import { ceilDiv, parseDecimalToUnits } from './amounts';

/** Rates are stored as integer units: fiat per 1 whole token, scaled by 1e6. */
export const RATE_DECIMALS = 6;

/**
 * Convert a fiat amount (decimal string) into crypto base units at the given rate.
 * Rounds UP by one base unit at most, so the merchant never receives less fiat
 * value than invoiced. No floating point anywhere.
 */
export function pegCryptoAmount(fiatAmount: string, rateUnits: bigint, tokenDecimals = 6): bigint {
  if (rateUnits <= 0n) throw new Error('rate must be positive');
  const fiatUnits = parseDecimalToUnits(fiatAmount, RATE_DECIMALS);
  if (fiatUnits <= 0n) throw new Error('fiat amount must be positive');
  return ceilDiv(fiatUnits * 10n ** BigInt(tokenDecimals), rateUnits);
}