import ecKeyUtils from "eckey-utils";
import { VapidKeys } from './VapidKeys.js';
import jwt from 'jsonwebtoken';
import crypto from 'crypto';
import DBService from './db.js';
import { fileURLToPath } from 'url';

const __filename = fileURLToPath(import.meta.url);

export interface VapidKeyData {
  publicKey: string;
  privateKey: string;
}

class VapidService {
  private static instance: VapidService;
  private dbService: DBService = DBService.getInstance();

  private constructor() {
  }


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


  public async createVAPIDKeys(): Promise<VapidKeys> {
    let result = new VapidKeys();
    if ( this.dbService.isReady ) {
      const keys = this.generateVAPIDKeys();
      await this.dbService.saveVapidKeys(keys['publicKey'], keys['privateKey']);

    } else {
      console.log(__filename, "Database is not ready.");

    }
    return result;
  }


  private generateVAPIDKeys(): VapidKeyData {
    const ecdh = crypto.createECDH('prime256v1');
    ecdh.generateKeys();
    const result = {
      publicKey: ecdh.getPublicKey().toString('base64'),
      privateKey: ecdh.getPrivateKey().toString('base64')
    };
    return result;
  }


  async getVapidKeys(): Promise<VapidKeys[]> {
    let result = await this.dbService.getVapidKeys();
    return result;
  }


  async createVapidAuthHeader(endpoint: string, expiration: number, subject: string, appKeys: VapidKeys): Promise<{ 'Authorization': string, 'Crypto-Key': string }> {
    const { publicKey, privateKey } = appKeys;

    const jwtInfo = {
      aud: new URL(endpoint).origin,
      exp: Math.floor((Date.now() / 1000) + expiration),
      sub: subject
    };
    const curveName = 'prime256v1';
    const ecdh = crypto.createECDH(curveName);
    const privateKeyBuffer = Buffer.from(privateKey, 'base64');
    ecdh.setPrivateKey(privateKeyBuffer);

    const pems = ecKeyUtils.generatePem({curveName, privateKey: ecdh.getPrivateKey(), publicKey: ecdh.getPublicKey() });
    
    const jwtToken = jwt.sign(jwtInfo, pems.privateKey, { algorithm: 'ES256' });

    return {
      'Authorization': `vapid t=${jwtToken}, k=${publicKey}`,
      'Crypto-Key': publicKey
    };
  }
}

(async ()=> {
  
})();

export default VapidService;