/**
 * Analytics tracking for Umami.
 *
 * Single typed wrapper around `window.umami.track()`. All events flow
 * through `track(name, data?)` — this gives us:
 *   - Refactor-safe event names (one place to maintain).
 *   - A schema for properties so we don't ship typos that fragment dashboards.
 *   - No-op on the server and never-throws semantics, so analytics outages
 *     can't take the app down.
 *
 * Umami is privacy-friendly (no cookies, no IPs, no PII), so it's safe to
 * include school identifiers and full search query text.
 */

export type EventName =
  // Discovery
  | 'search_submitted'
  | 'near_me_used'
  | 'empty_results'
  // Engagement
  | 'school_viewed'
  | 'place_viewed'
  | 'section_nav_used'
  | 'chart_metric_changed'
  | 'metric_compared_in_rankings'
  | 'external_link_clicked'
  // Conversion
  | 'compare_school_added'
  | 'compare_school_removed'
  | 'compare_viewed'
  | 'compare_metric_changed'
  | 'compare_shared'
  | 'compare_focus_school'
  // Operational
  | 'api_error'
  | 'results_load_more'
  | 'results_view_changed';

type Primitive = string | number | boolean;
type Payload = Record<string, Primitive>;

/**
 * Fire an event. No-ops if Umami isn't loaded yet (the script is `defer`)
 * or if we're rendering server-side. Never throws.
 */
export function track(name: EventName, data?: Payload): void {
  if (typeof window === 'undefined') return;
  const umami = (window as unknown as { umami?: { track?: (n: string, d?: Payload) => void } }).umami;
  if (!umami?.track) return;
  try {
    umami.track(name, data);
  } catch {
    // Analytics must never crash the app.
  }
}

/**
 * Categorise where the user navigated from, for funnel attribution
 * (mostly used on school_viewed). Only checks same-origin referrers.
 */
export type NavigationSource =
  'search' | 'rankings' | 'compare' | 'detail' | 'place' | 'direct';

/*
 * The in-app trail.
 *
 * document.referrer is written by the browser only when a *document* loads.
 * Every internal navigation here is an App Router soft navigation —
 * history.pushState, no new document — so document.referrer goes on naming
 * whatever opened the tab (usually nothing, or a search engine) for the whole
 * session. Reading it to answer "which page did they come from" therefore
 * returned 'direct' for essentially every in-app journey, including the one
 * the location layer exists to produce.
 *
 * Verified on staging: /schools/brentwood, click a school, the URL becomes
 * /school/… and document.referrer is still "".
 *
 * A module-level trail is the counterpart with exactly the right lifetime. It
 * survives soft navigation, and it dies on a real document load — which is
 * precisely when document.referrer becomes meaningful again, so the two cover
 * each other with no overlap.
 */
const TRAIL_LIMIT = 4;
const trail: string[] = [];

/** Record a path the user is now on. Called by RouteTrail on every route. */
export function recordVisitedPath(path: string): void {
  if (trail[trail.length - 1] === path) return;
  trail.push(path);
  if (trail.length > TRAIL_LIMIT) trail.shift();
}

/**
 * The most recent path that is not the one being viewed.
 *
 * Skipping the current path rather than taking trail[length - 2] is what
 * makes the answer independent of ordering: the trail is written by a
 * layout-level effect and read by a page-level one, and React orders those by
 * tree position — not a contract worth resting a measurement on. It also
 * gives the right answer when the user goes back to a page they came from.
 */
function previousInAppPath(): string | null {
  if (typeof window === 'undefined') return null;
  const current = window.location.pathname;
  for (let i = trail.length - 1; i >= 0; i -= 1) {
    if (trail[i] !== current) return trail[i];
  }
  return null;
}

function classifyPath(p: string): NavigationSource {
  if (p === '/' || p === '') return 'search';
  if (p.startsWith('/rankings')) return 'rankings';
  if (p.startsWith('/compare')) return 'compare';
  // `/schools/` before `/school/`: they differ by one letter and mean
  // different things — the location layer versus a single school. Checked
  // first so the narrower-looking prefix cannot shadow it if either string
  // is ever edited.
  if (p.startsWith('/schools/')) return 'place';
  if (p.startsWith('/school/')) return 'detail';
  return 'direct';
}

export function getNavigationSource(): NavigationSource {
  const internal = previousInAppPath();
  if (internal) return classifyPath(internal);

  // No trail means this is the first page of the document, so the referrer is
  // the only witness — and an honest one.
  if (typeof window === 'undefined' || !document.referrer) return 'direct';
  try {
    const ref = new URL(document.referrer);
    if (ref.origin !== window.location.origin) return 'direct';
    return classifyPath(ref.pathname);
  } catch {
    return 'direct';
  }
}

/** Split mobile vs desktop on a per-event basis. */
export function getViewport(): 'mobile' | 'desktop' {
  if (typeof window === 'undefined') return 'desktop';
  return window.matchMedia('(max-width: 640px)').matches ? 'mobile' : 'desktop';
}