const DB_NAME = 'SpanishDiary';
const DB_VERSION = 1;
const STORE_NAME = 'entries';

let db = null;

function openDb() {
  return new Promise((resolve, reject) => {
    if (db) { resolve(db); return; }
    const req = indexedDB.open(DB_NAME, DB_VERSION);
    req.onupgradeneeded = (e) => {
      const d = e.target.result;
      if (!d.objectStoreNames.contains(STORE_NAME)) {
        const store = d.createObjectStore(STORE_NAME, { keyPath: 'id' });
        store.createIndex('date', 'date', { unique: false });
      }
    };
    req.onsuccess = (e) => { db = e.target.result; resolve(db); };
    req.onerror = (e) => reject(e.target.error);
  });
}

function getAllEntries() {
  return openDb().then(db => {
    return new Promise((resolve, reject) => {
      const tx = db.transaction(STORE_NAME, 'readonly');
      const store = tx.objectStore(STORE_NAME);
      const index = store.index('date');
      const req = index.openCursor(null, 'prev');
      const results = [];
      req.onsuccess = (e) => {
        const cursor = e.target.result;
        if (cursor) { results.push(cursor.value); cursor.continue(); }
        else resolve(results);
      };
      req.onerror = (e) => reject(e.target.error);
    });
  });
}

function getEntry(id) {
  return openDb().then(db => {
    return new Promise((resolve, reject) => {
      const tx = db.transaction(STORE_NAME, 'readonly');
      const store = tx.objectStore(STORE_NAME);
      const req = store.get(id);
      req.onsuccess = () => resolve(req.result || null);
      req.onerror = (e) => reject(e.target.error);
    });
  });
}

function addEntry(entry) {
  return openDb().then(db => {
    return new Promise((resolve, reject) => {
      const tx = db.transaction(STORE_NAME, 'readwrite');
      const store = tx.objectStore(STORE_NAME);
      const req = store.add(entry);
      req.onsuccess = () => resolve(entry);
      req.onerror = (e) => reject(e.target.error);
    });
  });
}

function updateEntry(entry) {
  return openDb().then(db => {
    return new Promise((resolve, reject) => {
      const tx = db.transaction(STORE_NAME, 'readwrite');
      const store = tx.objectStore(STORE_NAME);
      const req = store.put(entry);
      req.onsuccess = () => resolve(entry);
      req.onerror = (e) => reject(e.target.error);
    });
  });
}

function deleteEntry(id) {
  return openDb().then(db => {
    return new Promise((resolve, reject) => {
      const tx = db.transaction(STORE_NAME, 'readwrite');
      const store = tx.objectStore(STORE_NAME);
      const req = store.delete(id);
      req.onsuccess = () => resolve();
      req.onerror = (e) => reject(e.target.error);
    });
  });
}