/**

  * Copyright 2005-2011 The Kuali Foundation

  *

  * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php

  *

  * 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 org.kuali.rice.krms.api.engine;

 import java.util.Map;

 import java.util.Set;

 /**

  * <p>An {@link TermResolver} implementor is a utility class used for resolution (reification) of {@link Term}s.  There are a

  * few key concepts to understand how {@link TermResolver}s function and work together.

  * </p>

  * <ul>

  * <li><b>they can require prerequisite {@link Term}s (which must not have any parameters)</b>.  If they do, when the {@link TermResolutionEngine} calls 

  * {@link #resolve(Map, Map)} it will pass the resolved prerequisites in the first argument.

  * <li><b>they can be chained.</b>  This means that if the {@link TermResolutionEngine} has {@link TermResolver}s (a &lt;- b) and 

  * (b <- c), and you have the fact 'c', you can ask for term 'a' and the engine will chain the resolvers together

  * to resolve it correctly.</li>

  * <li><b>they can be parameterized.</b> If an TermResolver takes parameters, they must be declared via the

  * {@link #getParameterNames()} method.  All declared parameters are considered to be required.  Parameters can be set

  * on the {@link Term} (via the constructor) that you are asking to resolve. When the {@link TermResolutionEngine} calls 

  * {@link #resolve(Map, Map)}, the parameters will be passed in to the second argument.</li>

  * <li><b>Parameterized {@link TermResolver}s can not be intermediates in a resolution plan.</b>  Another way to say 

  * this is that they can only be the last resolver in a chain.  For example, say

  * the {@link TermResolutionEngine} has {@link TermResolver}s (a <- b) which takes no parameters, 

  * (b <- c) which takes a parameter "foo", and you have the fact 'c'.  If you ask for Term 'a', the engine will not be able to resolve

  * it because it would need to use a parameterized Term as an intermediate step in resolution, and that isn't allowed.</li>

  * 

  * @author Kuali Rice Team (rice.collab@kuali.org)

  *

  * @param <T> the class of the resolved object 

  */

 public interface TermResolver <T> {

         /**

          * @return the names of the terms that this resolver requires to resolve its output, or an empty set if it has no prereqs;

          */

         Set<String> getPrerequisites();

         /**

          * @return the name of the term that the implementor resolves

          */

         String getOutput();

         /**

          * 

          * @return the names of any parameters that this {@link TermResolver} requires to churn out values for multiple {@link Term}s.  This may 

          * be null if no parameters are required.  If this is non-null/non-empty, then this resolver can not be used as an intermediate

          * in a term resolution chain.

          */

         Set<String> getParameterNames();

         /**

          * @return an integer representing the cost of resolving the term. 1 is cheap, Integer.MAX_INT is expensive.

          */

         int getCost();

         /**

          * @param resolvedPrereqs the resolved prereqs

          * @param parameters any parameters on the {@link Term} to be resolved (which must match those declared via {@link #getParameterNames()} 

          * @return the resolved fact value for the specified {@link Term}

          * @throws TermResolutionException if something bad happens during the term resolution process

          */

         T resolve(Map<String, Object> resolvedPrereqs, Map<String, String> parameters) throws TermResolutionException;

 }