package org.jbpm.services.task.persistence;

import static org.kie.internal.query.QueryParameterIdentifiers.ACTUAL_OWNER_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.ARCHIVED;
import static org.kie.internal.query.QueryParameterIdentifiers.BUSINESS_ADMIN_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.CREATED_BY_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.CREATED_ON_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.DEPLOYMENT_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.EXCLUDED_OWNER_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.EXPIRATION_TIME_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.POTENTIAL_OWNER_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.PROCESS_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.PROCESS_INSTANCE_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.PROCESS_SESSION_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.SKIPPABLE;
import static org.kie.internal.query.QueryParameterIdentifiers.STAKEHOLDER_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.SUB_TASKS_STRATEGY;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_ACTIVATION_TIME_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_DESCRIPTION_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_FORM_NAME_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_NAME_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_PARENT_ID_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_PRIORITY_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_STATUS_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_SUBJECT_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TASK_USER_ROLES_LIMIT_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.TYPE_LIST;
import static org.kie.internal.query.QueryParameterIdentifiers.WORK_ITEM_ID_LIST;

import java.util.ArrayList;
import java.util.Date;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.ServiceLoader;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

import javax.persistence.Tuple;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Expression;
import javax.persistence.criteria.From;
import javax.persistence.criteria.Join;
import javax.persistence.criteria.JoinType;
import javax.persistence.criteria.ListJoin;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;
import javax.persistence.criteria.Selection;
import javax.persistence.metamodel.Attribute;
import javax.persistence.metamodel.CollectionAttribute;
import javax.persistence.metamodel.ListAttribute;
import javax.persistence.metamodel.PluralAttribute;
import javax.persistence.metamodel.SetAttribute;
import javax.persistence.metamodel.SingularAttribute;

import org.jbpm.query.jpa.data.QueryCriteria;
import org.jbpm.query.jpa.data.QueryParameterIdentifiersUtil;
import org.jbpm.query.jpa.data.QueryWhere;
import org.jbpm.query.jpa.data.QueryWhere.QueryCriteriaType;
import org.jbpm.query.jpa.service.QueryModificationService;
import org.jbpm.services.task.impl.model.I18NTextImpl;
import org.jbpm.services.task.impl.model.I18NTextImpl_;
import org.jbpm.services.task.impl.model.OrganizationalEntityImpl;
import org.jbpm.services.task.impl.model.OrganizationalEntityImpl_;
import org.jbpm.services.task.impl.model.PeopleAssignmentsImpl;
import org.jbpm.services.task.impl.model.PeopleAssignmentsImpl_;
import org.jbpm.services.task.impl.model.TaskDataImpl;
import org.jbpm.services.task.impl.model.TaskDataImpl_;
import org.jbpm.services.task.impl.model.TaskImpl;
import org.jbpm.services.task.impl.model.TaskImpl_;
import org.jbpm.services.task.impl.model.UserImpl;
import org.jbpm.services.task.impl.model.UserImpl_;
import org.jbpm.services.task.query.TaskSummaryImpl;
import org.kie.api.task.UserGroupCallback;
import org.kie.api.task.model.Status;
import org.kie.api.task.model.TaskSummary;
import org.kie.internal.query.QueryParameterIdentifiers;
import org.kie.internal.task.api.TaskPersistenceContext;
import org.kie.internal.task.api.model.SubTasksStrategy;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class TaskSummaryQueryCriteriaUtil extends AbstractTaskQueryCriteriaUtil {

    public final static Logger logger = LoggerFactory.getLogger(TaskSummaryQueryCriteriaUtil.class);

    // Query Field Info -----------------------------------------------------------------------------------------------------------

    public final static Map<Class, Map<String, Attribute>> criteriaAttributes
        = new ConcurrentHashMap<Class, Map<String, Attribute>>();

    private ServiceLoader<QueryModificationService> queryModificationServiceLoader = ServiceLoader.load(QueryModificationService.class);

    @Override
    protected synchronized boolean initializeCriteriaAttributes() {
        if( TaskImpl_.id == null ) {
            // EMF/persistence has not been initialized:
            // When a persistence unit (EntityManagerFactory) is initialized,
            // the fields of classes annotated with @StaticMetamodel are filled using reflection
            return false;
        }
        // do not do initialization twice (slow performance, otherwise it doesn't matter)
        if( ! criteriaAttributes.isEmpty() ) {
            return true;
        }

