package org.kuali.rice.core.api.criteria;

 import org.kuali.rice.core.api.mo.ModelBuilder;

 import java.io.Serializable;

 /**

  * This class works withe the lookup framework to customize a query.  It currently can do the following things:

  *

  * <ul>

  *  <li>transform/remove predicates</li>

  *  <li>transform/remove query results</li>

  * </ul>

  *

  * <p>

  * The predicate transform will applied to the predicates in the incoming query yielding a

  * a predicate.  If the predicate does not need to be transformed then the function can return the

  * incoming argument.  If the predicate should be removed the transform should return null.

  * This is a way to remove or change a predicate before the query is executed.

  * This is a good way to add new predicates to a query or to limit the result of the query before

  * it is executed. Transforms also allow a predicate referencing a property path that does not exist

  * on database mapped object to be changed to something that is valid.

  * </p>

  *

  * <p>

  * The result transform will be applied to the results of the query after the query is executed.

  * If the result does not need to be transformed then the function can return the

  * incoming argument. This is a way to remove or change a result after the query is executed.

  * </p>

  *

  * <p>transformers should not have to deal with null items</p>

  */

 public class LookupCustomizer<T> {

     //FIXME: add wilcards to make predicate transform more flexible ie. EqualsPredicate to AndPredicate

     private final Transform<Predicate,Predicate> predicateTransform;

     private final Transform<T, T> resultTransform;

     private LookupCustomizer(Builder<T> builder) {

         this.predicateTransform = builder.getPredicateTransform() != null ? builder.getPredicateTransform() : IndentityTransform.<Predicate, Predicate>getInstance();

         this.resultTransform = builder.getResultTransform() != null ? builder.getResultTransform() : IndentityTransform.<T, T>getInstance();

     }

     public Transform<Predicate, Predicate> getPredicateTransform() {

         return predicateTransform;

     }

     public Transform<T, T> getResultTransform() {

         return resultTransform;

     }

     public static final class Builder<T> implements ModelBuilder, Serializable {

         private Transform<Predicate, Predicate> predicateTransform;

         private Transform<T, T> resultTransform;

         private Builder() {

         }

         public static <T> Builder<T> create() {

             return new Builder<T>();

         }

         public Transform<Predicate, Predicate> getPredicateTransform() {

             return predicateTransform;

         }

         public void setPredicateTransform(final Transform<Predicate, Predicate> predicateTransform) {

             this.predicateTransform = predicateTransform;

         }

         public Transform<T, T> getResultTransform() {

             return resultTransform;

         }

         public void setResultTransform(final Transform<T, T> resultTransform) {

             this.resultTransform = resultTransform;

         }

         @Override

         public LookupCustomizer<T> build() {

             return new LookupCustomizer<T>(this);

         }

     }

     public interface Transform<P, R> {

         R apply(P input);

     }

     /**

      * f: x -> x.  This function just returns the passed in parameter.

      *

      * @param <I> the type the function acts on.

      */

     private static final class IndentityTransform<I> implements Transform<I, I> {

         @SuppressWarnings("unchecked")

         private static final Transform INSTANCE = new IndentityTransform();

         @SuppressWarnings("unchecked")

         public static <P, R> Transform<P, R> getInstance() {

             return INSTANCE;

         }

         @Override

         public I apply(final I input) {

             return input;

         }

     }

 }