package org.simantics.structural2.variables;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.simantics.databoard.Bindings;
import org.simantics.db.ReadGraph;
import org.simantics.db.Resource;
import org.simantics.db.Statement;
import org.simantics.db.common.procedure.adapter.TransientCacheAsyncListener;
import org.simantics.db.common.request.BinaryRead;
import org.simantics.db.common.request.ResourceRead;
import org.simantics.db.common.request.TransientUnaryRead;
import org.simantics.db.common.utils.NameUtils;
import org.simantics.db.common.utils.NearestOwnerFinder;
import org.simantics.db.exception.DatabaseException;
import org.simantics.db.exception.NoSingleResultException;
import org.simantics.db.layer0.exception.MissingVariableException;
import org.simantics.db.layer0.exception.MissingVariableValueException;
import org.simantics.db.layer0.request.VariableRead;
import org.simantics.db.layer0.variable.Variable;
import org.simantics.db.service.CollectionSupport;
import org.simantics.db.service.QueryControl;
import org.simantics.layer0.Layer0;
import org.simantics.modeling.ModelingResources;
import org.simantics.structural.stubs.StructuralResource2;
import org.simantics.structural2.Functions;
import org.simantics.structural2.Functions.InterfaceResolution;
import org.simantics.structural2.queries.ConnectionSet;
import org.simantics.structural2.utils.StructuralUtils;
import org.simantics.structural2.utils.StructuralUtils.StructuralComponentClass;

import gnu.trove.map.hash.THashMap;
import gnu.trove.set.hash.THashSet;

public class ConnectionBrowser {

    /**
     * Finds the components connected by the connection. Also connections
     * in 
     * 
     * @param graph 
     * @param connection A connection whose related modules are searched.
     * @param configuration A variable that represents the composite where the connection belongs to.
     * @return A map whose keys are components and they are mapped to 
     *         related variables.
     */
    public static Collection<ResourceWithContext> findConnectedComponents(
            ReadGraph graph, Resource connection, Variable configuration) 
            throws DatabaseException {
        // Create state
        ArrayList<ResourceWithContext> result = 
            new ArrayList<ResourceWithContext>();
        THashSet<Resource> visitedConnections = new THashSet<Resource>();

        // Do actual work
        findConnectedComponents(graph, connection, configuration, result,
                visitedConnections);
        return result;
    }

    private static void findConnectedComponents(
            ReadGraph graph, Resource connection, Variable configuration,
            ArrayList<ResourceWithContext> result,
            THashSet<Resource> visitedConnections) throws DatabaseException {
         if(visitedConnections.add(connection)) {
             StructuralResource2 STR = StructuralResource2.getInstance(graph);
             Layer0 L0 = Layer0.getInstance(graph);

             // Browse related components
             for(Statement stat : graph.getStatements(connection, STR.Connects)) {
                 Resource component = stat.getObject();
                 Resource relation = graph.getInverse(stat.getPredicate());
                 //System.out.println(NameUtils.getSafeName(graph, component) + "." + NameUtils.getSafeName(graph, relation));
                 Resource boundConnection = graph.getPossibleObject(relation, STR.IsBoundBy);
                 Resource type = StructuralUtils.getPossibleComponentType(graph, configuration, component);
                 Resource def = type != null ? graph.getPossibleObject(type, STR.IsDefinedBy) : null;
                 if(boundConnection != null && def != null) {
                     // The connection point is bound in component type
                     Variable newContext = configuration.browsePossible(graph, component);
                     Resource newComposite = getCompositeOfConnection(graph, boundConnection);
                     if(newContext != null && newComposite != null) {
                         newContext = browse(graph, def, newContext, newComposite);
                         if (newContext != null)
                             findConnectedComponents(graph, boundConnection,
                                     newContext,
                                     result, visitedConnections);
                     }
                 }
                 else {
                     //System.out.println("added result");
                     // A primitive connection point
                     Variable context = configuration.browsePossible(graph, component);
                     if (context != null)
                         result.add(new ResourceWithContext(component, context)); 
                 }
             }

             // Browse over connection joins
             for(Resource join : graph.getObjects(connection, STR.IsJoinedBy))
                 for(Resource otherConnection : graph.getObjects(join, STR.Joins))
                     if(!connection.equals(otherConnection)) {
                         Resource sourceComposite = getCompositeOfConnection(graph, connection);
                         Resource targetComposite = getCompositeOfConnection(graph, otherConnection);
                         if (sourceComposite != null && targetComposite != null) {
                             Variable sibling = browseSibling(graph, 
                                     sourceComposite,
                                     configuration,
                                     targetComposite);
                             if (sibling != null)
                                 findConnectedComponents(graph, otherConnection,
                                         sibling, result, visitedConnections);
                         }
                     }

