export interface DateTimeBound {
  date: string
  hour: string
  minute: string
}

export const emptyDateTimeBound = (): DateTimeBound => ({
  date: '',
  hour: '00',
  minute: '00',
})

export function boundToIso(bound: DateTimeBound): string | undefined {
  if (!bound.date) return undefined
  const local = new Date(
    `${bound.date}T${bound.hour.padStart(2, '0')}:${bound.minute.padStart(2, '0')}:00`
  )
  if (Number.isNaN(local.getTime())) return undefined
  return local.toISOString()
}

export function formatBoundLabel(bound: DateTimeBound): string {
  if (!bound.date) return 'Datum wählen'
  return `${formatDateDe(bound.date)} ${bound.hour.padStart(2, '0')}:${bound.minute.padStart(2, '0')}`
}

export function formatDateDe(isoDate: string): string {
  const [y, m, d] = isoDate.split('-').map(Number)
  if (!y || !m || !d) return isoDate
  return new Date(y, m - 1, d).toLocaleDateString('de-DE', {
    day: '2-digit',
    month: '2-digit',
    year: 'numeric',
  })
}

export function pad2(n: number): string {
  return String(n).padStart(2, '0')
}

export const HOURS = Array.from({ length: 24 }, (_, i) => pad2(i))
export const MINUTES = Array.from({ length: 60 }, (_, i) => pad2(i))

const WEEKDAYS = ['Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa', 'So']
const MONTHS = [
  'Januar', 'Februar', 'März', 'April', 'Mai', 'Juni',
  'Juli', 'August', 'September', 'Oktober', 'November', 'Dezember',
]

export function getWeekdayLabels(): string[] {
  return WEEKDAYS
}

export function getMonthLabel(monthIndex: number): string {
  return MONTHS[monthIndex] ?? ''
}

/** Kalendertage inkl. Auffüllung für Mo-start Grid */
export function getCalendarDays(year: number, month: number) {
  const first = new Date(year, month, 1)
  const last = new Date(year, month + 1, 0)
  let startPad = first.getDay() - 1
  if (startPad < 0) startPad = 6

  const days: { date: string; day: number; currentMonth: boolean }[] = []

  for (let i = startPad - 1; i >= 0; i--) {
    const d = new Date(year, month, -i)
    days.push({
      date: toIsoDate(d),
      day: d.getDate(),
      currentMonth: false,
    })
  }

  for (let d = 1; d <= last.getDate(); d++) {
    days.push({
      date: toIsoDate(new Date(year, month, d)),
      day: d,
      currentMonth: true,
    })
  }

  const totalCells = Math.ceil((startPad + last.getDate()) / 7) * 7
  let nextDay = 1
  while (days.length < totalCells) {
    const d = new Date(year, month + 1, nextDay++)
    days.push({
      date: toIsoDate(d),
      day: d.getDate(),
      currentMonth: false,
    })
  }

  return days
}

export function toIsoDate(d: Date): string {
  return `${d.getFullYear()}-${pad2(d.getMonth() + 1)}-${pad2(d.getDate())}`
}

export function isBoundActive(bound: DateTimeBound): boolean {
  return Boolean(bound.date)
}