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

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

type DateInput = Date | string | null | undefined;

const toDate = (value: DateInput) =>
  value ? (value instanceof Date ? value : new Date(value)) : null;

export function formatDate(value: DateInput, fallback = "—") {
  const date = toDate(value);
  return date ? dateFormatter.format(date) : fallback;
}

export function formatDateTime(value: DateInput, fallback = "—") {
  const date = toDate(value);
  return date ? dateTimeFormatter.format(date) : fallback;
}

const relativeFormatter = new Intl.RelativeTimeFormat("en", {
  numeric: "auto",
});

const RELATIVE_UNITS: [Intl.RelativeTimeFormatUnit, number][] = [
  ["year", 365 * 24 * 60 * 60],
  ["month", 30 * 24 * 60 * 60],
  ["week", 7 * 24 * 60 * 60],
  ["day", 24 * 60 * 60],
  ["hour", 60 * 60],
  ["minute", 60],
];

/** "3 minutes ago", "in 2 days", "just now". */
export function formatRelative(value: DateInput, now = Date.now()) {
  const date = toDate(value);
  if (!date) return "—";
  const seconds = Math.round((date.getTime() - now) / 1000);
  for (const [unit, size] of RELATIVE_UNITS) {
    if (Math.abs(seconds) >= size) {
      return relativeFormatter.format(Math.round(seconds / size), unit);
    }
  }
  return "just now";
}

export function formatBytes(bytes: number) {
  if (bytes < 1024) return `${bytes} B`;
  const units = ["KB", "MB", "GB"];
  let value = bytes / 1024;
  let unit = 0;
  while (value >= 1024 && unit < units.length - 1) {
    value /= 1024;
    unit++;
  }
  return `${value.toFixed(value < 10 ? 1 : 0)} ${units[unit]}`;
}

export function pluralize(
  count: number,
  singular: string,
  plural = `${singular}s`,
) {
  return `${count} ${count === 1 ? singular : plural}`;
}