export function addDays(date: Date, days: number): Date {
  const result = new Date(date);
  result.setDate(result.getDate() + days);
  return result;
}

export function addMonths(date: Date, months: number): Date {
  const result = new Date(date);
  result.setMonth(result.getMonth() + months);
  return result;
}

export function addYears(date: Date, years: number): Date {
  const result = new Date(date);
  result.setFullYear(result.getFullYear() + years);
  return result;
}

export function isWeekend(date: Date): boolean {
  const day = date.getDay();
  return day === 0 || day === 6;
}

export function getFirstDayOfWeek(date: Date): Date {
  const result = new Date(date);
  const day = result.getDay();
  const diff = result.getDate() - day;
  result.setDate(diff);
  return result;
}

export function getWeekNumber(
  year: number,
  month: number,
  day: number
): number {
  const date = new Date(year, month, day);
  const firstDayOfYear = new Date(year, 0, 1);
  const pastDaysOfYear = (date.getTime() - firstDayOfYear.getTime()) / 86400000;
  return Math.ceil((pastDaysOfYear + firstDayOfYear.getDay() + 1) / 7);
}

export function isLeapYear(year: number): boolean {
  return (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;
}