/*
 * 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.accumulo.master.replication;

import static org.apache.accumulo.fate.util.UtilWaitThread.sleepUninterruptibly;

import java.util.concurrent.TimeUnit;

import org.apache.accumulo.core.client.AccumuloClient;
import org.apache.accumulo.core.conf.AccumuloConfiguration;
import org.apache.accumulo.core.conf.Property;
import org.apache.accumulo.master.Master;
import org.apache.accumulo.server.replication.WorkAssigner;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Driver for a {@link WorkAssigner}
 */
public class WorkDriver implements Runnable {
  private static final Logger log = LoggerFactory.getLogger(WorkDriver.class);

  private Master master;
  private AccumuloClient client;
  private AccumuloConfiguration conf;

  private WorkAssigner assigner;
  private String assignerImplName;

  public WorkDriver(Master master) {
    super();
    this.master = master;
    this.client = master.getContext();
    this.conf = master.getConfiguration();
    configureWorkAssigner();
  }

  protected void configureWorkAssigner() {
    String workAssignerClass = conf.get(Property.REPLICATION_WORK_ASSIGNER);

    if (assigner == null || !assigner.getClass().getName().equals(workAssignerClass)) {
      log.info("Initializing work assigner implementation of {}", workAssignerClass);

      try {
        Class<?> clz = Class.forName(workAssignerClass);
        Class<? extends WorkAssigner> workAssignerClz = clz.asSubclass(WorkAssigner.class);
        this.assigner = workAssignerClz.getDeclaredConstructor().newInstance();
      } catch (ReflectiveOperationException e) {
        log.error("Could not instantiate configured work assigner {}", workAssignerClass, e);
        throw new RuntimeException(e);
      }

      this.assigner.configure(conf, client);
      this.assignerImplName = assigner.getClass().getName();
    }
  }

  public String getName() {
    return assigner.getName();
  }

  @Override
  public void run() {
    log.info("Starting replication work assignment thread using {}", assignerImplName);

    while (master.stillMaster()) {
      // Assign the work using the configured implementation
      try {
        assigner.assignWork();
      } catch (Exception e) {
        log.error("Error while assigning work", e);
      }

      long sleepTime = conf.getTimeInMillis(Property.REPLICATION_WORK_ASSIGNMENT_SLEEP);
      log.trace("Sleeping {} ms before next work assignment", sleepTime);
      sleepUninterruptibly(sleepTime, TimeUnit.MILLISECONDS);

      // After each loop, make sure that the WorkAssigner implementation didn't change
      configureWorkAssigner();
    }
  }
}