/** Avance une date d’un mois, en gardant le jour du mois (ou le dernier jour si besoin). */
export function addUtcMonths(date: Date, months: number): Date {
  const year = date.getUTCFullYear()
  const month = date.getUTCMonth() + months
  const day = date.getUTCDate()
  const lastDay = new Date(Date.UTC(year, month + 1, 0)).getUTCDate()
  return new Date(Date.UTC(
    year,
    month,
    Math.min(day, lastDay),
    date.getUTCHours(),
    date.getUTCMinutes(),
    date.getUTCSeconds(),
    date.getUTCMilliseconds(),
  ))
}

/**
 * Recalcule la période en cours à partir de la date d’origine.
 * Sans fiche de paiement, les dates étaient écrites une fois (souvent +1 an) et ne bougeaient plus.
 */
export function rollBillingPeriod(
  periodStart: Date,
  now: Date = new Date(),
): { currentPeriodStart: Date; currentPeriodEnd: Date } {
  if (Number.isNaN(periodStart.getTime())) {
    const start = new Date(now)
    return { currentPeriodStart: start, currentPeriodEnd: addUtcMonths(start, 1) }
  }

  let start = new Date(periodStart)
  let end = addUtcMonths(start, 1)

  if (start.getTime() > now.getTime()) {
    return { currentPeriodStart: start, currentPeriodEnd: end }
  }

  let guard = 0
  while (end.getTime() <= now.getTime() && guard < 240) {
    start = end
    end = addUtcMonths(start, 1)
    guard += 1
  }

  return { currentPeriodStart: start, currentPeriodEnd: end }
}

export function periodsDiffer(
  a: { currentPeriodStart: Date; currentPeriodEnd: Date },
  b: { currentPeriodStart: Date; currentPeriodEnd: Date },
): boolean {
  return (
    a.currentPeriodStart.getTime() !== b.currentPeriodStart.getTime()
    || a.currentPeriodEnd.getTime() !== b.currentPeriodEnd.getTime()
  )
}