const MONTH_REGEX = /^\d{4}-(0[1-9]|1[0-2])$/

export function getCurrentMonth(): string {
  const d = new Date()
  const offset = 8 * 60 * 60 * 1000
  const local = new Date(d.getTime() + offset)
  return local.toISOString().slice(0, 7)
}

export function getMonthRange(m: string): { startDate: string; endDate: string } | null {
  if (!MONTH_REGEX.test(m)) return null
  const [year, mon] = m.split('-').map(Number)
  const startDate = `${m}-01`
  const lastDay = new Date(year, mon, 0).getDate()
  const endDate = `${m}-${String(lastDay).padStart(2, '0')}`
  return { startDate, endDate }
}