Musare/backend/src/JobQueue.ts

import Job, { JobStatus } from "@/Job";
import { JobOptions } from "@/types/JobOptions";
import JobStatistics, { JobStatisticsType } from "./JobStatistics";
import { JobDerived } from "./types/JobDerived";
import assertJobDerived from "./utils/assertJobDerived";

export class JobQueue {
	private _concurrency: number;

	private _isPaused: boolean;

	private _queue: Job[];

	private _active: Job[];

	private _processLock: boolean;

	private _callbacks: Record<
		string,
		{
			resolve: (value: unknown) => void;
			reject: (reason?: unknown) => void;
		}
	>;

	/**
	 * Job Queue
	 */
	public constructor() {
		this._concurrency = 50;
		this._isPaused = true;
		this._queue = [];
		this._active = [];
		this._callbacks = {};
		this._processLock = false;
	}

	/**
	 * pause - Pause queue
	 *
	 * Pause processing of jobs in queue, active jobs will not be paused.
	 */
	public pause() {
		this._isPaused = true;
	}

	/**
	 * resume - Resume queue
	 */
	public resume() {
		this._isPaused = false;
		this._process();
	}

	/**
	 * runJob - Run a job
	 */
	public async runJob(
		JobClass: Function,
		payload?: unknown,
		options?: JobOptions
	): Promise<unknown> {
		assertJobDerived(JobClass);
		return new Promise<unknown>((resolve, reject) => {
			this.queueJob(JobClass as JobDerived, payload, options)
				.then(uuid => {
					this._callbacks[uuid] = { resolve, reject };
				})
				.catch(reject);
		});
	}

	/**
	 * queueJob - Queue a job
	 */
	public async queueJob(
		JobClass: Function,
		payload?: unknown,
		options?: JobOptions
	): Promise<string> {
		assertJobDerived(JobClass);
		const job = new (JobClass as JobDerived)(payload, options);

		JobStatistics.updateStats(job.getPath(), JobStatisticsType.QUEUED);

		this._queue.push(job);
		this._process();

		return job.getUuid();
	}

	/**
	 * process - Process queue
	 */
	private async _process() {
		// If the process is locked, don't continue. This prevents running process at the same time which could lead to issues
		if (this._processLock) return;
		// If the queue is paused, we've reached the maximum number of active jobs, or there are no jobs in the queue, don't continue
		if (
			this._isPaused ||
			this._active.length >= this._concurrency ||
			this._queue.length === 0
		)
			return;

		// Lock the process function
		this._processLock = true;

		// Sort jobs based on priority, with a lower priority being preferred
		const jobs = this._queue.sort(
			(a, b) => a.getPriority() - b.getPriority()
		);

		// Loop through all jobs
		for (let i = 0; i < jobs.length; i += 1) {
			const job = jobs[i];

			// If the module of the job is not started, we can't run the job, so go to the next job in the queue
			// eslint-disable-next-line no-continue
			if (!job.getModule().canRunJobs()) continue;

			// Remove the job from the queue and add it to the active jobs array
			this._queue.splice(this._queue.indexOf(job), 1);

			// Execute the job
			this._active.push(job);

			const callback = this._callbacks[job.getUuid()];

			job.execute()
				.then(callback?.resolve)
				.catch(callback?.reject)
				.catch(() => {}) // Ignore errors, any handling required is in job or callback
				.finally(() => {
					delete this._callbacks[job.getUuid()];

					// If the current job is in the active jobs array, remove it, and then run the process function to run another job
					const activeJobIndex = this._active.indexOf(job);
					if (activeJobIndex > -1) {
						this._active.splice(activeJobIndex, 1);
					}

					this._process();
				});

			// Stop the for loop
			if (this._active.length >= this._concurrency) break;
		}

		// Unlock the process after the for loop is finished, so it can be run again
		this._processLock = false;
	}

	/**
	 * getStatus - Get status of job queue
	 *
	 * @returns Job queue status
	 */
	public getStatus() {
		return {
			isPaused: this._isPaused,
			queueLength: this._queue.length,
			activeLength: this._active.length,
			concurrency: this._concurrency
		};
	}

	/**
	 * getQueueStatus - Get statistics of queued or active jobs
	 *
	 * @param type - Job type filter
	 * @returns Job queue statistics
	 */
	public getQueueStatus(type?: JobStatus) {
		const status: Record<string, ReturnType<Job["toJSON"]>[]> = {};
		if (!type || type === JobStatus.ACTIVE)
			status.active = this._active.map(job => job.toJSON());
		if (!type || type === JobStatus.QUEUED)
			status.queue = this._queue.map(job => job.toJSON());
		return status;
	}
}

export default new JobQueue();