             // Browse to parents
             try {
                 for(Resource relation : graph.getObjects(connection, STR.Binds)) {
                     Resource composite = getCompositeOfConnection(graph, connection);
                     if (composite == null)
                         continue;

                     Variable curConfiguration = configuration;
                     while(!graph.hasStatement(composite, STR.Defines)) {
                         composite = graph.getSingleObject(composite, L0.PartOf);
                         curConfiguration = curConfiguration.getParent(graph);
                     }
                     Variable parent = curConfiguration.getParent(graph);
                     Resource component = curConfiguration.getRepresents(graph);
                     for(Resource c : graph.getObjects(component, relation))
                         findConnectedComponents(graph, c, 
                                 parent, result, visitedConnections);
                 }
             } catch(NoSingleResultException e) {
             } catch(MissingVariableException e) {
             } catch(MissingVariableValueException e) {
             }
         }
    }

    public static Collection<VariableConnectionPointDescriptor> drill(ReadGraph graph, VariableConnectionPointDescriptor pair) throws DatabaseException {

    	Collection<InterfaceResolution> interfaceDescription = pair.getInterfaceDescription(graph);
    	if(interfaceDescription != null && interfaceDescription.size() > 0) {

        	Variable cp = pair.getVariable(graph);
        	Variable context = cp.getParent(graph);
        	String cpName = cp.getName(graph);

        	Collection<VariableConnectionPointDescriptor> result = new ArrayList<VariableConnectionPointDescriptor>();
        	for(InterfaceResolution r : interfaceDescription) {
    			if(r.interfaceName.equals(cpName)) {
    				String path = Functions.resolveInterfacePath(graph, context, r.componentName, r.connectionPoint);
    				result.add(new BrowseConnectionDescriptor(context, path));
    			}
    		}
    		
    		if(result.isEmpty()) return null;
    		
    		return result;
    		
    	} else {
    		return Collections.singleton(pair);
    	}

    }
    
    public static class JoinConnections extends ResourceRead<Collection<Resource>> {

		public JoinConnections(Resource join) {
			super(join);
		}

		@Override
		public Collection<Resource> perform(ReadGraph graph) throws DatabaseException {
    		ConnectionSet cs = new ConnectionSet(graph);
    		cs.addJoin(graph, resource);
    		return cs.getConnections();
		}
    	
    }

    
    public static final class VariableChildren extends TransientUnaryRead<Variable, Map<Resource,Variable>> {

		public VariableChildren(ReadGraph graph, Variable variable) throws DatabaseException {
			super(graph, variable);
		}

		public VariableChildren(ReadGraph graph, QueryControl qc, Variable variable) throws DatabaseException {
			super(graph, qc, variable);
		}

		@Override
		public Map<Resource, Variable> perform(ReadGraph graph, Variable parameter) throws DatabaseException {
			CollectionSupport cs = graph.getService(CollectionSupport.class);
			Map<Resource,Variable> result = cs.createMap(Variable.class);
			for(Variable child : parameter.getChildren(graph)) {
				Resource represents = child.getPossibleRepresents(graph);
				if(represents != null) result.put(represents, child);
			}
			return result;
		}
    	
    }
    
    static Variable resolve(ReadGraph graph, Variable base, Resource component) throws DatabaseException {
    	Map<Resource,Variable> map = graph.syncRequest(new VariableChildren(graph, base), TransientCacheAsyncListener.<Map<Resource,Variable>>instance());
    	Variable result = map.get(component);
    	if(result != null) return result;
    	else {
    		Layer0 L0 = Layer0.getInstance(graph);
    		Resource parent = graph.getPossibleObject(component, L0.PartOf);
    		if(parent == null) return null;
    		Variable v = resolve(graph, base, parent);
    		if (v == null) return null;
        	map = graph.syncRequest(new VariableChildren(graph, v), TransientCacheAsyncListener.<Map<Resource,Variable>>instance());
    		return map.get(component);
    	}
    }
    
    public static class ConnectionComponentsWithAncestor extends TransientUnaryRead<Resource, List<Resource>> {

    	final private List<Resource> result;

