/** Kalendertag lokal als `YYYY-MM-DD` (für Vergleich mit DB). */
export function localDateKey(d: Date): string {
  const y = d.getFullYear();
  const m = String(d.getMonth() + 1).padStart(2, "0");
  const day = String(d.getDate()).padStart(2, "0");
  return `${y}-${m}-${day}`;
}

/** UI-Wert für `<input type="date" />` aus API-Wert. */
export function deadlineToDateInput(deadlineAt: string | null | undefined): string {
  if (!deadlineAt) return "";
  const s = deadlineAt.trim();
  if (/^\d{4}-\d{2}-\d{2}$/.test(s)) return s;
  const t = new Date(s);
  if (Number.isNaN(t.getTime())) return "";
  return localDateKey(t);
}

export type DeadlineTone = "none" | "upcoming" | "today" | "overdue";

/** Blau = künftig (nicht heute), Orange = heute fällig, Rot = überschritten. */
export function deadlineTone(deadlineAt: string | null | undefined): DeadlineTone {
  if (!deadlineAt) return "none";
  const key = deadlineToDateInput(deadlineAt);
  if (!key) return "none";
  const today = localDateKey(new Date());
  if (key < today) return "overdue";
  if (key === today) return "today";
  return "upcoming";
}

export function deadlineBadgeClass(tone: DeadlineTone): string {
  switch (tone) {
    case "upcoming":
      return "text-blue-500/70 text-blue-800 dark:text-blue-200";
    case "today":
      return "text-orange-500/80 text-orange-900 dark:text-orange-100";
    case "overdue":
      return "text-destructive/80 text-destructive";
    default:
      return "";
  }
}

export function formatDeadlineLabel(deadlineAt: string): string {
  const key = deadlineToDateInput(deadlineAt);
  if (!key) return deadlineAt;
  try {
    const [y, m, d] = key.split("-").map(Number);
    const dt = new Date(y, m - 1, d);
    return dt.toLocaleDateString(undefined, { dateStyle: "medium" });
  } catch {
    return key;
  }
}