/**
    * 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.wal;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Set;
  import java.util.concurrent.CopyOnWriteArrayList;
  import java.util.concurrent.atomic.AtomicBoolean;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.CellUtil;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  // imports for things that haven't moved from regionserver.wal yet.
  import org.apache.hadoop.hbase.regionserver.MultiVersionConcurrencyControl.WriteEntry;
  import org.apache.hadoop.hbase.regionserver.wal.WALActionsListener;
  import org.apache.hadoop.hbase.regionserver.wal.WALCoprocessorHost;
  import org.apache.hadoop.hbase.regionserver.wal.WALEdit;
  import org.apache.hadoop.hbase.util.FSUtils;
  
  /**
   * No-op implementation of {@link WALProvider} used when the WAL is disabled.
   *
   * Should only be used when severe data loss is acceptable.
   *
   */
  @InterfaceAudience.Private
  class DisabledWALProvider implements WALProvider {
  
    private static final Log LOG = LogFactory.getLog(DisabledWALProvider.class);
  
    WAL disabled;
  
    @Override
    public void init(final WALFactory factory, final Configuration conf,
        final List<WALActionsListener> listeners, String providerId) throws IOException {
      if (null != disabled) {
        throw new IllegalStateException("WALProvider.init should only be called once.");
      }
      if (null == providerId) {
        providerId = "defaultDisabled";
      }
      disabled = new DisabledWAL(new Path(FSUtils.getWALRootDir(conf), providerId), conf, null);
    }
  
    @Override
    public List<WAL> getWALs() throws IOException {
      List<WAL> wals = new ArrayList<WAL>();
      wals.add(disabled);
      return wals;
    }
  
    @Override
    public WAL getWAL(final byte[] identifier, byte[] namespace) throws IOException {
      return disabled;
    }
  
    @Override
    public void close() throws IOException {
      disabled.close();
    }
  
    @Override
    public void shutdown() throws IOException {
      disabled.shutdown();
    }
  
    private static class DisabledWAL implements WAL {
      protected final List<WALActionsListener> listeners =
          new CopyOnWriteArrayList<WALActionsListener>();
      protected final Path path;
      protected final WALCoprocessorHost coprocessorHost;
      protected final AtomicBoolean closed = new AtomicBoolean(false);
  
      public DisabledWAL(final Path path, final Configuration conf,
          final List<WALActionsListener> listeners) {
        this.coprocessorHost = new WALCoprocessorHost(this, conf);
       this.path = path;
       if (null != listeners) {
         for(WALActionsListener listener : listeners) {
           registerWALActionsListener(listener);
         }
       }
     }
 
     @Override
     public void registerWALActionsListener(final WALActionsListener listener) {
       listeners.add(listener);
     }
     
     @Override
     public boolean unregisterWALActionsListener(final WALActionsListener listener) {
       return listeners.remove(listener);
     }
 
     @Override
     public byte[][] rollWriter() {
       if (!listeners.isEmpty()) {
         for (WALActionsListener listener : listeners) {
           listener.logRollRequested(WALActionsListener.RollRequestReason.ERROR);
         }
         for (WALActionsListener listener : listeners) {
           try {
             listener.preLogRoll(path, path);
           } catch (IOException exception) {
             LOG.debug("Ignoring exception from listener.", exception);
           }
         }
         for (WALActionsListener listener : listeners) {
           try {
             listener.postLogRoll(path, path);
           } catch (IOException exception) {
             LOG.debug("Ignoring exception from listener.", exception);
           }
         }
       }
       return null;
     }
 
     @Override
     public byte[][] rollWriter(boolean force) {
       return rollWriter();
     }
 
     @Override
     public void shutdown() {
       if(closed.compareAndSet(false, true)) {
         if (!this.listeners.isEmpty()) {
           for (WALActionsListener listener : this.listeners) {
             listener.logCloseRequested();
           }
         }
       }
     }
 
     @Override
     public void close() {
       shutdown();
     }
 
     @Override
     public long append(HTableDescriptor htd, HRegionInfo info, WALKey key, WALEdit edits,
         boolean inMemstore) throws IOException {
       WriteEntry writeEntry = key.getMvcc().begin();
       if (!edits.isReplay()) {
         for (Cell cell : edits.getCells()) {
           CellUtil.setSequenceId(cell, writeEntry.getWriteNumber());
         }
       }
       key.setWriteEntry(writeEntry);
       if (!this.listeners.isEmpty()) {
         final long start = System.nanoTime();
         long len = 0;
         for (Cell cell : edits.getCells()) {
           len += CellUtil.estimatedSerializedSizeOf(cell);
         }
         final long elapsed = (System.nanoTime() - start)/1000000l;
         for (WALActionsListener listener : this.listeners) {
           listener.postAppend(len, elapsed, key, edits);
         }
       }
       return -1;
     }
 
     @Override
     public void sync() {
       if (!this.listeners.isEmpty()) {
         for (WALActionsListener listener : this.listeners) {
           listener.postSync(0l, 0);
         }
       }
     }
 
     @Override
     public void sync(long txid) {
       sync();
     }
 
     @Override
     public void sync(boolean forceSync) throws IOException {
       sync();
     }
 
     @Override
     public void sync(long txid, boolean forceSync) throws IOException {
       sync(txid);
     }
 
     @Override
     public Long startCacheFlush(final byte[] encodedRegionName, Set<byte[]> flushedFamilyNames) {
       if (closed.get()) return null;
       return HConstants.NO_SEQNUM;
     }
 
     @Override
     public void completeCacheFlush(final byte[] encodedRegionName) {
     }
 
     @Override
     public void abortCacheFlush(byte[] encodedRegionName) {
     }
 
     @Override
     public WALCoprocessorHost getCoprocessorHost() {
       return coprocessorHost;
     }
 
     @Override
     public long getEarliestMemstoreSeqNum(byte[] encodedRegionName) {
       return HConstants.NO_SEQNUM;
     }
 
     @Override
     public long getEarliestMemstoreSeqNum(byte[] encodedRegionName, byte[] familyName) {
       return HConstants.NO_SEQNUM;
     }
 
     @Override
     public String toString() {
       return "WAL disabled.";
     }
   }
 
   @Override
   public long getNumLogFiles() {
     return 0;
   }
 
   @Override
   public long getLogFileSize() {
     return 0;
   }
 }