pixel: add ensure fbc fallback

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 };
+}