/** Formatting helpers. All numerals are rendered in mono/tabular; all timestamps go through formatTime(). */

export type TimeMode = 'utc' | 'local';

const nf = (digits: number) => new Intl.NumberFormat('en-US', { minimumFractionDigits: digits, maximumFractionDigits: digits });
const NF0 = nf(0);
const NF1 = nf(1);
const NF2 = nf(2);

export function fmt(v: number | null | undefined, digits = 1): string {
  if (v == null || Number.isNaN(v)) return '—';
  return digits === 0 ? NF0.format(v) : digits === 2 ? NF2.format(v) : digits === 1 ? NF1.format(v) : nf(digits).format(v);
}
export const fmtInt = (v: number | null | undefined) => fmt(v, 0);

/** Signed delta with a true minus sign: +6.3 / −2.1 / 0.0 */
export function fmtDelta(v: number | null | undefined, digits = 1): string {
  if (v == null || Number.isNaN(v)) return '—';
  const s = fmt(Math.abs(v), digits);
  if (v > 0) return `+${s}`;
  if (v < 0) return `−${s}`;
  return s;
}

export function fmtPct(ratio: number | null | undefined, digits = 0): string {
  if (ratio == null || Number.isNaN(ratio)) return '—';
  return `${fmt(ratio * 100, digits)} %`;
}

export function fmtMs(v: number | null | undefined, digits = 0): string {
  if (v == null || Number.isNaN(v)) return '—';
  return `${fmt(v, digits)} ms`;
}

export function fmtBytes(b: number | null | undefined): string {
  if (b == null) return '—';
  const u = ['B', 'KB', 'MB', 'GB', 'TB'];
  let i = 0;
  let v = b;
  while (v >= 1024 && i < u.length - 1) {
    v /= 1024;
    i++;
  }
  return `${fmt(v, i === 0 ? 0 : 1)} ${u[i]}`;
}

export function fmtRatio(v: number | null | undefined): string {
  if (v == null || Number.isNaN(v)) return '—';
  return `${fmt(v, v >= 10 ? 0 : 1)}×`;
}

export function fmtDuration(seconds: number | null | undefined): string {
  if (seconds == null || Number.isNaN(seconds)) return '—';
  const s = Math.max(0, Math.round(seconds));
  if (s < 60) return `${s} s`;
  const m = Math.floor(s / 60);
  if (m < 60) return `${m} min`;
  const h = Math.floor(m / 60);
  const rm = m % 60;
  if (h < 48) return rm ? `${h} h ${rm} min` : `${h} h`;
  const d = Math.floor(h / 24);
  return `${d} d ${h % 24} h`;
}

/** "3 s ago", "2 min ago", "4 h ago" — relative to `nowMs`. */
export function fmtAgo(ts: string | number | Date | null | undefined, nowMs = Date.now()): string {
  if (!ts) return '—';
  const t = typeof ts === 'number' ? ts : new Date(ts).getTime();
  if (Number.isNaN(t)) return '—';
  const s = Math.max(0, Math.round((nowMs - t) / 1000));
  if (s < 60) return `${s} s ago`;
  const m = Math.floor(s / 60);
  if (m < 60) return `${m} min ago`;
  const h = Math.floor(m / 60);
  if (h < 48) return `${h} h ago`;
  return `${Math.floor(h / 24)} d ago`;
}

export type TimeStyle = 'time' | 'short' | 'full' | 'date' | 'month';

/** Single time formatter. UTC is the default (spec §67: UTC storage, local display with a toggle). */
export function formatTime(ts: string | number | Date | null | undefined, mode: TimeMode = 'utc', style: TimeStyle = 'short'): string {
  if (!ts) return '—';
  const d = ts instanceof Date ? ts : new Date(ts);
  if (Number.isNaN(d.getTime())) return '—';
  const tz = mode === 'utc' ? 'UTC' : undefined;
  const opts: Intl.DateTimeFormatOptions =
    style === 'time'
      ? { hour: '2-digit', minute: '2-digit', second: '2-digit', hour12: false, timeZone: tz }
      : style === 'date'
        ? { year: 'numeric', month: 'short', day: '2-digit', timeZone: tz }
        : style === 'month'
          ? { year: 'numeric', month: 'long', timeZone: tz }
          : style === 'full'
            ? { year: 'numeric', month: 'short', day: '2-digit', hour: '2-digit', minute: '2-digit', second: '2-digit', hour12: false, timeZone: tz, timeZoneName: 'short' }
            : { month: 'short', day: '2-digit', hour: '2-digit', minute: '2-digit', hour12: false, timeZone: tz };
  let out = new Intl.DateTimeFormat('en-GB', opts).format(d);
  if (mode === 'utc' && (style === 'short' || style === 'time')) out += ' UTC';
  return out;
}

export function isoDate(ts: string | Date): string {
  return (ts instanceof Date ? ts : new Date(ts)).toISOString().slice(0, 10);
}

export const MONTH_NAMES = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];