/*
    *
    * 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.wal;
  
  import java.io.IOException;
  import java.util.List;
  
  import org.apache.hadoop.hbase.Coprocessor;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.coprocessor.*;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.wal.WAL;
  import org.apache.hadoop.hbase.wal.WALKey;
  
  /**
   * Implements the coprocessor environment and runtime support for coprocessors
   * loaded within a {@link WAL}.
   */
  @InterfaceAudience.Private
  public class WALCoprocessorHost
      extends CoprocessorHost<WALCoprocessorHost.WALEnvironment> {
    
    /**
     * Encapsulation of the environment of each coprocessor
     */
    static class WALEnvironment extends CoprocessorHost.Environment
      implements WALCoprocessorEnvironment {
  
      private final WAL wal;
  
      final boolean useLegacyPre;
      final boolean useLegacyPost;
  
      @Override
      public WAL getWAL() {
        return wal;
      }
  
      /**
       * Constructor
       * @param implClass - not used
       * @param impl the coprocessor instance
       * @param priority chaining priority
       * @param seq load sequence
       * @param conf configuration
       * @param wal WAL
       */
      public WALEnvironment(Class<?> implClass, final Coprocessor impl,
          final int priority, final int seq, final Configuration conf,
          final WAL wal) {
        super(impl, priority, seq, conf);
        this.wal = wal;
        // Pick which version of the API we'll call.
        // This way we avoid calling the new version on older WALObservers so
        // we can maintain binary compatibility.
        // See notes in javadoc for WALObserver
        useLegacyPre = useLegacyMethod(impl.getClass(), "preWALWrite", ObserverContext.class,
            HRegionInfo.class, WALKey.class, WALEdit.class);
        useLegacyPost = useLegacyMethod(impl.getClass(), "postWALWrite", ObserverContext.class,
            HRegionInfo.class, WALKey.class, WALEdit.class);
      }
    }
  
    private final WAL wal;
  
    /**
     * Constructor
     * @param log the write ahead log
     * @param conf the configuration
     */
    public WALCoprocessorHost(final WAL log, final Configuration conf) {
      // We don't want to require an Abortable passed down through (FS)HLog, so
      // this means that a failure to load of a WAL coprocessor won't abort the
      // server. This isn't ideal, and means that security components that
      // utilize a WALObserver will have to check the observer initialization
      // state manually. However, WALObservers will eventually go away so it
      // should be an acceptable state of affairs.
      super(null);
      this.wal = log;
      // load system default cp's from configuration.
     loadSystemCoprocessors(conf, WAL_COPROCESSOR_CONF_KEY);
   }
 
   @Override
   public WALEnvironment createEnvironment(final Class<?> implClass,
       final Coprocessor instance, final int priority, final int seq,
       final Configuration conf) {
     return new WALEnvironment(implClass, instance, priority, seq, conf,
         this.wal);
   }
 
   /**
    * @param info
    * @param logKey
    * @param logEdit
    * @return true if default behavior should be bypassed, false otherwise
    * @throws IOException
    */
   public boolean preWALWrite(final HRegionInfo info, final WALKey logKey, final WALEdit logEdit)
       throws IOException {
     boolean bypass = false;
     if (this.coprocessors == null || this.coprocessors.isEmpty()) return bypass;
     ObserverContext<WALCoprocessorEnvironment> ctx = null;
     List<WALEnvironment> envs = coprocessors.get();
     for (int i = 0; i < envs.size(); i++) {
       WALEnvironment env = envs.get(i);
       if (env.getInstance() instanceof WALObserver) {
         final WALObserver observer = (WALObserver)env.getInstance();
         ctx = ObserverContext.createAndPrepare(env, ctx);
         Thread currentThread = Thread.currentThread();
         ClassLoader cl = currentThread.getContextClassLoader();
         try {
           currentThread.setContextClassLoader(env.getClassLoader());
           if (env.useLegacyPre) {
             if (logKey instanceof HLogKey) {
               observer.preWALWrite(ctx, info, (HLogKey)logKey, logEdit);
             } else {
               legacyWarning(observer.getClass(),
                   "There are wal keys present that are not HLogKey.");
             }
           } else {
             observer.preWALWrite(ctx, info, logKey, logEdit);
           }
         } catch (Throwable e) {
           handleCoprocessorThrowable(env, e);
         } finally {
           currentThread.setContextClassLoader(cl);
         }
         bypass |= ctx.shouldBypass();
         if (ctx.shouldComplete()) {
           break;
         }
       }
     }
     return bypass;
   }
 
   /**
    * @param info
    * @param logKey
    * @param logEdit
    * @throws IOException
    */
   public void postWALWrite(final HRegionInfo info, final WALKey logKey, final WALEdit logEdit)
       throws IOException {
     if (this.coprocessors == null || this.coprocessors.isEmpty()) return;
     ObserverContext<WALCoprocessorEnvironment> ctx = null;
     List<WALEnvironment> envs = coprocessors.get();
     for (int i = 0; i < envs.size(); i++) {
       WALEnvironment env = envs.get(i);
       if (env.getInstance() instanceof WALObserver) {
         final WALObserver observer = (WALObserver)env.getInstance();
         ctx = ObserverContext.createAndPrepare(env, ctx);
         Thread currentThread = Thread.currentThread();
         ClassLoader cl = currentThread.getContextClassLoader();
         try {
           currentThread.setContextClassLoader(env.getClassLoader());
           if (env.useLegacyPost) {
             if (logKey instanceof HLogKey) {
               observer.postWALWrite(ctx, info, (HLogKey)logKey, logEdit);
             } else {
               legacyWarning(observer.getClass(),
                   "There are wal keys present that are not HLogKey.");
             }
           } else {
             observer.postWALWrite(ctx, info, logKey, logEdit);
           }
         } catch (Throwable e) {
           handleCoprocessorThrowable(env, e);
         } finally {
           currentThread.setContextClassLoader(cl);
         }
         if (ctx.shouldComplete()) {
           break;
         }
       }
     }
   }
 }