export class DateHelper {
  public static async adjustTimestampByTimezone(
    timestamp: number | null,
    timezone: number | null
  ): Promise<number | null> {
    if (!timestamp) {
      return null;
    }

    if (!timezone) {
      return null;
    }

    const minutes: number = timezone * -60;

    const milliseconds: number = minutes * 60000;

    return timestamp - milliseconds;
  }

  public static async getTimestampWithoutTimezone(
    year: number | null,
    month: number | null,
    date: number | null
  ): Promise<number | null> {
    if (!year) {
      return null;
    }

    if (month == null) {
      return null;
    }

    if (!date) {
      return null;
    }

    const timestamp: number = new Date(year, month, date).getTime();

    const timezone: number = (new Date().getTimezoneOffset() / 60) * -1;

    return await DateHelper.adjustTimestampByTimezone(timestamp, timezone);
  }

  public static async toDate(timestamp: number): Promise<number | null> {
    if (!timestamp) {
      return null;
    }

    return await DateHelper.getTimestampWithoutTimezone(
      new Date(timestamp).getUTCFullYear(),
      new Date(timestamp).getUTCMonth(),
      new Date(timestamp).getUTCDate()
    );
  }
}