new-site/api/src/fx.ts

/**
 * CAD → USD foreign exchange conversion.
 *
 * Source: Bank of Canada daily exchange rate (Valet API).
 * Caches the rate for 24 hours.
 *
 * cadToUsdCents(cadCents):
 *   1. Fetch current CAD/USD rate (e.g., 1 CAD = 0.73 USD)
 *   2. Convert CAD cents to USD cents
 *   3. Add 10% buffer to cover fluctuations
 *   4. Round UP to the nearest whole dollar (100 cents)
 */

let cachedRate: { rate: number; fetchedAt: number } | null = null;
const CACHE_TTL_MS = 24 * 60 * 60 * 1000; // 24 hours
const BUFFER_PCT = 0.10; // 10% buffer on top of spot rate
const FALLBACK_RATE = 0.72; // conservative fallback if API is unreachable

/**
 * Fetch the current CAD/USD exchange rate from the Bank of Canada.
 * Returns how many USD 1 CAD buys (e.g., 0.73).
 */
async function fetchCadUsdRate(): Promise<number> {
  // Bank of Canada Valet API — FXCADUSD is the official daily rate
  const url = "https://www.bankofcanada.ca/valet/observations/FXCADUSD/json?recent=1";

  try {
    const resp = await fetch(url, {
      signal: AbortSignal.timeout(8000),
      headers: { "Accept": "application/json" },
    });

    if (!resp.ok) {
      throw new Error(`Bank of Canada API returned ${resp.status}`);
    }

    const data = await resp.json() as {
      observations: Array<{ d: string; FXCADUSD: { v: string } }>;
    };

    const obs = data.observations;
    if (!obs || obs.length === 0) {
      throw new Error("No observations returned from Bank of Canada");
    }

    const rate = parseFloat(obs[obs.length - 1].FXCADUSD.v);
    if (isNaN(rate) || rate <= 0 || rate > 2) {
      throw new Error(`Invalid rate value: ${obs[obs.length - 1].FXCADUSD.v}`);
    }

    console.log(`[fx] Bank of Canada CAD/USD rate: ${rate} (date: ${obs[obs.length - 1].d})`);
    return rate;
  } catch (err) {
    console.warn(`[fx] Failed to fetch Bank of Canada rate: ${err}. Using fallback ${FALLBACK_RATE}`);
    return FALLBACK_RATE;
  }
}

/**
 * Get the current CAD/USD rate (cached for 24h).
 */
async function getCadUsdRate(): Promise<number> {
  const now = Date.now();
  if (cachedRate && (now - cachedRate.fetchedAt) < CACHE_TTL_MS) {
    return cachedRate.rate;
  }

  const rate = await fetchCadUsdRate();
  cachedRate = { rate, fetchedAt: now };
  return rate;
}

/**
 * Convert CAD cents to USD cents with 10% buffer, rounded UP to nearest whole dollar.
 *
 * Example: C$350 (35000 cents) at rate 0.73:
 *   35000 * 0.73 = 25550 USD cents
 *   25550 * 1.10 = 28105 (with 10% buffer)
 *   Round up to $282.00 = 28200 cents
 */
export async function cadToUsdCents(cadCents: number): Promise<number> {
  const rate = await getCadUsdRate();
  const usdCentsRaw = cadCents * rate;
  const withBuffer = usdCentsRaw * (1 + BUFFER_PCT);
  // Round UP to nearest 100 (whole dollar)
  const rounded = Math.ceil(withBuffer / 100) * 100;
  return rounded;
}

/**
 * Synchronous version using cached rate (returns 0 if not yet fetched).
 * Use for display purposes only — call cadToUsdCents() for order pricing.
 */
export function cadToUsdCentsSync(cadCents: number): number {
  if (!cachedRate) return 0;
  const usdCentsRaw = cadCents * cachedRate.rate;
  const withBuffer = usdCentsRaw * (1 + BUFFER_PCT);
  return Math.ceil(withBuffer / 100) * 100;
}

/**
 * Get the current cached rate info (for display/debugging).
 */
export async function getFxInfo(): Promise<{ rate: number; withBuffer: number; fetchedAt: string }> {
  const rate = await getCadUsdRate();
  return {
    rate,
    withBuffer: rate * (1 + BUFFER_PCT),
    fetchedAt: cachedRate ? new Date(cachedRate.fetchedAt).toISOString() : "never",
  };
}

/**
 * Pre-warm the cache at startup.
 */
export async function warmFxCache(): Promise<void> {
  await getCadUsdRate();
}