const pad = (n: number) => String(n).padStart(2, '0');

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

export function formatChatTime(timestampSec: number): string {
  const date = new Date(timestampSec * 1000);
  const now = new Date();
  const time = `${pad(date.getHours())}:${pad(date.getMinutes())}`;

  if (sameDay(date, now)) {
    return time;
  }

  const yesterday = new Date(now);
  yesterday.setDate(yesterday.getDate() - 1);
  if (sameDay(date, yesterday)) {
    return `昨天 ${time}`;
  }

  if (date.getFullYear() === now.getFullYear()) {
    return `${date.getMonth() + 1}月${date.getDate()}日 ${time}`;
  }

  return `${date.getFullYear()}年${date.getMonth() + 1}月${date.getDate()}日 ${time}`;
}

export function shouldShowTimestamp(currentSec: number, previousSec?: number): boolean {
  if (previousSec === undefined) return true;
  return currentSec - previousSec > 5 * 60;
}