const decimalFormatter = new Intl.NumberFormat("de-DE", {
  minimumFractionDigits: 2,
  maximumFractionDigits: 4
});

const currencyFormatter = new Intl.NumberFormat("de-DE", {
  style: "currency",
  currency: "EUR",
  minimumFractionDigits: 2,
  maximumFractionDigits: 4
});

export const unitOptions = ["Stck", "kg", "g", "L", "mg", "ml", "qm", "m", "cm", "mm"];
export const taxRateOptions = ["0", "7", "19"];

export function formatDecimal(value: string | number | null | undefined): string {
  const number = toNumber(value);
  return number === null ? "" : decimalFormatter.format(number);
}

export function formatEuro(value: string | number | null | undefined): string {
  const number = toNumber(value);
  return number === null ? "-" : currencyFormatter.format(number);
}

export function normalizeDecimal(value: string | number | null | undefined): string | null {
  if (value === null || value === undefined || value === "") return null;
  const text = String(value).trim();
  if (!text) return null;
  const compact = text.replace(/\s/g, "");
  if (compact.includes(",")) return compact.replace(/\./g, "").replace(",", ".");
  const dotCount = (compact.match(/\./g) ?? []).length;
  if (dotCount > 1) return compact.replace(/\./g, "");
  if (/^-?\d{1,3}\.\d{3}$/.test(compact)) return compact.replace(".", "");
  return compact;
}

export function formatDecimalInput<T extends Record<string, unknown>>(target: T, key: keyof T) {
  const normalized = normalizeDecimal(target[key] as string | number | null | undefined);
  target[key] = (normalized === null ? null : formatDecimal(normalized)) as T[keyof T];
}

export function decimalString(value: string | number | null | undefined, fallback = "0"): string {
  return normalizeDecimal(value) ?? fallback;
}

export function normalizeTaxRate(value: string | number | null | undefined, fallback = "19"): string {
  const normalized = normalizeDecimal(value);
  if (normalized === null) return fallback;
  const number = Number(normalized);
  if (!Number.isFinite(number)) return normalized;
  const compact = String(number);
  return taxRateOptions.includes(compact) ? compact : normalized;
}

function toNumber(value: string | number | null | undefined): number | null {
  if (value === null || value === undefined || value === "") return null;
  const normalized = normalizeDecimal(value);
  if (normalized === null) return null;
  const number = Number(normalized);
  return Number.isFinite(number) ? number : null;
}