else if (minIndex == maxIndex) {// even termination case
         break;
       } else if ((minIndex + 1) == maxIndex) {// odd termination case
         diff = populateNonRowFieldsAndCompareTo(maxIndex, key);
         if(diff > 0){
           diff = populateNonRowFieldsAndCompareTo(minIndex, key);
         }
         break;
       } else if (diff < 0) {// keep going forward
         minIndex = currentCellIndex;
       } else {// went past it, back up
         maxIndex = currentCellIndex;
       }
     }
 
     if (diff == 0) {
       return CellScannerPosition.AT;
 
     } else if (diff < 0) {// we are before key
       if (beforeOnMiss) {
         return CellScannerPosition.BEFORE;
       }
       if (next()) {
         return CellScannerPosition.AFTER;
       }
       return CellScannerPosition.AFTER_LAST;
 
     } else {// we are after key
       if (!beforeOnMiss) {
         return CellScannerPosition.AFTER;
       }
       if (previous()) {
         return CellScannerPosition.BEFORE;
       }
       return CellScannerPosition.BEFORE_FIRST;
     }
   }
 
   /**
    * compare this.row to key.row but starting at the current rowLength
    * @param key Cell being searched for
    * @return true if row buffer contents match key.row
    */
   protected boolean rowMatchesAfterCurrentPosition(Cell key) {
     if (!currentRowNode.hasOccurrences()) {
       return false;
     }
     int thatRowLength = key.getRowLength();
     if (rowLength != thatRowLength) {
       return false;
     }
     return true;
   }
 
   // TODO move part of this to Cell comparator?
   /**
    * Compare only the bytes within the window of the current token
    * @param key
    * @return return -1 if key is lessThan (before) this, 0 if equal, and 1 if key is after
    */
   protected int compareToCurrentToken(Cell key) {
     int startIndex = rowLength - currentRowNode.getTokenLength();
     int endIndexExclusive = startIndex + currentRowNode.getTokenLength();
     for (int i = startIndex; i < endIndexExclusive; ++i) {
       if (i >= key.getRowLength()) {// key was shorter, so it's first
         return -1;
       }
       byte keyByte = CellTool.getRowByte(key, i);
       byte thisByte = rowBuffer[i];
       if (keyByte == thisByte) {
         continue;
       }
       return UnsignedBytes.compare(keyByte, thisByte);
     }
     return 0;
   }
 
   protected void followLastFansUntilExhausted(){
     while(currentRowNode.hasFan()){
       followLastFan();
     }
   }
 
 
 	/****************** complete seek when token mismatch ******************/
 
   /**
    * @param searcherIsAfterInputKey <0: input key is before the searcher's position<br/>
    *          >0: input key is after the searcher's position
    */
   protected CellScannerPosition fixRowTokenMissReverse(int searcherIsAfterInputKey) {
     if (searcherIsAfterInputKey < 0) {//searcher position is after the input key, so back up
       boolean foundPreviousRow = previousRow(true);
       if(foundPreviousRow){
         populateLastNonRowFields();
         return CellScannerPosition.BEFORE;
       }else{
         return CellScannerPosition.BEFORE_FIRST;
       }
 
     }else{//searcher position is before the input key
       if(currentRowNode.hasOccurrences()){
         populateFirstNonRowFields();
         return CellScannerPosition.BEFORE;
       }
       boolean foundNextRow = nextRow();
       if(foundNextRow){
         return CellScannerPosition.AFTER;
       }else{
         return CellScannerPosition.AFTER_LAST;
       }
     }
   }
 
   /**
    * @param searcherIsAfterInputKey <0: input key is before the searcher's position<br/>
    *                   >0: input key is after the searcher's position
    */
   protected CellScannerPosition fixRowTokenMissForward(int searcherIsAfterInputKey) {
     if (searcherIsAfterInputKey < 0) {//searcher position is after the input key
       if(currentRowNode.hasOccurrences()){
         populateFirstNonRowFields();
         return CellScannerPosition.AFTER;
       }
       boolean foundNextRow = nextRow();
       if(foundNextRow){
         return CellScannerPosition.AFTER;
       }else{
         return CellScannerPosition.AFTER_LAST;
       }
 
     }else{//searcher position is before the input key, so go forward
       discardCurrentRowNode(true);
       boolean foundNextRow = nextRow();
       if(foundNextRow){
         return CellScannerPosition.AFTER;
       }else{
         return CellScannerPosition.AFTER_LAST;
       }
     }
   }
 
 
   /****************** complete seek when fan mismatch ******************/
 
   protected CellScannerPosition fixRowFanMissReverse(int fanInsertionPoint){
     if(fanInsertionPoint == 0){//we need to back up a row
       boolean foundPreviousRow = previousRow(true);//true -> position on last cell in row
       if(foundPreviousRow){
         populateLastNonRowFields();
         return CellScannerPosition.BEFORE;
       }
       return CellScannerPosition.BEFORE_FIRST;
     }
 
     //follow the previous fan, but then descend recursively forward
     followFan(fanInsertionPoint - 1);
     followLastFansUntilExhausted();
     populateLastNonRowFields();
     return CellScannerPosition.BEFORE;
   }
 
   protected CellScannerPosition fixRowFanMissForward(int fanInsertionPoint){
     if(fanInsertionPoint >= currentRowNode.getFanOut()){
       discardCurrentRowNode(true);
       if (!nextRow()) {
         return CellScannerPosition.AFTER_LAST;
       } else {
         return CellScannerPosition.AFTER;
       }
     }
 
     followFan(fanInsertionPoint);
     if(hasOccurrences()){
       populateFirstNonRowFields();
       return CellScannerPosition.AFTER;
     }
 
     if(nextRowInternal()){
       populateFirstNonRowFields();
       return CellScannerPosition.AFTER;
 
     }else{
       return CellScannerPosition.AFTER_LAST;
     }
   }
 
 }