/**
    *
    * 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.util;
  
  import java.io.IOException;
  import java.util.Collections;
  import java.util.Map;
  import java.util.TreeMap;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.hbase.HBaseConfiguration;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.regionserver.HRegion;
  import org.apache.hadoop.hbase.wal.WAL;
  import org.apache.hadoop.hbase.wal.WALFactory;
  
  /**
   * Contains utility methods for manipulating HBase meta tables.
   * Be sure to call {@link #shutdown()} when done with this class so it closes
   * resources opened during meta processing (ROOT, META, etc.).  Be careful
   * how you use this class.  If used during migrations, be careful when using
   * this class to check whether migration is needed.
   */
  @InterfaceAudience.Private
  public class MetaUtils {
    private static final Log LOG = LogFactory.getLog(MetaUtils.class);
    private final Configuration conf;
    private final FSTableDescriptors descriptors;
    private FileSystem fs;
    private WALFactory walFactory;
    private HRegion metaRegion;
    private Map<byte [], HRegion> metaRegions = Collections.synchronizedSortedMap(
      new TreeMap<byte [], HRegion>(Bytes.BYTES_COMPARATOR));
  
    /** Default constructor
     * @throws IOException e
     */
    public MetaUtils() throws IOException {
      this(HBaseConfiguration.create());
    }
  
    /**
     * @param conf Configuration
     * @throws IOException e
     */
    public MetaUtils(Configuration conf) throws IOException {
      this.conf = conf;
      conf.setInt(HConstants.HBASE_CLIENT_RETRIES_NUMBER, 1);
      this.metaRegion = null;
      this.descriptors = new FSTableDescriptors(conf);
      initialize();
    }
  
    /**
     * Verifies that DFS is available and that HBase is off-line.
     * @throws IOException e
     */
    private void initialize() throws IOException {
      this.fs = FileSystem.get(this.conf);
    }
  
    /**
     * @return the WAL associated with the given region
     * @throws IOException e
     */
    public synchronized WAL getLog(HRegionInfo info) throws IOException {
      if (this.walFactory == null) {
        String logName = 
            HConstants.HREGION_LOGDIR_NAME + "_" + System.currentTimeMillis();
        final Configuration walConf = new Configuration(this.conf);
        FSUtils.setRootDir(walConf, fs.getHomeDirectory());
        this.walFactory = new WALFactory(walConf, null, logName);
      }
      final byte[] region = info.getEncodedNameAsBytes();
      return info.isMetaRegion() ? walFactory.getMetaWAL(region) : walFactory.getWAL(region);
    }
 
   /**
    * @return HRegion for meta region
    * @throws IOException e
    */
   public synchronized HRegion getMetaRegion() throws IOException {
     return this.metaRegion == null? openMetaRegion(): this.metaRegion;
   }
 
   /**
    * Closes catalog regions if open. Also closes and deletes the WAL. You
    * must call this method if you want to persist changes made during a
    * MetaUtils edit session.
    */
   public synchronized void shutdown() {
     if (this.metaRegion != null) {
       try {
         this.metaRegion.close();
       } catch (IOException e) {
         LOG.error("closing meta region", e);
       } finally {
         this.metaRegion = null;
       }
     }
     try {
       for (HRegion r: metaRegions.values()) {
         LOG.info("CLOSING hbase:meta " + r.toString());
         r.close();
       }
     } catch (IOException e) {
       LOG.error("closing meta region", e);
     } finally {
       metaRegions.clear();
     }
     try {
       if (this.walFactory != null) {
         this.walFactory.close();
       }
     } catch (IOException e) {
       LOG.error("closing WAL", e);
     }
   }
 
   private synchronized HRegion openMetaRegion() throws IOException {
     if (this.metaRegion != null) {
       return this.metaRegion;
     }
     this.metaRegion = HRegion.openHRegion(HRegionInfo.FIRST_META_REGIONINFO,
       descriptors.get(TableName.META_TABLE_NAME), getLog(HRegionInfo.FIRST_META_REGIONINFO),
       this.conf);
     this.metaRegion.compactStores();
     return this.metaRegion;
   }
 }