/*
 * Copyright 2014 Open Networking Laboratory
 *
 * 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 org.onlab.onos.cli;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.Multimap;
import org.apache.karaf.shell.commands.Command;
import org.onlab.onos.cluster.ClusterService;
import org.onlab.onos.cluster.ControllerNode;
import org.onlab.onos.mastership.MastershipAdminService;
import org.onlab.onos.mastership.MastershipService;
import org.onlab.onos.net.DeviceId;
import org.onlab.onos.net.device.DeviceService;

import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import static com.google.common.collect.Lists.newArrayList;
import static org.onlab.onos.net.MastershipRole.MASTER;

/**
 * Forces device mastership rebalancing.
 */
@Command(scope = "onos", name = "balance-masters",
        description = "Forces device mastership rebalancing")
public class BalanceMastersCommand extends AbstractShellCommand {

    @Override
    protected void execute() {
        ClusterService service = get(ClusterService.class);
        MastershipService mastershipService = get(MastershipService.class);
        MastershipAdminService adminService = get(MastershipAdminService.class);

        List<ControllerNode> nodes = newArrayList(service.getNodes());

        Multimap<ControllerNode, DeviceId> controllerDevices = HashMultimap.create();

        // Create buckets reflecting current ownership.
        for (ControllerNode node : nodes) {
            Set<DeviceId> devicesOf = mastershipService.getDevicesOf(node.id());
            controllerDevices.putAll(node, devicesOf);
            print("Node %s has %d devices.", node.id(), devicesOf.size());
        }

        int rounds = nodes.size();
        for (int i = 0; i < rounds; i++) {
            // Iterate over the buckets and find the smallest and the largest.
            ControllerNode smallest = findBucket(true, nodes, controllerDevices);
            ControllerNode largest = findBucket(false, nodes, controllerDevices);
            balanceBuckets(smallest, largest, controllerDevices, adminService);
        }
    }

    private ControllerNode findBucket(boolean min, Collection<ControllerNode> nodes,
                                      Multimap<ControllerNode, DeviceId> controllerDevices) {
        int xSize = min ? Integer.MAX_VALUE : -1;
        ControllerNode xNode = null;
        for (ControllerNode node : nodes) {
            int size = controllerDevices.get(node).size();
            if ((min && size < xSize) || (!min && size > xSize)) {
                xSize = size;
                xNode = node;
            }
        }
        return xNode;
    }

    // FIXME: enhance to better handle cases where smallest cannot take any of the devices from largest

    private void balanceBuckets(ControllerNode smallest, ControllerNode largest,
                                Multimap<ControllerNode, DeviceId> controllerDevices,
                                MastershipAdminService adminService) {
        Collection<DeviceId> minBucket = controllerDevices.get(smallest);
        Collection<DeviceId> maxBucket = controllerDevices.get(largest);
        int bucketCount = controllerDevices.keySet().size();
        int deviceCount = get(DeviceService.class).getDeviceCount();

        int delta = (maxBucket.size() - minBucket.size()) / 2;
        delta = Math.min(deviceCount / bucketCount, delta);

        if (delta > 0) {
            print("Attempting to move %d nodes from %s to %s...",
                  delta, largest.id(), smallest.id());

            int i = 0;
            Iterator<DeviceId> it = maxBucket.iterator();
            while (it.hasNext() && i < delta) {
                DeviceId deviceId = it.next();
                print("Setting %s as the master for %s", smallest.id(), deviceId);
                adminService.setRole(smallest.id(), deviceId, MASTER);
                controllerDevices.put(smallest, deviceId);
                it.remove();
                i++;
            }
        }
    }

}