import ms from 'ms';
import * as x from 'x-value';

export const rateExpressionSymbol = Symbol();

export const RateExpression = x.atomic(rateExpressionSymbol, value => {
  if (typeof value !== 'string') {
    throw new TypeError('Expected a rate expression string');
  }

  getRateExpressionValue(value);
});

export type RateExpression = x.Nominal<'rate expression', string>;

export function getRateExpressionValue(value: string): number {
  const groups = /^rate\((.+)\)$/.exec(value);

  if (!groups) {
    throw new TypeError('Expected a rate expression string like `rate(15m)`');
  }

  const [, interval] = groups;

  const rateInterval = ms(interval);

  if (rateInterval === undefined) {
    throw new TypeError('Invalid rate expression');
  }

  return rateInterval;
}