/**
 * 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.yarn.server.resourcemanager.reservation;

import org.apache.hadoop.classification.InterfaceAudience.LimitedPrivate;
import org.apache.hadoop.classification.InterfaceStability.Unstable;
import org.apache.hadoop.yarn.api.records.Resource;
import org.apache.hadoop.yarn.server.resourcemanager.reservation.exceptions.MismatchedUserException;
import org.apache.hadoop.yarn.server.resourcemanager.reservation.exceptions.PlanningException;
import org.apache.hadoop.yarn.server.resourcemanager.reservation.exceptions.ResourceOverCommitException;
import org.apache.hadoop.yarn.util.resource.Resources;

/**
 * This policy enforce a simple physical cluster capacity constraints, by
 * validating that the allocation proposed fits in the current plan. This
 * validation is compatible with "updates" and in verifying the capacity
 * constraints it conceptually remove the prior version of the reservation.
 */
@LimitedPrivate("yarn")
@Unstable
public class NoOverCommitPolicy implements SharingPolicy {

  @Override
  public void validate(Plan plan, ReservationAllocation reservation)
      throws PlanningException {

    ReservationAllocation oldReservation =
        plan.getReservationById(reservation.getReservationId());

    // check updates are using same name
    if (oldReservation != null
        && !oldReservation.getUser().equals(reservation.getUser())) {
      throw new MismatchedUserException(
          "Updating an existing reservation with mismatching user:"
              + oldReservation.getUser() + " != " + reservation.getUser());
    }

    long startTime = reservation.getStartTime();
    long endTime = reservation.getEndTime();
    long step = plan.getStep();

    // for every instant in time, check we are respecting cluster capacity
    for (long t = startTime; t < endTime; t += step) {
      Resource currExistingAllocTot = plan.getTotalCommittedResources(t);
      Resource currNewAlloc = reservation.getResourcesAtTime(t);
      Resource currOldAlloc = Resource.newInstance(0, 0);
      if (oldReservation != null) {
        oldReservation.getResourcesAtTime(t);
      }
      // check the cluster is never over committed
      // currExistingAllocTot + currNewAlloc - currOldAlloc >
      // capPlan.getTotalCapacity()
      if (Resources.greaterThan(plan.getResourceCalculator(), plan
          .getTotalCapacity(), Resources.subtract(
          Resources.add(currExistingAllocTot, currNewAlloc), currOldAlloc),
          plan.getTotalCapacity())) {
        throw new ResourceOverCommitException("Resources at time " + t
            + " would be overcommitted by " + "accepting reservation: "
            + reservation.getReservationId());
      }
    }
  }

  @Override
  public long getValidWindow() {
    // this policy has no "memory" so the valid window is set to zero
    return 0;
  }

  @Override
  public void init(String planQueuePath,
      ReservationSchedulerConfiguration conf) {
    // nothing to do for this policy
  }

}