/*
 * user-db.js — IndexedDB storage for the user portal.
 *
 * Stores task data (including heavy base64 image dataUrls) in IndexedDB
 * instead of localStorage to avoid the ~5 MB browser quota.
 *
 * IndexedDB provides hundreds of MB of storage (browser-managed, quota-based)
 * which makes it suitable for image-heavy task data.
 *
 * Usage:
 *   import { openUserDB, loadTaskData, saveTaskData, getStorageEstimate } from './user-db.js';
 *
 *   await openUserDB();               // Call once on init
 *   const data = await loadTaskData(); // Returns the full taskData object
 *   await saveTaskData(data);          // Persist updated taskData
 *   const est = await getStorageEstimate(); // Get usage info
 */

/* ── Constants ──────────────────────────────────────────────────────────── */

const DB_NAME = 'user-portal-db';
const DB_VERSION = 1;
const STORE_TASK_DATA = 'taskData';

/* ── Module-level DB reference ──────────────────────────────────────────── */

let db = null;

/* ── Open / create database ─────────────────────────────────────────────── */

/**
 * Opens the IndexedDB database. Must be called once before any read/write.
 * Creates the object store on first run or version upgrade.
 */
export function openUserDB() {
  return new Promise((resolve, reject) => {
    const request = indexedDB.open(DB_NAME, DB_VERSION);

    request.onerror = () => reject(request.error);

    request.onsuccess = () => {
      db = request.result;
      resolve(db);
    };

    request.onupgradeneeded = () => {
      const database = request.result;
      /* Single store keyed by taskId — each entry holds one task's data */
      if (!database.objectStoreNames.contains(STORE_TASK_DATA)) {
        database.createObjectStore(STORE_TASK_DATA, { keyPath: 'taskId' });
      }
    };
  });
}

/* ── Read all task data ─────────────────────────────────────────────────── */

/**
 * Loads all task data from IndexedDB and returns it as a plain object
 * keyed by taskId (same shape as the old localStorage structure).
 *
 * @returns {Promise<Object>} e.g. { "task-123": { visitDate: "", records: {...} }, ... }
 */
export function loadTaskData() {
  return new Promise((resolve, reject) => {
    if (!db) { resolve({}); return; }
    const tx = db.transaction(STORE_TASK_DATA, 'readonly');
    const store = tx.objectStore(STORE_TASK_DATA);
    const request = store.getAll();

    request.onsuccess = () => {
      const result = {};
      for (const entry of request.result) {
        const { taskId, ...data } = entry;
        result[taskId] = data;
      }
      resolve(result);
    };
    request.onerror = () => reject(request.error);
  });
}

/* ── Save all task data ─────────────────────────────────────────────────── */

/**
 * Persists the full taskData object into IndexedDB.
 * Each taskId becomes a separate record in the store for efficient access.
 *
 * @param {Object} taskData - Object keyed by taskId
 * @returns {Promise<void>}
 */
export function saveTaskData(taskData) {
  return new Promise((resolve, reject) => {
    if (!db) { reject(new Error('Database not open')); return; }
    const tx = db.transaction(STORE_TASK_DATA, 'readwrite');
    const store = tx.objectStore(STORE_TASK_DATA);

    for (const [taskId, data] of Object.entries(taskData)) {
      store.put({ taskId, ...data });
    }

    tx.oncomplete = () => resolve();
    tx.onerror = () => reject(tx.error);
  });
}

/* ── Save single task entry ─────────────────────────────────────────────── */

/**
 * Saves or updates a single task's data. More efficient than saving everything
 * when only one task changed.
 *
 * @param {string} taskId
 * @param {Object} data - The task data (visitDate, records, etc.)
 * @returns {Promise<void>}
 */
export function saveOneTaskData(taskId, data) {
  return new Promise((resolve, reject) => {
    if (!db) { reject(new Error('Database not open')); return; }
    const tx = db.transaction(STORE_TASK_DATA, 'readwrite');
    const store = tx.objectStore(STORE_TASK_DATA);
    store.put({ taskId, ...data });

    tx.oncomplete = () => resolve();
    tx.onerror = () => reject(tx.error);
  });
}

/* ── Delete a task entry ────────────────────────────────────────────────── */

/**
 * Removes a single task's data from IndexedDB.
 *
 * @param {string} taskId
 * @returns {Promise<void>}
 */
export function deleteTaskData(taskId) {
  return new Promise((resolve, reject) => {
    if (!db) { reject(new Error('Database not open')); return; }
    const tx = db.transaction(STORE_TASK_DATA, 'readwrite');
    const store = tx.objectStore(STORE_TASK_DATA);
    store.delete(taskId);

    tx.oncomplete = () => resolve();
    tx.onerror = () => reject(tx.error);
  });
}

/* ── Storage estimate ───────────────────────────────────────────────────── */

/**
 * Returns an estimate of IndexedDB usage (if the StorageManager API is available).
 * Falls back to counting serialized task data size.
 *
 * @param {Object} taskData - Current in-memory taskData for fallback sizing
 * @returns {Promise<{usedMB: string, quotaMB: string, pct: number}>}
 */
export async function getStorageEstimate(taskData) {
  /* Try the modern Storage API (available in secure contexts) */
  if (navigator.storage && navigator.storage.estimate) {
    const est = await navigator.storage.estimate();
    const usedMB = ((est.usage || 0) / (1024 * 1024)).toFixed(2);
    const quotaMB = ((est.quota || 0) / (1024 * 1024)).toFixed(0);
    const pct = est.quota ? Math.min(100, ((est.usage / est.quota) * 100)) : 0;
    return { usedMB, quotaMB, pct: Math.round(pct) };
  }

  /* Fallback: estimate from serialized data */
  const json = JSON.stringify(taskData || {});
  const bytes = json.length * 2; /* UTF-16 */
  const usedMB = (bytes / (1024 * 1024)).toFixed(2);
  return { usedMB, quotaMB: '∞', pct: 0 };
}