export const MYSQL_UNSIGNED_INT_MAX = 4_294_967_295;

export interface LegacyMoneyOptions {
  nullable?: boolean;
  maxCents?: number;
  field?: string;
}

function describeField(field: string | undefined): string {
  return field ? ` for ${field}` : '';
}

export function legacyDecimalToCents(
  value: unknown,
  options: LegacyMoneyOptions = {}
): number | null {
  const field = describeField(options.field);

  if (value === null || value === undefined) {
    if (options.nullable) {
      return null;
    }
    throw new Error(`Legacy money value${field} cannot be null.`);
  }

  if (typeof value !== 'string' && typeof value !== 'number') {
    throw new Error(`Legacy money value${field} must be a decimal string or number.`);
  }

  if (typeof value === 'number' && !Number.isFinite(value)) {
    throw new Error(`Legacy money value${field} must be finite.`);
  }

  const decimal = String(value);
  const match = /^(\d+)(?:\.(\d{1,2}))?$/.exec(decimal);
  if (!match) {
    throw new Error(
      `Legacy money value${field} must be a non-negative decimal with at most two fractional digits.`
    );
  }

  const wholeCents = BigInt(match[1]) * 100n;
  const fraction = (match[2] ?? '').padEnd(2, '0');
  const cents = wholeCents + BigInt(fraction || '0');
  const maxCents = options.maxCents ?? MYSQL_UNSIGNED_INT_MAX;

  if (!Number.isSafeInteger(maxCents) || maxCents < 0) {
    throw new Error('Legacy money maxCents must be a non-negative safe integer.');
  }

  if (cents > BigInt(maxCents)) {
    throw new Error(`Legacy money value${field} exceeds the target cents column limit.`);
  }

  return Number(cents);
}