xValidator function

String? Function(String?) xValidator(List<TextXValidationRule> rules, { OnFailureCallBack? onFailureCallBack, })

A function that builds and returns a String Function(String value) which triggers the provided validation rules.

This function performs a validation loop for each rule in the provided list. If a rule is of type IsOptional, the validation process marks the item as optional, meaning that if the validation fails and the value is null, there will be no error. However, if the validation fails and the value is not null, it returns the first failed error message.

Implementation

String? Function(String?) xValidator(
  List<TextXValidationRule> rules, {
  OnFailureCallBack? onFailureCallBack,
}) {
  return (String? input) {
    // If the input is empty, return null (no error)
    if (input == null) return null;

    var isOptional = false; // Flag to track if the validation is optional

    /// Will contain the first failed rule message
    String? msg;

    for (final rule in rules) {
      /// If any rule is of type `IsOptional`,
      /// the validator loop will mark the validation process as optional,
      /// and it will not consider any failure from any rule.
      /// Otherwise, it works as usual and validates the next rule,
      /// returning only the first failure.
      if (rule is IsOptional) isOptional = true;

      /// Call the validate function and
      /// if it returns null, there will be no error;
      /// otherwise, it will return the failure message,
      /// which serves as the validation error for the entire process.
      msg = rule.isValid(input)
          ? null
          : (rule.error ?? XValidatorsLocalization.translate(rule));

      /// If the failure message `msg` has a value,
      /// it means some rule has failed.
      /// Return only the first failure,
      /// and there is no reason to continue validating the remaining rules.
      if (msg != null) {
        onFailureCallBack?.call(input, rules, rule);
        break;
      }
    }

    // If it's optional and the input is empty, return null (no error)
    if (isOptional && isEmpty(input)) return null;

    return msg;
  };
}