package org.kuali.rice.krms.framework.engine;

 import java.util.Collections;

 import java.util.HashMap;

 import java.util.Map;

 import java.util.Map.Entry;

 import org.apache.commons.lang.ObjectUtils;

 import org.kuali.rice.krms.api.engine.EngineResults;

 import org.kuali.rice.krms.api.engine.ExecutionEnvironment;

 import org.kuali.rice.krms.api.engine.ExecutionOptions;

 import org.kuali.rice.krms.api.engine.SelectionCriteria;

 import org.kuali.rice.krms.api.engine.Term;

 import org.kuali.rice.krms.api.engine.TermResolutionEngine;

 import org.kuali.rice.krms.api.engine.TermResolutionException;

 import org.kuali.rice.krms.api.engine.TermResolver;

 public final class BasicExecutionEnvironment implements ExecutionEnvironment {

         private final SelectionCriteria selectionCriteria;

         private final Map<Term, Object> facts;

         private final ExecutionOptions executionOptions;

         private final EngineResults engineResults;

         private final TermResolutionEngine termResolutionEngine;

         public BasicExecutionEnvironment(SelectionCriteria selectionCriteria, Map<Term, Object> facts, ExecutionOptions executionOptions, TermResolutionEngine termResolutionEngine) {

                 if (selectionCriteria == null) {

                         throw new IllegalArgumentException("Selection criteria must not be null.");

                 }

                 if (facts == null) {

                         throw new IllegalArgumentException("Facts must not be null.");

                 }

                 this.selectionCriteria = selectionCriteria;

                 this.executionOptions = new ExecutionOptions(executionOptions);

                 this.engineResults = new EngineResultsImpl();

                 // TODO: inject this (will have to make it non-final)

                 this.termResolutionEngine = new TermResolutionEngineImpl();

                 // Add facts

                 this.facts = new HashMap<Term, Object>(facts.size());

                 this.facts.putAll(facts);

                 for (Entry<Term, Object> factsEntry : facts.entrySet()) {

                         this.termResolutionEngine.addTermValue(factsEntry.getKey(), factsEntry.getValue());

                 }

         }

         @Override

         public SelectionCriteria getSelectionCriteria() {

                 return this.selectionCriteria;

         }

         @Override

         public Map<Term, Object> getFacts() {

                 return Collections.unmodifiableMap(facts);

         }

         @Override

         public void addTermResolver(TermResolver<?> termResolver) {

                 termResolutionEngine.addTermResolver(termResolver);

         }

         @Override

         public <T> T resolveTerm(Term term) throws TermResolutionException {

                 T value;

                 // This looks funny, but works around a javac bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6302954

                 // Specifically, using <T> below works around it.

                 value = termResolutionEngine.<T>resolveTerm(term);

                 publishFact(term, value);

                 return value;

         }

         @Override

         public boolean publishFact(Term factName, Object factValue) {

                 if (facts.containsKey(factName) && ObjectUtils.equals(facts.get(factName), factValue)) {

                         return false;

                 }

                 facts.put(factName, factValue);

                 termResolutionEngine.addTermValue(factName, factValue);

                 return true;

         }

         @Override

         public ExecutionOptions getExecutionOptions() {

                 return executionOptions;

         }

         @Override

         public EngineResults getEngineResults() {

                 return engineResults;

         }

 }