/*
    *
    * 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.regionserver;
  
  import java.io.IOException;
  import java.util.NavigableSet;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.KeyValue;
  import org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode;
  import org.apache.hadoop.hbase.util.Bytes;
  
  /**
   * This class is used for the tracking and enforcement of columns and numbers
   * of versions during the course of a Get or Scan operation, when explicit
   * column qualifiers have been asked for in the query.
   *
   * With a little magic (see {@link ScanQueryMatcher}), we can use this matcher
   * for both scans and gets.  The main difference is 'next' and 'done' collapse
   * for the scan case (since we see all columns in order), and we only reset
   * between rows.
   *
   * <p>
   * This class is utilized by {@link ScanQueryMatcher} mainly through two methods:
   * <ul><li>{@link #checkColumn} is called when a Put satisfies all other
   * conditions of the query.
   * <ul><li>{@link #getNextRowOrNextColumn} is called whenever ScanQueryMatcher
   * believes that the current column should be skipped (by timestamp, filter etc.)
   * <p>
   * These two methods returns a 
   * {@link org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode}
   * to define what action should be taken.
   * <p>
   * This class is NOT thread-safe as queries are never multi-threaded
   */
  @InterfaceAudience.Private
  public class ExplicitColumnTracker implements ColumnTracker {
  
    private final int maxVersions;
    private final int minVersions;
  
    // hint for the tracker about how many KVs we will attempt to search via next()
    // before we schedule a (re)seek operation
    private final int lookAhead; 
  
   /**
    * Contains the list of columns that the ExplicitColumnTracker is tracking.
    * Each ColumnCount instance also tracks how many versions of the requested
    * column have been returned.
    */
    private final ColumnCount[] columns;
    private int index;
    private ColumnCount column;
    /** Keeps track of the latest timestamp included for current column.
     * Used to eliminate duplicates. */
    private long latestTSOfCurrentColumn;
    private long oldestStamp;
    private int skipCount;
  
    /**
     * Default constructor.
     * @param columns columns specified user in query
     * @param minVersions minimum number of versions to keep
     * @param maxVersions maximum versions to return per column
     * @param oldestUnexpiredTS the oldest timestamp we are interested in,
     *  based on TTL 
     * @param lookAhead number of KeyValues to look ahead via next before
     *  (re)seeking
     */
    public ExplicitColumnTracker(NavigableSet<byte[]> columns, int minVersions,
        int maxVersions, long oldestUnexpiredTS, int lookAhead) {
      this.maxVersions = maxVersions;
      this.minVersions = minVersions;
      this.lookAhead = lookAhead;
      this.oldestStamp = oldestUnexpiredTS;
      this.columns = new ColumnCount[columns.size()];
      int i=0;
      for(byte [] column : columns) {
        this.columns[i++] = new ColumnCount(column);
      }
      reset();
    }
 
     /**
    * Done when there are no more columns to match against.
    */
   public boolean done() {
     return this.index >= columns.length;
   }
 
   public ColumnCount getColumnHint() {
     return this.column;
   }
 
   /**
    * {@inheritDoc}
    */
   @Override
   public ScanQueryMatcher.MatchCode checkColumn(byte [] bytes, int offset,
       int length, byte type) {
     // delete markers should never be passed to an
     // *Explicit*ColumnTracker
     assert !KeyValue.isDelete(type);
     do {
       // No more columns left, we are done with this query
       if(done()) {
         return ScanQueryMatcher.MatchCode.SEEK_NEXT_ROW; // done_row
       }
 
       // No more columns to match against, done with storefile
       if(this.column == null) {
         return ScanQueryMatcher.MatchCode.SEEK_NEXT_ROW; // done_row
       }
 
       // Compare specific column to current column
       int ret = Bytes.compareTo(column.getBuffer(), column.getOffset(),
           column.getLength(), bytes, offset, length);
 
