// Privacy-first analytics. Sends only content-free, categorical events to
// Umami, and only when the tracker script is actually present (gated by the
// NEXT_PUBLIC_UMAMI_* env vars in components/Analytics.tsx). With no script
// loaded — local dev, forks, a non-matching data-domains host, or a visitor
// with Do Not Track — `window.umami` is undefined and every call here is a
// silent no-op: zero runtime impact, no errors.
//
// RULE: never pass free text (player prompts, custom world/style guides,
// uploaded images, vision output) or any per-user identifier. Only enums,
// indices, counts and booleans — that is what keeps these events as
// privacy-friendly as the cookieless page-view baseline.

declare global {
  interface Window {
    umami?: {
      track: (event: string, data?: Record<string, unknown>) => void;
    };
  }
}

// Per-event payload schema. Fixing each event's allowed fields turns the RULE
// above into a compile-time guarantee: an event simply has no slot for a prompt,
// world/style guide or vision string, so free text can't be attached by mistake
// (a bare `Record<string, string>` would happily accept it). Keep every field an
// enum, index, count or boolean. `never` marks events that carry no payload.
type AnalyticsEventData = {
  game_start:
    | {
        source: "prompt";
        gender: string;
        art_style: string;
        plot_style: string;
        pacing: string;
        tts: boolean;
        has_prompt: boolean;
        has_style_ref: boolean;
      }
    | { source: "curated"; gender: string; tts: boolean; card: string }
    | { source: "custom" };
  art_style_select: { style: string };
  style_image_upload: { ok: boolean };
  scene_reached: { scene_index: number };
  choice_select: {
    scene_index: number;
    choice_index: number;
    kind: "advance-beat" | "change-scene";
  };
  vision_click: { result: "insert-beat" | "change-scene" };
  tts_toggle: { muted: boolean };
  fullscreen_toggle: { on: boolean };
  play_heartbeat: never;
};

export type AnalyticsEvent = keyof AnalyticsEventData;

// Payload is required for events that define one and forbidden for those typed
// `never` (the conditional rest tuple collapses to `[]`), so `track("game_start")`
// without data and `track("play_heartbeat", {...})` with data are both errors.
export function track<E extends AnalyticsEvent>(
  event: E,
  ...[data]: AnalyticsEventData[E] extends never ? [] : [AnalyticsEventData[E]]
): void {
  if (typeof window === "undefined") return;
  try {
    window.umami?.track(event, data as Record<string, unknown> | undefined);
  } catch {
    // Analytics must never throw into the app.
  }
}