const THOUSAND = 1000;
const MILLION = 1_000_000;
const MINUTE_MS = 60_000;
const HOUR_MS = 3_600_000;
const DAY_MS = 86_400_000;
const KB = 1024;
const WHITESPACE = /\s+/g;

export function fmtTokens(n: number | null | undefined): string {
  if (n === null || n === undefined) {
    return "–";
  }
  if (n >= MILLION) {
    return `${(n / MILLION).toFixed(n >= 10 * MILLION ? 0 : 1)}M`;
  }
  if (n >= THOUSAND) {
    return `${(n / THOUSAND).toFixed(n >= 10 * THOUSAND ? 0 : 1)}k`;
  }
  return String(n);
}

export function fmtMoney(usd: number | null | undefined): string {
  if (usd === null || usd === undefined) {
    return "–";
  }
  if (usd === 0) {
    return "$0";
  }
  if (usd < 0.01) {
    return `$${usd.toFixed(4)}`;
  }
  if (usd < 1) {
    return `$${usd.toFixed(3)}`;
  }
  return `$${usd.toFixed(2)}`;
}

export function fmtPct(fraction: number | null | undefined): string {
  if (fraction === null || fraction === undefined) {
    return "–";
  }
  return `${Math.round(fraction * 100)}%`;
}

export function fmtDuration(ms: number | null | undefined): string {
  if (ms === null || ms === undefined) {
    return "–";
  }
  if (ms < THOUSAND) {
    return `${Math.round(ms)}ms`;
  }
  if (ms < MINUTE_MS) {
    return `${(ms / THOUSAND).toFixed(1)}s`;
  }
  if (ms < HOUR_MS) {
    const minutes = Math.floor(ms / MINUTE_MS);
    const seconds = Math.round((ms % MINUTE_MS) / THOUSAND);
    return `${minutes}m${String(seconds).padStart(2, "0")}s`;
  }
  const hours = Math.floor(ms / HOUR_MS);
  const minutes = Math.round((ms % HOUR_MS) / MINUTE_MS);
  return `${hours}h${String(minutes).padStart(2, "0")}m`;
}

export function fmtSeconds(seconds: number | null | undefined): string {
  return seconds === null || seconds === undefined
    ? "–"
    : fmtDuration(seconds * THOUSAND);
}

export function fmtBytes(bytes: number | null | undefined): string {
  if (bytes === null || bytes === undefined) {
    return "–";
  }
  if (bytes >= KB * KB * KB) {
    return `${(bytes / (KB * KB * KB)).toFixed(2)} GB`;
  }
  if (bytes >= KB * KB) {
    return `${(bytes / (KB * KB)).toFixed(0)} MB`;
  }
  if (bytes >= KB) {
    return `${(bytes / KB).toFixed(0)} kB`;
  }
  return `${bytes} B`;
}

export function parseDate(iso: string | null | undefined): Date | null {
  if (!iso) {
    return null;
  }
  const date = new Date(iso);
  return Number.isNaN(date.getTime()) ? null : date;
}

export function fmtTime(iso: string | null | undefined): string {
  const date = parseDate(iso);
  return date
    ? date.toLocaleTimeString(undefined, {
        hour: "2-digit",
        minute: "2-digit",
        second: "2-digit",
      })
    : "–";
}

export function fmtDateTime(iso: string | null | undefined): string {
  const date = parseDate(iso);
  return date
    ? date.toLocaleString(undefined, {
        day: "numeric",
        hour: "2-digit",
        minute: "2-digit",
        month: "short",
      })
    : "–";
}

export function fmtRelative(
  iso: string | null | undefined,
  now = Date.now()
): string {
  const date = parseDate(iso);
  if (!date) {
    return "–";
  }
  const diff = now - date.getTime();
  const abs = Math.abs(diff);
  const suffix = diff >= 0 ? "ago" : "from now";
  if (abs < MINUTE_MS) {
    return diff >= 0 ? "just now" : "in <1m";
  }
  if (abs < HOUR_MS) {
    return `${Math.round(abs / MINUTE_MS)}m ${suffix}`;
  }
  if (abs < DAY_MS) {
    return `${Math.round(abs / HOUR_MS)}h ${suffix}`;
  }
  return `${Math.round(abs / DAY_MS)}d ${suffix}`;
}

export function fmtCountdown(iso: string | null | undefined, now = Date.now()) {
  const date = parseDate(iso);
  if (!date) {
    return "–";
  }
  const left = date.getTime() - now;
  if (left <= 0) {
    return "resets now";
  }
  if (left < HOUR_MS) {
    return `resets in ${Math.ceil(left / MINUTE_MS)}m`;
  }
  if (left < DAY_MS) {
    const hours = Math.floor(left / HOUR_MS);
    const minutes = Math.round((left % HOUR_MS) / MINUTE_MS);
    return `resets in ${hours}h ${String(minutes).padStart(2, "0")}m`;
  }
  const days = Math.floor(left / DAY_MS);
  const hours = Math.round((left % DAY_MS) / HOUR_MS);
  return `resets in ${days}d ${hours}h`;
}

export function elapsedMs(from: string, to: string | null, now = Date.now()) {
  const a = parseDate(from)?.getTime();
  const b = to ? parseDate(to)?.getTime() : now;
  if (a === undefined || b === undefined) {
    return 0;
  }
  return Math.max(0, b - a);
}

export function clip(text: string, max: number): string {
  const one = text.replace(WHITESPACE, " ").trim();
  return one.length > max ? `${one.slice(0, max - 1)}…` : one;
}

export function shortId(id: string | null | undefined): string {
  return id ? id.slice(0, 8) : "–";
}

export function cacheShare(input: number, cacheRead: number): number | null {
  const total = input + cacheRead;
  return total > 0 ? cacheRead / total : null;
}