svelte-kit-vice/src/uix/active-uix/prefs.ts

import { readActivePrefsSlot, type ActivePrefs, type ActivePrefsSlot } from '$prefs';
import type { Direction } from '$libs/direction';
import type { LocaleSource } from '$libs/locale';

export interface ActiveUixPrefsView {
	getDir(): Direction;
	onPreferenceChange(handler: () => void): () => void;
}

const DEFAULT_DIR: Direction = 'ltr';

export const readActiveUixPrefsSlot = readActivePrefsSlot as <T>(
	prefs: unknown,
	key: string
) => ActivePrefsSlot<T> | undefined;

export function createLocaleSourceFromPrefs(prefs: ActivePrefs): LocaleSource | undefined {
	const localeSlot = readActiveUixPrefsSlot<string>(prefs, 'locale');
	if (!localeSlot) return undefined;
	return {
		get: () => localeSlot.get(),
		onChange: (handler) => localeSlot.onChange(handler)
	};
}

export function connectLangsToPrefs(
	langs: { setLocale(locale: string): void },
	prefs: ActivePrefs
): (() => void) | undefined {
	const languageSlot = readActiveUixPrefsSlot<string>(prefs, 'language');
	if (!languageSlot) return undefined;

	langs.setLocale(languageSlot.get());
	return languageSlot.onChange((value) => langs.setLocale(value));
}

export function createActiveUixPrefsView(prefs: ActivePrefs): ActiveUixPrefsView {
	return {
		getDir(): Direction {
			return readActiveUixPrefsSlot<Direction>(prefs, 'direction')?.get() ?? DEFAULT_DIR;
		},
		onPreferenceChange(handler: () => void): () => void {
			const detachers = [
				readActiveUixPrefsSlot<Direction>(prefs, 'direction')?.onChange(handler)
			].filter((off): off is () => void => typeof off === 'function');

			return () => {
				for (const detach of detachers) detach();
			};
		}
	};
}