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Core components for a scheduler
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/*
 * Copyright  2020 The BtrPlace Authors. All rights reserved.
 * Use of this source code is governed by a LGPL-style
 * license that can be found in the LICENSE.txt file.
 */

package org.btrplace.scheduler;

import org.btrplace.model.Instance;
import org.btrplace.model.Model;
import org.btrplace.model.constraint.MinMTTR;
import org.btrplace.model.constraint.OptConstraint;
import org.btrplace.model.constraint.SatConstraint;
import org.btrplace.plan.ReconfigurationPlan;

import java.util.Collection;

/**
 * Basic interface for a VM scheduler.
 *
 * @author Fabien Hermenier
 */
@CoreConstraint(name = "noVMsOnOfflineNodes", inv = "!(n : nodes) nodeState(n) /= online --> card(hosted(n)) = 0")
@CoreConstraint(name = "toRunning", inv = "!(v : vms) vmState(v) = running --> ^vmState(v) : {ready, running, sleeping}")
@CoreConstraint(name = "toReady", inv = "!(v : vms) vmState(v) = ready --> ^vmState(v) : {ready, running}")
@CoreConstraint(name = "toSleeping", inv = "!(v : vms) vmState(v) = sleeping --> ^vmState(v) : {running, sleeping}")
@FunctionalInterface
public interface Scheduler {

    /**
     * Compute a reconfiguration plan to reach a solution to the model.
     * The computation is delegated to {@link #solve(Instance)}
     * @param mo     the current model
     * @param cstrs the satisfaction-oriented constraints that must be considered
     * @param obj   the optimization-oriented constraint that must be considered
     * @return {@code null} if there is no solution or the plan to execute to reach a new solution that satisfies every constraints.
     * Accordingly, an empty plan denotes a model that already satisfies all the constraints
     * @throws SchedulerException if an error occurred while trying to solve the problem
     */
    default ReconfigurationPlan solve(Model mo, Collection cstrs, OptConstraint obj) throws SchedulerException {
        return solve(new Instance(mo, cstrs, obj));
    }

    /**
     * Compute a reconfiguration plan to reach a solution to the model.
     * The {@link org.btrplace.model.constraint.MinMTTR} optimization constraint is used and the computation
     * is delegated to {@link #solve(Instance)}.
     *
     * @param mo    the current model
     * @param cstrs the satisfaction-oriented constraints that must be considered
     * @return the plan to execute to reach the new solution or {@code null} if there is no
     * solution.
     * @throws SchedulerException if an error occurred while trying to solve the problem
     */
    default ReconfigurationPlan solve(Model mo, Collection cstrs) throws SchedulerException {
        return solve(mo, cstrs, new MinMTTR());
    }

    /**
     * Compute a reconfiguration plan to reach a solution to an instance.
     *
     * @param i the instance to solve
     * @return {@code null} if there is no solution or the plan to execute to reach a new solution that satisfies every constraints.
     * Accordingly, an empty plan denotes a model that already satisfies all the constraints
     * @throws SchedulerException if an error occurred while trying to solve the problem
     */
    ReconfigurationPlan solve(Instance i) throws SchedulerException;
}