function removeTime(date: Date): Date {
  return new Date(date.setHours(0, 0, 0, 0));
}
export class FullDate {
  private _date: Date;

  constructor();
  constructor(copyFrom: FullDate);
  constructor(date: Date);
  constructor(s: string);
  constructor(n: number);
  constructor(y: number, m: number, d?: number);
  constructor(...argv: [any?, number?, number?]) {
    this._date = removeTime((() => {
      if (argv.length == 0) return new Date();
      if (argv.length == 1) {
        const arg = argv[0];
        if (arg instanceof FullDate) return new Date(+arg);
        if (arg instanceof Date) return arg;
        if (typeof arg === 'string') {
          const tokens = /^(\d+)-(\d+)-(\d+)$/g.exec(arg)?.slice(1, 4);
          if (tokens) return new Date(+tokens[0], +tokens[1]-1, +tokens[2]);
        }
        return new Date(arg);
      }
      return new Date(argv[0], (argv[1] ?? 1)-1, argv[2] ?? 1);
    })());
  }
  toString(): string {
    const d = this._date;
    const f = (s: any) => ('0'+s).slice(-2);
    return `${d.getFullYear()}-${
      f(d.getMonth()+1)}-${f(d.getDate())}`;
  }
  toJSON(): string {
    return this.toString();
  }
  valueOf(): number {
    return this._date.valueOf();
  }
  // getter
  get date(): Date {
    return new Date(this._date);
  }
  get year(): number {
    return this._date.getFullYear();
  }
  get month(): number {
    return this._date.getMonth()+1;
  }
  get day(): number {
    return this._date.getDate();
  }
  get dayOfWeek(): number {
    return this._date.getDay();
  }
  // setter
  set year(val: number) {
    this._date.setFullYear(val);
  }
  set month(val: number) {
    this._date.setMonth(val-1);
  }
  set day(val: number) {
    this._date.setDate(val);
  }
  // func
  advance(period: number): this {
    this._date = new Date(this._date.valueOf()+period*86400e3);
    return this;
  }
  advanced(period: number): FullDate {
    return new FullDate(this._date.valueOf()+period*86400e3);
  }
  distanceFrom(d0: FullDate): number {
    return (this.valueOf()-d0.valueOf())/86400e3;
  }
}