import { logError } from "./logService";

/**
 * Data-change channel (#396, ADR 0022).
 *
 * The writes that may move a counter read elsewhere (the getting-started path
 * reads `COUNTERS_SQL` and the import folder) call `notifyDataChanged()` once
 * they have succeeded. The message only says "data that counters read may have
 * changed": it carries no payload, and the data layer does not know who
 * listens. Subscribers re-read on their own terms (the onboarding provider
 * waits 150 ms to group a burst, then ignores any stale answer).
 *
 * Modeled on `logService.subscribe`, without React.
 */

type DataChangedListener = () => void;

const listeners = new Set<DataChangedListener>();

/**
 * Tells every subscriber that data read by counters may have changed. Never
 * throws: a subscriber that fails is logged and the others still run, so a
 * write that succeeded is never reported as failed because of a listener.
 */
export function notifyDataChanged(): void {
  // Iterate over a copy: a listener may unsubscribe while being called.
  for (const listener of [...listeners]) {
    try {
      listener();
    } catch (e) {
      logError(
        "Data events: a subscriber failed",
        e instanceof Error ? e.message : String(e),
      );
    }
  }
}

/** Subscribes to data changes. Returns the function that unsubscribes. */
export function subscribeDataChanged(listener: DataChangedListener): () => void {
  listeners.add(listener);
  return () => {
    listeners.delete(listener);
  };
}