/src/main/scala/com/comcast/xfinity/sirius/api/impl/paxos/LeaderHelper.scala

/*
 *  Copyright 2012-2014 Comcast Cable Communications Management, LLC
 *
 *  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.comcast.xfinity.sirius.api.impl.paxos

import com.comcast.xfinity.sirius.api.impl.paxos.PaxosMessages._
import collection.immutable.SortedMap
import com.comcast.xfinity.sirius.util.RichJTreeMap

/**
 * Some helpers for more complex operations on the Leader.  Ideally this
 * stuff would be in a companion object, but because we want to mock it,
 * and Maven doesn't support ScalaMock (yet), we have this.
 */
class LeaderHelper {

  /**
   * Overlays x with all entries from y, with the side effect of modifying x.
   *
   * Returns reference to x- this is an artifact of when this was immutable and more
   * complex, this method should get factored out soon.
   *
   * @param x a RichJTreeMap which is modified in place, being overlayed with all values
   *          from y
   * @param y values to overlay on x
   * @return reference to x, which is mutated
   */
  def update[T](x: RichJTreeMap[Long, T], y: RichJTreeMap[Long, T]): RichJTreeMap[Long, T] = {
    x.putAll(y)
    x
  }

  /**
   * Takes a Set of PValues and produces a java TreeMap from slot (Long) to Command, retaining the Command
   * associated with the highest Ballot for each slot.
   *
   * @param pvals
   * @return
   */
  def pmax(pvals: Set[PValue]): RichJTreeMap[Long, Command] = {
    val maxPValBySlot = pvals.groupBy(_.slotNum).mapValues(
      pvals => pvals.maxBy(_.ballot)
    )

    val slotsToCommands = maxPValBySlot.mapValues(_.proposedCommand)

    RichJTreeMap(slotsToCommands)
  }
}