pixel: add ensure fbc fallback

src/lib/conversion/client.ts

@@ -1,3 +1,4 @@
+import { getFbpFbc } from '../metapixel/fbc.ts';
 import type { TrackingManager } from '$lib/tracking.svelte';
 import type {
 	ConversionErrorResponseBody,
@@ -42,13 +43,12 @@ export class ConversionClient {
 		}
 	): Promise<ConversionResponseBody | ConversionErrorResponseBody> {
 		// Extract user data
-		const fbp = await cookieStore.get('_fbp');
+		const { fbp, fbc } = getFbpFbc();
-		const fbc = await cookieStore.get('_fbc');
 
 		const user: ConversionUserData = {
 			...options.user,
-			fbp: fbp?.value,
+			fbp,
-			fbc: fbc?.value
+			fbc
 		};
 
 		// Get event source URL & extract UTM params if present

src/lib/metapixel/MetaPixel.svelte

@@ -11,6 +11,7 @@ PixelControl interface.
 	import type { TrackingManager } from '../tracking.svelte.ts';
 	import { onNavigate } from '$app/navigation';
 	import { PixelControl, type PixelControlOptions } from './pixel-control.ts';
+	import { ensureFbc, type EnsureFbcOptions } from './fbc.ts';
 
 	interface Props {
 		/**
@@ -37,6 +38,11 @@ PixelControl interface.
 
 	let pixel = $state<PixelControl | null>(null);
 
+	const ensureFbcOptions: EnsureFbcOptions = $derived({
+		sameSite: 'Lax',
+		pixelLoaded: PixelControl.baseLoaded && !PixelControl.baseFailed
+	});
+
 	onMount(() => {
 		if (!trackingManager) {
 			throw new Error('MetaPixel component requires a TrackingManager to manage consent.');
@@ -47,6 +53,7 @@ PixelControl interface.
 		trackingManager.runWithConsent(() => {
 			if (autoPageView && pixel) {
 				pixel.pageView();
+				ensureFbc(ensureFbcOptions);
 			}
 		});
 	});
@@ -55,6 +62,7 @@ PixelControl interface.
 		trackingManager?.runWithConsent(() => {
 			if (autoPageView && pixel) {
 				pixel.pageView();
+				ensureFbc(ensureFbcOptions);
 			}
 		});
 	});

src/lib/metapixel/fbc.ts

@@ -0,0 +1,88 @@
+import log from 'loglevel';
+
+export type EnsureFbcOptions = {
+	days?: number; // cookie lifetime, default 180
+	domain?: string; // optional cookie domain
+	sameSite?: 'Lax' | 'Strict' | 'None'; // default Lax
+	secure?: boolean; // default inferred from location.protocol === 'https:'
+	pixelLoaded?: boolean; // if true, skip manual set and let Pixel handle it
+};
+
+function getParam(name: string): string | undefined {
+	const params = new URLSearchParams(location.search);
+	const v = params.get(name);
+	return v || undefined;
+}
+
+function getCookie(name: string): string | undefined {
+	return document.cookie
+		.split('; ')
+		.find((c) => c.startsWith(name + '='))
+		?.split('=')[1];
+}
+
+function setCookie(
+	name: string,
+	value: string,
+	{
+		days = 180,
+		domain,
+		sameSite = 'Lax',
+		secure
+	}: Pick<EnsureFbcOptions, 'days' | 'domain' | 'sameSite' | 'secure'> = {}
+) {
+	const d = new Date();
+	d.setTime(d.getTime() + days * 864e5);
+	const parts = [
+		`${name}=${encodeURIComponent(value)}`,
+		`expires=${d.toUTCString()}`,
+		'path=/',
+		`SameSite=${sameSite}`
+	];
+	if (domain) parts.push(`domain=${domain}`);
+	const isSecure = secure ?? location.protocol === 'https:';
+	if (isSecure) parts.push('Secure');
+	document.cookie = parts.join('; ');
+}
+
+function isValidFbc(value: string | undefined): boolean {
+	if (!value) return false;
+	// Expect "fb.1.<unix>.<fbclid>"
+	if (!value.startsWith('fb.1.')) return false;
+	const parts = value.split('.');
+	return parts.length >= 4 && /^\d+$/.test(parts[2]) && parts[3].length > 0;
+}
+
+/**
+ * Ensure _fbc cookie exists when landing URL contains fbclid.
+ * Call after consent. If pixelLoaded is true, it skips manual setting.
+ */
+export function ensureFbc(options: EnsureFbcOptions = {}) {
+	try {
+		const { pixelLoaded = false, ...cookieOpts } = options;
+
+		if (pixelLoaded) throw new Error('Pixel loaded, skipping manual _fbc set'); // Let the Pixel set _fbc if it’s active
+
+		const fbclid = getParam('fbclid');
+		if (!fbclid) throw new Error('No fbclid param present');
+
+		const existing = getCookie('_fbc');
+		if (isValidFbc(existing)) throw new Error('_fbc cookie already present and valid');
+
+		const ts = Math.floor(Date.now() / 1000);
+		const fbc = `fb.1.${ts}.${fbclid}`;
+		setCookie('_fbc', fbc, cookieOpts);
+		log.debug('[ensureFbc] Set _fbc cookie:', fbc);
+	} catch (e) {
+		log.debug('[ensureFbc]', (e as Error).message);
+	}
+}
+
+/**
+ * Helper to read both _fbp and _fbc for your CAPI payload.
+ */
+export function getFbpFbc(): { fbp?: string; fbc?: string } {
+	const fbp = getCookie('_fbp');
+	const fbc = getCookie('_fbc');
+	return { fbp, fbc };
+}

src/lib/metapixel/index.ts

@@ -1,2 +1,4 @@
 export { default as MetaPixel } from './MetaPixel.svelte';
 export { PixelControl, type PixelControlOptions } from './pixel-control.ts';
+export * from './fbc.ts';
+export * from './pixel-control.ts';

src/lib/metapixel/pixel-control.ts

@@ -68,7 +68,8 @@ export class PixelControl {
 	private _trackingManager: MaybeGetter<TrackingManager | undefined>;
 	private _conversionClient?: ConversionClient = undefined;
 
-	private static _baseLoaded: boolean = false;
+	private static _baseLoaded: boolean = $state(false);
+	private static _baseFailed: boolean = $state(false);
 	private static _registeredPixels: Record<string, PixelControl> = {};
 
 	/** Indicates whether the Meta Pixel base script has been loaded. */
@@ -76,6 +77,11 @@ export class PixelControl {
 		return this._baseLoaded;
 	}
 
+	/** Indicates whether the Meta Pixel base script has failed to load. */
+	static get baseFailed(): boolean {
+		return this._baseFailed;
+	}
+
 	/**
 	 * Ensures that the Meta Pixel base has been loaded before
 	 * allowing further operations.
@@ -111,15 +117,18 @@ export class PixelControl {
 
 	/** Loads the Meta Pixel base script. */
 	static async load() {
-		if (this._baseLoaded && !!window.fbq) return;
+		if (this._baseLoaded && !this.baseFailed && !!window.fbq) return;
 		if (!window.fbq) {
 			try {
 				await loadMetaPixel(); // Load the Meta Pixel script
 			} catch (e) {
 				log.warn('[PixelControl] Failed to load Meta Pixel script, all events will be queued.', e);
-			}
+				this._baseFailed = true;
-		}
+				return;
+			} finally {
 				this._baseLoaded = true;
+			}
+		}
 		log.debug('[PixelControl] Meta Pixel base script loaded.');
 	}