/** Exact, browser-safe amounts. No wallet RPC, exchange rate, custody or signing policy. */
export const XMR_ATOMIC_UNITS = 1_000_000_000_000n;
// Preserve the existing processor decimal parser's ten-whole-digit encoding bound.
// This is NOT a supply limit, an exposure approval, or a wallet-RPC uint64 guarantee.
export const MAX_XMR_AMOUNT = 10_000_000_000n * XMR_ATOMIC_UNITS - 1n;
export const XMR_RPC_UINT64_MAX = (1n << 64n) - 1n;

export function assertXmrAmount(amount: bigint): void {
  if (typeof amount !== 'bigint' || amount < 0n || amount > MAX_XMR_AMOUNT) {
    throw new Error('Invalid bounded atomic XMR amount');
  }
}

/** Decimal user/processor input; never coerce, trim, round, or accept floating point. */
export function parseXmr(value: string): bigint {
  if (typeof value !== 'string' || value.length > 23 || !/^(0|[1-9]\d{0,9})(\.\d{1,12})?(?![\s\S])/.test(value)) {
    throw new Error('Invalid bounded XMR decimal');
  }
  const [whole, fraction = ''] = value.split('.');
  return BigInt(whole) * XMR_ATOMIC_UNITS + BigInt(fraction.padEnd(12, '0'));
}

/** Canonical display/processor decimal: always twelve fractional places. */
export function formatXmr(amount: bigint): string {
  assertXmrAmount(amount);
  return `${amount / XMR_ATOMIC_UNITS}.${(amount % XMR_ATOMIC_UNITS).toString().padStart(12, '0')}`;
}

/** JSON/signature/storage representation: canonical base-ten integer string, not a JSON number. */
export function parseAtomicXmr(value: string): bigint {
  if (typeof value !== 'string' || value.length > 22 || !/^(0|[1-9]\d{0,21})(?![\s\S])/.test(value)) {
    throw new Error('Invalid canonical atomic XMR string');
  }
  const amount = BigInt(value);
  assertXmrAmount(amount);
  return amount;
}

export function atomicXmrString(amount: bigint): string {
  assertXmrAmount(amount);
  return amount.toString();
}

/** RPC amounts need lossless JSON encoding too; Number(amount) is not safe. */
export function assertXmrRpcAmount(amount: bigint): void {
  assertXmrAmount(amount);
  if (amount > XMR_RPC_UINT64_MAX) throw new Error('XMR amount exceeds wallet-RPC uint64');
}

/** Independently round commissions down; all sub-atomic remainders stay with the seller. */
export function xmrCommission(gross: bigint, bps: number): bigint {
  assertXmrAmount(gross);
  if (!Number.isSafeInteger(bps) || bps < 0 || bps > 10_000) throw new Error('Invalid commission basis points');
  return gross * BigInt(bps) / 10_000n;
}