/**
 * NAM-403: the pure decision logic behind full-page screenreader announcements.
 * RN-free and side-effect-free so it runs under the jest node environment. The
 * React AnnouncementProvider owns state (live-region text, video subscription)
 * and delegates every decision here.
 *
 * Contract (see TV Full-Page Announcement):
 *  - First focus of a primary button announces the composite (page text + label).
 *  - Subsequent focuses and auxiliary buttons speak only their own label, which
 *    the OS screenreader reads naturally — so this machine returns null for them.
 *  - While a video plays, the announcement is deferred and flushed on video end.
 */
import type { ButtonAnnouncementKind } from './a11yAnnouncement';

export interface AnnouncementFocusInput {
  kind: ButtonAnnouncementKind;
  ownLabel: string;
  videoPlaying: boolean;
  buildComposite: () => string;
}

export interface AnnouncementMachine {
  /** Returns text to speak now via the live region, or null (natural read / deferred). */
  onFocus(input: AnnouncementFocusInput): string | null;
  /** Flush a deferred announcement when video playback stops. */
  onVideoStopped(): string | null;
  /** Reset per-page state (call on page change). */
  reset(): void;
}

export function createAnnouncementMachine(): AnnouncementMachine {
  let pageAnnounced = false;
  let deferred: string | null = null;

  return {
    onFocus({ kind, ownLabel, videoPlaying, buildComposite }) {
      if (videoPlaying) {
        // Defer: the button is hidden from a11y during playback, so nothing is
        // spoken now; the flush on video end says the composite (first primary
        // focus) or the focused button's own label.
        deferred = kind === 'primary' && !pageAnnounced ? buildComposite() : ownLabel;
        if (kind === 'primary') pageAnnounced = true;
        return null;
      }
      if (kind === 'auxiliary') return null; // natural focus read handles it
      if (pageAnnounced) return null; // subsequent focus -> natural read
      pageAnnounced = true;
      return buildComposite();
    },

    onVideoStopped() {
      if (deferred == null) return null;
      const text = deferred;
      deferred = null;
      return text;
    },

    reset() {
      pageAnnounced = false;
      deferred = null;
    },
  };
}