import { describe, it, expect, beforeEach, vi } from 'vitest';
import { get } from 'svelte/store';
import { persisted } from '$state';

beforeEach(() => localStorage.clear());

describe('persisted', () => {
	it('uses the initial value when storage is empty', () => {
		const s = persisted('k1', 42);
		expect(get(s)).toBe(42);
	});
	it('writes updates to localStorage', () => {
		const s = persisted('k2', { n: 1 });
		s.set({ n: 2 });
		expect(JSON.parse(localStorage.getItem('k2')!)).toEqual({ n: 2 });
	});
	it('rehydrates a value written by a previous instance', () => {
		persisted('k3', 'a').set('b');
		const s2 = persisted('k3', 'a');
		expect(get(s2)).toBe('b');
	});

	/**
	 * Regression: constructing a store used to broadcast the value it had just
	 * read, so opening a second tab pushed its stale snapshot over the first one.
	 */
	it('does not broadcast the value read at construction', () => {
		const posted: unknown[] = [];
		class SpyChannel {
			onmessage: ((e: { data: unknown }) => void) | null = null;
			postMessage(v: unknown) {
				posted.push(v);
			}
		}
		vi.stubGlobal('BroadcastChannel', SpyChannel);

		localStorage.setItem('k4', JSON.stringify({ n: 1 }));
		const s = persisted('k4', { n: 0 });
		expect(get(s)).toEqual({ n: 1 });
		expect(posted).toEqual([]); // nothing announced merely by mounting

		s.set({ n: 2 });
		expect(posted).toEqual([{ n: 2 }]); // local changes still propagate

		vi.unstubAllGlobals();
	});
});