const MINUTE_MS = 60_000;
const HOUR_MS = 60 * MINUTE_MS;
const DAY_MS = 24 * HOUR_MS;
const MONTH_MS = 30 * DAY_MS;
const YEAR_MS = 365 * DAY_MS;

export function formatShortRelativeTime(timestamp: number, now: number): string {
  const elapsed = Math.max(0, now - timestamp);

  if (elapsed < MINUTE_MS) return 'just now';
  if (elapsed < HOUR_MS) return `${Math.floor(elapsed / MINUTE_MS)}m ago`;
  if (elapsed < DAY_MS) return `${Math.floor(elapsed / HOUR_MS)}h ago`;
  if (elapsed < MONTH_MS) return `${Math.floor(elapsed / DAY_MS)}d ago`;
  if (elapsed < YEAR_MS) return `${Math.floor(elapsed / MONTH_MS)}mo ago`;
  return `${Math.floor(elapsed / YEAR_MS)}y ago`;
}

export function formatExactTime(timestamp: number): string {
  return new Intl.DateTimeFormat(undefined, { dateStyle: 'medium', timeStyle: 'short' }).format(timestamp);
}

/** Time of day only. Paired with a day divider so history is not full of dates. */
export function formatTimeOfDay(timestamp: number): string {
  return new Intl.DateTimeFormat(undefined, { timeStyle: 'short' }).format(timestamp);
}

export function isSameDay(left: number, right: number): boolean {
  const a = new Date(left);
  const b = new Date(right);
  return a.getFullYear() === b.getFullYear()
    && a.getMonth() === b.getMonth()
    && a.getDate() === b.getDate();
}

/** "Today" / "Yesterday" / an explicit date, for message-history day dividers. */
export function formatDayLabel(timestamp: number, now: number): string {
  if (isSameDay(timestamp, now)) return 'Today';
  if (isSameDay(timestamp, now - DAY_MS)) return 'Yesterday';
  return new Intl.DateTimeFormat(undefined, { dateStyle: 'full' }).format(timestamp);
}

export const STALE_REPLY_THRESHOLD_MS = 12 * HOUR_MS;
export const CRITICAL_REPLY_THRESHOLD_MS = 48 * HOUR_MS;

export type ConversationAge = 'fresh' | 'stale' | 'critical';

/**
 * How overdue an unanswered conversation is. Only meaningful for conversations
 * waiting on us — "3d ago" on a conversation we already replied to is fine, but
 * on one awaiting a reply it is the thing the operator most needs to notice.
 */
export function conversationAge(timestamp: number, now: number): ConversationAge {
  const elapsed = Math.max(0, now - timestamp);
  if (elapsed >= CRITICAL_REPLY_THRESHOLD_MS) return 'critical';
  if (elapsed >= STALE_REPLY_THRESHOLD_MS) return 'stale';
  return 'fresh';
}