// Which rotor dial to draw.
//
// Two compasses ship: the current one (night map, square scale, mouse pointer,
// target marker) and the original small light-map dial. Neither is more correct
// than the other — one operator reads the big map at a glance, another wants the
// compact dial that was there before — so it is a preference, not a migration.
//
// A UI preference rather than a settings-database key: it decides what a widget
// looks like, nothing is transmitted from it, and it belongs to the screen it is
// read on. It is portable all the same (see lib/uiPref), so a copied folder
// keeps the dial its owner chose.
import { writeUiPref } from '@/lib/uiPref';

export const KEY_ROTOR_STYLE = 'opslog.rotorStyle';

export type RotorStyle = 'modern' | 'classic';

export function rotorStyle(): RotorStyle {
  try {
    return localStorage.getItem(KEY_ROTOR_STYLE) === 'classic' ? 'classic' : 'modern';
  } catch {
    return 'modern';
  }
}

// Same shape as the distance unit: the compasses are rendered from two call
// sites, and a preference changed in Settings has to reach both without either
// of them polling for it.
const listeners = new Set<() => void>();

export function setRotorStyle(style: RotorStyle): void {
  writeUiPref(KEY_ROTOR_STYLE, style);
  listeners.forEach((l) => l());
}

export function subscribeRotorStyle(fn: () => void): () => void {
  listeners.add(fn);
  return () => { listeners.delete(fn); };
}