package org.kuali.common.util.validate;
   
   import java.lang.reflect.Field;
   import java.util.HashSet;
   import java.util.Set;
   
   import javax.validation.ConstraintValidator;
   import javax.validation.ConstraintValidatorContext;
   
  import org.kuali.common.util.ReflectionUtils;
  
  import com.google.common.collect.HashMultiset;
  import com.google.common.collect.Multiset;
  
  public class UniqueFieldNamesValidator implements ConstraintValidator<UniqueFieldNames, Object> {
  
  	@Override
  	public void initialize(UniqueFieldNames constraintAnnotation) {
  	}
  
  	@Override
  	public boolean isValid(Object instance, ConstraintValidatorContext constraintContext) {
  
  		// Extract every field in the type hierarchy
  		Set<Field> fields = ReflectionUtils.getAllFields(instance.getClass());
  
  		// These field names are duplicated
  		Set<String> duplicates = getDuplicateFieldNames(fields);
  
  		if (duplicates.size() == 0) {
  			return true;
  		} else {
  			constraintContext.disableDefaultConstraintViolation();
  			String path = ReflectionUtils.getDeclarationPath(instance.getClass());
  			for (String duplicate : duplicates) {
  				String error = "Duplicate field declaration: In type [" + path + "] the field [" + duplicate + "] appears more than once in the type hierarchy";
  				constraintContext.buildConstraintViolationWithTemplate(error).addConstraintViolation();
  			}
  			return false;
  		}
  	}
  
  	protected Set<String> getDuplicateFieldNames(Set<Field> fields) {
  		// Keep track of field name counts
  		Multiset<String> multiset = HashMultiset.create();
  		for (Field field : fields) {
  			multiset.add(field.getName());
  		}
  
  		Set<String> duplicates = new HashSet<String>();
  		for (String fieldName : multiset) {
  			int count = multiset.count(fieldName);
  			if (count > 1) {
  				duplicates.add(fieldName);
  			}
  		}
  		return duplicates;
  	}
  }