import { ethTimeLabel, toAmharicDisplay } from './ethiopic';

/** Wire values carrying no time of day, e.g. a date column serialised as `2026-08-10`. */
const DATE_ONLY = /^\d{4}-\d{2}-\d{2}$/;

/** Midnight UTC — how backends commonly serialise a plain date column. */
const UTC_MIDNIGHT = /T00:00:00(\.0+)?Z$/;

/**
 * The one way a date is shown to a user.
 *
 * Timestamps render in the viewer's local timezone — `2026-08-10T06:57:34.507Z`
 * reads as `Aug 10, 2026 9:57am` in Addis. Values with no real time of day
 * render as a bare date: a birth date or a licence expiry stamped `12:00am`
 * reads as precision the data does not have. Those are also formatted in UTC,
 * because parsing `2026-08-10` yields UTC midnight, and converting that to a
 * behind-UTC local timezone would show the previous day.
 *
 * `language` is a parameter rather than read from i18next because each app runs
 * a DEDICATED i18n instance, not the global singleton (see `app/i18n/config.ts`)
 * — the same reason `localized()` in licensing.helpers.ts takes one. Components
 * should not call this directly; use `useDateDisplayer()` so the text actually
 * re-renders when the language changes.
 */
export function dateDisplayer(
  value: string | number | Date | null | undefined,
  language = 'en',
): string {
  if (value === null || value === undefined || value === '') return '—';

  const date = new Date(value);
  if (Number.isNaN(date.getTime())) return '—';

  const dateOnly =
    typeof value === 'string' && (DATE_ONLY.test(value) || UTC_MIDNIGHT.test(value));

  if (language.startsWith('am')) {
    const day = toAmharicDisplay(date); // ሐምሌ 22/2018
    return dateOnly ? day : `${day} - ${ethTimeLabel(date)}`;
  }

  const day = date.toLocaleDateString('en-US', {
    month: 'short',
    day: 'numeric',
    year: 'numeric',
    ...(dateOnly ? { timeZone: 'UTC' } : {}),
  });
  if (dateOnly) return day;

  // Intl gives "9:57 AM"; the house format is "9:57am".
  const time = date
    .toLocaleTimeString('en-US', { hour: 'numeric', minute: '2-digit' })
    .replace(' ', '')
    .toLowerCase();

  return `${day} ${time}`;
}