import { addDays, format, isAfter, isSameDay, isSameMonth, startOfDay, startOfISOWeek, subDays } from 'date-fns'
import type { WeekDateRange } from './types'

const capitalizeFirstLetter = (value: string): string => {
  if (!value) return value
  return value.charAt(0).toUpperCase() + value.slice(1)
}

export const getOverlappingMonths = (week: Date, locale = 'sv-SE'): string => {
  const startDayMonth = startOfISOWeek(week)
  const endDayMonth = addDays(startDayMonth, 6)
  const shortMonthFormatter = new Intl.DateTimeFormat(locale, { month: 'short' })
  const longMonthFormatter = new Intl.DateTimeFormat(locale, { month: 'long' })

  if (!isSameMonth(startDayMonth, endDayMonth)) {
    return `${capitalizeFirstLetter(shortMonthFormatter.format(startDayMonth).replace('.', ''))} - ${capitalizeFirstLetter(
      shortMonthFormatter.format(endDayMonth).replace('.', ''),
    )}`
  }

  return capitalizeFirstLetter(longMonthFormatter.format(startOfISOWeek(week)))
}

export const getDaysInWeek = (weekStart: Date): Date[] => {
  const startOfWeek = startOfISOWeek(weekStart)
  const day = subDays(startOfWeek, 1)
  const calendar: Date[] = []

  for (let index = 0; index < 7; index++) {
    calendar.push(addDays(day, index + 1))
  }

  return calendar
}

export const getDaysOfLastWeek = (week: Date): Date[] => getDaysInWeek(week)

export const getStartAndEndRangeFromWeek = (week: Date[]): Partial<WeekDateRange> => {
  const lastDay = week.at(-1)
  const firstDay = week.at(0)

  return {
    endDate: lastDay ? format(lastDay, 'yyyy-MM-dd') : undefined,
    startDate: firstDay ? format(firstDay, 'yyyy-MM-dd') : undefined,
  }
}

export const checkIfDateIsBeforeToday = (date: Date): boolean => {
  const startOfDate = startOfDay(date)
  const startOfToday = startOfDay(new Date())
  return isAfter(startOfToday, startOfDate)
}

export const checkIfDateIsEnabled = (date: Date, enabledDates: Date[]): boolean =>
  enabledDates.some((enabledDate) => isSameDay(enabledDate, date))