import * as crypto from 'crypto';
import { config } from '../config';

const ALGORITHM = 'aes-256-gcm';
const IV_LENGTH = 16;
const AUTH_TAG_LENGTH = 16;

/**
 * Derive a 32-byte key from the encryption key string.
 * Uses SHA-256 so any length passphrase works.
 */
function deriveKey(): Buffer {
  return crypto.createHash('sha256').update(config.credentialEncryptionKey).digest();
}

/**
 * Encrypt a plaintext password.
 * Returns base64 string: iv(16) + authTag(16) + ciphertext
 */
export function encryptPassword(plaintext: string): string {
  const key = deriveKey();
  const iv = crypto.randomBytes(IV_LENGTH);
  const cipher = crypto.createCipheriv(ALGORITHM, key, iv);

  const encrypted = Buffer.concat([
    cipher.update(plaintext, 'utf8'),
    cipher.final(),
  ]);

  const authTag = cipher.getAuthTag();

  // Format: iv + authTag + ciphertext
  const combined = Buffer.concat([iv, authTag, encrypted]);
  return combined.toString('base64');
}

/**
 * Decrypt an encrypted password string.
 * Input is base64 string: iv(16) + authTag(16) + ciphertext
 */
export function decryptPassword(encrypted: string): string {
  const key = deriveKey();
  const combined = Buffer.from(encrypted, 'base64');

  const iv = combined.subarray(0, IV_LENGTH);
  const authTag = combined.subarray(IV_LENGTH, IV_LENGTH + AUTH_TAG_LENGTH);
  const ciphertext = combined.subarray(IV_LENGTH + AUTH_TAG_LENGTH);

  const decipher = crypto.createDecipheriv(ALGORITHM, key, iv);
  decipher.setAuthTag(authTag);

  const decrypted = Buffer.concat([
    decipher.update(ciphertext),
    decipher.final(),
  ]);

  return decrypted.toString('utf8');
}

/**
 * Get the Turnitin password for an account.
 * If encryption key is set, tries to decrypt. Otherwise uses shared password.
 */
export function getAccountPassword(encryptedPassword?: string | null): string {
  if (encryptedPassword && config.credentialEncryptionKey) {
    try {
      return decryptPassword(encryptedPassword);
    } catch {
      // Fallback to shared password if decryption fails
    }
  }
  return config.turnitinSharedPassword;
}