/**
 * Shared date/time formatters for the message timeline.
 *
 * - `formatTime` — short clock time ("2:34 PM"), used in message rows.
 * - `formatFullDateTime` — verbose string for tooltips
 *   ("Wednesday, April 2, 2026 at 2:34 PM").
 * - `isSameDay` — compare two unix-second timestamps.
 *
 * Relative labels ("Today", "Yesterday", "June 20", "Yesterday at 9:05 AM") are
 * not here: chat and the Inbox share them from `shared/lib/datetime.ts`. What
 * stays in this file is the absolute end of the range — a bare clock time, the
 * verbose tooltip string, and same-day comparison.
 *
 * `formatTime` is for places with only enough room for a clock: the hover gutter
 * that replaces the avatar on continuation rows. A message header uses the
 * relative ladder instead, because the day divider that supplies its date
 * scrolls away while the messages under it stay on screen.
 */

const TIME_FORMATTER = new Intl.DateTimeFormat("en-US", {
  hour: "numeric",
  minute: "2-digit",
});

const DAY_PERIOD_SUFFIX_RE = /[\s\u00a0\u202f]*(?:AM|PM)$/i;

const FULL_DATE_TIME_FORMATTER = new Intl.DateTimeFormat("en-US", {
  weekday: "long",
  year: "numeric",
  month: "long",
  day: "numeric",
  hour: "numeric",
  minute: "2-digit",
});

const SHORT_MONTH_DAY_FORMATTER = new Intl.DateTimeFormat("en-US", {
  month: "short",
  day: "numeric",
});

/** Short clock time, e.g. "2:34 PM". */
export function formatTime(unixSeconds: number): string {
  return TIME_FORMATTER.format(new Date(unixSeconds * 1_000));
}

/** Short clock time with the AM/PM marker removed, e.g. "2:34". */
export function formatTimeWithoutDayPeriod(time: string): string {
  return time.replace(DAY_PERIOD_SUFFIX_RE, "").trim();
}

/** Full date + time for tooltips, e.g. "Wednesday, April 2, 2026 at 2:34 PM". */
export function formatFullDateTime(unixSeconds: number): string {
  return FULL_DATE_TIME_FORMATTER.format(new Date(unixSeconds * 1_000));
}

/** True when two unix-second timestamps fall on the same calendar day (local time). */
export function isSameDay(a: number, b: number): boolean {
  return isSameDayDate(new Date(a * 1_000), new Date(b * 1_000));
}

/**
 * Unix-seconds timestamp of local midnight for the calendar day containing
 * `unixSeconds`. Two timestamps on the same calendar day map to the same value,
 * so it is a stable identifier for a day group that does not shift when an
 * older message is prepended into that day.
 */
export function startOfLocalDaySeconds(unixSeconds: number): number {
  const date = new Date(unixSeconds * 1_000);
  date.setHours(0, 0, 0, 0);
  return Math.floor(date.getTime() / 1_000);
}

/** Short month + day, e.g. "May 19". No ordinal suffix, per the writing standard. */
export function formatShortMonthDay(unixSeconds: number): string {
  return SHORT_MONTH_DAY_FORMATTER.format(new Date(unixSeconds * 1_000));
}

/**
 * Relative thread-summary timestamp with expanded units, e.g. "3 hours ago",
 * falling back to "on May 19" for older replies.
 */
export function formatThreadSummaryLastReplyTime(
  unixSeconds: number,
  nowSeconds = Date.now() / 1_000,
): string {
  const diff = Math.max(0, nowSeconds - unixSeconds);

  if (diff < 60) return "just now";
  if (diff < 3_600) return formatAgo(Math.floor(diff / 60), "minute");
  if (diff < 86_400) return formatAgo(Math.floor(diff / 3_600), "hour");
  if (diff < 604_800) return formatAgo(Math.floor(diff / 86_400), "day");

  return `on ${formatShortMonthDay(unixSeconds)}`;
}

function isSameDayDate(a: Date, b: Date): boolean {
  return (
    a.getFullYear() === b.getFullYear() &&
    a.getMonth() === b.getMonth() &&
    a.getDate() === b.getDate()
  );
}

function formatAgo(value: number, unit: string): string {
  return `${value} ${unit}${value === 1 ? "" : "s"} ago`;
}