import fp from 'lodash/fp'
import i18n from '../config/i18n' // TODO: Remove i18n dependency and allow user to define the text used as day names

/**
 * get the first day of the week containing given day
 *
 * @remarks This function assumes that the forst day of the week always is a monday
 *
 * @param date - Date which specifies the week
 * @returns the first date of the week
 */
export function getFirstDayOfWeek(date: Date): Date {
  const firstWeekday = new Date(date.getTime())
  firstWeekday.setDate(firstWeekday.getDate() - ((firstWeekday.getDay() + 6) % 7))
  return firstWeekday
}

/**
 * Generates all dates within a month, given a date within that month.
 *
 * @remarks
 * First date is the first monday, the first week of that month
 *
 * @param date - A date within the month
 */
export function* generateCalendar(date: Date): IterableIterator<Date> {
  const nrDays = 7 * 6 // 6 weeks
  let firstDay = new Date(date.getTime())
  firstDay.setDate(1) // Adjust to the first date of this month
  firstDay = getFirstDayOfWeek(firstDay)

  for (let day = 0; day < nrDays; day++) {
    const d = new Date(firstDay.getTime())
    d.setDate(d.getDate() + day)
    yield d
  }
}

export const rawDayNames = [
  i18n.t('common:calendar.monday'),
  i18n.t('common:calendar.tuesday'),
  i18n.t('common:calendar.wednesday'),
  i18n.t('common:calendar.thursday'),
  i18n.t('common:calendar.friday'),
  i18n.t('common:calendar.saturday'),
  i18n.t('common:calendar.sunday'),
]

export const months = [
  i18n.t('common:calendar.january'),
  i18n.t('common:calendar.february'),
  i18n.t('common:calendar.march'),
  i18n.t('common:calendar.april'),
  i18n.t('common:calendar.may'),
  i18n.t('common:calendar.june'),
  i18n.t('common:calendar.july'),
  i18n.t('common:calendar.august'),
  i18n.t('common:calendar.september'),
  i18n.t('common:calendar.october'),
  i18n.t('common:calendar.november'),
  i18n.t('common:calendar.december'),
]

export const getShorteningFn = (length: number): ((str: string) => string) => fp.flow(fp.take(length), fp.join(''))

export const getDayNames = (l?: number): string[] => (l ? rawDayNames.map(getShorteningFn(l)) : rawDayNames)

export const monthName = (d: Date, length?: number): string => {
  const m: string = months[d.getMonth()]
  return length ? getShorteningFn(length)(m) : m
}