@lightbend/akkaserverless-javascript-sdk/src/replicated-data/vote.js

Akka Serverless JavaScript SDK

/*
 * Copyright 2021 Lightbend 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.
 */

const util = require('util');

/**
 * @classdesc A Vote Replicated Data type.
 *
 * A Vote Replicated Data type allows all nodes an a cluster to vote on a condition, such as whether a user is online.
 *
 * @constructor module:akkaserverless.replicatedentity.Vote
 * @implements module:akkaserverless.replicatedentity.ReplicatedData
 */
function Vote() {
  let currentSelfVote = false;
  let currentVotesFor = 0;
  let currentTotalVoters = 1;
  let delta = null;

  /**
   * The number of nodes that have voted for this condition.
   *
   * @name module:akkaserverless.replicatedentity.Vote#votesFor
   * @type {number}
   * @readonly
   */
  Object.defineProperty(this, 'votesFor', {
    get: function () {
      return currentVotesFor;
    },
  });

  /**
   * The total number of nodes that have voted.
   *
   * @name module:akkaserverless.replicatedentity.Vote#totalVoters
   * @type {number}
   * @readonly
   */
  Object.defineProperty(this, 'totalVoters', {
    get: function () {
      return currentTotalVoters;
    },
  });

  /**
   * Whether at least one node has voted for this condition.
   *
   * @name module:akkaserverless.replicatedentity.Vote#atLeastOne
   * @type {boolean}
   * @readonly
   */
  Object.defineProperty(this, 'atLeastOne', {
    get: function () {
      return currentVotesFor > 0;
    },
  });

  /**
   * Whether a majority of nodes have voted for this condition.
   *
   * @name module:akkaserverless.replicatedentity.Vote#majority
   * @type {boolean}
   * @readonly
   */
  Object.defineProperty(this, 'majority', {
    get: function () {
      return currentVotesFor > currentTotalVoters / 2;
    },
  });

  /**
   * Whether all of nodes have voted for this condition.
   *
   * @name module:akkaserverless.replicatedentity.Vote#all
   * @type {boolean}
   * @readonly
   */
  Object.defineProperty(this, 'all', {
    get: function () {
      return currentVotesFor === currentTotalVoters;
    },
  });

  /**
   * The current nodes vote.
   *
   * Setting this will update the current nodes vote accordingly.
   *
   * @name module:akkaserverless.replicatedentity.Vote#vote
   * @type {boolean}
   */
  Object.defineProperty(this, 'vote', {
    get: function () {
      return currentSelfVote;
    },
    set: function (value) {
      if (value && !currentSelfVote) {
        currentSelfVote = true;
        currentVotesFor += 1;
        delta = true;
      } else if (!value && currentSelfVote) {
        currentSelfVote = false;
        currentVotesFor -= 1;
        delta = false;
      }
    },
  });

  this.getAndResetDelta = function (initial) {
    if (initial) {
      delta = currentSelfVote;
    }
    if (delta !== null) {
      const vote = delta;
      delta = null;
      return {
        vote: {
          selfVote: vote,
        },
      };
    } else {
      return null;
    }
  };

  this.applyDelta = function (delta) {
    if (!delta.vote) {
      throw new Error(util.format('Cannot apply delta %o to Vote', delta));
    }
    currentSelfVote = delta.vote.selfVote;
    currentVotesFor = delta.vote.votesFor;
    currentTotalVoters = delta.vote.totalVoters;
  };

  this.toString = function () {
    return 'Vote(' + currentSelfVote + ')';
  };
}

module.exports = Vote;