feat: add initial Scheduler class

1 files changed, 68 insertions, 0 deletions

diff --git a/lib/scheduler.ts b/lib/scheduler.ts
new file mode 100644
index 0000000..449ac39
--- /dev/null
+++ b/lib/scheduler.ts
@@ -0,0 +1,68 @@
+import cron from 'cron';
+import Bluebird from 'bluebird';
+import { EventModel } from './model';
+
+const CronJob = cron.CronJob;
+
+class Scheduler {
+  jobs: cron.CronJob[];
+  Model: EventModel<any>;
+
+  constructor(model: EventModel<any>) {
+    this.Model = model;
+    this.jobs = [];
+
+    const job = new CronJob('*/10 * * * * *', () => this.updateJobs());
+    job.start();
+  }
+
+  startAllJobs() {
+    this.jobs.forEach(job => job.start());
+  }
+
+  stopAllJobs() {
+    this.jobs.forEach(job => job.stop());
+  }
+
+  async rescheduleMissedEvents() {
+    const missedEvents = await this.Model.findMissedEvents();
+    return Bluebird.map(missedEvents, event => event.save());
+  }
+
+  async updateJobs() {
+    // Reschedule missed events before we stop jobs to avoid
+    // accidentally stopping the job that has not triggered yet
+    // (if event schedule resonates with updateJobs schedule)
+    await this.rescheduleMissedEvents();
+
+    this.stopAllJobs();
+
+    const events = await this.Model.findNextEvents();
+    if (!events.length) console.log('WARNING: no upcoming events');
+    this.jobs = events.map(event => new CronJob(
+      event.schedule,
+      () => this.run(event.id)
+    ));
+
+    this.startAllJobs();
+  }
+
+  async run(id: string) {
+    const event = await this.Model.findById(id);
+    // TODO: handle the case when event is deleted
+    if (!event) return;
+
+    try {
+      event.start();
+      // TODO: put actual handler here
+      await new Promise(res => setTimeout(res, 5000));
+      return event.complete();
+    } catch (error) {
+      event.fail(error);
+    }
+  }
+}
+
+
+export default Scheduler;
+