tracking manager: add localStorage persistence

src/lib/tracking.svelte.ts

@@ -1,4 +1,6 @@
-import { setContext, getContext, onDestroy } from 'svelte';
+import { browser } from '$app/environment';
+import log from 'loglevel';
+import { onDestroy, onMount, createContext } from 'svelte';
 
 /**
  * Options for initializing the TrackingManager.
@@ -36,17 +38,69 @@ type InternalService<T> = Service<T> & {
  * Manages user tracking preferences and services that require consent.
  */
 export class TrackingManager {
+	/** tracking consent, persisted to localStorage by saveOpts */
 	private _consent: boolean | null = $state(null);
 	private _services: Record<string, InternalService<unknown>> = {};
 	private _changeCallbacks: Array<(consent: boolean | null) => void> = [];
 	private _consentQueue: Array<() => void> = [];
 
+	/**
+	 * Saves consent state to localStorage if browser storage is available.
+	 * Automatically called after updating consent.
+	 * @throws Error if storage is not available.
+	 */
+	saveOpts(): TrackingManager {
+		if (!browser || !window?.localStorage) {
+			throw new Error('Cannot access localStorage to save tracking state');
+		}
+
+		window.localStorage.setItem(
+			'trackingOpts',
+			JSON.stringify({ consent: this._consent } as TrackingManagerOpts)
+		);
+		return this;
+	}
+
+	/**
+	 * Loads tracking options from localStorage if available. Suitable to call
+	 * after initialization, e.g. in onMount after a TrackingManager is created.
+	 * @throws Error if storage is not available.
+	 */
+	loadOpts(): TrackingManager {
+		if (!browser || !window?.localStorage) {
+			throw new Error('Cannot access localStorage to load tracking state');
+		}
+
+		const raw = window.localStorage.getItem('trackingOpts');
+		if (raw) {
+			const opts = JSON.parse(raw) as TrackingManagerOpts;
+			if (opts.consent !== undefined && opts.consent !== null) {
+				this.setConsent(opts.consent);
+			}
+			log.debug('[TrackingManager] Loaded tracking options from storage:', opts);
+		}
+
+		return this;
+	}
+
+	/**
+	 * Creates a TrackingManager instance.
+	 * @param opts Optional initial options.
+	 */
 	constructor(opts?: TrackingManagerOpts) {
 		if (opts) {
 			if (opts.consent !== undefined) this._consent = opts.consent;
 		}
 	}
 
+	/**
+	 * Creates a TrackingManager instance from localStorage data.
+	 * @throws Error if storage is not available.
+	 */
+	static fromLocalStorage(): TrackingManager {
+		return new TrackingManager().loadOpts();
+	}
+
 	/** Indicates whether tracking is currently allowed. */
 	get consent() {
 		return this._consent;
@@ -78,7 +132,7 @@ export class TrackingManager {
 
 	/**
 	 * Sets whether tracking is consented. If set to true, all queued callbacks
-	 * will be executed.
+	 * will be executed. Automatically persists to localStorage if available.
 	 */
 	setConsent(value: boolean) {
 		if (this._consent === value) return;
@@ -95,6 +149,7 @@ export class TrackingManager {
 		this._changeCallbacks.forEach((cb) => {
 			cb(this._consent);
 		});
+		this.saveOpts();
 	}
 
 	/**
@@ -113,16 +168,23 @@ export class TrackingManager {
 
 	/**
 	 * Runs callback immediately if we have consent already or queues it for later.
-	 * Removes callback from queue onDestroy.
 	 * @param callback The function to run when consent is granted.
 	 */
 	runWithConsent(callback: () => void) {
-		if (this._consent) {
-			callback();
-		} else {
-			this._consentQueue.push(callback);
-		}
+		if (this._consent) callback();
+		else this._consentQueue.push(callback);
+	}
 
+	/**
+	 * Runs callback onMount if we have consent already or queues it for later.
+	 * Removes the callback from the queue onDestroy.
+	 * @param callback The function to run when consent is granted.
+	 */
+	lifecycleWithConsent(callback: () => void) {
+		onMount(() => {
+			if (this._consent) callback();
+			else this._consentQueue.push(callback);
+		});
 		onDestroy(() => {
 			this._consentQueue = this._consentQueue.filter((cb) => cb !== callback);
 		});
@@ -192,19 +254,31 @@ export class TrackingManager {
 	}
 }
 
-const trackingManagerKey = Symbol();
+const [getTrackingContext, setTrackingContext] = createContext<TrackingManager>();
 
 /**
  * Gets the TrackingManager from context, or creates one if it doesn't exist.
- * @param initializer Optional initializer function to customize the TrackingManager.
+ * If called from the browser, attempts to load saved state from localStorage.
  * @returns The TrackingManager instance.
  */
 export const getTrackingManager = (): TrackingManager => {
-	const saved = getContext<TrackingManager>(trackingManagerKey);
-	if (saved) return saved;
+	try {
+		const saved = getTrackingContext();
+		if (saved) {
+			log.debug('[TrackingManager] Using existing instance from context');
+			return saved;
+		}
+	} catch {
+		// ignore missing context, we'll create a new one
+	}
+
+	log.debug('[TrackingManager] Creating new instance');
+	const manager = $state(new TrackingManager());
+	setTrackingContext(manager);
+
+	if (browser) {
+		manager.loadOpts();
+	}
 
-	console.debug('initializing a new TrackingManager');
-	const manager = new TrackingManager();
-	setContext(trackingManagerKey, manager);
 	return manager;
 };