Refresh Scheduler

Refresh Scheduler Pattern

The refresh scheduler manages periodic data fetching for all panels, pausing when the tab is hidden and flushing stale data when the user returns.

Implementation

Create src/services/refresh-scheduler.ts:

export interface RefreshRegistration {
  name: string;
  fn: () => Promise<void>;
  intervalMs: number;
  condition?: () => boolean;
}

interface RunnerEntry {
  timer: ReturnType<typeof setInterval> | null;
  intervalMs: number;
  fn: () => Promise<void>;
  condition?: () => boolean;
  lastRun: number;
}

export class RefreshScheduler {
  private runners = new Map<string, RunnerEntry>();
  private inFlight = new Set<string>();
  private hiddenSince = 0;
  private visibilityHandler: (() => void) | null = null;

  constructor() {
    this.visibilityHandler = () => this.onVisibilityChange();
    document.addEventListener('visibilitychange', this.visibilityHandler);
  }

  private onVisibilityChange(): void {
    if (document.hidden) {
      this.hiddenSince = Date.now();
      // Pause all timers
      for (const entry of this.runners.values()) {
        if (entry.timer) {
          clearInterval(entry.timer);
          entry.timer = null;
        }
      }
    } else {
      // Resume and flush stale
      this.flushStaleRefreshes();
      for (const [name, entry] of this.runners) {
        if (!entry.timer) {
          entry.timer = setInterval(() => this.runRefresh(name), entry.intervalMs);
        }
      }
    }
  }

  private async runRefresh(name: string): Promise<void> {
    const entry = this.runners.get(name);
    if (!entry) return;
    if (this.inFlight.has(name)) return;
    if (entry.condition && !entry.condition()) return;

    this.inFlight.add(name);
    try {
      await entry.fn();
      entry.lastRun = Date.now();
    } catch (err) {
      console.error(`[Refresh] ${name} failed:`, err);
    } finally {
      this.inFlight.delete(name);
    }
  }

  scheduleRefresh(
    name: string,
    fn: () => Promise<void>,
    intervalMs: number,
    condition?: () => boolean,
  ): void {
    // Clean up existing
    const existing = this.runners.get(name);
    if (existing?.timer) clearInterval(existing.timer);

    const entry: RunnerEntry = {
      timer: null,
      intervalMs,
      fn,
      condition,
      lastRun: 0,
    };

    if (!document.hidden) {
      entry.timer = setInterval(() => this.runRefresh(name), intervalMs);
    }

    this.runners.set(name, entry);
  }

  /**
   * After returning from hidden, flush all runners whose data
   * is older than their interval. Stagger to avoid API burst.
   */
  flushStaleRefreshes(): void {
    if (!this.hiddenSince) return;
    const hiddenMs = Date.now() - this.hiddenSince;
    this.hiddenSince = 0;

    let stagger = 0;
    for (const [name, entry] of this.runners) {
      if (hiddenMs < entry.intervalMs) continue;
      const delay = stagger;
      stagger += 150; // 150ms between each flush
      setTimeout(() => this.runRefresh(name), delay);
    }
  }

  registerAll(registrations: RefreshRegistration[]): void {
    for (const reg of registrations) {
      this.scheduleRefresh(reg.name, reg.fn, reg.intervalMs, reg.condition);
    }
  }

  /** Manually trigger a specific refresh immediately */
  trigger(name: string): void {
    this.runRefresh(name);
  }

  destroy(): void {
    if (this.visibilityHandler) {
      document.removeEventListener('visibilitychange', this.visibilityHandler);
    }
    for (const entry of this.runners.values()) {
      if (entry.timer) clearInterval(entry.timer);
    }
    this.runners.clear();
    this.inFlight.clear();
  }
}

Usage

// src/main.ts
import { RefreshScheduler } from './services/refresh-scheduler';

const scheduler = new RefreshScheduler();

// Register panel refresh intervals
scheduler.registerAll([
  { name: 'stocks', fn: () => stockPanel.refresh(), intervalMs: 60_000 },
  { name: 'news',   fn: () => newsPanel.refresh(),  intervalMs: 5 * 60_000 },
  { name: 'email',  fn: () => emailPanel.refresh(), intervalMs: 2 * 60_000 },
  { name: 'calendar', fn: () => calendarPanel.refresh(), intervalMs: 5 * 60_000 },
]);

Key Behaviors

1. Pause when hidden — stops all intervals when tab is not visible
2. Flush on return — refreshes stale panels with 150ms stagger to avoid API burst
3. In-flight guard — prevents duplicate requests for the same panel
4. Configurable intervals — each panel has its own refresh rate
5. Condition guard — optional condition function to skip refresh (e.g. panel hidden)