// Pure helpers for the deliberate offline MODE — its device-scoped persistence and the readiness
// decision — kept out of the reactive module (offline.svelte.ts) so they unit-test in the node env.
// The deliberate offline mode is distinct from connection.svelte.ts's transient "can we reach the
// gateway" signal: it is the player's own sticky choice, and it gates the network, tints the chrome
// and shows only local games.

import type { Variant } from './model';

const STORAGE_KEY = 'scrabble.offlineMode';

/** loadOfflinePref reads the persisted offline-mode flag (device-scoped); false when unset or when
 *  storage is unavailable, so a device that cannot persist simply starts online. */
export function loadOfflinePref(): boolean {
  try {
    return typeof localStorage !== 'undefined' && localStorage.getItem(STORAGE_KEY) === '1';
  } catch {
    return false;
  }
}

/** saveOfflinePref persists the offline-mode flag (best-effort). */
export function saveOfflinePref(on: boolean): void {
  try {
    if (typeof localStorage !== 'undefined') localStorage.setItem(STORAGE_KEY, on ? '1' : '0');
  } catch {
    /* best-effort — a failed persist just reverts to online on the next launch */
  }
}

/**
 * offlineReady reports whether the device can play offline right now: at least one variant is
 * enabled and every enabled variant's dictionary is already available on the device (hasDict). The
 * offline toggle uses it to decide whether flipping to offline can succeed immediately.
 */
export function offlineReady(enabled: readonly Variant[], hasDict: (v: Variant) => boolean): boolean {
  return enabled.length > 0 && enabled.every((v) => hasDict(v));
}

/** missingDicts lists the enabled variants whose dictionary is not yet available — the ones the
 *  toggle must fetch (or wait on) before offline mode can be entered. */
export function missingDicts(enabled: readonly Variant[], hasDict: (v: Variant) => boolean): Variant[] {
  return enabled.filter((v) => !hasDict(v));
}

/**
 * raceOfflineReady runs the dictionary fetch `run` against a `budgetMs` wait and reports whether
 * offline mode can be entered now: ready only when the fetch resolves with nothing still failed
 * before the budget elapses. On a timeout the caller stops waiting but does NOT abort `run` — it
 * keeps warming the on-device cache so a later flip to offline is instant. The sleep is injected so
 * the logic stays pure and unit-tests in the node env.
 */
export async function raceOfflineReady(
  run: Promise<{ failed: readonly unknown[] }>,
  budgetMs: number,
  sleep: (ms: number) => Promise<void> = (ms) => new Promise((r) => setTimeout(r, ms)),
): Promise<boolean> {
  const elapsed = sleep(budgetMs).then(() => null);
  const res = await Promise.race([run, elapsed]);
  return res !== null && res.failed.length === 0;
}

/**
 * offlinePreloadEligible reports whether a background dictionary preload should run in this
 * context: an installed standalone web PWA (not a Telegram/VK mini-app, not a plain browser tab)
 * with a confirmed email, currently online. Elsewhere the preload is wasted bandwidth — the context
 * has no offline mode to prepare for — so kickDictPreload skips it. Mirrors the Settings offline
 * toggle's eligibility so the two never disagree.
 */
export function offlinePreloadEligible(opts: {
  hasEmail: boolean;
  standalone: boolean;
  inTelegram: boolean;
  inVK: boolean;
  online: boolean;
}): boolean {
  return opts.hasEmail && opts.standalone && !opts.inTelegram && !opts.inVK && opts.online;
}

/**
 * shouldBootOffline decides whether a cold start skips the network and launches straight into
 * offline mode: the deliberate offline flag is persisted-on AND a prior online session left a cached
 * session and profile to start from. Without both (e.g. cleared storage, or a never-online install),
 * the app must boot online once first — the caller then drops the sticky flag and continues online.
 */
export function shouldBootOffline(opts: { offlineActive: boolean; hasSession: boolean; hasProfile: boolean }): boolean {
  return opts.offlineActive && opts.hasSession && opts.hasProfile;
}