Looking for a more declarative way to write a schema with conditional validation?

Schema.Trim.pipe(
  Schema.filter((value) => {
    if (value.length === 0) return true;
    if (value.length > 20) {
      return Model must not exceed 20 characters long;
    }
    const modelReg = new RegExp(/^[a-zA-Z0-9]+$/);
    if (!modelReg.test(value)) {
      return 'Model must contain only letters and numbers';
    }

    return true;
  }),
);