/**
 * Copyright 2011 The Apache Software Foundation
 *
 * 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.index.coprocessor.regionserver;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.KeyValue;
import org.apache.hadoop.hbase.regionserver.RegionScanner;
import org.apache.hadoop.hbase.util.Bytes;

// TODO better name
public class SeekPointFetcher {

  private static final Log LOG = LogFactory.getLog(SeekPointFetcher.class);
  private RegionScanner indexRegionScanner;

  public SeekPointFetcher(RegionScanner indexRegionScanner) {
    this.indexRegionScanner = indexRegionScanner;
  }

  /**
   * Fetches the next N seek points for the scan.
   * @param seekPoints
   * @param noOfSeekPoints
   * @return false when the scan on the index table for having no more rows remaining.
   * @throws IOException
   */
  public synchronized boolean nextSeekPoints(List<byte[]> seekPoints, int noOfSeekPoints)
      throws IOException {
    boolean hasMore = true;
    List<KeyValue> indexScanResult = new ArrayList<KeyValue>();
    for (int i = 0; i < noOfSeekPoints; i++) {
      hasMore = indexRegionScanner.next(indexScanResult);
      if (indexScanResult.size() > 0) {
        populateSeekPointsWithTableRowKey(seekPoints, indexScanResult.get(0));
      }
      indexScanResult.clear();
      if (hasMore == false) break;
    }
    // TODO log the seekpoints INFO level.
    return hasMore;
  }

  private void populateSeekPointsWithTableRowKey(List<byte[]> seekPoints, KeyValue kv) {
    byte[] row = kv.getRow();
    // Row key of the index table entry = region startkey + index name + column value(s)
    // + actual table rowkey.
    // Every row in the index table will have exactly one KV in that. The value will be
    // 4 bytes. First 2 bytes specify length of the region start key bytes part in the
    // rowkey. Last 2 bytes specify the offset to the actual table rowkey part within the
    // index table rowkey.
    byte[] value = kv.getValue();
    short actualRowKeyOffset = Bytes.toShort(value, 2);
    if (LOG.isTraceEnabled()) {
      LOG.trace("row value for the index table " + Bytes.toString(row));
    }
    byte[] actualTableRowKey = new byte[row.length - actualRowKeyOffset];
    System.arraycopy(row, actualRowKeyOffset, actualTableRowKey, 0, actualTableRowKey.length);
    seekPoints.add(actualTableRowKey);
  }

  public synchronized void close() throws IOException {
    this.indexRegionScanner.close();
  }
}