		public ConnectionComponentsWithAncestor(ReadGraph graph, Resource conn) throws DatabaseException {
			this(graph, conn, null);
		}

    	public ConnectionComponentsWithAncestor(ReadGraph graph, QueryControl qc, Resource conn, List<Resource> result) throws DatabaseException {
			super(graph, qc, conn);
			this.result = result;
    	}

		public ConnectionComponentsWithAncestor(ReadGraph graph, Resource conn, List<Resource> result) throws DatabaseException {
			super(graph, conn);
			this.result = result;
		}

		private ConnectionSet connSet(ReadGraph graph, Resource r ) throws DatabaseException {
			ConnectionSet cs = new ConnectionSet(graph);
			cs.addConnection(graph, r);
			return cs;
		}
		
		@Override
		public List<Resource> perform(ReadGraph graph, Resource resource) throws DatabaseException {
			
			if(result != null) return result;
			
			Layer0 L0 = Layer0.getInstance(graph);
			StructuralResource2 STR = StructuralResource2.getInstance(graph);
			CollectionSupport colls = graph.getService(CollectionSupport.class);
			THashSet<Resource> ancestorGenerators = new THashSet<Resource>();
			Set<Resource> parts = colls.createSet();
			ConnectionSet cs = connSet(graph, resource);
            for(Resource connRes : cs.getConnections()) {
            	for(Statement stm : graph.getStatements(connRes, STR.Connects)) {
            		Resource component = stm.getObject();
            		Resource parent = graph.getPossibleObject(component, L0.PartOf);
            		if(parent != null && !graph.isInstanceOf(component, ModelingResources.getInstance(graph).ReferenceElement))
            			ancestorGenerators.add(parent);
            	}
            	parts.add(connRes);
            }
            for (Resource join : cs.getJoins()) {
            	parts.add(join);
            	for (Resource composite : graph.getObjects(join, STR.JoinsComposite))
            		ancestorGenerators.add(composite);
            }
            Resource ancestor = ancestorGenerators.size() == 1 ? ancestorGenerators.iterator().next() : NearestOwnerFinder.getNearestOwnerFromDirectOwners(graph, ancestorGenerators);
            
            List<Resource> result = colls.createList();
            result.add(ancestor);
            result.addAll(colls.asSortedList(parts));
            
            if(parameter != WITH_PARENT) {
            	for(int i=1;i<result.size();i++) {
	            	Resource r = result.get(i);
	            	// Cache 'em all
	            	if(!r.equals(resource))
	            		graph.syncRequest(new ConnectionComponentsWithAncestor(graph, r, result), TransientCacheAsyncListener.<List<Resource>>instance());
	            }
            }
            
            return result;
            
		}
    	
    }
    
    public static Collection<VariableConnectionPointDescriptor> climb(ReadGraph graph, Variable child, Resource cp, String subPath_) throws DatabaseException {
        
    	boolean isStructural = false;

    	Variable curConfiguration = child.getParent(graph);

    	{

			Collection<InterfaceResolution> interfaceDescription = Functions.computeInterfacePaths(graph, curConfiguration);
    		if(interfaceDescription != null) {
    			isStructural = interfaceDescription != Functions.BUILTIN_STRUCTURAL_CPS;
    			if(interfaceDescription.size() > 0) {
    				
    				if(subPath_ == null) {
    					
    					String childName = child.getName(graph);
    					for(InterfaceResolution r : interfaceDescription) {
    						if(r.componentName.equals(childName) && r.connectionPoint.equals(cp)) {
    							Variable pConn = curConfiguration.getPossibleProperty(graph, r.interfaceName);
    							if(pConn != null) {
    								Resource cp2 = pConn.getPossiblePredicateResource(graph);
    								Collection<VariableConnectionPointDescriptor> res = climb(graph, curConfiguration, cp2, null);
    								if(res != null) return res;
    							}
    							return Collections.emptyList();
    						}
    					}

    				} else {
    					throw new UnsupportedOperationException("");
    				}
    			}
    		}

    	}
        
        if(child instanceof StandardProceduralChildVariable) {
        	
        	Variable conn = child.getPossibleProperty(graph, cp);
            FixedConnection fc = (FixedConnection)conn.getValue(graph);
            Set<VariableConnectionPointDescriptor> result = new THashSet<VariableConnectionPointDescriptor>(1+fc.size());
            result.add(new ComponentConnectionDescriptor(child, cp));
            fc.addConnectionDescriptors(graph, curConfiguration, result);
            return result;
            