        // TaskImpl
        addCriteria(criteriaAttributes, TASK_ACTIVATION_TIME_LIST,  TaskImpl.class, TaskDataImpl_.activationTime);
        addCriteria(criteriaAttributes, ARCHIVED,                   TaskImpl_.archived);
        addCriteria(criteriaAttributes, CREATED_ON_LIST,            TaskImpl.class, TaskDataImpl_.createdOn);
        addCriteria(criteriaAttributes, DEPLOYMENT_ID_LIST,         TaskImpl.class, TaskDataImpl_.deploymentId);
        addCriteria(criteriaAttributes, EXPIRATION_TIME_LIST,       TaskImpl.class, TaskDataImpl_.expirationTime);
        addCriteria(criteriaAttributes, TASK_FORM_NAME_LIST,        TaskImpl_.formName);
        addCriteria(criteriaAttributes, PROCESS_ID_LIST,            TaskImpl.class, TaskDataImpl_.processId);
        addCriteria(criteriaAttributes, PROCESS_INSTANCE_ID_LIST,   TaskImpl.class, TaskDataImpl_.processInstanceId);
        addCriteria(criteriaAttributes, PROCESS_SESSION_ID_LIST,    TaskImpl.class, TaskDataImpl_.processSessionId);
        addCriteria(criteriaAttributes, SKIPPABLE,                  TaskImpl.class, TaskDataImpl_.skipable);
        addCriteria(criteriaAttributes, TASK_STATUS_LIST,           TaskImpl.class, TaskDataImpl_.status);
        addCriteria(criteriaAttributes, SUB_TASKS_STRATEGY,         TaskImpl_.subTaskStrategy);
        addCriteria(criteriaAttributes, TASK_ID_LIST,               TaskImpl_.id);
        addCriteria(criteriaAttributes, TASK_PARENT_ID_LIST,        TaskImpl.class, TaskDataImpl_.parentId);
        addCriteria(criteriaAttributes, TYPE_LIST,                  TaskImpl_.taskType);
        addCriteria(criteriaAttributes, WORK_ITEM_ID_LIST,          TaskImpl.class, TaskDataImpl_.workItemId);
        addCriteria(criteriaAttributes, TASK_PRIORITY_LIST,         TaskImpl.class, TaskImpl_.priority);

        addCriteria(criteriaAttributes, TASK_DESCRIPTION_LIST,      TaskImpl_.descriptions);
        addCriteria(criteriaAttributes, TASK_NAME_LIST,             TaskImpl_.names);
        addCriteria(criteriaAttributes, TASK_SUBJECT_LIST,          TaskImpl_.subjects);

        addCriteria(criteriaAttributes, ACTUAL_OWNER_ID_LIST,       TaskImpl.class, TaskDataImpl_.actualOwner);
        addCriteria(criteriaAttributes, CREATED_BY_LIST,            TaskImpl.class, TaskDataImpl_.createdBy); // initiator

        addCriteria(criteriaAttributes, BUSINESS_ADMIN_ID_LIST,     TaskImpl.class, PeopleAssignmentsImpl_.businessAdministrators);
        addCriteria(criteriaAttributes, POTENTIAL_OWNER_ID_LIST,    TaskImpl.class, PeopleAssignmentsImpl_.potentialOwners);
        addCriteria(criteriaAttributes, STAKEHOLDER_ID_LIST,        TaskImpl.class, PeopleAssignmentsImpl_.taskStakeholders);
        addCriteria(criteriaAttributes, EXCLUDED_OWNER_ID_LIST,     TaskImpl.class, PeopleAssignmentsImpl_.excludedOwners);


        return true;
    }

    private static final Set<String> taskUserRoleLimitingListIds = new HashSet<String>();
    static {
        taskUserRoleLimitingListIds.add(ACTUAL_OWNER_ID_LIST);
        taskUserRoleLimitingListIds.add(CREATED_BY_LIST);
        taskUserRoleLimitingListIds.add(BUSINESS_ADMIN_ID_LIST);
        taskUserRoleLimitingListIds.add(POTENTIAL_OWNER_ID_LIST);
        taskUserRoleLimitingListIds.add(STAKEHOLDER_ID_LIST);
    }

    public TaskSummaryQueryCriteriaUtil(TaskPersistenceContext persistenceContext) {
        super(persistenceContext);
        initialize(criteriaAttributes);
    }

    public TaskSummaryQueryCriteriaUtil() {
        initialize(criteriaAttributes);
    }

