typescript validation

strings.ts

/**
 * A string guaranteed to have a length within the range [L,H)
 */
export type WithinRangeString<L extends number, H extends number> = string &
  IWithinRangeStringTag<L, H>;

function validateWithinRangeString<L extends number, H extends number>(
  arg: string,
  l: L,
  h: H
): Option<ReadonlyArray<string>> {
  interface IWithinRangeStringObj {
    readonly arg: string;
    readonly length: number;
  }
  const validationRules: IValidationRules<IWithinRangeStringObj> = {
    arg: [[isString, "not string"]],
    length: [[gt(l), "too short"], [lt(h), "too long"]]
  };
  const validation = validateAll([
    { arg, length: arg.length },
    validationRules
  ]);
  if (hasErrors(validation)) {
    return option(getErrorStrings(validation));
  } else {
    return none;
  }
}

export function isWithinRangeString<L extends number, H extends number>(
  arg: string,
  l: L,
  h: H
): arg is WithinRangeString<L, H> {
  return validateWithinRangeString(arg, l, h).match({
    none: always(true),
    some: always(false)
  });
}

export function toWithinRangeString<L extends number, H extends number>(
  arg: string,
  l: L,
  h: H
): Either<ReadonlyArray<string>, WithinRangeString<L, H>> {
  return isWithinRangeString(arg, l, h)
    ? right(arg)
    : left(validateWithinRangeString(arg, l, h).getOrElse([]));
}