const PRICE_LOCALE = 'de-DE';

export function getBrutto(netto, kSteuerklasse) {
  const rate = { 1: 19, 2: 7, 3: 0 }[kSteuerklasse] ?? 19;
  return netto * (1 + rate / 100);
}

/** Currency display, e.g. `6,60 €`. */
export function formatPrice(amount) {
  if (amount == null || !Number.isFinite(Number(amount))) return '';
  return new Intl.NumberFormat(PRICE_LOCALE, {
    style: 'currency',
    currency: 'EUR',
  }).format(amount);
}

/**
 * Amount without currency symbol (for fields with a separate € adornment).
 * e.g. `6,60` / `1.234,56`
 */
export function formatPriceAmount(amount, { minFractionDigits = 2, maxFractionDigits = 2 } = {}) {
  if (amount == null || !Number.isFinite(Number(amount))) return '';
  return new Intl.NumberFormat(PRICE_LOCALE, {
    minimumFractionDigits: minFractionDigits,
    maximumFractionDigits: maxFractionDigits,
  }).format(amount);
}

/**
 * Parse de-DE (or plain) price input → number.
 * Accepts `6,60`, `1.234,56`, and plain `6.60`.
 */
export function parsePriceInput(value) {
  if (value === '' || value == null) return null;
  let normalized = String(value).trim().replace(/\s/g, '');
  if (normalized === '') return null;

  if (normalized.includes(',')) {
    // de-DE: thousand `.`, decimal `,`
    normalized = normalized.replace(/\./g, '').replace(',', '.');
  }

  const parsed = Number(normalized);
  return Number.isFinite(parsed) && parsed >= 0 ? parsed : null;
}

/** Convert gross (brutto) → net for PUT /prices. Rounded to 4 decimal places. */
export function netFromGross(gross, taxRate) {
  if (gross == null || taxRate == null) return null;
  if (!Number.isFinite(gross) || !Number.isFinite(taxRate) || taxRate < 0) return null;
  const factor = 1 + taxRate / 100;
  if (factor <= 0) return null;
  return Math.round((gross / factor) * 10000) / 10000;
}