export function getMonthDays(year: number, month: number) {
  const firstDay = new Date(year, month, 1);
  const lastDay = new Date(year, month + 1, 0);

  // Start from the Monday before or on the first day
  const startDate = new Date(firstDay);
  const dayOfWeek = startDate.getDay();
  const diff = dayOfWeek === 0 ? 6 : dayOfWeek - 1; // Monday = 0
  startDate.setDate(startDate.getDate() - diff);

  // Generate 6 weeks (42 days) to always fill the grid
  const days: Date[] = [];
  const current = new Date(startDate);
  for (let i = 0; i < 42; i++) {
    days.push(new Date(current));
    current.setDate(current.getDate() + 1);
  }

  return { days, firstDay, lastDay };
}

export function getWeekDays(date: Date) {
  const startOfWeek = new Date(date);
  const day = startOfWeek.getDay();
  const diff = day === 0 ? 6 : day - 1; // Monday start
  startOfWeek.setDate(startOfWeek.getDate() - diff);
  startOfWeek.setHours(0, 0, 0, 0);

  const days: Date[] = [];
  for (let i = 0; i < 7; i++) {
    const d = new Date(startOfWeek);
    d.setDate(d.getDate() + i);
    days.push(d);
  }
  return days;
}

export function isSameDay(a: Date, b: Date) {
  return (
    a.getFullYear() === b.getFullYear() &&
    a.getMonth() === b.getMonth() &&
    a.getDate() === b.getDate()
  );
}

export function isToday(date: Date) {
  return isSameDay(date, new Date());
}

export function getMonthRange(year: number, month: number) {
  const { days } = getMonthDays(year, month);
  return {
    start: days[0],
    end: new Date(days[days.length - 1].getTime() + 86400000 - 1),
  };
}

export function getWeekRange(date: Date) {
  const days = getWeekDays(date);
  return {
    start: days[0],
    end: new Date(days[6].getTime() + 86400000 - 1),
  };
}

export function formatMonthYear(date: Date) {
  return new Intl.DateTimeFormat("en-US", {
    month: "long",
    year: "numeric",
  }).format(date);
}

export function formatWeekdayShort(date: Date) {
  return new Intl.DateTimeFormat("en-US", { weekday: "short" }).format(date);
}

export function formatHour(hour: number) {
  if (hour === 0) return "12 AM";
  if (hour < 12) return `${hour} AM`;
  if (hour === 12) return "12 PM";
  return `${hour - 12} PM`;
}