// IndexedDB 存储封装
const DB = (function () {
  const DB_NAME = 'calendar_reminder';
  const DB_VERSION = 2; // 升级版本以创建 outbox 队列
  const STORE_EVENTS = 'events';
  const STORE_OUTBOX = 'outbox';

  let _db;

  function openDB() {
    return new Promise((resolve, reject) => {
      const req = indexedDB.open(DB_NAME, DB_VERSION);
      req.onupgradeneeded = (ev) => {
        const db = ev.target.result;
        // 事件存储
        if (!db.objectStoreNames.contains(STORE_EVENTS)) {
          const store = db.createObjectStore(STORE_EVENTS, { keyPath: 'id' });
          store.createIndex('by_start', 'start');
          store.createIndex('by_updated', 'updatedAt');
        }
        // 离线 outbox 队列
        if (!db.objectStoreNames.contains(STORE_OUTBOX)) {
          db.createObjectStore(STORE_OUTBOX, { keyPath: 'id' });
        }
      };
      req.onsuccess = () => {
        _db = req.result;
        resolve(_db);
      };
      req.onerror = () => reject(req.error);
    });
  }

  function tx(storeName, mode = 'readonly') {
    const t = _db.transaction(storeName, mode);
    return t.objectStore(storeName);
  }

  async function initDB() {
    if (_db) return _db;
    return await openDB();
  }

  function addEvent(ev) {
    return new Promise((resolve, reject) => {
      const store = tx(STORE_EVENTS, 'readwrite');
      const req = store.add(ev);
      req.onsuccess = () => resolve(ev);
      req.onerror = () => reject(req.error);
    });
  }

  function updateEvent(ev) {
    return new Promise((resolve, reject) => {
      const store = tx(STORE_EVENTS, 'readwrite');
      const req = store.put(ev);
      req.onsuccess = () => resolve(ev);
      req.onerror = () => reject(req.error);
    });
  }

  function deleteEvent(id) {
    return new Promise((resolve, reject) => {
      const store = tx(STORE_EVENTS, 'readwrite');
      const req = store.delete(id);
      req.onsuccess = () => resolve();
      req.onerror = () => reject(req.error);
    });
  }

  function getEvent(id) {
    return new Promise((resolve, reject) => {
      const store = tx(STORE_EVENTS, 'readonly');
      const req = store.get(id);
      req.onsuccess = () => resolve(req.result);
      req.onerror = () => reject(req.error);
    });
  }

  function listEventsByMonth(year, month) {
    // month: 1..12
    const start = new Date(Date.UTC(year, month - 1, 1, 0, 0, 0));
    const end = new Date(Date.UTC(year, month, 0, 23, 59, 59));
    return new Promise((resolve, reject) => {
      const store = tx(STORE_EVENTS, 'readonly');
      const idx = store.index('by_start');
      const range = IDBKeyRange.bound(start.toISOString(), end.toISOString());
      const result = [];
      const req = idx.openCursor(range);
      req.onsuccess = (e) => {
        const cursor = e.target.result;
        if (cursor) {
          result.push(cursor.value);
          cursor.continue();
        } else {
          resolve(result);
        }
      };
      req.onerror = () => reject(req.error);
    });
  }

  // --- Outbox 队列 ---
  function genId() { return Date.now() + '-' + Math.random().toString(36).slice(2); }

  function addOutbox(entry) {
    return new Promise((resolve, reject) => {
      const store = tx(STORE_OUTBOX, 'readwrite');
      const req = store.add(entry);
      req.onsuccess = () => resolve(entry);
      req.onerror = () => reject(req.error);
    });
  }

  function addOutboxUpsert(ev) {
    const entry = { id: genId(), type: 'upsert', payload: ev, timestamp: new Date().toISOString() };
    return addOutbox(entry);
  }

  function addOutboxDelete(id) {
    const entry = { id: genId(), type: 'delete', payload: { id }, timestamp: new Date().toISOString() };
    return addOutbox(entry);
  }

  function listOutbox() {
    return new Promise((resolve, reject) => {
      const store = tx(STORE_OUTBOX, 'readonly');
      const result = [];
      const req = store.openCursor();
      req.onsuccess = (e) => {
        const cursor = e.target.result;
        if (cursor) { result.push(cursor.value); cursor.continue(); }
        else { resolve(result); }
      };
      req.onerror = () => reject(req.error);
    });
  }

  function removeOutbox(id) {
    return new Promise((resolve, reject) => {
      const store = tx(STORE_OUTBOX, 'readwrite');
      const req = store.delete(id);
      req.onsuccess = () => resolve();
      req.onerror = () => reject(req.error);
    });
  }

  return {
    initDB,
    addEvent,
    updateEvent,
    deleteEvent,
    getEvent,
    listEventsByMonth,
    // outbox
    addOutboxUpsert,
    addOutboxDelete,
    listOutbox,
    removeOutbox,
  };
})();

window.DB = DB;