    // Implementation specific methods --------------------------------------------------------------------------------------------

    public List<TaskSummary> doCriteriaQuery(String userId, UserGroupCallback userGroupCallback, QueryWhere queryWhere) {

        // 1. create builder and query instances
        CriteriaBuilder builder = getCriteriaBuilder();
        CriteriaQuery<Tuple> criteriaQuery = builder.createTupleQuery();

        // 2. query base
        Root<TaskImpl> taskRoot = criteriaQuery.from(TaskImpl.class);
        criteriaQuery = criteriaQuery.multiselect(
                taskRoot.get(TaskImpl_.id),                                                         // 0
                taskRoot.get(TaskImpl_.name),                                                       // 1
                taskRoot.get(TaskImpl_.subject),                                                    // 2
                taskRoot.get(TaskImpl_.description),                                                // 3

                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.status),                         // 4
                taskRoot.get(TaskImpl_.priority),                                                   // 5
                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.skipable),                       // 6

                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.actualOwner).get(UserImpl_.id),  // 7
                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.createdBy).get(UserImpl_.id),    // 8

                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.createdOn),                      // 9
                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.activationTime),                 // 10
                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.expirationTime),                 // 11

                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.processId),                      // 12
                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.processSessionId),               // 13
                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.processInstanceId),              // 14
                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.deploymentId),                   // 15

                taskRoot.get(TaskImpl_.subTaskStrategy),                                            // 16
                taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.parentId)                        // 17
                );
        taskRoot.join(TaskImpl_.taskData); // added for convienence sake, since other logic expects to find this join

        checkExistingCriteriaForUserBasedLimit(queryWhere, userId, userGroupCallback);
        for( QueryModificationService queryModificationService : queryModificationServiceLoader ) {
            queryModificationService.optimizeCriteria(queryWhere);
        }

        // 4. process query criteria
        fillCriteriaQuery(criteriaQuery, queryWhere, builder, TaskImpl.class);

        // 5. retrieve result (after also applying meta-criteria)
        useDistinctWhenLefOuterJoinsPresent(criteriaQuery);
        List<Tuple> result = createQueryAndCallApplyMetaCriteriaAndGetResult(queryWhere, criteriaQuery, builder);

        List<TaskSummary> taskSummaryList = new ArrayList<TaskSummary>(result.size());
        for( Tuple tupleRow : result ) {
            int i = 0;
            //@formatter:off
            TaskSummaryImpl taskSummaryImpl = new TaskSummaryImpl(
               // id
               tupleRow.get(i++, Long.class),
               // name, subject, description
               tupleRow.get(i++, String.class), tupleRow.get(i++, String.class), tupleRow.get(i++, String.class),
               // status, prio, skippable
               tupleRow.get(i++, Status.class), tupleRow.get(i++, Integer.class), tupleRow.get(i++, Boolean.class),
               // actual owner, created by
               tupleRow.get(i++, String.class), tupleRow.get(i++, String.class),
               // created on, activation time, expiration time
               tupleRow.get(i++, Date.class), tupleRow.get(i++, Date.class), tupleRow.get(i++, Date.class),
               // process id, process session id, process inst id, deployment id
               tupleRow.get(i++, String.class), tupleRow.get(i++, Long.class), tupleRow.get(i++, Long.class), tupleRow.get(i++, String.class),
               tupleRow.get(i++, SubTasksStrategy.class),
               tupleRow.get(i++, Long.class) );
            //@formatter:on
            taskSummaryList.add(taskSummaryImpl);

