@lightbend/akkaserverless-javascript-sdk/src/replicated-data/counter.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');
const Long = require('long');

/**
 * @classdesc A Replicated Counter data type.
 *
 * A counter that can be incremented and decremented.
 *
 * The value is stored as a 64-bit signed long, hence values over `2^63 - 1` and less than `2^63` can't be represented.
 *
 * @constructor module:akkaserverless.replicatedentity.ReplicatedCounter
 * @implements module:akkaserverless.replicatedentity.ReplicatedData
 */
function ReplicatedCounter() {
  let currentValue = Long.ZERO;
  let delta = Long.ZERO;

  /**
   * The value as a long.
   *
   * @name module:akkaserverless.replicatedentity.ReplicatedCounter#longValue
   * @type {Long}
   * @readonly
   */
  Object.defineProperty(this, 'longValue', {
    get: function () {
      return currentValue;
    },
  });

  /**
   * The value as a number. Note that once the value exceeds `2^53`, this will not be an accurate
   * representation of the value. If you expect it to exceed `2^53`, {@link module:akkaserverless.replicatedentity.ReplicatedCounter#longValue}
   * should be used instead.
   *
   * @name module:akkaserverless.replicatedentity.ReplicatedCounter#value
   * @type {number}
   * @readonly
   */
  Object.defineProperty(this, 'value', {
    get: function () {
      return currentValue.toNumber();
    },
  });

  /**
   * Increment the counter by the given number.
   *
   * @function module:akkaserverless.replicatedentity.ReplicatedCounter#increment
   * @param {Long|number} increment The amount to increment the counter by. If negative, it will be decremented instead.
   * @returns {module:akkaserverless.replicatedentity.ReplicatedCounter} This counter.
   */
  this.increment = function (increment) {
    currentValue = currentValue.add(increment);
    delta = delta.add(increment);
    return this;
  };

  /**
   * Decrement the counter by the given number.
   *
   * @function module:akkaserverless.replicatedentity.ReplicatedCounter#decrement
   * @param {Long|number} decrement The amount to decrement the counter by. If negative, it will be incremented instead.
   * @returns {module:akkaserverless.replicatedentity.ReplicatedCounter} This counter.
   */
  this.decrement = function (decrement) {
    currentValue = currentValue.subtract(decrement);
    delta = delta.subtract(decrement);
    return this;
  };

  this.getAndResetDelta = function (initial) {
    if (!delta.isZero() || initial) {
      const currentDelta = {
        counter: {
          change: delta,
        },
      };
      delta = Long.ZERO;
      return currentDelta;
    } else {
      return null;
    }
  };

  this.applyDelta = function (delta) {
    if (!delta.counter) {
      throw new Error(
        util.format('Cannot apply delta %o to ReplicatedCounter', delta),
      );
    }
    currentValue = currentValue.add(delta.counter.change);
  };

  this.toString = function () {
    return 'ReplicatedCounter(' + currentValue + ')';
  };
}

module.exports = ReplicatedCounter;