        } else {

            Resource res = cp;
            Resource represents = child.getRepresents(graph);

        	if(isStructural) {

        		Collection<Resource> conns = graph.getObjects(represents, res);
        		HashSet<VariableConnectionPointDescriptor> result = new HashSet<VariableConnectionPointDescriptor>();
        		for(Resource c : conns) {
        			List<Resource> rs = graph.syncRequest(new ConnectionComponentsWithAncestor(graph, c), TransientCacheAsyncListener.<List<Resource>>instance()); 
        			result.addAll(graph.syncRequest(ConnectionVariables.forStructural(graph, curConfiguration, rs)));
        		}
        		return result;
        		
        	} else {

            	Resource connection = graph.getPossibleObject(represents, res);
            	if(connection != null) {
            		List<Resource> rs = graph.syncRequest(new ConnectionComponentsWithAncestor(graph, connection), TransientCacheAsyncListener.<List<Resource>>instance());
            		return graph.syncRequest(ConnectionVariables.forConfiguration(graph, curConfiguration, rs));
            	}
            	else {
            		Collection<Resource> conns = graph.getObjects(represents, res);
            		HashSet<VariableConnectionPointDescriptor> result = new HashSet<VariableConnectionPointDescriptor>();
            		for(Resource c : conns) {
            			List<Resource> rs = graph.syncRequest(new ConnectionComponentsWithAncestor(graph, c), TransientCacheAsyncListener.<List<Resource>>instance()); 
            			result.addAll(graph.syncRequest(ConnectionVariables.forConfiguration(graph, curConfiguration, rs)));
            		}
            		return result;
            	}
        		
        	}
        	
        }
        
    }
    
    public static void reportDescriptor(ReadGraph graph, VariableConnectionPointDescriptor d) throws DatabaseException {

    	if(d instanceof ActualConnectionDescriptor) {
    		ActualConnectionDescriptor d2 = (ActualConnectionDescriptor)d; 
    		
    		System.err.println("--ActualConnectionPointDescriptor2");
    		System.err.println("---root: " + d2.root.getURI(graph));
    		System.err.println("---component: " + graph.getPossibleURI(d2.component));
    		System.err.println("---type: " + graph.getPossibleURI(d2.componentType));
    		System.err.println("---cp: " + graph.getPossibleURI(d2.cp));
    		System.err.println("---var: " + d2.getVariable(graph).getURI(graph));
    	}
    	
    }
    
    public static class ConnectionVariables extends BinaryRead<Variable, List<Resource>, Collection<VariableConnectionPointDescriptor>> {

    	private ConnectionVariables(Variable parameter1, List<Resource> parameter2) {
			super(parameter1, parameter2);
		}

		public static ConnectionVariables forConfiguration(ReadGraph graph, Variable configuration, List<Resource> rs) throws DatabaseException {
			return new ConnectionVariables(parent(graph, configuration, rs.get(0)), rs);
		}

		public static ConnectionVariables forStructural(ReadGraph graph, Variable configuration, List<Resource> rs) throws DatabaseException {
			return new ConnectionVariables(configuration, rs);
		}

		/**
		 * Finds the parent variable of <code>configuration</code> that
		 * represents <code>ancestor</code>.
		 * 
		 * @param graph
		 * @param configuration
		 * @param ancestor
		 * @return
		 * @throws DatabaseException if no parent was found that represents ancestor
		 */
		private static Variable parent(ReadGraph graph, Variable configuration, Resource ancestor) throws DatabaseException {
    		Variable v = configuration;
    		Resource represents = v.getRepresents(graph);
    		while(!represents.equals(ancestor)) {
    			v = v.getParent(graph);
    			if (v == null) {
					throw new DatabaseException(
							"parent representing ancestor not found for variable, configuration="
									+ safeURI(graph, configuration)
									+ ", ancestor="
									+ NameUtils.getURIOrSafeNameInternal(graph, ancestor));
    			}
        		represents = v.getRepresents(graph);
    		}
    		return v;
		}

