/**
 * @factory/ui — pure display formatters (no DOM, no external imports).
 *
 * All time-based functions accept an injectable `now`/`iso` so output is
 * deterministic in tests. Locale-dependent output goes through `Intl`.
 */

const BYTES_UNITS = ["B", "KB", "MB", "GB", "TB", "PB"] as const;

/**
 * Format a byte count with 1024 steps. 0 → "0 B", values under 10 in a unit
 * get one decimal ("1.5 MB"), larger values are rounded to an integer.
 * Non-finite/negative input is clamped to 0.
 */
export function formatBytes(n: number): string {
  if (!Number.isFinite(n) || n < 0) return "0 B";
  if (n < 1024) return `${Math.round(n)} B`;
  let value = n;
  let unit = 0;
  while (value >= 1024 && unit < BYTES_UNITS.length - 1) {
    value /= 1024;
    unit += 1;
  }
  const label = BYTES_UNITS[unit] ?? "B";
  // one decimal when <10 (and non-integer): "1.5 KB"; integers stay plain: "1 KB"
  const text =
    value < 10 && !Number.isInteger(value) ? value.toFixed(1) : String(Math.round(value));
  return `${text} ${label}`;
}

/** Locale-aware integer/decimal formatting (defaults to the runtime locale). */
export function formatNumber(n: number, locale?: string): string {
  return new Intl.NumberFormat(locale, { maximumFractionDigits: 2 }).format(n);
}

const MINUTE_MS = 60_000;
const HOUR_MS = 60 * MINUTE_MS;
const DAY_MS = 24 * HOUR_MS;

function parseDate(iso: string): number {
  const t = Date.parse(iso);
  return Number.isNaN(t) ? 0 : t;
}

/**
 * Deterministic relative time against an injectable `now` (default: wall clock).
 * Buckets: <1m "just now" (never future-clamped), minutes → "5m ago",
 * hours → "2h ago", days → "3d ago", beyond 7 days → locale date.
 */
export function formatRelativeTime(iso: string, now?: number): string {
  const nowMs = now ?? Date.now();
  const thenMs = parseDate(iso);
  if (thenMs <= 0) return "";
  const diff = nowMs - thenMs;
  if (diff < MINUTE_MS) return "just now";
  if (diff < HOUR_MS) return `${Math.floor(diff / MINUTE_MS)}m ago`;
  if (diff < DAY_MS) return `${Math.floor(diff / HOUR_MS)}h ago`;
  if (diff < 7 * DAY_MS) return `${Math.floor(diff / DAY_MS)}d ago`;
  return formatDate(iso);
}

/** "1.2s", "3m 04s", "1h 02m 03s" — ms → compact human duration. */
export function formatDurationMs(ms: number): string {
  if (!Number.isFinite(ms) || ms < 0) return "0s";
  const totalSeconds = Math.round(ms / 1000);
  if (totalSeconds < 60) {
    const seconds = ms / 1000;
    return seconds < 10 ? `${seconds.toFixed(1)}s` : `${Math.round(seconds)}s`;
  }
  const hours = Math.floor(totalSeconds / 3600);
  const minutes = Math.floor((totalSeconds % 3600) / 60);
  const seconds = totalSeconds % 60;
  if (hours > 0) {
    return `${hours}h ${String(minutes).padStart(2, "0")}m ${String(seconds).padStart(2, "0")}s`;
  }
  return `${minutes}m ${String(seconds).padStart(2, "0")}s`;
}

/**
 * Initials for an avatar: "Ada Lovelace" → "AL". A single word takes its first
 * two characters uppercased ("Grace" → "GR"). Empty/whitespace → "".
 * At most 2 characters, non-letter/digit words are skipped.
 */
export function initials(name: string): string {
  const words = name.trim().split(/\s+/).filter(Boolean);
  if (words.length === 0) return "";
  if (words.length === 1) {
    const w = words[0] ?? "";
    return w.slice(0, 2).toUpperCase();
  }
  let out = "";
  for (const w of words) {
    if (out.length >= 2) break;
    out += (w[0] ?? "").toUpperCase();
  }
  return out;
}

/** Truncate to `n` visible characters with an ellipsis when longer. */
export function truncate(s: string, n: number): string {
  if (n < 0 || s.length <= n) return s;
  return `${s.slice(0, n)}…`;
}

/** Locale-safe date formatting; injectable locale, defaults to runtime locale. */
export function formatDate(iso: string, opts?: { locale?: string }): string {
  const t = parseDate(iso);
  if (t <= 0) return "";
  return new Date(t).toLocaleDateString(opts?.locale, {
    year: "numeric",
    month: "short",
    day: "numeric",
  });
}