       // Column Matches. Return include code. The caller would call checkVersions
       // to limit the number of versions.
       if(ret == 0) {
         return ScanQueryMatcher.MatchCode.INCLUDE;
       }
 
       resetTS();
 
       if (ret > 0) {
         // The current KV is smaller than the column the ExplicitColumnTracker
         // is interested in, so seek to that column of interest.
         return this.skipCount++ < this.lookAhead ? ScanQueryMatcher.MatchCode.SKIP
             : ScanQueryMatcher.MatchCode.SEEK_NEXT_COL;
       }
 
       // The current KV is bigger than the column the ExplicitColumnTracker
       // is interested in. That means there is no more data for the column
       // of interest. Advance the ExplicitColumnTracker state to next
       // column of interest, and check again.
       if (ret <= -1) {
         ++this.index;
         this.skipCount = 0;
         if (done()) {
           // No more to match, do not include, done with this row.
           return ScanQueryMatcher.MatchCode.SEEK_NEXT_ROW; // done_row
         }
         // This is the recursive case.
         this.column = this.columns[this.index];
       }
     } while(true);
   }
 
   @Override
   public ScanQueryMatcher.MatchCode checkVersions(byte[] bytes, int offset, int length,
       long timestamp, byte type, boolean ignoreCount) throws IOException {
     assert !KeyValue.isDelete(type);
     if (ignoreCount) return ScanQueryMatcher.MatchCode.INCLUDE;
     // Check if it is a duplicate timestamp
     if (sameAsPreviousTS(timestamp)) {
       // If duplicate, skip this Key
       return ScanQueryMatcher.MatchCode.SKIP;
     }
     int count = this.column.increment();
     if (count >= maxVersions || (count >= minVersions && isExpired(timestamp))) {
       // Done with versions for this column
       ++this.index;
       this.skipCount = 0;
       resetTS();
       if (done()) {
         // We have served all the requested columns.
         this.column = null;
         return ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_ROW;
       }
       // We are done with current column; advance to next column
       // of interest.
       this.column = this.columns[this.index];
       return ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_COL;
     }
     setTS(timestamp);
     return ScanQueryMatcher.MatchCode.INCLUDE;
   }
 
   // Called between every row.
   public void reset() {
     this.index = 0;
     this.skipCount = 0;
     this.column = this.columns[this.index];
     for(ColumnCount col : this.columns) {
       col.setCount(0);
     }
     resetTS();
   }
 
   private void resetTS() {
     latestTSOfCurrentColumn = HConstants.LATEST_TIMESTAMP;
   }
 
   private void setTS(long timestamp) {
     latestTSOfCurrentColumn = timestamp;
   }
 
   private boolean sameAsPreviousTS(long timestamp) {
     return timestamp == latestTSOfCurrentColumn;
   }
 
   private boolean isExpired(long timestamp) {
     return timestamp < oldestStamp;
   }
 
   /**
    * This method is used to inform the column tracker that we are done with
    * this column. We may get this information from external filters or
    * timestamp range and we then need to indicate this information to
    * tracker. It is required only in case of ExplicitColumnTracker.
    * @param bytes
    * @param offset
    * @param length
    */
   public void doneWithColumn(byte [] bytes, int offset, int length) {
     while (this.column != null) {
       int compare = Bytes.compareTo(column.getBuffer(), column.getOffset(),
           column.getLength(), bytes, offset, length);
       resetTS();
       if (compare <= 0) {
         ++this.index;
         this.skipCount = 0;
         if (done()) {
           // Will not hit any more columns in this storefile
           this.column = null;
         } else {
           this.column = this.columns[this.index];
         }
         if (compare <= -1)
           continue;
       }
       return;
     }
   }
 
   public MatchCode getNextRowOrNextColumn(byte[] bytes, int offset,
       int qualLength) {
     doneWithColumn(bytes, offset,qualLength);
 
     if (getColumnHint() == null) {
       return MatchCode.SEEK_NEXT_ROW;
     } else {
       return MatchCode.SEEK_NEXT_COL;
     }
   }
 
   public boolean isDone(long timestamp) {
     return minVersions <= 0 && isExpired(timestamp);
   }
 }