/** Includes child writes registered by tasks that are already running. */
export class DatabaseBackgroundWork {
  private pending = new Set<Promise<unknown>>()

  track<T>(task: Promise<T>): Promise<T> {
    this.pending.add(task)
    void task.then(() => this.pending.delete(task), () => this.pending.delete(task))
    return task
  }

  async drain(timeoutMs = 30_000): Promise<void> {
    let timer: ReturnType<typeof setTimeout> | undefined
    const timeout = new Promise<never>((_, reject) => {
      timer = setTimeout(() => reject(new Error("Не удалось дождаться фоновых записей; операция с базой отменена")), timeoutMs)
    })
    try {
      while (this.pending.size) await Promise.race([Promise.allSettled([...this.pending]), timeout])
    } finally { if (timer) clearTimeout(timer) }
  }
}

export const databaseBackgroundWork = new DatabaseBackgroundWork()