import { Injectable } from '@angular/core';
import { TokenResponse } from '@core/typings/token.typing';
import { environment } from '@environment';

@Injectable({ providedIn: 'root' })
export class TokenAdapterService {
  private isLocalhost = environment.isLocalhost;
  // time difference (in ms), between the browser clock and the server clock
  // a negative diff means the server is ahead, a positive means the browser is ahead
  private diff = 0;
  // takes the date returned from the API (when the api sent the response)
  // and determines the difference between the date from the server and the date of the user's computer
  private async offsetTime (
    expirationDate: Date
  ) {
    await this.ensureDiffIsSet();

    return new Date(expirationDate.getTime() + this.diff).toISOString();
  }

  private async ensureDiffIsSet () {
    if (!this.diff) {
      const serverTimeRaw = this.isLocalhost ?
        '' :
        await this.getServerTime();
      if (serverTimeRaw) {
        const browserDate = new Date();
        const apiDate = new Date(serverTimeRaw);
        this.diff = browserDate.getTime() - apiDate.getTime();
      }
    }
  }

  private getServerTime () {
    const xmlHttp = this.getXHR();
    xmlHttp.open('HEAD', location.href.toString());
    xmlHttp.setRequestHeader('Content-Type', 'text/html');
    xmlHttp.send('');

    return new Promise<string>((res, rej) => {
      xmlHttp.addEventListener('load', () => {
        res(xmlHttp.getResponseHeader('Date'));
      });

      xmlHttp.addEventListener('error', () => {
        res('');
      });
    });
  }

  private getXHR () {
    return new XMLHttpRequest();
  }

  async handleTokenRequest<T extends TokenResponse> (
    body: T
  ): Promise<T> {
    const expirationDate = new Date(body.expiration);
    const refreshExpiration = new Date(body.refreshTokenExpiration);

    body.expiration = await this.offsetTime(expirationDate);
    body.refreshTokenExpiration = await this.offsetTime(refreshExpiration);

    return body;
  }
}