Analytics

1/** Lightweight analytics + A/B testing - no external SDK required. */
2 
3export type AnalyticsEvent = {
4  name: string;
5  properties?: Record<string, string | number | boolean>;
6};
7 
8export type Experiment = {
9  id: string;
10  variants: string[];
11  weights?: number[];
12};
13 
14const STORAGE_PREFIX = "ms_";
15const EXPERIMENT_PREFIX = `${STORAGE_PREFIX}exp_`;
16 
17function isBrowser(): boolean {
18  return typeof window !== "undefined";
19}
20 
21/** Assign and persist a variant for an experiment (sticky per user). */
22export function getExperimentVariant(experiment: Experiment): string {
23  if (!isBrowser()) return experiment.variants[0] ?? "";
24 
25  const key = `${EXPERIMENT_PREFIX}${experiment.id}`;
26  const stored = localStorage.getItem(key);
27  if (stored && experiment.variants.includes(stored)) return stored;
28 
29  const weights = experiment.weights ?? experiment.variants.map(() => 1);
30  const total = weights.reduce((a, b) => a + b, 0);
31  let roll = Math.random() * total;
32  let variant = experiment.variants[0] ?? "";
33  for (let i = 0; i < experiment.variants.length; i++) {
34    roll -= weights[i] ?? 0;
35    if (roll <= 0) {
36      variant = experiment.variants[i] ?? variant;
37      break;
38    }
39  }
40 
41  localStorage.setItem(key, variant);
42  trackEvent("experiment_assigned", {
43    experiment_id: experiment.id,
44    variant,
45  });
46  return variant;
47}
48 
49/** Track an event - forwards to Plausible/GA if configured, always logs in dev. */
50export function trackEvent(
51  name: string,
52  properties?: Record<string, string | number | boolean>
53): void {
54  if (!isBrowser()) return;
55 
56  const payload: AnalyticsEvent = { name, properties };
57 
58  if (process.env.NODE_ENV === "development") {
59    console.debug("[analytics]", payload);
60  }
61 
62  // Plausible custom events
63  const plausible = (
64    window as Window & { plausible?: (e: string, o?: { props: Record<string, string | number | boolean> }) => void }
65  ).plausible;
66  if (plausible) {
67    plausible(name, properties ? { props: properties } : undefined);
68  }
69 
70  // Google Analytics 4
71  const gtag = (
72    window as Window & { gtag?: (...args: unknown[]) => void }
73  ).gtag;
74  if (gtag) {
75    gtag("event", name, properties);
76  }
77 
78  // Local event buffer for debugging
79  try {
80    const key = `${STORAGE_PREFIX}events`;
81    const existing = JSON.parse(localStorage.getItem(key) ?? "[]") as AnalyticsEvent[];
82    existing.push({ ...payload, properties: { ...properties, ts: Date.now() } as Record<string, string | number | boolean> });
83// … truncated