content: /*
   * Copyright © 2018-2025 Commonwealth Scientific and Industrial Research
   * Organisation (CSIRO) ABN 41 687 119 230.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package au.csiro.pathling.views.validation;
  
  import jakarta.validation.ConstraintValidator;
  import jakarta.validation.ConstraintValidatorContext;
  import java.lang.reflect.Field;
  import java.util.Arrays;
  import java.util.List;
  
  /**
   * Validator implementation for the {@link AtMostOneNonNull} constraint.
   * <p>
   * This validator ensures that at most one of the specified fields has a non-null value. It uses
   * reflection to access the field values and count how many are non-null.
   */
  public class AtMostOneNonNullValidator implements
      ConstraintValidator<AtMostOneNonNull, Object> {
  
    private List<String> fieldNames;
  
    @Override
    public void initialize(final AtMostOneNonNull constraintAnnotation) {
      fieldNames = Arrays.asList(constraintAnnotation.value());
    }
  
    @Override
    public boolean isValid(final Object value, final ConstraintValidatorContext context) {
      if (value == null) {
        return true; // Let @NotNull handle this case
      }
  
      int nonNullCount = 0;
      final Class<?> clazz = value.getClass();
  
      for (final String fieldName : fieldNames) {
        try {
          final Field field = clazz.getDeclaredField(fieldName);
          field.setAccessible(true);
          if (field.get(value) != null) {
            nonNullCount++;
          }
        } catch (final NoSuchFieldException | IllegalAccessException e) {
          // If we can't access the field, we'll assume it's null
          // This shouldn't happen with proper usage of the annotation
        }
      }
  
      return nonNullCount <= 1;
    }
  }
  