/* ============================================================================
   LOCALE-AWARE FORMATTING
   ----------------------------------------------------------------------------
   Thin `Intl` wrappers so a route never hard-codes a date pattern. Arabic uses
   ar-LY with the `latn` numbering system: the approved draft copy writes
   Arabic dates and figures in Western digits ("30 يونيو", "2025"), so Eastern
   Arabic numerals would contradict the source content.
   ========================================================================= */

import { INTL_LOCALE, type Locale } from "./config";

const NUMBERING_SYSTEM = "latn";

/** The BCP-47 tag (with numbering system) handed to `Intl`. */
export function intlLocale(locale: Locale): string {
  return `${INTL_LOCALE[locale]}-u-nu-${NUMBERING_SYSTEM}`;
}

function toDate(value: Date | string | number): Date | null {
  const date = value instanceof Date ? value : new Date(value);
  return Number.isNaN(date.getTime()) ? null : date;
}

export type DateStyle = "full" | "long" | "medium" | "short";

/** "12 March 2026" / "12 مارس 2026". Returns "" for an unparseable input. */
export function formatDate(
  value: Date | string | number | null | undefined,
  locale: Locale,
  options: Intl.DateTimeFormatOptions = { dateStyle: "long" },
): string {
  if (value === null || value === undefined) return "";
  const date = toDate(value);
  if (!date) return "";

  return new Intl.DateTimeFormat(intlLocale(locale), options).format(date);
}

/** Date plus time of day, for an event card or an event detail page. */
export function formatDateTime(
  value: Date | string | number | null | undefined,
  locale: Locale,
  options: Intl.DateTimeFormatOptions = {
    dateStyle: "long",
    timeStyle: "short",
  },
): string {
  return formatDate(value, locale, options);
}

/** "12–14 March 2026". Falls back to a single date when `end` is missing. */
export function formatDateRange(
  start: Date | string | number,
  end: Date | string | number | null | undefined,
  locale: Locale,
  options: Intl.DateTimeFormatOptions = { dateStyle: "long" },
): string {
  const from = toDate(start);
  if (!from) return "";

  const to = end === null || end === undefined ? null : toDate(end);
  if (!to || from.getTime() === to.getTime()) {
    return formatDate(from, locale, options);
  }

  return new Intl.DateTimeFormat(intlLocale(locale), options).formatRange(
    from,
    to,
  );
}

/** The machine-readable value for `<time dateTime>` - always ISO, never localised. */
export function toIsoDate(
  value: Date | string | number | null | undefined,
): string | undefined {
  if (value === null || value === undefined) return undefined;
  return toDate(value)?.toISOString();
}

export function formatNumber(
  value: number,
  locale: Locale,
  options?: Intl.NumberFormatOptions,
): string {
  return new Intl.NumberFormat(intlLocale(locale), options).format(value);
}

/** "1.2 MB" - used by the resources list for a download's file size. */
export function formatFileSize(bytes: number, locale: Locale): string {
  const units = ["B", "KB", "MB", "GB"] as const;
  let size = Math.max(0, bytes);
  let unit = 0;

  while (size >= 1024 && unit < units.length - 1) {
    size /= 1024;
    unit += 1;
  }

  const formatted = formatNumber(size, locale, {
    maximumFractionDigits: unit === 0 ? 0 : 1,
  });
  return `${formatted} ${units[unit]}`;
}