/*
 * 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.reef.runtime.common.driver.resourcemanager;

import org.apache.reef.annotations.audience.DriverSide;
import org.apache.reef.annotations.audience.Private;
import org.apache.reef.runtime.common.driver.DriverStatusManager;
import org.apache.reef.runtime.common.driver.evaluator.pojos.State;
import org.apache.reef.runtime.common.driver.idle.DriverIdleManager;
import org.apache.reef.runtime.common.driver.idle.DriverIdlenessSource;
import org.apache.reef.runtime.common.driver.idle.IdleMessage;
import org.apache.reef.tang.InjectionFuture;
import org.apache.reef.wake.EventHandler;

import javax.inject.Inject;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Manages the status of the Resource Manager.
 */
@DriverSide
@Private
public final class ResourceManagerStatus implements EventHandler<RuntimeStatusEvent>,
    DriverIdlenessSource {
  private static final Logger LOG = Logger.getLogger(ResourceManagerStatus.class.getName());

  private static final String COMPONENT_NAME = "ResourceManager";
  private static final IdleMessage IDLE_MESSAGE =
      new IdleMessage(COMPONENT_NAME, "No outstanding requests or allocations", true);

  private final ResourceManagerErrorHandler resourceManagerErrorHandler;
  private final DriverStatusManager driverStatusManager;
  private final InjectionFuture<DriverIdleManager> driverIdleManager;

  // Mutable state.
  private State state =  State.INIT;
  private int outstandingContainerRequests = 0;
  private int containerAllocationCount = 0;

  @Inject
  ResourceManagerStatus(final ResourceManagerErrorHandler resourceManagerErrorHandler,
                        final DriverStatusManager driverStatusManager,
                        final InjectionFuture<DriverIdleManager> driverIdleManager) {
    this.resourceManagerErrorHandler = resourceManagerErrorHandler;
    this.driverStatusManager = driverStatusManager;
    this.driverIdleManager = driverIdleManager;
  }

  @Override
  public synchronized void onNext(final RuntimeStatusEvent runtimeStatusEvent) {
    final State newState = runtimeStatusEvent.getState();
    LOG.log(Level.FINEST, "Runtime status " + runtimeStatusEvent);
    this.outstandingContainerRequests = runtimeStatusEvent.getOutstandingContainerRequests().orElse(0);
    this.containerAllocationCount = runtimeStatusEvent.getContainerAllocationList().size();
    this.setState(runtimeStatusEvent.getState());

    switch (newState) {
    case FAILED:
      this.onRMFailure(runtimeStatusEvent);
      break;
    case DONE:
      this.onRMDone(runtimeStatusEvent);
      break;
    case RUNNING:
      this.onRMRunning(runtimeStatusEvent);
      break;
    case INIT:
    case SUSPEND:
    case KILLED:
      break;
    default:
      throw new RuntimeException("Unknown state: " + newState);
    }
  }

  /**
   * Change the state of the Resource Manager to be RUNNING.
   */
  public synchronized void setRunning() {
    this.setState(State.RUNNING);
  }

  /**
   * @return idle, if there are no outstanding requests or allocations. Not idle else.
   */
  @Override
  public synchronized IdleMessage getIdleStatus() {
    if (this.isIdle()) {
      return IDLE_MESSAGE;
    } else {
      final String message = new StringBuilder("There are ")
          .append(this.outstandingContainerRequests)
          .append(" outstanding container requests and ")
          .append(this.containerAllocationCount)
          .append(" allocated containers")
          .toString();
      return new IdleMessage(COMPONENT_NAME, message, false);
    }
  }


  private synchronized void onRMFailure(final RuntimeStatusEvent runtimeStatusEvent) {
    assert runtimeStatusEvent.getState() == State.FAILED;
    this.resourceManagerErrorHandler.onNext(runtimeStatusEvent.getError().get());
  }

  private synchronized void onRMDone(final RuntimeStatusEvent runtimeStatusEvent) {
    assert runtimeStatusEvent.getState() == State.DONE;
    LOG.log(Level.INFO, "Resource Manager shutdown happened. Triggering Driver shutdown.");
    this.driverStatusManager.onComplete();
  }

  private synchronized void onRMRunning(final RuntimeStatusEvent runtimeStatusEvent) {
    assert runtimeStatusEvent.getState() == State.RUNNING;
    if (this.isIdle()) {
      this.driverIdleManager.get().onPotentiallyIdle(IDLE_MESSAGE);
    }
  }


  private synchronized boolean isIdle() {
    return this.hasNoOutstandingRequests()
        && this.hasNoContainersAllocated();
  }

  private synchronized boolean isRunning() {
    return State.RUNNING.equals(this.state);
  }

  /**
  *
  * Checks if the ResourceManager can switch from the current state to the target state.
  * See REEF-826 for the state transition matrix.
  *
  * @param from current state
  * @param to   state to switch to
  *
  * @return true if the transition is legal; false otherwise
  *
  */
  private synchronized boolean isLegalStateTransition(final State from,
                                                      final State to) {

    // handle diagonal elements of the transition matrix
    if (from.equals(to)){
      LOG.finest("Transition from " + from + " state to the same state.");
      return true;
    }

    // handle non-diagonal elements
    switch (from) {

    case INIT:
      switch (to) {
      case RUNNING:
      case SUSPEND:
      case DONE:
      case FAILED:
      case KILLED:
        return true;
      default:
        return false;
      }

    case RUNNING:
      switch (to) {
      case SUSPEND:
      case DONE:
      case FAILED:
      case KILLED:
        return true;
      default:
        return false;
      }

    case SUSPEND:
      switch (to) {
      case RUNNING:
      case FAILED:
      case KILLED:
        return true;
      default:
        return false;
      }

    case DONE:
    case FAILED:
    case KILLED:
      return false;

    default:
      return false;

    }

  }

  private synchronized void setState(final State newState) {

    if (isLegalStateTransition(this.state, newState)) {
      this.state = newState;
    } else {
      throw new IllegalStateException("Resource manager attempts illegal state transition from "
                + this.state + " to "
                + newState);
    }

  }


  private synchronized boolean hasNoOutstandingRequests() {
    return this.outstandingContainerRequests == 0;
  }

  private synchronized boolean hasNoContainersAllocated() {
    return this.containerAllocationCount == 0;
  }

}