using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Opc.Ua;
using Opc.Ua.Client;

namespace OpcUaHelper
{
    /// <summary>
    /// Defines numerous re-useable utility functions.
    /// </summary>
    public partial class ClientUtils
    {
        /// <summary>
        /// Handles an exception.
        /// </summary>
        public static void HandleException(string caption, Exception e)
        {
            //ExceptionDlg.Show(caption, e);
        }

        /// <summary>
        /// Returns the application icon.
        /// </summary>
        public static System.Drawing.Icon GetAppIcon()
        {
            try
            {
                return new Icon("App.ico");
            }
            catch (Exception)
            {
                return null;
            }
        }

        #region DisplayText Lookup
        /// <summary>
        /// Gets the display text for the access level attribute.
        /// </summary>
        /// <param name="accessLevel">The access level.</param>
        /// <returns>The access level formatted as a string.</returns>
        public static string GetAccessLevelDisplayText(byte accessLevel)
        {
            StringBuilder buffer = new StringBuilder();

            if (accessLevel == AccessLevels.None)
            {
                buffer.Append("None");
            }

            if ((accessLevel & AccessLevels.CurrentRead) == AccessLevels.CurrentRead)
            {
                buffer.Append("Read");
            }

            if ((accessLevel & AccessLevels.CurrentWrite) == AccessLevels.CurrentWrite)
            {
                if (buffer.Length > 0)
                {
                    buffer.Append(" | ");
                }

                buffer.Append("Write");
            }

            if ((accessLevel & AccessLevels.HistoryRead) == AccessLevels.HistoryRead)
            {
                if (buffer.Length > 0)
                {
                    buffer.Append(" | ");
                }

                buffer.Append("HistoryRead");
            }

            if ((accessLevel & AccessLevels.HistoryWrite) == AccessLevels.HistoryWrite)
            {
                if (buffer.Length > 0)
                {
                    buffer.Append(" | ");
                }

                buffer.Append("HistoryWrite");
            }

            if ((accessLevel & AccessLevels.SemanticChange) == AccessLevels.SemanticChange)
            {
                if (buffer.Length > 0)
                {
                    buffer.Append(" | ");
                }

                buffer.Append("SemanticChange");
            }

            return buffer.ToString();
        }

        /// <summary>
        /// Gets the display text for the event notifier attribute.
        /// </summary>
        /// <param name="eventNotifier">The event notifier.</param>
        /// <returns>The event notifier formatted as a string.</returns>
        public static string GetEventNotifierDisplayText(byte eventNotifier)
        {
            StringBuilder buffer = new StringBuilder();

            if (eventNotifier == EventNotifiers.None)
            {
                buffer.Append("None");
            }

            if ((eventNotifier & EventNotifiers.SubscribeToEvents) == EventNotifiers.SubscribeToEvents)
            {
                buffer.Append("Subscribe");
            }

            if ((eventNotifier & EventNotifiers.HistoryRead) == EventNotifiers.HistoryRead)
            {
                if (buffer.Length > 0)
                {
                    buffer.Append(" | ");
                }

                buffer.Append("HistoryRead");
            }

            if ((eventNotifier & EventNotifiers.HistoryWrite) == EventNotifiers.HistoryWrite)
            {
                if (buffer.Length > 0)
                {
                    buffer.Append(" | ");
                }

                buffer.Append("HistoryWrite");
            }

            return buffer.ToString();
        }

        /// <summary>
        /// Gets the display text for the value rank attribute.
        /// </summary>
        /// <param name="valueRank">The value rank.</param>
        /// <returns>The value rank formatted as a string.</returns>
        public static string GetValueRankDisplayText(int valueRank)
        {
            switch (valueRank)
            {
                case ValueRanks.Any: return "Any";
                case ValueRanks.Scalar: return "Scalar";
                case ValueRanks.ScalarOrOneDimension: return "ScalarOrOneDimension";
                case ValueRanks.OneOrMoreDimensions: return "OneOrMoreDimensions";
                case ValueRanks.OneDimension: return "OneDimension";
                case ValueRanks.TwoDimensions: return "TwoDimensions";
            }

            return valueRank.ToString();
        }

        /// <summary>
        /// Gets the display text for the specified attribute.
        /// </summary>
        /// <param name="session">The currently active session.</param>
        /// <param name="attributeId">The id of the attribute.</param>
        /// <param name="value">The value of the attribute.</param>
        /// <returns>The attribute formatted as a string.</returns>
        public static string GetAttributeDisplayText(Session session, uint attributeId, Variant value)
        {
            if (value == Variant.Null)
            {
                return String.Empty;
            }

            switch (attributeId)
            {
                case Attributes.AccessLevel:
                case Attributes.UserAccessLevel:
                    {
                        byte? field = value.Value as byte?;

