feat: add scheduler (#30)

packages/server/src/scheduler/scheduler.ts

@@ -0,0 +1,73 @@
+import { CronJob } from 'cron';
+import { ScheduleRepo } from '../repos/schedules/schedules.js';
+import { RunRepo } from '../repos/runs/runs.js';
+
+type SchedulerOptions = {
+  runs: RunRepo;
+  schedules: ScheduleRepo;
+};
+
+type RunningSchedule = {
+  id: string;
+  job: CronJob;
+  stop: () => Promise<void>;
+};
+
+class Scheduler {
+  #running: RunningSchedule[] = [];
+  #options: SchedulerOptions;
+
+  constructor(options: SchedulerOptions) {
+    this.#options = options;
+    const { schedules } = this.#options;
+    schedules.on('added', this.#add);
+    schedules.on('removed', this.#remove);
+  }
+
+  #remove = async (id: string) => {
+    const current = this.#running.filter((r) => r.id === id);
+    await Promise.all(current.map((r) => r.stop()));
+    this.#running = this.#running.filter((r) => r.id !== id);
+  };
+
+  #add = async (id: string) => {
+    const { schedules, runs } = this.#options;
+    const current = this.#running.filter((r) => r.id === id);
+    await Promise.all(current.map((r) => r.stop()));
+    const schedule = await schedules.get(id);
+    if (!schedule) {
+      return;
+    }
+    const job = new CronJob(schedule.cron, async () => {
+      await runs.create({
+        loadId: schedule.load,
+      });
+    });
+    const stop = async () => {
+      job.stop();
+    };
+    this.#running.push({
+      id: schedule.id,
+      job,
+      stop,
+    });
+  };
+
+  public stop = async () => {
+    for (const running of this.#running) {
+      await running.stop();
+      this.#running = this.#running.filter((r) => r !== running);
+    }
+  };
+
+  public start = async () => {
+    const { schedules } = this.#options;
+    await this.stop();
+    const all = await schedules.find({});
+    for (const schedule of all) {
+      await this.#add(schedule.id);
+    }
+  };
+}
+
+export { Scheduler };