        }
        return taskSummaryList;
    }

    /**
     * This method checks whether or not the query *already* contains a limiting criteria (in short, a criteria that limits results
     * of the query) that refers to the user or (the user's groups).  If there is no user/group limiting criteria, then a
     * {@link QueryCriteria} with the user and group ids is added to the {@link QueryWhere} instance
     * </p>
     * If this method returns true, then there is no need to add additional criteria to the query to limit the query results
     * to tasks that the user may see -- there is already query present in the query that takes care of this.
     *
     * @param queryWhere The {@link QueryWhere} instance containing the query criteria
     * @param userId The string user id of the user calling the query
     * @param userGroupCallback A {@link UserGroupCallback} instance in order to retrieve the groups of the given user
     */
    private void checkExistingCriteriaForUserBasedLimit(QueryWhere queryWhere, String userId, UserGroupCallback userGroupCallback) {
        List<String> groupIds = userGroupCallback.getGroupsForUser(userId);
        Set<String> userAndGroupIds = new HashSet<String>();
        if( groupIds != null ) {
            userAndGroupIds.addAll(groupIds);
        }
        userAndGroupIds.add(userId);
        if( ! criteriaListForcesUserLimitation(userAndGroupIds, queryWhere.getCriteria()) ) {
            addUserRolesLimitCriteria(queryWhere, userId, groupIds);
        }
    }

    /**
     * This method calls itself recursively to determine whether or not the given {@link List}<{@link QueryCriteria}> contains a
     * user/group limiting criteria.
     *
     * @param userAndGroupIds A set containing the user id and all group ids
     * @param criteriaList The {@link List} of {@link QueryCriteria} to search
     * @return Whether or not the {@link QueryCriteria} list contains a user/group limiting criteria
     */
    private static boolean criteriaListForcesUserLimitation(Set<String> userAndGroupIds, List<QueryCriteria> criteriaList) {
        boolean userLimitiationIntersection = false;
        if( criteriaList.isEmpty() ) {
            return false;
        }
        for( QueryCriteria criteria : criteriaList ) {
          if( criteria.isUnion() ) {
              return false;
          }
          if( criteria.isGroupCriteria() ) {
              if( criteriaListForcesUserLimitation(userAndGroupIds, criteria.getCriteria()) ) {
                  return true;
              }
              continue;
          }
          // intersection criteria
          if( taskUserRoleLimitingListIds.contains(criteria.getListId()) ) {
              for( Object param : criteria.getParameters() ) {
                  if( userAndGroupIds.contains(param) )  {
                      return true;
                  }
              }
          }
        }
        return userLimitiationIntersection;
    }

    /**
     * Adds an (intersecting) {@link QueryCriteria} that limits the results to results that the user is allowed to see
     *
     * @param queryWhere The {@link QueryWhere} instance that defines the query criteria
     * @param userId The user id
     * @param groupIds The user's group ids
     */
    private void addUserRolesLimitCriteria( QueryWhere queryWhere, String userId, List<String> groupIds ) {
        List<QueryCriteria> newBaseCriteriaList = new ArrayList<QueryCriteria>(2);

        // user role limiting criteria
        QueryCriteria userRolesLimitingCriteria = new QueryCriteria(
                QueryParameterIdentifiers.TASK_USER_ROLES_LIMIT_LIST,
                false,
                QueryCriteriaType.NORMAL,
                2);
        userRolesLimitingCriteria.setFirst(true);
        userRolesLimitingCriteria.getValues().add(userId);
        userRolesLimitingCriteria.getValues().add(groupIds);
        newBaseCriteriaList.add(userRolesLimitingCriteria);

        // original criteria list in a new group
        if( ! queryWhere.getCriteria().isEmpty() ) {
            QueryCriteria originalBaseCriteriaGroup = new QueryCriteria(false);
            originalBaseCriteriaGroup.setCriteria(queryWhere.getCriteria());
            newBaseCriteriaList.add(originalBaseCriteriaGroup);
        }

        queryWhere.setCriteria(newBaseCriteriaList);
    }


    /*
     * (non-Javadoc)
     * @see org.jbpm.query.jpa.impl.QueryCriteriaUtil#getEntityField(javax.persistence.criteria.CriteriaQuery, java.lang.Class, java.lang.String)
     */
    @Override
    protected <T> Expression getEntityField(CriteriaQuery<T> query, String listId, Attribute attr) {
        if( attr == null ) {
            return null;
        }
        Root<TaskImpl> taskRoot = null;
        Join<TaskImpl, TaskDataImpl> taskDataJoin = null;
        Join<TaskImpl, PeopleAssignmentsImpl> peopAssignJoin = null;

