export class IndexedDBService {
  private db: IDBDatabase | null = null;
  private readonly DB_NAME = 'NGRX Storage';
  private readonly STORE_NAME = 'keyvaluepairs';

  async init(): Promise<void> {
    if (this.db) {
        return;
    }

    return new Promise((resolve, reject) => {
      const request = indexedDB.open(this.DB_NAME, 3);

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

      request.onupgradeneeded = (event) => {
        const db = (event.target as IDBOpenDBRequest).result;
        if (!db.objectStoreNames.contains(this.STORE_NAME)) {
          db.createObjectStore(this.STORE_NAME);
        }
      };
    });
  }

  async getItem(key: string): Promise<any> {
    await this.init();
    return new Promise((resolve, reject) => {
      if (!this.db) {
        reject(new Error('Database not initialized'));
        return;
      }

      const transaction = this.db.transaction(this.STORE_NAME, 'readonly');
      const store = transaction.objectStore(this.STORE_NAME);
      const request = store.get(key);

      request.onerror = () => reject(request.error);
      request.onsuccess = () => {
        try {
          const value = request.result;
          resolve(value ? JSON.parse(value) : null);
        } catch {
          resolve(request.result);
        }
      };
    });
  }

  async setItem(key: string, value: any): Promise<void> {
    await this.init();
    return new Promise((resolve, reject) => {
      if (!this.db) {
        reject(new Error('Database not initialized'));
        return;
      }

      const transaction = this.db.transaction(this.STORE_NAME, 'readwrite');
      const store = transaction.objectStore(this.STORE_NAME);
      const serialized = typeof value === 'string' ? value : JSON.stringify(value);
      const request = store.put(serialized, key);

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

  async removeItem(key: string): Promise<void> {
    await this.init();
    return new Promise((resolve, reject) => {
      if (!this.db) {
        reject(new Error('Database not initialized'));
        return;
      }

      const transaction = this.db.transaction(this.STORE_NAME, 'readwrite');
      const store = transaction.objectStore(this.STORE_NAME);
      const request = store.delete(key);

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

  async keys(): Promise<string[]> {
    await this.init();
    return new Promise((resolve, reject) => {
      if (!this.db) {
        reject(new Error('Database not initialized'));
        return;
      }

      const transaction = this.db.transaction(this.STORE_NAME, 'readonly');
      const store = transaction.objectStore(this.STORE_NAME);
      const request = store.getAllKeys();

      request.onerror = () => reject(request.error);
      request.onsuccess = () => resolve(Array.from(request.result as string[]));
    });
  }
}