const number = new Intl.NumberFormat("en-US");

/** 12.345 -> "12.345", 83.2 -> "1:23.200", 3723.5 -> "1:02:03.500". */
export function formatTime(seconds: number): string {
  const ms = Math.round(seconds * 1000);
  const h = Math.floor(ms / 3_600_000);
  const m = Math.floor((ms % 3_600_000) / 60_000);
  const s = Math.floor((ms % 60_000) / 1000);
  const rest = String(ms % 1000).padStart(3, "0");
  if (h > 0) return `${h}:${String(m).padStart(2, "0")}:${String(s).padStart(2, "0")}.${rest}`;
  if (m > 0) return `${m}:${String(s).padStart(2, "0")}.${rest}`;
  return `${s}.${rest}`;
}

/** Signed difference, e.g. "+1.204" or "−0.500". */
export function formatDelta(seconds: number): string {
  const sign = seconds < 0 ? "−" : "+";
  return sign + formatTime(Math.abs(seconds));
}

export function formatNumber(n: number): string {
  return number.format(n);
}

const rtf = new Intl.RelativeTimeFormat("en", { numeric: "auto" });
const UNITS: [Intl.RelativeTimeFormatUnit, number][] = [
  ["year", 31_536_000],
  ["month", 2_592_000],
  ["week", 604_800],
  ["day", 86_400],
  ["hour", 3_600],
  ["minute", 60],
];

/** Unix seconds -> "3 weeks ago". */
export function timeAgo(unixSeconds: number, now = Date.now() / 1000): string {
  // Never show "in 3 minutes" when a server clock is slightly ahead.
  const diff = Math.min(0, unixSeconds - now);
  for (const [unit, size] of UNITS) {
    if (Math.abs(diff) >= size) return rtf.format(Math.round(diff / size), unit);
  }
  return "just now";
}

/** Unix seconds -> "27 Sep 2026, 14:03:09" in the viewer's own time zone. */
export function formatDate(unixSeconds: number): string {
  return new Date(unixSeconds * 1000).toLocaleString("en-GB", {
    day: "numeric",
    month: "short",
    year: "numeric",
    hour: "2-digit",
    minute: "2-digit",
    second: "2-digit",
    hour12: false,
  });
}

export function serverLabel(tag: string): string {
  return tag.toUpperCase();
}

/** Which bonus band a position is in, for the label next to the multiplier. */
export function bonusLabel(position: number, completions: number): string | null {
  if (completions < 100) return null;
  const x = (position - 1) / completions;
  if (x < 0.01) return "Top 1%";
  if (x < 0.05) return "Top 5%";
  return null;
}

/** How many players on a board get points (half from 200 completions on). */
export function pointedCount(completions: number): number {
  return completions < 200 ? completions : Math.floor(completions / 2);
}