        for( Root root : query.getRoots() ) {
            if( TaskImpl.class.equals(root.getJavaType()) ) {
               taskRoot = (Root<TaskImpl>) root;
               for( Join<TaskImpl, ?> join : taskRoot.getJoins() ) {
                  if( TaskDataImpl.class.equals(join.getJavaType()) ) {
                      taskDataJoin = (Join<TaskImpl, TaskDataImpl>) join;
                  } else if( PeopleAssignmentsImpl.class.equals(join.getJavaType()) )  {
                      peopAssignJoin = (Join<TaskImpl, PeopleAssignmentsImpl>) join;
                  }
               }
            }
        }
        assert taskRoot != null : "Unable to find TaskImpl Root in query!";
        if( taskDataJoin == null ) {
            taskDataJoin = taskRoot.join(TaskImpl_.taskData);
        }
        assert taskDataJoin != null : "Unable to find TaskDataImpl Join in query!";

        return taskImplSpecificGetEntityField(query, taskRoot,
                taskDataJoin, peopAssignJoin,
                listId, attr);
    }

    @SuppressWarnings("unchecked")
    public static <T> Expression taskImplSpecificGetEntityField(CriteriaQuery<T> query,
            Root<TaskImpl> taskRoot,
            Join<TaskImpl, TaskDataImpl> taskDataJoin,
            Join<TaskImpl, PeopleAssignmentsImpl> peopleAssignJoin,
            String listId, Attribute attr) {
        Expression entityField = null;

        if( attr != null ) {
            if( listId.equals(TASK_DESCRIPTION_LIST)
                    || listId.equals(TASK_NAME_LIST)
                    || listId.equals(TASK_SUBJECT_LIST) ) {

                // we can *not* query on @LOB annotated fields (and it would be inefficient for a query api to do this?)
                // so we query on the (max 255 char length) string equivalent fields
                entityField = getJoinedEntityField(taskRoot, (Attribute<TaskImpl, I18NTextImpl>) attr, I18NTextImpl_.shortText);
            } else if( listId.equals(ACTUAL_OWNER_ID_LIST)
                    || listId.equals(CREATED_BY_LIST) ) {
                if( taskDataJoin == null ) {
                    taskDataJoin = taskRoot.join(TaskImpl_.taskData);
                }

                // task -> taskData -> (actualOwn/createdBy) UserImpl ->  id
                entityField = getJoinedEntityField(taskDataJoin, (Attribute<TaskDataImpl, UserImpl>) attr, UserImpl_.id);
            } else if( listId.equals(BUSINESS_ADMIN_ID_LIST)
                || listId.equals(POTENTIAL_OWNER_ID_LIST)
                || listId.equals(STAKEHOLDER_ID_LIST)
                || listId.equals(EXCLUDED_OWNER_ID_LIST) ) {
                if( peopleAssignJoin == null ) {
                    peopleAssignJoin = taskRoot.join(TaskImpl_.peopleAssignments);
                }

                // task -> peopleAssignments -> (bus admin/pot owner/stake holder/excl user) OrganizationalEntityImpl ->  id
                entityField = getJoinedEntityField(peopleAssignJoin, (Attribute<PeopleAssignmentsImpl, OrganizationalEntityImpl>) attr, OrganizationalEntityImpl_.id);
            } else {
                if( taskDataJoin == null ) {
                    taskDataJoin = taskRoot.join(TaskImpl_.taskData);
                }
                Class attrType = attr.getDeclaringType().getJavaType();
                From [] taskRoots = { taskRoot, taskDataJoin };
                for( From from : taskRoots ) {
                    if( from.getJavaType().equals(attrType) ) {
                        if( attr != null ) {
                            if( attr instanceof SingularAttribute ) {
                                entityField = from.get((SingularAttribute) attr);
                            } else if( attr instanceof PluralAttribute ) {
                                entityField = from.get((PluralAttribute) attr);
                            } else {
                                throw new IllegalStateException("Unexpected attribute type when processing criteria with list id " + listId + ": " + attr.getClass().getName() );
                            }
                            break;
                        }
                    }
                }
            }
        }

