import type { InvalidationEvent } from "./invalidation";

export interface RefreshScheduler {
  connected(): void;
  notified(event: InvalidationEvent): void;
  dispose(): void;
}

export interface RefreshSchedulerOptions {
  delayMs?: number;
  duplicateWindowMs?: number;
  now?: () => number;
}

export function createRefreshScheduler(
  refresh: () => void,
  options: RefreshSchedulerOptions = {},
): RefreshScheduler {
  const delayMs = options.delayMs ?? 75;
  const duplicateWindowMs = options.duplicateWindowMs ?? 2_000;
  const now = options.now ?? Date.now;
  let pending: ReturnType<typeof setTimeout> | undefined;
  let lastEventKey: string | undefined;
  let lastEventAt = 0;

  const schedule = (event?: InvalidationEvent) => {
    if (event) {
      const key = `${event.type}:${event.id}:${event.version}`;
      const timestamp = now();
      if (
        key === lastEventKey &&
        timestamp - lastEventAt < duplicateWindowMs
      ) {
        return;
      }
      lastEventKey = key;
      lastEventAt = timestamp;
    }
    if (pending) return;
    pending = setTimeout(() => {
      pending = undefined;
      refresh();
    }, delayMs);
  };

  return {
    connected() {
      schedule();
    },
    notified(event) {
      schedule(event);
    },
    dispose() {
      if (pending) clearTimeout(pending);
      pending = undefined;
    },
  };
}