/**
 * offlineQueue.ts — WS-2 Field Expansion
 * 오프라인 중 제출 요청을 IndexedDB에 큐잉하고,
 * 온라인 복귀 시 Background Sync(또는 폴링) 로 재전송.
 */

export interface QueueItem {
  id?: number;
  url: string;
  method: string;
  headers: Record<string, string>;
  body: string;
  enqueuedAt: number;
  /** 원본 미션 ID — UI 표시용 */
  missionId: string | null;
  /** 사용자 ID */
  userId: string;
}

interface SyncRegistration extends ServiceWorkerRegistration {
  sync: {
    register: (tag: string) => Promise<void>;
  };
}

// ── DB 초기화 ─────────────────────────────────────────────────────────────────
const DB_NAME = 'carboany-queue';
const DB_VERSION = 1;
const STORE = 'queue';

let _db: IDBDatabase | null = null;

function openDb(): Promise<IDBDatabase> {
  if (_db) return Promise.resolve(_db);
  return new Promise((resolve, reject) => {
    const req = indexedDB.open(DB_NAME, DB_VERSION);
    req.onupgradeneeded = (e) => {
      const db = (e.target as IDBOpenDBRequest).result;
      if (!db.objectStoreNames.contains(STORE)) {
        db.createObjectStore(STORE, { keyPath: 'id', autoIncrement: true });
      }
    };
    req.onsuccess = (e) => {
      _db = (e.target as IDBOpenDBRequest).result;
      resolve(_db!);
    };
    req.onerror = () => reject(req.error);
  });
}

// ── Enqueue ───────────────────────────────────────────────────────────────────
export async function enqueueSubmission(item: Omit<QueueItem, 'id' | 'enqueuedAt'>): Promise<void> {
  const db = await openDb();
  const entry: Omit<QueueItem, 'id'> = { ...item, enqueuedAt: Date.now() };
  await new Promise<void>((res, rej) => {
    const tx = db.transaction(STORE, 'readwrite');
    const req = tx.objectStore(STORE).add(entry);
    req.onsuccess = () => res();
    req.onerror = () => rej(req.error);
  });

  // Background Sync 등록 (지원하는 브라우저)
  if ('serviceWorker' in navigator && 'SyncManager' in window) {
    const reg = await navigator.serviceWorker.ready;
    await (reg as SyncRegistration).sync.register('carboany-offline-queue').catch(() => {});
  }
}

// ── Flush (온라인 복귀 시 호출) ───────────────────────────────────────────────
export async function flushQueue(
  onSuccess?: (item: QueueItem) => void,
  onError?: (item: QueueItem, err: unknown) => void
): Promise<void> {
  const db = await openDb();
  const items = await getAllItems(db);
  if (items.length === 0) return;

  for (const item of items) {
    try {
      const res = await fetch(item.url, {
        method: item.method,
        headers: item.headers,
        body: item.body,
      });
      if (res.ok) {
        await deleteItem(db, item.id!);
        onSuccess?.(item);
      } else {
        onError?.(item, new Error(`HTTP ${res.status}`));
      }
    } catch (err) {
      onError?.(item, err);
    }
  }
}

// ── 큐 크기 조회 ──────────────────────────────────────────────────────────────
export async function getQueueSize(): Promise<number> {
  const db = await openDb();
  return new Promise((res, rej) => {
    const tx = db.transaction(STORE, 'readonly');
    const req = tx.objectStore(STORE).count();
    req.onsuccess = () => res(req.result);
    req.onerror = () => rej(req.error);
  });
}

// ── 내부 유틸 ─────────────────────────────────────────────────────────────────
function getAllItems(db: IDBDatabase): Promise<QueueItem[]> {
  return new Promise((res, rej) => {
    const tx = db.transaction(STORE, 'readonly');
    const req = tx.objectStore(STORE).getAll();
    req.onsuccess = () => res(req.result as QueueItem[]);
    req.onerror = () => rej(req.error);
  });
}

function deleteItem(db: IDBDatabase, id: number): Promise<void> {
  return new Promise((res, rej) => {
    const tx = db.transaction(STORE, 'readwrite');
    const req = tx.objectStore(STORE).delete(id);
    req.onsuccess = () => res();
    req.onerror = () => rej(req.error);
  });
}