        return entityField;
    }

    /**
     * This retrieves the correct field ({@link Expression}) that should be used when building the {@link Predicate}.
     * </p>
     * This field is necessary because of the amount of joins and the complexity in the human-task schema.
     *
     * @param grandparentJoin This is the parent join,
     *                        for example the join between TaskDataImpl -> PeopleAssignments
     * @param parentJoinAttr This is the {@link Attribute} with the information over the join (from the parent) that we need to create,
     *                       for example the {@link SingularAttribute}<{@link PeopleAssignmentsImpl}, {@link OrganizationalEntityImpl}> {@link Attribute}.
     * @param fieldAttr This is the {@link Attribute} with the actual attribute that we create an {@link Expression} to build a {@link Predicate} for,
     *                  for example the {@link OrganizationalEntityImpl_#id} field.
     * @return an {@link Expression} that can be used in a predicate with the values/parameters from a {@link QueryCriteria} instance
     */
    @SuppressWarnings("unchecked")
    public static <F,T> Expression getJoinedEntityField(From<?, F> grandparentJoin, Attribute<?, T> parentJoinAttr, SingularAttribute fieldAttr) {
        // task -> * -> origJoin -> (fieldParentAttr field in) tojoinType ->  fieldAttr

        Class toAttrJoinType;
        if( parentJoinAttr instanceof SingularAttribute ) {
            toAttrJoinType = parentJoinAttr.getJavaType();
        } else if( parentJoinAttr instanceof PluralAttribute ) {
            toAttrJoinType = ((PluralAttribute) parentJoinAttr).getElementType().getJavaType();
        } else {
            String joinName = parentJoinAttr.getDeclaringType().getJavaType().getSimpleName() + "." + parentJoinAttr.getName();
            throw new IllegalStateException("Unknown attribute type encountered when trying to join " + joinName );
        }

        Join<F, T> fieldParentJoin = null;
        for( Join<F, ?> join : grandparentJoin.getJoins() ) {
           if( join.getJavaType().equals(toAttrJoinType) ) {
              if( join.getAttribute().equals(parentJoinAttr) )  {
                  fieldParentJoin = (Join<F, T>) join;
                  if( ! JoinType.INNER.equals(fieldParentJoin.getJoinType()) ) {
                      // This a criteria set by the user (as opposed to the user-limiting criteria) -- it MUST be followed
                      // This means that the join is not optional (LEFT) but mandatory (INNER)
                      fieldParentJoin = null;
                  }
                  break;
              }
           }
        }
        if( fieldParentJoin == null ) {
            if( parentJoinAttr instanceof SingularAttribute) {
                fieldParentJoin = grandparentJoin.join((SingularAttribute) parentJoinAttr);
            } else if( parentJoinAttr instanceof CollectionAttribute) {
                fieldParentJoin = grandparentJoin.join((CollectionAttribute) parentJoinAttr);
            } else if( parentJoinAttr instanceof ListAttribute) {
                fieldParentJoin = grandparentJoin.join((ListAttribute) parentJoinAttr);
            } else if( parentJoinAttr instanceof SetAttribute) {
                fieldParentJoin = grandparentJoin.join((SetAttribute) parentJoinAttr);
            } else {
                throw new IllegalStateException("Unknown attribute type encountered when trying to join" + parentJoinAttr.getName() );
            }
        }
        return fieldParentJoin.get(fieldAttr);
    }

    @Override
    protected <R,T> Predicate implSpecificCreatePredicateFromSingleCriteria(
            CriteriaQuery<R> query,
            CriteriaBuilder builder,
            Class queryType,
            QueryCriteria criteria,
            QueryWhere queryWhere) {

