// Pure helpers for the pricing picker's band row and its local-currency ≈
// display (docs/pricing-bands.md). Framework-free and DOM-free so they're
// unit-testable in Node (home/test/fx.test.mjs); home.js does the wiring.
//
// Billing is EUR everywhere — the ≈ figure is a labelled estimate from the
// ECB reference-rate snapshot home serves at /api/fx, converted client-side.
// Currency choice comes from the BROWSER LOCALE, never IP (privacy-consistent
// with the honor picker: nothing about the buyer is detected or stored).

// The band vocabulary, in display order, with the picker's short names and
// the one-line explanations (lock-and-key voice; aggregate cross-subsidy
// only — never a per-space claim, never "discount", never "eligible").
export const BANDS = [
  { key: "supporter", name: "Supporter",
    line: "The supporter price. Paying supports free spaces for those who can't — the difference doesn't go to us, it goes to the free pool." },
  { key: "base", name: "Standard",
    line: "The standard price. It covers your space's costs with margin for resilience — the books are public." },
  { key: "reduced", name: "Reduced",
    line: "The reduced price, carried by supporters. It's yours as long as you need it." },
  { key: "solidarity", name: "Solidarity",
    line: "The solidarity price, carried by supporters. It's yours as long as you need it." },
];

export function bandName(key) {
  const b = BANDS.find((b) => b.key === key);
  return (b && b.name) || key;
}

// bandsOffered: which of the four bands this price book can actually sell —
// base always; a non-base band once ANY tier defines it.
export function bandsOffered(tiers) {
  return BANDS.filter((b) => b.key === "base" ||
    (tiers || []).some((t) => t.bands && t.bands[b.key])).map((b) => b.key);
}

// tierForBand resolves what a tier shows under a selected band: its own
// label/eur for base or when it doesn't offer the band (flagged so the UI can
// say "standard price" instead of implying a reduction), the band's otherwise.
export function tierForBand(tier, band) {
  if (band !== "base" && tier.bands && tier.bands[band]) {
    const b = tier.bands[band];
    return { label: b.label, eur: b.eur || 0, band, offered: true };
  }
  return { label: tier.label, eur: tier.eur || 0, band: "base", offered: band === "base" };
}

// regionCurrency maps a BCP-47 locale to the display currency for the ≈
// figure: "" for the euro area (billed in EUR — nothing to approximate),
// unknown regions, and currencies the ECB feed doesn't quote.
const REGION_CURRENCY = {
  US: "USD", GB: "GBP", JP: "JPY", BG: "BGN", CZ: "CZK", DK: "DKK",
  HU: "HUF", PL: "PLN", RO: "RON", SE: "SEK", CH: "CHF", LI: "CHF",
  IS: "ISK", NO: "NOK", TR: "TRY", AU: "AUD", BR: "BRL", CA: "CAD",
  CN: "CNY", HK: "HKD", ID: "IDR", IL: "ILS", IN: "INR", KR: "KRW",
  MX: "MXN", MY: "MYR", NZ: "NZD", PH: "PHP", SG: "SGD", TH: "THB",
  ZA: "ZAR",
};

export function regionCurrency(locale) {
  try {
    const region = new Intl.Locale(locale).maximize().region;
    return REGION_CURRENCY[region] || "";
  } catch {
    return "";
  }
}

// approxLocal renders the ≈ string for a EUR amount — "≈ $8.20" — or "" when
// the currency or its rate is unknown (the UI simply shows no figure; an
// absent estimate beats a wrong one). Small amounts keep cents; larger ones
// round to whole units (an estimate pretending cent precision reads wrong).
export function approxLocal(eur, currency, rates, locale) {
  if (!eur || !currency || !rates || !rates[currency]) return "";
  const amount = eur * rates[currency];
  try {
    // Cents show as a pair or not at all ("$5.50" / "$6", never "$5.5"), and
    // only under 20 units — an estimate pretending cent precision reads wrong.
    const cents = amount < 20 && Math.round(amount * 100) % 100 !== 0 ? 2 : 0;
    const fmt = new Intl.NumberFormat(locale || undefined, {
      style: "currency", currency,
      minimumFractionDigits: cents, maximumFractionDigits: cents,
    });
    return "≈ " + fmt.format(amount);
  } catch {
    return "";
  }
}

// capNote states the +15% annual-review promise in money, not percent (the
// Ofcom shape: pounds-and-pence at the point of sale): "renewal can never add
// more than €0.75/year without your say-so". Empty when the sticker is
// unknown — the generic sentence beside it still carries the promise.
export function capNote(eur, locale) {
  if (!eur) return "";
  const cap = eur * 0.15;
  const cents = Math.round(cap * 100) % 100 !== 0 ? 2 : 0;
  const fmt = new Intl.NumberFormat(locale || undefined, {
    style: "currency", currency: "EUR",
    minimumFractionDigits: cents, maximumFractionDigits: cents,
  });
  return "never more than " + fmt.format(cap) + " more at renewal without your say-so";
}