import type { Cookies } from '@sveltejs/kit';
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 from browser cookies.
 */
export function getFbpFbc(): { fbp?: string; fbc?: string } {
	const fbp = getCookie('_fbp');
	const fbc = getCookie('_fbc');
	return { fbp, fbc };
}

/**
 * Helper to read both _fbp and _fbc for your CAPI payload from cookies object.
 */
export function getFbpFbcFromCookies(cookies: Cookies): { fbp?: string; fbc?: string } {
	const fbp = cookies.get('_fbp') || undefined;
	const fbc = cookies.get('_fbc') || undefined;
	return { fbp, fbc };
}