const normalizeDate = (input) =>
  typeof input?.toDate === 'function' ? input.toDate() : new Date(input)

const buildMonthKey = (timestamp) => {
  const date = normalizeDate(timestamp)
  const year = date.getUTCFullYear()
  const month = String(date.getUTCMonth() + 1).padStart(2, '0')
  return `${year}-${month}`
}

const buildPreviousMonthContext = (referenceDate) => {
  const current = referenceDate ? new Date(referenceDate) : new Date()
  current.setUTCHours(0, 0, 0, 0)
  current.setUTCDate(1)

  const target = new Date(current)
  target.setUTCMonth(target.getUTCMonth() - 1)

  const year = target.getUTCFullYear()
  const monthIndex = target.getUTCMonth()
  const rangeStart = new Date(Date.UTC(year, monthIndex, 1, 0, 0, 0, 0))
  const rangeEnd = new Date(Date.UTC(year, monthIndex + 1, 0, 23, 59, 59, 999))
  const monthKey = buildMonthKey(rangeStart)

  return {
    year,
    month: monthIndex + 1,
    monthKey,
    rangeStart,
    rangeEnd,
  }
}

module.exports = {
  buildMonthKey,
  buildPreviousMonthContext,
}