seahaven-ap/src/dashboard/invoice-date-format.ts

function startOfLocalDay(date: Date): Date {
  return new Date(date.getFullYear(), date.getMonth(), date.getDate());
}

function formatUnit(count: number, unit: "day" | "month" | "year", future: boolean): string {
  const noun = count === 1 ? unit : `${unit}s`;
  return future ? `in ${count} ${noun}` : `${count} ${noun} ago`;
}

export function formatSlashDate(value: string | null | undefined): string {
  if (!value) {
    return "—";
  }
  const parsed = new Date(`${value.slice(0, 10)}T00:00:00`);
  if (Number.isNaN(parsed.getTime())) {
    return value;
  }
  return new Intl.DateTimeFormat("en-US", {
    year: "numeric",
    month: "2-digit",
    day: "2-digit",
  }).format(parsed);
}

export function formatRelativeFromIsoDate(
  value: string | null | undefined,
  now: Date = new Date(),
): string {
  if (!value) {
    return "";
  }
  const parsed = new Date(`${value.slice(0, 10)}T00:00:00`);
  if (Number.isNaN(parsed.getTime())) {
    return "";
  }

  const dayMs = 24 * 60 * 60 * 1000;
  const days = Math.round(
    (startOfLocalDay(now).getTime() - startOfLocalDay(parsed).getTime()) / dayMs,
  );
  if (days === 0) {
    return "today";
  }

  const future = days < 0;
  const absDays = Math.abs(days);
  if (absDays < 30) {
    return formatUnit(absDays, "day", future);
  }
  const months = Math.floor(absDays / 30);
  if (months < 12) {
    return formatUnit(months, "month", future);
  }
  const years = Math.floor(months / 12);
  return formatUnit(years, "year", future);
}