import { useCallback, useRef } from 'react';
import { defineChannel } from 'hooks/usePanelChannel';

/**
 * "The connection changed — anyone reading NPM should read it again."
 *
 * ── Why a channel and not the URL ──
 *
 * `docs/navigation-audit.md` draws the line: anything ADDRESSABLE goes in the URL, and a channel is only
 * for a signal — "something changed, re-read it". This is the second kind. Nobody wants to link to "the
 * moment after the connection was saved", and there is nothing to select.
 *
 * ── Why it is needed at all ──
 *
 * The panels are siblings in a workspace layout. `ConnectionPanel` cannot call into `CertificatesPanel`
 * and should not try — they are mounted independently and neither owns the other. Before this, saving a
 * connection left both panels showing whatever they had failed to load a minute earlier, and the only fix
 * a person had was a manual refresh. Reported on 2026-08-25 the first time a connection was saved through
 * the form.
 *
 * ── The nonce is a plain counter, and that is not an accident ──
 *
 * Copied deliberately from `officerdev/src/channels.ts`, which records why. `setSignal(n => n + 1)` is
 * WRONG here: the functional setter applies against the value captured at render, so two bumps inside one
 * render window both compute `snapshot + 1` and the second silently overwrites the first — nobody
 * re-reads. `Date.now()` has the same flaw in miniature, two bumps in one millisecond being one number.
 * A module counter never reads React state, so it cannot be wrong however often it is called.
 */
const useConnectionChangedChannel = defineChannel<number>('proxy-manager:connection-changed', 0);

let nonce = 0;

export const useConnectionChanged = () => {
  const [signal, setSignal] = useConnectionChangedChannel();

  // The setter is a fresh closure every render and this `bump` goes into dependency lists, so it is read
  // through a ref — stable identity without freezing the first render's setter.
  const setRef = useRef(setSignal);
  setRef.current = setSignal;
  const bump = useCallback(() => setRef.current(++nonce), []);

  return [signal, bump] as const;
};