fix race condition in isfollowing

src/lib/stores/cacheSeguidos.js

@@ -0,0 +1,134 @@
+import { browser } from '$app/environment';
+import { writable } from 'svelte/store';
+
+class FollowCache {
+	constructor() {
+		if (browser) {
+			this.loadFromStorage();
+		}
+	}
+
+	/** @type {Map<string, boolean | Promise<boolean>>} */
+	#cache = new Map();
+
+	/** @type {import('svelte/store').Writable<Map<string, boolean>>} */
+	store = writable(new Map());
+
+	/** @param {string} userId */
+	get(userId) {
+		const value = this.#cache.get(userId);
+		return value instanceof Promise ? undefined : value;
+	}
+
+  	/** @param {string} userId */
+	has(userId) {
+		return this.#cache.has(userId);
+	}
+
+	/**
+	 * @param {string} userId
+	 * @param {() => Promise<boolean>} fetchFn
+	 */
+	async getOrFetch(userId, fetchFn) {
+		const existing = this.#cache.get(userId);
+
+		if (existing !== undefined) {
+			if (existing instanceof Promise) {
+				return existing;
+			}
+			return existing;
+		}
+
+		const promise = fetchFn()
+			.then((result) => {
+				this.#setFinal(userId, result);
+				return result;
+			})
+			.catch((err) => {
+				this.#cache.delete(userId);
+				this.#updateStore();
+				throw err;
+			});
+
+		this.#cache.set(userId, promise);
+		this.#updateStore();
+
+		return promise;
+	}
+
+	/**
+	 * @param {string} userId
+	 * @param {boolean} isFollowed
+	 */
+	set(userId, isFollowed) {
+		this.#setFinal(userId, isFollowed);
+	}
+
+	/**
+	 * @param {string} userId
+	 * @param {boolean} value
+	 */
+	#setFinal(userId, value) {
+		this.#cache.set(userId, value);
+		this.#updateStore();
+		this.saveToStorage();
+
+		if (browser) {
+			window.dispatchEvent(
+				new CustomEvent('followCacheUpdated', {
+					detail: { userId, isFollowed: value }
+				})
+			);
+		}
+	}
+
+	#updateStore() {
+		const filtered = Array.from(this.#cache.entries())
+			.filter(([_, v]) => typeof v === 'boolean');
+
+		this.store.set(
+			/** @type {Map<string, boolean>} */
+			(new Map(filtered))
+		);
+	}
+
+	/** @param {string} userId */
+	delete(userId) {
+		this.#cache.delete(userId);
+		this.#updateStore();
+		this.saveToStorage();
+	}
+
+	clear() {
+		this.#cache.clear();
+		this.store.set(new Map());
+		this.saveToStorage();
+	}
+
+	saveToStorage() {
+		if (!browser) return;
+		const filtered = Array.from(this.#cache.entries())
+			.filter(([_, v]) => typeof v === 'boolean');
+
+		const data = Object.fromEntries(filtered);
+		sessionStorage.setItem('follow-cache', JSON.stringify(data));
+	}
+
+	loadFromStorage() {
+		if (!browser) return;
+
+		try {
+			const stored = sessionStorage.getItem('follow-cache');
+			if (!stored) return;
+			const data = JSON.parse(stored);
+
+			this.#cache = new Map(Object.entries(data));
+			this.#updateStore();
+
+		} catch (err) {
+			console.error('Error cargando follow-cache:', err);
+		}
+	}
+}
+
+export const cacheSeguidos = new FollowCache();