import { EncryptionUtils } from '@repo/utils';
import type { IStorageService } from './storage.interface';
import { ENCRYPTED_KEYS } from './storage.key';

// ─── Types ──────────────────────────────────────────────────────

interface IndexedDBConfig {
  /** Database name. @default 'app_db' */
  dbName?: string;
  /** Object store name. @default 'kv_store' */
  storeName?: string;
  /** Database version. @default 1 */
  version?: number;
}

// ─── Helpers ────────────────────────────────────────────────────

/**
 * Open (or create) an IndexedDB database with a simple key-value store.
 * Returns a Promise that resolves with the IDBDatabase instance.
 */
function openDatabase(
  dbName: string,
  storeName: string,
  version: number,
): Promise<IDBDatabase> {
  return new Promise((resolve, reject) => {
    const request = indexedDB.open(dbName, version);

    request.onupgradeneeded = () => {
      const db = request.result;
      if (!db.objectStoreNames.contains(storeName)) {
        db.createObjectStore(storeName);
      }
    };

    request.onsuccess = () => resolve(request.result);
    request.onerror = () => reject(request.error);
  });
}

/**
 * Execute a single IndexedDB transaction and return the result.
 * Handles open → transaction → request → close lifecycle cleanly.
 */
function withTransaction<R>(
  db: IDBDatabase,
  storeName: string,
  mode: IDBTransactionMode,
  operation: (store: IDBObjectStore) => IDBRequest<R>,
): Promise<R> {
  return new Promise((resolve, reject) => {
    const tx = db.transaction(storeName, mode);
    const store = tx.objectStore(storeName);
    const request = operation(store);

    request.onsuccess = () => resolve(request.result);
    request.onerror = () => reject(request.error);
  });
}

// ─── Service ────────────────────────────────────────────────────

/**
 * Enterprise-grade IndexedDB wrapper with optional AES encryption.
 *
 * Uses a simple key-value object store pattern. Keys listed in
 * `ENCRYPTED_KEYS` are automatically encrypted/decrypted using
 * `@repo/utils` `EncryptionUtils`.
 *
 * Unlike localStorage, IndexedDB has no 5MB size limit — making
 * it suitable for large payloads like cached API responses, offline
 * data, or file blobs.
 *
 * @example
 * ```ts
 * const idb = new IndexedDBService({ dbName: 'my_app' });
 * await idb.setItem('large_dataset', hugePayload);
 * const data = await idb.getItem<HugePayload>('large_dataset');
 * ```
 */
export class IndexedDBService implements IStorageService {
  private readonly encryption: EncryptionUtils;
  private readonly dbName: string;
  private readonly storeName: string;
  private readonly version: number;
  private dbPromise: Promise<IDBDatabase> | null = null;

  constructor(config?: IndexedDBConfig, encryptionUtils?: EncryptionUtils) {
    this.encryption = encryptionUtils ?? EncryptionUtils.getInstance();
    this.dbName = config?.dbName ?? 'app_db';
    this.storeName = config?.storeName ?? 'kv_store';
    this.version = config?.version ?? 1;
  }

  /** Lazy-open the database connection (cached). */
  private getDB(): Promise<IDBDatabase> {
    if (!this.dbPromise) {
      this.dbPromise = openDatabase(this.dbName, this.storeName, this.version);
    }
    return this.dbPromise;
  }

  private shouldEncrypt(key: string): boolean {
    return ENCRYPTED_KEYS.has(key);
  }

  async setItem<T>(key: string, value: T): Promise<void> {
    const db = await this.getDB();
    const serialized = JSON.stringify(value);
    const payload = this.shouldEncrypt(key)
      ? this.encryption.encrypt(serialized)
      : serialized;

    await withTransaction(db, this.storeName, 'readwrite', (store) =>
      store.put(payload, key),
    );
  }

  async getItem<T>(key: string): Promise<T | null> {
    const db = await this.getDB();

    const raw = await withTransaction<string | undefined>(
      db,
      this.storeName,
      'readonly',
      (store) => store.get(key) as IDBRequest<string | undefined>,
    );

    if (raw === undefined || raw === null) return null;

    try {
      if (this.shouldEncrypt(key)) {
        const decrypted = this.encryption.decrypt(raw);
        if (!decrypted) return null;
        return JSON.parse(decrypted) as T;
      }
      return JSON.parse(raw) as T;
    } catch {
      console.warn(`[core-storage] Failed to parse IndexedDB key "${key}". Removing corrupt entry.`);
      await this.removeItem(key);
      return null;
    }
  }

  async removeItem(key: string): Promise<void> {
    const db = await this.getDB();
    await withTransaction(db, this.storeName, 'readwrite', (store) =>
      store.delete(key),
    );
  }

  async clear(): Promise<void> {
    const db = await this.getDB();
    await withTransaction(db, this.storeName, 'readwrite', (store) =>
      store.clear(),
    );
  }

  async hasItem(key: string): Promise<boolean> {
    const value = await this.getItem(key);
    return value !== null;
  }

  async keys(): Promise<string[]> {
    const db = await this.getDB();
    return withTransaction<string[]>(
      db,
      this.storeName,
      'readonly',
      (store) => store.getAllKeys() as IDBRequest<string[]>,
    );
  }
}