Added experimental job scheduling feature

no issue

- This method should be used with caution and should serve as a playground for upcoming new feature of scheduled jobs support

ghost/job-manager/lib/job-manager.js

@@ -1,5 +1,7 @@
 const fastq = require('fastq');
+const later = require('@breejs/later');
 const pWaitFor = require('p-wait-for');
+const isCronExpression = require('./is-cron-expression');
 
 const worker = async (task, callback) => {
     try {
@@ -21,6 +23,7 @@ const handler = (error, result) => {
 class JobManager {
     constructor(logging) {
         this.queue = fastq(this, worker, 1);
+        this.schedule = [];
         this.logging = logging;
     }
 
@@ -38,7 +41,44 @@ class JobManager {
         }, handler);
     }
 
+    /**
+     * Schedules recuring job
+     *
+     * @param {Function|String} job - function or path to a file defining a job
+     * @param {Object} data - data to be passed into the joba
+     * @param {String} when - cron or human readable schedule format
+     */
+    scheduleJob(job, data, when) {
+        let schedule;
+
+        schedule = later.parse.text(when);
+
+        if (isCronExpression(when)) {
+            schedule = later.parse.cron(when);
+        }
+
+        if ((schedule.error && schedule.error !== -1) || schedule.schedules.length === 0) {
+            throw new Error('Invalid schedule format');
+        }
+
+        this.logging.info(`Scheduling job. Next run on: ${later.schedule(schedule).next()}`);
+
+        const cancelInterval = later.setInterval(() => {
+            this.logging.info(`Scheduled job added to the queue.`);
+            this.addJob(job, data);
+        }, schedule);
+
+        this.schedule.push(cancelInterval);
+    }
+
+    /**
+     * @param {import('p-wait-for').Options} [options]
+     */
     async shutdown(options) {
+        this.schedule.forEach((cancelHandle) => {
+            cancelHandle.clear();
+        });
+
         if (this.queue.idle()) {
             return;
         }

ghost/job-manager/package.json

@@ -24,6 +24,7 @@
     "sinon": "9.2.1"
   },
   "dependencies": {
+    "@breejs/later": "4.0.2",
     "cron-parser": "2.17.0",
     "fastq": "1.9.0",
     "p-wait-for": "3.1.0"

ghost/job-manager/test/job-manager.test.js

@@ -9,5 +9,18 @@ describe('Job Manager', function () {
         const jobManager = new JobManager();
 
         should.exist(jobManager.addJob);
+        should.exist(jobManager.scheduleJob);
+    });
+
+    describe('Schedule Job', function () {
+        it ('fails to run for invalid scheduling expression', function () {
+            const jobManager = new JobManager();
+
+            try {
+                jobManager.scheduleJob(() => {}, {}, 'invalid expression');
+            } catch (err) {
+                err.message.should.equal('Invalid schedule format');
+            }
+        });
     });
 });