		@Override
		public Collection<VariableConnectionPointDescriptor> perform(ReadGraph graph) throws DatabaseException {
			if(parameter == null) return Collections.emptyList();
    		Layer0 L0 = Layer0.getInstance(graph);
			StructuralResource2 STR = StructuralResource2.getInstance(graph);
            ArrayList<VariableConnectionPointDescriptor> result = null;
            for(int i=1;i<parameter2.size();i++) {
            	Resource connRes = parameter2.get(i);
            	for(Statement stm : graph.getStatements(connRes, STR.Connects)) {
            		Resource component = stm.getObject();
            		Resource connectionPoint = graph.getInverse(stm.getPredicate());
            		if(result == null) result = new ArrayList<VariableConnectionPointDescriptor>();
            		String componentName = graph.getRelatedValue(component, L0.HasName, Bindings.STRING);
            		Variable possibleChild = parameter.getPossibleChild(graph, componentName);
            		if(possibleChild != null) {
            		    Resource type = possibleChild.getPossibleType(graph, STR.Component);
            		    if(type != null) {
                            result.add(new ActualConnectionDescriptor(parameter, component, possibleChild.getType(graph), connectionPoint));
            		    } else {
                            throw new DatabaseException("Child does not have a structural type: " + possibleChild.getURI(graph));
            		    }
            		} else {
            		    Resource type = graph.getPossibleType(component, STR.Component);
            		    if(type != null) {
                            result.add(new ActualConnectionDescriptor(parameter, component, type, connectionPoint));
            		    } else {
                            throw new DatabaseException("Child with name " + componentName + " does not have a structural type: " + parameter.getURI(graph));
            		    }
            		}
            	}
            }
            if(result == null) return Collections.emptyList();
            return result;
		}
    	
    }
    
    static class IsLeafType extends ResourceRead<Boolean> {

		protected IsLeafType(Resource type) {
			super(type);
		}

		@Override
		public Boolean perform(ReadGraph graph) throws DatabaseException {
			
			StructuralComponentClass clazz = StructuralComponentClass.get(graph, resource);
			return StructuralComponentClass.PRIMITIVE.equals(clazz);

		}
    	
    }
    
    static class ChildMapOfVariable extends VariableRead<Map<Resource,Variable>> {

		public ChildMapOfVariable(Variable variable) {
			super(variable);
		}

		@Override
		public Map<Resource, Variable> perform(ReadGraph graph) throws DatabaseException {
			HashMap<Resource,Variable> result = new HashMap<Resource,Variable>();
			for(Variable child : variable.getChildren(graph)) {
				Resource represents = child.getPossibleRepresents(graph);
				if(represents != null) result.put(represents, child);
			}
			return result;
		}
    	
    }

    /**
     * Given a root composite, related variable and some other component inside the composite,
     * finds the related variable for that component.
     */
    public static Variable browse(ReadGraph graph, Resource root, Variable rootContext, Resource target) throws DatabaseException {
        if(target.equals(root))
            return rootContext;
        else {
            Layer0 L0 = Layer0.getInstance(graph);
            String name = (String)graph.getPossibleRelatedValue(target, L0.HasName, Bindings.STRING);
            Resource parent = graph.getPossibleObject(target, L0.PartOf);
            if(name == null || parent == null)
                return null;
            Variable parentVariable = browse(graph, root, rootContext, parent);
            if(parentVariable == null)
                return null;
            return parentVariable.getPossibleChild(graph, name);
        }
    }

    /**
     * Finds a variable whose location related to sourceContext is the same as 
     * between target and source. In other words, the method solves {@code targetContext}
     * in the following equations:
     * <pre>
     *     URI(source)        = resourceURIBase + sourceSuffix
     *     URI(sourceContext) = variableURIBase + sourceSuffix
     *     URI(target)        = resourceURIBase + targetSuffix
     *     URI(targetContext) = variableURIBase + targetSuffix
     * </pre>
     */
    public static Variable browseSibling(ReadGraph graph, Resource source, Variable sourceContext, Resource target) throws DatabaseException {
        Layer0 L0 = Layer0.getInstance(graph);
        THashMap<Resource, Variable> sourceMap = new THashMap<Resource, Variable>();
        while(source != null && sourceContext != null) {
            sourceMap.put(source, sourceContext);
            source = graph.getPossibleObject(source, L0.PartOf);
            sourceContext = sourceContext.getParent(graph);
        }
        return browseSibling(graph, sourceMap, target);
    }

    private static Variable browseSibling(ReadGraph graph, THashMap<Resource, Variable> sourceMap, Resource target) throws DatabaseException {
        Layer0 L0 = Layer0.getInstance(graph);
        Variable result = sourceMap.get(target);
        if(result != null)
            return result;
        String name = (String)graph.getPossibleRelatedValue(target, L0.HasName, Bindings.STRING);
        Resource parent = graph.getPossibleObject(target, L0.PartOf);
        if(name == null || parent == null)
            return null;
        Variable parentVariable = browseSibling(graph, sourceMap, parent);
        if(parentVariable == null)
            return null;
        return parentVariable.getPossibleChild(graph, name);
    }