                        if (field != null)
                        {
                            return GetAccessLevelDisplayText(field.Value);
                        }

                        break;
                    }

                case Attributes.EventNotifier:
                    {
                        byte? field = value.Value as byte?;

                        if (field != null)
                        {
                            return GetEventNotifierDisplayText(field.Value);
                        }

                        break;
                    }

                case Attributes.DataType:
                    {
                        return session.NodeCache.GetDisplayText(value.Value as NodeId);
                    }

                case Attributes.ValueRank:
                    {
                        int? field = value.Value as int?;

                        if (field != null)
                        {
                            return GetValueRankDisplayText(field.Value);
                        }

                        break;
                    }

                case Attributes.NodeClass:
                    {
                        int? field = value.Value as int?;

                        if (field != null)
                        {
                            return ((NodeClass)field.Value).ToString();
                        }

                        break;
                    }

                case Attributes.NodeId:
                    {
                        NodeId field = value.Value as NodeId;

                        if (!NodeId.IsNull(field))
                        {
                            return field.ToString();
                        }

                        return "Null";
                    }
            }

            // check for byte strings.
            if (value.Value is byte[])
            {
                return Utils.ToHexString(value.Value as byte[]);
            }

            // use default format.
            return value.ToString();
        }
        #endregion

        #region Browse
        /// <summary>
        /// Browses the address space and returns the references found.
        /// </summary>
        /// <param name="session">The session.</param>
        /// <param name="nodesToBrowse">The set of browse operations to perform.</param>
        /// <param name="throwOnError">if set to <c>true</c> a exception will be thrown on an error.</param>
        /// <returns>
        /// The references found. Null if an error occurred.
        /// </returns>
        public static ReferenceDescriptionCollection Browse(Session session, BrowseDescriptionCollection nodesToBrowse, bool throwOnError)
        {
            return Browse(session, null, nodesToBrowse, throwOnError);
        }

        /// <summary>
        /// Browses the address space and returns the references found.
        /// </summary>
        public static ReferenceDescriptionCollection Browse(Session session, ViewDescription view, BrowseDescriptionCollection nodesToBrowse, bool throwOnError)
        {
            try
            {
                ReferenceDescriptionCollection references = new ReferenceDescriptionCollection();
                BrowseDescriptionCollection unprocessedOperations = new BrowseDescriptionCollection();

                while (nodesToBrowse.Count > 0)
                {
                    // start the browse operation.
                    BrowseResultCollection results = null;
                    DiagnosticInfoCollection diagnosticInfos = null;

                    session.Browse(
                        null,
                        view,
                        0,
                        nodesToBrowse,
                        out results,
                        out diagnosticInfos);

                    ClientBase.ValidateResponse(results, nodesToBrowse);
                    ClientBase.ValidateDiagnosticInfos(diagnosticInfos, nodesToBrowse);

                    ByteStringCollection continuationPoints = new ByteStringCollection();

                    for (int ii = 0; ii < nodesToBrowse.Count; ii++)
                    {
                        // check for error.
                        if (StatusCode.IsBad(results[ii].StatusCode))
                        {
                            // this error indicates that the server does not have enough simultaneously active 
                            // continuation points. This request will need to be resent after the other operations
                            // have been completed and their continuation points released.
                            if (results[ii].StatusCode == StatusCodes.BadNoContinuationPoints)
                            {
                                unprocessedOperations.Add(nodesToBrowse[ii]);
                            }

                            continue;
                        }

                        // check if all references have been fetched.
                        if (results[ii].References.Count == 0)
                        {
                            continue;
                        }

                        // save results.
                        references.AddRange(results[ii].References);

                        // check for continuation point.
                        if (results[ii].ContinuationPoint != null)
                        {
                            continuationPoints.Add(results[ii].ContinuationPoint);
                        }
                    }

                    // process continuation points.
                    ByteStringCollection revisedContiuationPoints = new ByteStringCollection();

                    while (continuationPoints.Count > 0)
                    {
                        // continue browse operation.
                        session.BrowseNext(
                            null,
                            false,
                            continuationPoints,
                            out results,
                            out diagnosticInfos);

                        ClientBase.ValidateResponse(results, continuationPoints);
                        ClientBase.ValidateDiagnosticInfos(diagnosticInfos, continuationPoints);

                        for (int ii = 0; ii < continuationPoints.Count; ii++)
                        {
                            // check for error.
                            if (StatusCode.IsBad(results[ii].StatusCode))
                            {
                                continue;
                            }

