import {isValidIso, parseDisplayToIso} from './dateFormat'

const DATETIME_RE = /^(\d{4}-\d{2}-\d{2})T(\d{2}):(\d{2}):(\d{2})$/

export function isValidIsoDateTime(s: string): boolean {
  const m = DATETIME_RE.exec(s)
  if (!m) return false
  const [, date, hh, mm, ss] = m
  if (!isValidIso(date)) return false
  const h = Number(hh)
  const min = Number(mm)
  const sec = Number(ss)
  return h >= 0 && h <= 23 && min >= 0 && min <= 59 && sec >= 0 && sec <= 59
}

export function formatIsoDateTimeToDisplay(s: string | null): string {
  if (!s || !isValidIsoDateTime(s)) return ''
  const [date, time] = s.split('T')
  const [y, mo, d] = date.split('-')
  const [hh, mm] = time.split(':')
  return `${d}/${mo}/${y} ${hh}:${mm}`
}

export function splitDateTime(s: string | null): {date: string | null; time: string} {
  if (!s || !isValidIsoDateTime(s)) return {date: null, time: ''}
  const [date, time] = s.split('T')
  return {date, time: time.slice(0, 5)}
}

export function parseDisplayToIsoDateTime(display: string): string | null {
  const match = /^(\d{2}\/\d{2}\/\d{4}) (\d{2}):(\d{2})$/.exec(display.trim())
  if (!match) return null
  const [, datePart, hh, mm] = match
  const iso = parseDisplayToIso(datePart)
  if (!iso) return null
  if (Number(hh) > 23 || Number(mm) > 59) return null
  return `${iso}T${hh}:${mm}:00`
}

export function composeDateTime(date: string, time: string): string {
  const t = time || '00:00'
  return `${date}T${t}:00`
}