import { ActiveSymbol } from './symbols.ts';
import { isState } from './guards.ts';
import type { Active } from './types.ts';

/**
 * Wraps a reactive container in a readonly view, preventing external mutation.
 * If the container is already readonly, it is returned as-is with no extra wrapping.
 *
 * @example
 * const count   = state(0);          // State<number>       — mutable
 * const roCount = readonly(count);   // Reactive<number>    — readonly
 *
 * roCount.current = 1; // TS error: cannot assign to readonly property
 * count.current   = 1; // still works — original is unaffected
 */
export function readonly<T>(source: Active<T>): Active<T> {
	// Already readonly — return as-is, no unnecessary wrapping.
	if (!isState(source)) return source;

	return {
		[ActiveSymbol]: true,
		get current() {
			return source.current;
		}
	};
}