/**
 * Locale-aware date/time formatting helpers.
 *
 * Built on top of next-intl's format API, which wraps Intl.DateTimeFormat /
 * Intl.RelativeTimeFormat using the active request locale. These helpers add
 * three things on top of raw next-intl:
 *
 *   1. Tolerant input — accepts string | Date | null | undefined and returns
 *      a stable em-dash for missing values, so call sites don't need to
 *      conditionally render.
 *   2. Two presets used everywhere in the portal (`dateTime`, `dateOnly`)
 *      so the four locales render consistently. German/French/Italian use
 *      24h DD.MM.YYYY HH:mm; English uses 12h MMM D, YYYY h:mm a.
 *   3. A `relative` helper that auto-picks the right unit (minute/hour/day/
 *      week/month) based on the elapsed delta.
 *
 * Usage in client components:
 *
 *   import { useFormatter } from "next-intl";
 *   import { formatDateTime, formatRelative } from "@/lib/format";
 *
 *   const f = useFormatter();
 *   <span>{formatDateTime(req.createdAt, f)}</span>
 *   <span title={formatDateTime(req.createdAt, f)}>
 *     {formatRelative(req.createdAt, f)}
 *   </span>
 *
 * Usage in server components:
 *
 *   import { getFormatter } from "next-intl/server";
 *   const f = await getFormatter();
 *   ...same calls...
 */

// next-intl's `useFormatter()` (client) and `getFormatter()` (server) return
// the same shape. We derive the type from useFormatter's return so we stay
// in sync with next-intl version bumps without hand-maintaining a mirror.
import type { useFormatter } from "next-intl";
type Formatter = ReturnType<typeof useFormatter>;

const FALLBACK = "—";

function toDate(value: string | Date | null | undefined): Date | null {
  if (!value) return null;
  if (value instanceof Date) return Number.isNaN(value.getTime()) ? null : value;
  const d = new Date(value);
  return Number.isNaN(d.getTime()) ? null : d;
}

/**
 * Full date+time, locale-formatted. Returns "—" if the value is missing.
 *
 *   de: 25.04.2026, 14:30
 *   en: Apr 25, 2026, 2:30 PM
 *   fr: 25 avr. 2026, 14:30
 *   it: 25 apr 2026, 14:30
 */
export function formatDateTime(
  value: string | Date | null | undefined,
  formatter: Formatter
): string {
  const d = toDate(value);
  if (!d) return FALLBACK;
  return formatter.dateTime(d, {
    year: "numeric",
    month: "short",
    day: "numeric",
    hour: "2-digit",
    minute: "2-digit",
  });
}

/**
 * Date only, locale-formatted. Use in dense table cells.
 */
export function formatDateOnly(
  value: string | Date | null | undefined,
  formatter: Formatter
): string {
  const d = toDate(value);
  if (!d) return FALLBACK;
  return formatter.dateTime(d, {
    year: "numeric",
    month: "short",
    day: "numeric",
  });
}

/**
 * Relative time ("2 hours ago", "vor 2 Stunden", etc.).
 * Picks the unit automatically based on the magnitude of the delta.
 * Returns "—" if the value is missing.
 *
 * Anchors against `now` (defaults to current time) so SSR and client
 * render the same string when called within a single request.
 */
export function formatRelative(
  value: string | Date | null | undefined,
  formatter: Formatter,
  now: Date = new Date()
): string {
  const d = toDate(value);
  if (!d) return FALLBACK;

  const diffMs = d.getTime() - now.getTime();
  const absSeconds = Math.abs(diffMs) / 1000;

  let unit: Intl.RelativeTimeFormatUnit;
  if (absSeconds < 60) unit = "second";
  else if (absSeconds < 3_600) unit = "minute";
  else if (absSeconds < 86_400) unit = "hour";
  else if (absSeconds < 604_800) unit = "day";
  else if (absSeconds < 2_592_000) unit = "week";
  else if (absSeconds < 31_536_000) unit = "month";
  else unit = "year";

  return formatter.relativeTime(d, { now, unit });
}