export function getWeekViewEventOffset(
    { event, startOfWeek, excluded = [] }: { event: CalendarEvent, startOfWeek: Date, excluded?: number[] }): number {
    if (event.start < startOfWeek) {
        return 0;
    }
    const distance: number = dateFns.differenceInDays(event.start, startOfWeek);
    return distance - getExcludedDays({ startDate: startOfWeek, days: distance, excluded });
}

export function getMonthView({
  events = [],
  viewDate,
  weekStartsOn,
  excluded = [],
}: {
  events?: CalendarEvent[];
  viewDate: Date;
  weekStartsOn: number;
  excluded?: number[];
}): MonthView {
  if (!events) {
    events = [];
  }

  const start: Date = dateFns.startOfWeek(dateFns.startOfMonth(viewDate), { weekStartsOn });
  const end: Date = dateFns.endOfWeek(dateFns.endOfMonth(viewDate), { weekStartsOn });
  const eventsInMonth: CalendarEvent[] = getEventsInPeriod({
    events,
    periodStart: start,
    periodEnd: end,
  });
  const days: MonthViewDay[] = [];
  for (let i: number = 0; i < dateFns.differenceInDays(end, start) + 1; i++) {
    const date: Date = dateFns.addDays(start, i);
    if (!excluded.some((e) => date.getDay() === e)) {
      const day: MonthViewDay = getWeekDay({ date }) as MonthViewDay;
      const calEvents: CalendarEvent[] = getEventsInPeriod({
        events: eventsInMonth,
        periodStart: dateFns.startOfDay(date),
        periodEnd: dateFns.endOfDay(date),
      });
      day.inMonth = dateFns.isSameMonth(date, viewDate);
      day.events = calEvents;
      day.badgeTotal = calEvents.length;
      days.push(day);
    }
  }

  const totalDaysVisibleInWeek: number = DAYS_IN_WEEK - excluded.length;
  const rows: number = Math.floor(days.length / totalDaysVisibleInWeek);
  const rowOffsets: number[] = [];
  for (let i: number = 0; i < rows; i++) {
    rowOffsets.push(i * totalDaysVisibleInWeek);
  }

  return {
    rowOffsets,
    totalDaysVisibleInWeek,
    days,
  };
}

function getWeekViewEventSpan(
    { event, offset, startOfWeek, excluded }: { event: CalendarEvent, offset: number, startOfWeek: Date, excluded: number[] }): number {
    const begin: Date = event.start < startOfWeek ? startOfWeek : event.start;
    let span: number = 1;
    if (event.end) {
        span = dateFns.differenceInDays(dateFns.addMinutes(dateFns.endOfDay(event.end), 1), dateFns.startOfDay(begin));
    }
    const totalLength: number = offset + span;
    if (totalLength > DAYS_IN_WEEK) {
        span = DAYS_IN_WEEK - offset;
    }
    return span - getExcludedDays({ startDate: begin, days: span, excluded });
}

export function differenceInDays(dateLeft: Date, dateRight: Date): number {
  return _differenceInDays(dateLeft, dateRight);
}