/**
 * Static-address mode disambiguation ("cent dust"): when several invoices share one
 * receiving address, each gets a unique random suffix in the 4th decimal place region
 * (0.0001–0.0999) so incoming amounts map to exactly one invoice.
 */

/** One dust step = 0.0001 in 6-decimal base units. */
export const DUST_STEP = 100n;
export const DUST_MAX_STEPS = 999;

export function applyCentDust(
  baseAmount: bigint,
  isTaken: (candidate: bigint) => boolean,
  random: () => number = Math.random,
): bigint {
  for (let attempt = 0; attempt < 500; attempt++) {
    const steps = 1 + Math.floor(random() * DUST_MAX_STEPS);
    const candidate = baseAmount + BigInt(steps) * DUST_STEP;
    if (!isTaken(candidate)) return candidate;
  }
  // Random attempts exhausted (pathological collision rate) — sweep deterministically.
  for (let steps = 1; steps <= DUST_MAX_STEPS; steps++) {
    const candidate = baseAmount + BigInt(steps) * DUST_STEP;
    if (!isTaken(candidate)) return candidate;
  }
  throw new Error('no unique dust suffix available — too many concurrent invoices at this amount');
}