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;
  	}
  
  }