// Copyright: © 2026 TWWIM UG. All rights reserved. (www.twwim.com)

import { Currency, VAT_RATES, isCurrency } from '@archer/domain';

/**
 * Currency-aware price breakdown for checkout-style displays.
 *
 * Mirrors `Price.applyTax()` from @archer/domain — single source of truth for
 * what VAT rate applies per currency (EUR 19%, USD 0%). Same math the backend
 * uses in `CreatePaymentIntentUseCase` and `PurchaseCommandsUseCase`, so the
 * displayed gross is byte-identical to what Stripe will actually charge.
 *
 * Inputs are major units (e.g. 79.00 EUR, 94.99 USD). Outputs are major-unit
 * numbers rounded to 2 dp, ready for display.
 */
export interface CheckoutBreakdown {
  net: number;
  vatRate: number;
  vat: number;
  gross: number;
  currency: Currency;
  currencySymbol: string;
}

const CURRENCY_SYMBOLS: Record<Currency, string> = {
  [Currency.EUR]: '€',
  [Currency.USD]: '$',
};

/**
 * Resolve a currency from a string the API gave us, defaulting to EUR when
 * absent or unrecognised. EUR-default preserves pre-multicurrency display
 * behaviour for legacy responses without a currency field.
 */
export function resolveCurrency(input: string | null | undefined): Currency {
  if (input && isCurrency(input)) return input as Currency;
  return Currency.EUR;
}

export function resolveCheckoutBreakdown(netMajor: number, currencyInput: string | null | undefined): CheckoutBreakdown {
  const currency = resolveCurrency(currencyInput);
  const vatRate = VAT_RATES[currency];
  const net = round2(netMajor);
  const vat = round2(net * vatRate);
  const gross = round2(net + vat);
  return { net, vatRate, vat, gross, currency, currencySymbol: CURRENCY_SYMBOLS[currency] };
}

/** Single-line price label, e.g. "€79.00" or "$94.99". */
export function formatPlanPrice(amountMajor: number, currencyInput: string | null | undefined): string {
  const currency = resolveCurrency(currencyInput);
  const symbol = CURRENCY_SYMBOLS[currency];
  return `${symbol}${amountMajor.toFixed(2)}`;
}

function round2(n: number): number {
  return Math.round(n * 100) / 100;
}