        Predicate predicate = null;
        String listId = criteria.getListId();
        if( TASK_USER_ROLES_LIMIT_LIST.equals(listId) ) {
            predicate = createTaskUserRolesLimitPredicate(criteria, query, builder);
        } else {
            for( QueryModificationService queryModService : queryModificationServiceLoader ) {
                if( queryModService.accepts(listId) ) {
                    return queryModService.createPredicate(criteria, query, builder);
                }
            }
            throw new IllegalStateException("List id " + QueryParameterIdentifiersUtil.getQueryParameterIdNameMap().get(Integer.parseInt(criteria.getListId()))
                    + " is not supported for queries on " + TaskImpl.class.getSimpleName() + ".");
        }
        return predicate;
    }
    
    

    @SuppressWarnings("unchecked")
    private static <T> Predicate createTaskUserRolesLimitPredicate(QueryCriteria criteria, CriteriaQuery<T> criteriaQuery, CriteriaBuilder builder) {
            String userId = (String) criteria.getValues().get(0);
            List<String> groupIds = (List<String>) criteria.getValues().get(1);

        Root<TaskImpl> taskRoot = getRoot(criteriaQuery, TaskImpl.class);
        assert taskRoot != null : "TaskImpl Root instance could not be found in query!";

        boolean groupIdsPresent = (groupIds.size() > 0);

        int numPredicates = groupIdsPresent ? 5 : 2;

        // joins that apply to the user id's
        Predicate [] userGroupLimitingPredicates = new Predicate[numPredicates];
        userGroupLimitingPredicates[0] = builder.equal(taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.actualOwner).get(UserImpl_.id), userId);
        userGroupLimitingPredicates[1] = builder.equal(taskRoot.get(TaskImpl_.taskData).get(TaskDataImpl_.createdBy).get(UserImpl_.id), userId);

        Join<TaskImpl,TaskDataImpl> taskDataJoin = null;
        Join<TaskImpl,PeopleAssignmentsImpl> peopleAssignJoin = null;
        if( taskRoot != null ) {
            for( Join<TaskImpl,?> join : taskRoot.getJoins() ) {
                if( join.getJavaType().equals(PeopleAssignmentsImpl.class) ) {
                    peopleAssignJoin = (Join<TaskImpl, PeopleAssignmentsImpl>) join;
                } else if( join.getJavaType().equals(TaskDataImpl.class) ) {
                    taskDataJoin = (Join<TaskImpl,TaskDataImpl>) join;
                }
            }
        }
        assert taskDataJoin != null : "TaskImpl -> TaskDataImpl join could not be found in query!";

        // joins that apply to the group id's
        if( groupIdsPresent ) {
            if( peopleAssignJoin == null ) {
                peopleAssignJoin = taskRoot.join(TaskImpl_.peopleAssignments);
            }

            ListJoin<PeopleAssignmentsImpl,OrganizationalEntityImpl> [] groupJoins
                = getPeopleAssignmentsJoins(peopleAssignJoin);

            for( int i = 0; i < groupJoins.length; ++i ) {
                userGroupLimitingPredicates[i+2] =
                        builder.or(
                                builder.equal( groupJoins[i].get(OrganizationalEntityImpl_.id), userId ),
                                groupJoins[i].get(OrganizationalEntityImpl_.id).in(groupIds) );
            }
        }

        return builder.or(userGroupLimitingPredicates);
    }

    private static ListJoin<PeopleAssignmentsImpl,OrganizationalEntityImpl> [] getPeopleAssignmentsJoins(
            Join<TaskImpl,PeopleAssignmentsImpl> peopleAssignJoin) {

        ListJoin<PeopleAssignmentsImpl,OrganizationalEntityImpl>  [] joins = new ListJoin[3];

        for( Join<PeopleAssignmentsImpl,?> join : peopleAssignJoin.getJoins() ) {
            String joinFieldName = join.getAttribute().getName();
            if( PeopleAssignmentsImpl_.businessAdministrators.getName().equals(joinFieldName) ) {
                joins[0] = (ListJoin<PeopleAssignmentsImpl,OrganizationalEntityImpl>) join;
            } else if( PeopleAssignmentsImpl_.potentialOwners.getName().equals(joinFieldName) ) {
                joins[1] = (ListJoin<PeopleAssignmentsImpl,OrganizationalEntityImpl>) join;
            }  else if( PeopleAssignmentsImpl_.taskStakeholders.getName().equals(joinFieldName) ) {
                joins[2] = (ListJoin<PeopleAssignmentsImpl,OrganizationalEntityImpl>) join;
            }
        }

