// Lightweight relative-time formatter for the native package.
//
// Mirrors the wording the builder web app produces via formatRelativeTime
// ("5 minutes ago", "2 hours ago") so the home screen reads identically,
// without depending on Intl.RelativeTimeFormat — which is not reliably
// available across the JS engines the native app ships on.

const DIVISIONS: Array<{ amount: number; unit: string }> = [
  { amount: 60, unit: 'minute' },
  { amount: 24, unit: 'hour' },
  { amount: 7, unit: 'day' },
  { amount: 4.34524, unit: 'week' },
  { amount: 12, unit: 'month' },
  { amount: Number.POSITIVE_INFINITY, unit: 'year' },
];

/** "just now" / "5 minutes ago" / "2 hours ago" / "3 days ago" — or '' if unparseable. */
export function formatRelativeTime(input?: string | number | null): string {
  const ms = toMs(input);
  if (ms == null) return '';

  const seconds = (Date.now() - ms) / 1000;
  if (seconds < 45) return 'just now';

  let duration = seconds / 60; // start in minutes
  for (const division of DIVISIONS) {
    if (Math.abs(duration) < division.amount) {
      const value = Math.round(duration);
      return `${value} ${division.unit}${value === 1 ? '' : 's'} ago`;
    }
    duration /= division.amount;
  }
  return '';
}

const WEEKDAYS = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];
export const DAY_MS = 86_400_000;

/**
 * Chat-app style timestamp, like a messaging inbox:
 *   today      -> "9:41 AM"
 *   yesterday  -> "Yesterday"
 *   this week  -> "Mon"
 *   older      -> "3/14/26"
 */
export function formatChatTimestamp(input?: string | number | null): string {
  const ms = toMs(input);
  if (ms == null) return '';

  const date = new Date(ms);
  const now = new Date();
  const startOfToday = new Date(now.getFullYear(), now.getMonth(), now.getDate()).getTime();

  if (ms >= startOfToday) {
    let hours = date.getHours();
    const minutes = date.getMinutes();
    const meridiem = hours >= 12 ? 'PM' : 'AM';
    hours %= 12;
    if (hours === 0) hours = 12;
    return `${hours}:${String(minutes).padStart(2, '0')} ${meridiem}`;
  }
  if (ms >= startOfToday - DAY_MS) return 'Yesterday';
  if (ms >= startOfToday - 6 * DAY_MS) return WEEKDAYS[date.getDay()];

  const year = String(date.getFullYear()).slice(-2);
  return `${date.getMonth() + 1}/${date.getDate()}/${year}`;
}

function toMs(input?: string | number | null): number | null {
  if (input == null) return null;
  if (typeof input === 'number') return Number.isFinite(input) ? input : null;

  // Match the builder's parseUTCDate: treat tz-less datetimes as UTC.
  const str = String(input).trim();
  if (!str) return null;
  const hasTimezone = /([zZ]|[+-]\d{2}:?\d{2})$/.test(str);
  const isDateOnly = /^\d{4}-\d{2}-\d{2}$/.test(str);
  const normalized = hasTimezone ? str : str + (isDateOnly ? 'T00:00:00Z' : 'Z');
  const ms = Date.parse(normalized);
  return Number.isNaN(ms) ? null : ms;
}