// "Save for offline": fetch chapters ahead of time so they open without a connection. Fetching is
// all it takes — the service worker (public/sw.js) keeps every Bible-text response it sees. Only the
// free translations (BSB, NET) can be saved; the licensed ones' terms don't allow bulk copies.
import { CHAPTER_COUNTS } from './bibleUtils.jsx';
import { fetchChapter, isLicensed } from './bibleText.js';

const KEY = 'offline-saved';

// { 'BSB': ['JHN', 'PSA'] }: whole books saved on this device, per translation.
export function loadSavedBooks() {
  try {
    const raw = JSON.parse(localStorage.getItem(KEY) || '{}');
    return raw && typeof raw === 'object' && !Array.isArray(raw) ? raw : {};
  } catch { return {}; }
}

export function markBookSaved(translation, book) {
  const all = loadSavedBooks();
  all[translation] = [...new Set([...(all[translation] ?? []), book])];
  try { localStorage.setItem(KEY, JSON.stringify(all)); } catch { /* storage full or unavailable */ }
  return all;
}

export const canSaveOffline = (translation) => !isLicensed(translation);

export const bookRefs = (book) => Array.from({ length: CHAPTER_COUNTS[book] ?? 0 }, (_, i) => ({ book, chapter: i + 1 }));
export const bibleRefs = () => Object.keys(CHAPTER_COUNTS).flatMap(bookRefs);

// Fetches every chapter in `refs` ([{ book, chapter }]) a few at a time, calling onProgress(done, total)
// as each lands. Resolves { done, failed } — a chapter that fails doesn't stop the rest. Pass `signal`
// to stop early.
export async function downloadChapters(translation, refs, { onProgress, signal, concurrency = 4 } = {}) {
  const queue = [...refs];
  let done = 0;
  let failed = 0;
  const worker = async () => {
    while (queue.length > 0 && !signal?.aborted) {
      const { book, chapter } = queue.shift();
      try { await fetchChapter(translation, book, chapter, { signal }); done += 1; } catch { if (!signal?.aborted) failed += 1; }
      onProgress?.(done + failed, refs.length);
    }
  };
  await Promise.all(Array.from({ length: Math.min(concurrency, refs.length) }, worker));
  return { done, failed };
}