const NANO = 1_000_000_000n;

export type ProtoDecimal = { units?: string | number; nano?: string | number };
export type Decimal = { value: bigint; scale: number };

export function decimal(value: ProtoDecimal): Decimal {
  return {
    value: BigInt(value.units ?? 0) * NANO + BigInt(value.nano ?? 0),
    scale: 9,
  };
}

export function add(left: Decimal, right: Decimal): Decimal {
  const scale = Math.max(left.scale, right.scale);
  return {
    value:
      left.value * 10n ** BigInt(scale - left.scale) +
      right.value * 10n ** BigInt(scale - right.scale),
    scale,
  };
}

export function subtract(left: Decimal, right: Decimal): Decimal {
  return add(left, { value: -right.value, scale: right.scale });
}

export function multiply(left: Decimal, right: Decimal): Decimal {
  return { value: left.value * right.value, scale: left.scale + right.scale };
}

export function isZero(value: Decimal): boolean {
  return value.value === 0n;
}

export function formatDecimal({ value, scale }: Decimal): string {
  if (value === 0n) return '0';
  const sign = value < 0n ? '-' : '';
  const digits = (value < 0n ? -value : value)
    .toString()
    .padStart(scale + 1, '0');
  const whole = digits.slice(0, -scale) || '0';
  const fraction = digits.slice(-scale).replace(/0+$/, '');
  return `${sign}${whole}${fraction ? `.${fraction}` : ''}`;
}