Introduce ValidationState

[hohwille]

Currently our validation is not implemented well:

IDEasy/cli/src/main/java/com/devonfw/tools/ide/commandlet/Commandlet.java

Lines 202 to 216 in eae8fd2

	public boolean validate() {
	// avoid validation exception if not a candidate to be run.
	for (Property<?> property : this.propertiesList) {
	if (property.isRequired() && (property.getValue() == null)) {
	return false;
	}
	}
	for (Property<?> property : this.propertiesList) {
	if (!property.validate()) {
	return false;
	}
	}
	return true;
	}

IDEasy/cli/src/main/java/com/devonfw/tools/ide/property/Property.java

Lines 456 to 467 in eae8fd2

	public boolean validate() {
	if (this.required && (getValue() == null)) {
	return false;
	}
	if (this.validator != null) {
	for (V value : this.value) {
	this.validator.accept(value);
	}
	}
	return true;
	}

So we have validation result as boolean and also the concept to throw an exception if the validation fails in a properties validator.
Both approaches are not well designed.

Instead we should create an interface ValidationResult

public interface ValidationResult {
  boolean isValid();

  String getErrorMessage();
}

Then we can create an implementation ValidationState:

public class ValidationState implements ValidationResult {
  private final StringBuilder errorMessage;
  
  public boolean isValid() {
    return (this.errorMessage == null);
  }
  
  public String getErrorMessage() {
    if (this.errorMessage == null) {
      return null;
    }
    return this.errorMessage.toString();
  }

  public void addErrorMessage(String error) {
    if (this.errorMessage == null) {
      this.errorMessage = new StringBuilder(error.length());
    } else {
      this.errorMessage.append('\n');
    }
    this.errorMessage.append(error);
  }
}

This is just a design suggestion as starting point. We can also have a immutable implementation(s) of ValidationResult and have a ValidationResult toResult() method in ValidationState.

The final idea is that internal validation methods will take a ValidationState object as argument. This also applies for the validators of the Property classes. Here we need to change from Consumer<V> to a custom interface:

@FunctionalInterface
public interface PropertyValidator<V> {
  void validate(V value, ValidationState validationState);
}

The main API should take no argument and return ValidationResult.

An alternative approach is to skip the ValidationState and always return ValidationState and then add some aggregation logic that can compose multiple ValidationState objects into one. IMHO the latter approach is slightly more complex.

[hohwille]

FYI: some inspiration for more complex design:

• https://github.com/m-m-m/validation/blob/master/core/src/main/java/io/github/mmm/validation/ValidationResult.java
• https://github.com/m-m-m/validation/blob/master/core/src/main/java/io/github/mmm/validation/ValidationResultValid.java
• https://github.com/m-m-m/validation/blob/master/core/src/main/java/io/github/mmm/validation/ValidationFailure.java
• https://github.com/m-m-m/validation/blob/master/core/src/main/java/io/github/mmm/validation/ValidationResultBuilder.java