import { AES, enc } from 'crypto-js';
import { ENC_STORAGE_KEY } from './encryption-key';

/**
 * Interface defining encryption service methods.
 */
interface IEncryptionUtils {
  encrypt(data: string): string;
  decrypt(encryptedData: string): string;
}

export class EncryptionUtils implements IEncryptionUtils {
  private readonly _key: string;

  /**
   * @param key - Encryption key used for encrypting and decrypting data.
   * If not provided, defaults to ENC_STORAGE_KEY.
   */
  constructor(key: string = ENC_STORAGE_KEY) {
    if (!key) {
      throw new Error('[EncryptionUtils] Encryption key is missing/empty.');
    }
    this._key = key;
  }

  /**
   * Encrypts the given data string.
   * Returns an empty string '' if input data is empty.
   */
  public encrypt(data: string): string {
    if (!data) {
      return '';
    }
    return AES.encrypt(data, this._key).toString();
  }

  /**
   * Decrypts the given encrypted data string.
   * Returns an empty string '' if input is empty or decryption fails.
   */
  public decrypt(encryptedData: string): string {
    if (!encryptedData) {
      return '';
    }

    try {
      const bytes = AES.decrypt(encryptedData, this._key);
      const originalText = bytes.toString(enc.Utf8);

      // If decryption yields an empty string, consider it a failure
      if (!originalText) {
        return '';
      }

      return originalText;
    } catch (error) {
      console.error('[EncryptionUtils] Decryption failed:', error);
      return '';
    }
  }

  /**
   * Get the singleton instance of EncryptionUtils.
   * Uses the default ENC_STORAGE_KEY.
   * @return EncryptionUtils instance
   */

  private static instance: EncryptionUtils;

  public static getInstance(): EncryptionUtils {
    if (!EncryptionUtils.instance) {
      EncryptionUtils.instance = new EncryptionUtils();
    }
    return EncryptionUtils.instance;
  }
}