com.continuuity.loom.layout.change.ClusterLayoutTracker.java Source code

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Here is the source code for com.continuuity.loom.layout.change.ClusterLayoutTracker.java

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/*
 * Copyright 2012-2014, Continuuity, Inc.
 *
 * Licensed 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 com.continuuity.loom.layout.change;

import com.continuuity.loom.layout.ClusterLayout;
import com.google.common.collect.Lists;

import java.util.Deque;
import java.util.Queue;

/**
 * Helper for keeping track of changes made to a {@link com.continuuity.loom.layout.ClusterLayout}.
 */
public class ClusterLayoutTracker {
    private final Deque<ClusterLayoutChange> changes;
    private final Deque<ClusterLayout> states;

    /**
     * Create a layout change tracker given some starting layout.
     *
     * @param startingLayout starting layout of the cluster.
     */
    public ClusterLayoutTracker(ClusterLayout startingLayout) {
        this.changes = Lists.newLinkedList();
        this.states = Lists.newLinkedList();
        this.states.add(startingLayout);
    }

    /**
     * Adds a change to the layout if the change can be applied to the current layout, returning whether or not
     * the change was added.
     *
     * @param change Change to add, assuming it can be applied to the current layout.
     * @return True if the change was added, false if not.
     */
    public boolean addChangeIfValid(ClusterLayoutChange change) {
        ClusterLayout currentLayout = getCurrentLayout();
        if (change.canApplyChange(currentLayout)) {
            changes.addLast(change);
            states.addLast(change.applyChange(currentLayout));
            return true;
        }
        return false;
    }

    /**
     * Remove the last change performed on the cluster layout.
     */
    public void removeLastChange() {
        changes.removeLast();
        states.removeLast();
    }

    /**
     * Get the current layout of the cluster.
     *
     * @return Current layout of the cluster.
     */
    public ClusterLayout getCurrentLayout() {
        return states.getLast();
    }

    /**
     * Get the changes that were applied to the starting cluster layout.
     *
     * @return Changes that were applied to the starting cluster layout.
     */
    public Queue<ClusterLayoutChange> getChanges() {
        return changes;
    }
}