import type { PrefsDimension } from '$libs/prefs';
import { unitSystemFromLocales, UNIT_SYSTEMS, type UnitSystem } from '$libs/units';

export interface UnitSystemDimensionOptions {
	readonly catalog?: readonly UnitSystem[];
	readonly default?: UnitSystem;
}

export function unitSystemDimension(
	options: UnitSystemDimensionOptions = {}
): PrefsDimension<UnitSystem> {
	const catalog = options.catalog ?? UNIT_SYSTEMS;
	const fallback = options.default ?? 'metric';
	return {
		defaultValue: fallback,
		validate(value) {
			if (typeof value !== 'string') return { ok: false, reason: 'unsupported_unit_system' };
			if (!catalog.includes(value as UnitSystem)) {
				return { ok: false, reason: 'unsupported_unit_system' };
			}
			return { ok: true, value: value as UnitSystem };
		},
		resolve(intent, env) {
			if (intent !== undefined) return intent;
			if (env.unitSystem !== undefined && catalog.includes(env.unitSystem)) {
				return env.unitSystem;
			}
			return unitSystemFromLocales(env.locales ?? [], catalog, fallback);
		},
		catalog: () => catalog
	};
}