CalendarDate.ts

export class CalendarDate {
  private readonly date: Date;

  constructor(date: Date) {
    this.date = new Date(date);
  }

  public static today(): CalendarDate {
    return new CalendarDate(new Date());
  }

  public static parseUTC(value: string): CalendarDate {
    return new CalendarDate(new Date(value));
  }

  public static create(year: number, month: number, day: number): CalendarDate {
    return new CalendarDate(new Date(year, month - 1, day));
  }
  /*
     Parses dd.MM.yyyy and dd.MM.yy format of dates
     @returns parsed date or null, when invalid format 
   */
  public static parseRussian(value: string): CalendarDate | null {
    const tokens = value.split('.');
    if (tokens.length === 3) {
      const day = parseInt(tokens[0], 10);
      const month = parseInt(tokens[1], 10);
      let year = parseInt(tokens[2], 10);
      if (year < 100) year += 2000;
      return new CalendarDate(new Date(year, month - 1, day));
    }
    return null;
  }

  public get year(): number {
    return this.date.getFullYear();
  }

  public get month(): number {
    return this.date.getMonth() + 1;
  }

  public get day(): number {
    return this.date.getDate();
  }

  public compare(other: CalendarDate): 'greater' | 'equal' | 'less' {
    if (this.year > other.year) return 'greater';
    if (this.year < other.year) return 'less';

    if (this.month > other.month) return 'greater';
    if (this.month < other.month) return 'less';

    if (this.day > other.day) return 'greater';
    if (this.day < other.day) return 'less';

    return 'equal';
  }

  public addYears(value: number): CalendarDate {
    const copy = new Date(this.year + value, this.month - 1, this.day);
    return new CalendarDate(copy);
  }

  public addMonths(value: number): CalendarDate {
    const copy = new Date(this.year, this.month - 1 + value, this.day);
    return new CalendarDate(copy);
  }

  public addDays(value: number): CalendarDate {
    const copy = new Date(this.year, this.month - 1, this.day + value);
    return new CalendarDate(copy);
  }

  public ge(other: CalendarDate): boolean {
    const comp = this.compare(other);
    return comp === 'greater' || comp === 'equal';
  }

  public le(other: CalendarDate): boolean {
    const comp = this.compare(other);
    return comp === 'less' || comp === 'equal';
  }

  public gt(other: CalendarDate): boolean {
    const comp = this.compare(other);
    return comp === 'greater';
  }

  public lt(other: CalendarDate): boolean {
    const comp = this.compare(other);
    return comp === 'less';
  }

  public equal(other: CalendarDate): boolean {
    const comp = this.compare(other);
    return comp === 'equal';
  }

  public toDate(): Date {
    return new Date(this.date);
  }

  /*
    Implementation of gregorian->JDN conversion
    <br>
    https://ru.wikipedia.org/wiki/Юлианская_дата#Вычисление_юлианской_даты_по_дате_календаря
    @return Julian Day Number of date
   */
  public getJDN(): number {
    const a = Math.floor((14 - this.month) / 12);
    const y = this.year + 4800 - a;
    const m = this.month + 12 * a - 3;
    return (
      this.day +
      Math.floor((153 * m + 2) / 5) +
      365 * y +
      Math.floor(y / 4) -
      Math.floor(y / 100) +
      Math.floor(y / 400) -
      32045
    );
  }

  public formatAsRussia(): string {
    return `${this.day.toString().padStart(2, '0')}.${this.month.toString().padStart(2, '0')}.${this.year}`;
  }

  public formatUTC(): string {
    return `${this.year}-${this.month.toString().padStart(2, '0')}-${this.day.toString().padStart(2, '0')}`;
  }
}