// Helpers for Persian (Shamsi) dates and relative time labels used across the site.

const PERSIAN_DIGITS = ['۰', '۱', '۲', '۳', '۴', '۵', '۶', '۷', '۸', '۹'];

/** Convert any latin digits in a string (or a number) to Persian digits. */
export const toPersianDigits = (value: string | number): string =>
  String(value).replace(/\d/g, (digit) => PERSIAN_DIGITS[Number(digit)] ?? digit);

type DatedPost = { publishedAt?: string; slug: string; time: string };

/**
 * Resolve the publish timestamp of a post.
 *
 * Posts created by the TASS agent embed `Date.now()` at the end of their slug,
 * so we can recover a real timestamp even for older posts that only stored the
 * placeholder string "هم‌اکنون".
 */
export const getPublishedAt = (post: DatedPost): Date | null => {
  if (post.publishedAt) {
    const date = new Date(post.publishedAt);
    return Number.isNaN(date.getTime()) ? null : date;
  }

  const match = post.slug.match(/(\d{13})$/);
  if (match) {
    const date = new Date(Number(match[1]));
    return Number.isNaN(date.getTime()) ? null : date;
  }

  return null;
};

/** Derive an ISO timestamp for a post, or null when none can be inferred. */
export const derivePublishedAt = (post: DatedPost): string | undefined => {
  const date = getPublishedAt(post);
  return date ? date.toISOString() : undefined;
};

/** Exact Shamsi date + time, e.g. "۱۴ تیر ۱۴۰۵، ۱۴:۳۰". */
export const formatShamsiDate = (date: Date): string => {
  const formatter = new Intl.DateTimeFormat('fa-IR-u-ca-persian', {
    year: 'numeric',
    month: 'long',
    day: 'numeric',
    hour: '2-digit',
    minute: '2-digit',
  });

  return toPersianDigits(formatter.format(date));
};

/** Short Shamsi date without time, e.g. "۱۴ تیر ۱۴۰۵". */
export const formatShamsiDay = (date: Date): string => {
  const formatter = new Intl.DateTimeFormat('fa-IR-u-ca-persian', {
    year: 'numeric',
    month: 'long',
    day: 'numeric',
  });

  return toPersianDigits(formatter.format(date));
};

/**
 * Relative Persian time label: "هم‌اکنون", "۲ دقیقه پیش", "۱۰ دقیقه پیش",
 * "۳ ساعت پیش", "۵ روز پیش" — and falls back to an exact Shamsi date for
 * anything older than a month.
 */
export const formatRelativeTime = (date: Date): string => {
  const now = Date.now();
  const diffSeconds = Math.max(0, Math.round((now - date.getTime()) / 1000));

  if (diffSeconds < 60) {
    return 'هم‌اکنون';
  }

  const diffMinutes = Math.floor(diffSeconds / 60);

  if (diffMinutes < 60) {
    return `${toPersianDigits(diffMinutes)} دقیقه پیش`;
  }

  const diffHours = Math.floor(diffMinutes / 60);

  if (diffHours < 24) {
    return `${toPersianDigits(diffHours)} ساعت پیش`;
  }

  const diffDays = Math.floor(diffHours / 24);

  if (diffDays < 30) {
    return `${toPersianDigits(diffDays)} روز پیش`;
  }

  return formatShamsiDay(date);
};

/** Relative label for a post, falling back to its stored `time` string. */
export const formatPostRelativeTime = (post: DatedPost): string => {
  const date = getPublishedAt(post);
  return date ? formatRelativeTime(date) : post.time;
};

/** Exact Shamsi label for a post, falling back to its stored `time` string. */
export const formatPostShamsiDate = (post: DatedPost): string => {
  const date = getPublishedAt(post);
  return date ? formatShamsiDate(date) : post.time;
};