        if( joins[0] == null ) {
            joins[0] = peopleAssignJoin.join(PeopleAssignmentsImpl_.businessAdministrators, JoinType.LEFT);
        }
        if( joins[1] == null ) {
            joins[1] = peopleAssignJoin.join(PeopleAssignmentsImpl_.potentialOwners, JoinType.LEFT);
        }
        if( joins[2] == null ) {
            joins[2] = peopleAssignJoin.join(PeopleAssignmentsImpl_.taskStakeholders, JoinType.LEFT);
        }
        assert joins[0] != null : "Could not find business administrators join!";
        assert joins[1] != null : "Could not find potential owners join!";
        assert joins[2] != null : "Could not find task stakeholders join!";

        return joins;
    }

    private <T> void useDistinctWhenLefOuterJoinsPresent(CriteriaQuery<T> criteriaQuery) {
        boolean useDistinct = false;
        Root<TaskImpl> taskRoot = null;
        ROOTS_FOR: for( Root root : criteriaQuery.getRoots() ) {
           if( TaskImpl.class.equals(root.getJavaType()) ) {
               taskRoot = (Root<TaskImpl>) root;
               for( Join<TaskImpl, ?> taskJoin : taskRoot.getJoins() ) {
                  if( PeopleAssignmentsImpl.class.equals(taskJoin.getJavaType()) )  {
                      Join<TaskImpl, PeopleAssignmentsImpl> peopleAssignJoin = (Join<TaskImpl, PeopleAssignmentsImpl>) taskJoin;
                      if( JoinType.LEFT.equals(peopleAssignJoin.getJoinType()) ) {
                          useDistinct = true;
                          break ROOTS_FOR;
                      }
                      for( Join peopleAssignJoinJoin : peopleAssignJoin.getJoins() ) {
                          if( JoinType.LEFT.equals(peopleAssignJoinJoin.getJoinType()) ) {
                             useDistinct = true;
                             break ROOTS_FOR;
                          }
                      }
                  }
               }
            }
        }
        if( useDistinct ) {
            criteriaQuery.distinct(true);
        }
    }

    @Override
    protected <T,R> Expression getOrderByExpression(CriteriaQuery<R> query, Class<T> queryType, String orderByListId) {
        List<Selection<?>> selections = query.getSelection().getCompoundSelectionItems();
        Selection orderBySelection = null;
        if( orderByListId.equals(QueryParameterIdentifiers.TASK_ID_LIST) ) {
           orderBySelection = selections.get(0);
        } else if( orderByListId.equals(QueryParameterIdentifiers.TASK_NAME_LIST) ) {
           orderBySelection = selections.get(1);
        } else if( orderByListId.equals(QueryParameterIdentifiers.TASK_STATUS_LIST) ) {
           orderBySelection = selections.get(4);
        } else if( orderByListId.equals(QueryParameterIdentifiers.CREATED_BY_LIST) ) {
           orderBySelection = selections.get(8);
        } else if( orderByListId.equals(QueryParameterIdentifiers.CREATED_ON_LIST) ) {
           orderBySelection = selections.get(9);
        } else if( orderByListId.equals(QueryParameterIdentifiers.PROCESS_INSTANCE_ID_LIST) ) {
           orderBySelection = selections.get(14);
        }
        return (Expression<?>) orderBySelection;
    }
    
    public static <Q,T> Predicate taskSpecificCreatePredicateFromSingleCriteria(
            CriteriaQuery<Q> query, CriteriaBuilder builder,
            QueryCriteria criteria, QueryWhere queryWhere) {
        Predicate predicate = null;
        String listId = criteria.getListId();
        if( TASK_USER_ROLES_LIMIT_LIST.equals(listId) ) {
            predicate = createTaskUserRolesLimitPredicate(criteria, query, builder);
        } else {
            throw new IllegalStateException("List id " + QueryParameterIdentifiersUtil.getQueryParameterIdNameMap().get(Integer.parseInt(criteria.getListId()))
                    + " is not supported for queries on " + TaskImpl.class.getSimpleName() + ".");
        }
        return predicate;
    }

}
