100 lines
2.6 KiB
JavaScript
100 lines
2.6 KiB
JavaScript
const EventEmitter = require('events').EventEmitter;
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const logging = require('@tryghost/logging');
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/**
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* @template T
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* @typedef {import('./').ConstructorOf<T>} ConstructorOf<T>
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*/
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/**
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* @template Data
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* @typedef {object} IEvent
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* @prop {Date} timestamp
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* @prop {Data} data
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*/
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class DomainEvents {
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/**
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* @private
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* @type EventEmitter
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*/
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static ee = new EventEmitter;
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/**
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* @template Data
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* @template {IEvent<Data>} EventClass
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* @param {ConstructorOf<EventClass>} Event
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* @param {(event: EventClass) => Promise<void> | void} handler
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*
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* @returns {void}
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*/
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static subscribe(Event, handler) {
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DomainEvents.ee.on(Event.name, async (event) => {
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try {
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await handler(event);
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} catch (e) {
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logging.error('Unhandled error in event handler for event: ' + Event.name);
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logging.error(e);
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}
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if (this.#trackingEnabled) {
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this.#onProcessed();
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}
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});
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}
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/**
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* @template Data
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* @param {IEvent<Data>} event
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* @returns {void}
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*/
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static dispatch(event) {
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DomainEvents.dispatchRaw(event.constructor.name, event);
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}
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/**
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* Dispatch an event in case you don't have an instance of the event class, but you do have the event name and event data.
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* @template Data
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* @param {string} name
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* @param {Data} data
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* @returns {void}
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*/
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static dispatchRaw(name, data) {
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if (this.#trackingEnabled) {
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this.#dispatchCount += DomainEvents.ee.listenerCount(name);
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}
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DomainEvents.ee.emit(name, data);
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}
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// Methods and properties below are only for testing purposes
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static #awaitQueue = [];
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static #dispatchCount = 0;
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static #processedCount = 0;
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static #trackingEnabled = process.env.NODE_ENV?.startsWith('test');
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/**
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* Waits for all the events in the queue to be dispatched and fully processed (async).
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*/
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static allSettled() {
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return new Promise((resolve) => {
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if (this.#processedCount >= this.#dispatchCount) {
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// Resolve immediately if there are no events in the queue
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resolve();
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return;
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}
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this.#awaitQueue.push({resolve});
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});
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}
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static #onProcessed() {
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this.#processedCount += 1;
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if (this.#processedCount >= this.#dispatchCount) {
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for (const item of this.#awaitQueue) {
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item.resolve();
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}
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this.#awaitQueue = [];
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}
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}
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}
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module.exports = DomainEvents;
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