    /**
     * Returns the composite where the connection given as a parameter resides.
     */
    public static Resource getCompositeOfConnection(ReadGraph graph, Resource connection) throws DatabaseException {
        Layer0 L0 = Layer0.getInstance(graph);
        StructuralResource2 STR = StructuralResource2.getInstance(graph);
        // First from connected components
        for(Resource component : graph.getObjects(connection, STR.Connects))
            for(Resource composite : graph.getObjects(component, L0.PartOf))
                return composite;
        // It could be that the connection is only supported by joins (input flag -> output flag) - use diagram info TODO!!
        Resource connToDiagramConn = graph.getPossibleResource("http://www.simantics.org/Modeling-1.2/ConnectionToDiagramConnection");
        if(connToDiagramConn != null) {
            Resource diagramConnection = graph.getPossibleObject(connection, connToDiagramConn);
            if(diagramConnection != null) {
                Resource diagram = graph.getPossibleObject(diagramConnection, L0.PartOf);
                if(diagram != null) {
                    Resource diagramToComposite = graph.getPossibleResource("http://www.simantics.org/Modeling-1.2/DiagramToComposite");
                    if(diagramToComposite != null) {
                        return graph.getPossibleObject(diagram, diagramToComposite);
                    }
                }
            }
        }
        return null;
    }
    
	static class Flatten extends BinaryRead<Variable,Resource,Collection<VariableConnectionPointDescriptor>> {

		public Flatten(Variable parameter1,
				Resource parameter2) {
			super(parameter1, parameter2);
		}

		@Override
		public Collection<VariableConnectionPointDescriptor> perform(ReadGraph graph)
				throws DatabaseException {
			return doFlatten(graph, parameter, parameter2, null);
		}
		
	}
    
    public static Collection<VariableConnectionPointDescriptor> flatten(ReadGraph graph, Variable child, Resource cp, Resource relationType) throws DatabaseException {

    	if(relationType == null) return graph.syncRequest(new Flatten(child, cp));

    	return doFlatten(graph, child, cp, relationType);

    }

	public static Collection<VariableConnectionPointDescriptor> doFlatten(ReadGraph graph, Variable child, Resource cp, Resource relationType) throws DatabaseException {
    	
        Set<VariableConnectionPointDescriptor> result = null;
        Set<VariableConnectionPointDescriptor> needDrill = null;
        
		Collection<VariableConnectionPointDescriptor> climbed = climb(graph, child, cp, null);
        for(VariableConnectionPointDescriptor desc : climbed) {
        	if(!desc.isLeaf(graph)) {
        		if(needDrill == null)
        			needDrill = new THashSet<VariableConnectionPointDescriptor>(climbed.size());
        		needDrill.add(desc);
        	} else {
                if(relationType != null) {
                    if(!filterByRelationType(graph, desc, relationType))
                        continue;
                }
        		if(result == null)
        			result = new THashSet<VariableConnectionPointDescriptor>(climbed.size());
        		result.add(desc);
        	}
        }
        
        if(needDrill != null) {
            /*
             * There were some descriptors that require drill
             */
            for(VariableConnectionPointDescriptor top : needDrill) {
                Collection<VariableConnectionPointDescriptor> drilled = drill(graph, top);
                if(drilled != null) {
                    for(VariableConnectionPointDescriptor drill : drilled) {
                        if(relationType != null) {
                            if(!filterByRelationType(graph, drill, relationType))
                                continue;
                        }
                        if(result == null)
                            result = new THashSet<VariableConnectionPointDescriptor>(climbed.size());
                        result.add(drill);
                    }
                }
            }
        }

        if (result != null) {
            return result;
        } else {
            return Collections.emptySet();
        }
    }
    
    private static boolean filterByRelationType(ReadGraph graph, VariableConnectionPointDescriptor desc, Resource relationType) throws DatabaseException {
        Resource predicateResource = desc.getConnectionPointResource(graph);
        return predicateResource != null && graph.isInstanceOf(predicateResource, relationType);
    }

    private static String safeURI(ReadGraph graph, Variable v) {
        if (v == null)
            return "null variable";
        try {
            return v.getURI(graph);
        } catch (DatabaseException e) {
            return v.toString();
        }
    }
}