import { Transporter, createTransport } from 'nodemailer';

type MailSettings = {
  smtpHostString: string;
  smtpPort: number;
  password: string;
  sender: string;
};

export class MailUtil {
  private transporter: Transporter;

  private settings: MailSettings;

  private static instance: MailUtil;

  static getInstance() {
    if (!MailUtil.instance) {
      MailUtil.instance = new MailUtil({
        smtpHostString: `${process.env.MAIL_SMTP_HOST}`,
        smtpPort: parseInt(`${process.env.MAIL_SMTP_PORT}`, 0),
        password: `${process.env.MAIL_AUTH_PASS}`,
        sender: `${process.env.MAIL_AUTH_USER}`
      });
    }
    return MailUtil.instance;
  }

  constructor(settings: MailSettings) {
    this.settings = settings;
    this.transporter = createTransport({
      host: this.settings.smtpHostString,
      port: this.settings.smtpPort,
      secure: true,
      auth: {
        user: this.settings.sender,
        pass: this.settings.password
      }
    });
  }

  async sendMail(options: {
    to: string;
    subject: string;
    text: string;
  }): Promise<void> {
    return new Promise<void>((resolve, reject: (error: Error) => void) => {
      this.transporter.sendMail(
        {
          from: this.settings.sender,
          to: options.to,
          subject: options.subject,
          text: options.text
        },
        error => {
          if (error) {
            reject(error);
          } else {
            resolve();
          }
        }
      );
    });
  }
}