                            // check if all references have been fetched.
                            if (results[ii].References.Count == 0)
                            {
                                continue;
                            }

                            // save results.
                            references.AddRange(results[ii].References);

                            // check for continuation point.
                            if (results[ii].ContinuationPoint != null)
                            {
                                revisedContiuationPoints.Add(results[ii].ContinuationPoint);
                            }
                        }

                        // check if browsing must continue;
                        revisedContiuationPoints = continuationPoints;
                    }

                    // check if unprocessed results exist.
                    nodesToBrowse = unprocessedOperations;
                }

                // return complete list.
                return references;
            }
            catch (Exception exception)
            {
                if (throwOnError)
                {
                    throw new ServiceResultException(exception, StatusCodes.BadUnexpectedError);
                }

                return null;
            }
        }

        /// <summary>
        /// Browses the address space and returns the references found.
        /// </summary>
        /// <param name="session">The session.</param>
        /// <param name="nodeToBrowse">The NodeId for the starting node.</param>
        /// <param name="throwOnError">if set to <c>true</c> a exception will be thrown on an error.</param>
        /// <returns>
        /// The references found. Null if an error occurred.
        /// </returns>
        public static ReferenceDescriptionCollection Browse(Session session, BrowseDescription nodeToBrowse, bool throwOnError)
        {
            return Browse(session, null, nodeToBrowse, throwOnError);
        }

        /// <summary>
        /// Browses the address space and returns the references found.
        /// </summary>
        public static ReferenceDescriptionCollection Browse(Session session, ViewDescription view, BrowseDescription nodeToBrowse, bool throwOnError)
        {
            try
            {
                ReferenceDescriptionCollection references = new ReferenceDescriptionCollection();

                // construct browse request.
                BrowseDescriptionCollection nodesToBrowse = new BrowseDescriptionCollection();
                nodesToBrowse.Add(nodeToBrowse);

                // start the browse operation.
                BrowseResultCollection results = null;
                DiagnosticInfoCollection diagnosticInfos = null;

                session.Browse(
                    null,
                    view,
                    0,
                    nodesToBrowse,
                    out results,
                    out diagnosticInfos);

                ClientBase.ValidateResponse(results, nodesToBrowse);
                ClientBase.ValidateDiagnosticInfos(diagnosticInfos, nodesToBrowse);

                do
                {
                    // check for error.
                    if (StatusCode.IsBad(results[0].StatusCode))
                    {
                        throw new ServiceResultException(results[0].StatusCode);
                    }

                    // process results.
                    for (int ii = 0; ii < results[0].References.Count; ii++)
                    {
                        references.Add(results[0].References[ii]);
                    }

                    // check if all references have been fetched.
                    if (results[0].References.Count == 0 || results[0].ContinuationPoint == null)
                    {
                        break;
                    }

                    // continue browse operation.
                    ByteStringCollection continuationPoints = new ByteStringCollection();
                    continuationPoints.Add(results[0].ContinuationPoint);

                    session.BrowseNext(
                        null,
                        false,
                        continuationPoints,
                        out results,
                        out diagnosticInfos);

                    ClientBase.ValidateResponse(results, continuationPoints);
                    ClientBase.ValidateDiagnosticInfos(diagnosticInfos, continuationPoints);
                }
                while (true);

                //return complete list.
                return references;
            }
            catch (Exception exception)
            {
                if (throwOnError)
                {
                    throw new ServiceResultException(exception, StatusCodes.BadUnexpectedError);
                }

                return null;
            }
        }

        /// <summary>
        /// Browses the address space and returns all of the supertypes of the specified type node.
        /// </summary>
        /// <param name="session">The session.</param>
        /// <param name="typeId">The NodeId for a type node in the address space.</param>
        /// <param name="throwOnError">if set to <c>true</c> a exception will be thrown on an error.</param>
        /// <returns>
        /// The references found. Null if an error occurred.
        /// </returns>
        public static ReferenceDescriptionCollection BrowseSuperTypes(Session session, NodeId typeId, bool throwOnError)
        {
            ReferenceDescriptionCollection supertypes = new ReferenceDescriptionCollection();

            try
            {
                // find all of the children of the field.
                BrowseDescription nodeToBrowse = new BrowseDescription();

                nodeToBrowse.NodeId = typeId;
                nodeToBrowse.BrowseDirection = BrowseDirection.Inverse;
                nodeToBrowse.ReferenceTypeId = ReferenceTypeIds.HasSubtype;
                nodeToBrowse.IncludeSubtypes = false; // more efficient to use IncludeSubtypes=False when possible.
                nodeToBrowse.NodeClassMask = 0; // the HasSubtype reference already restricts the targets to Types. 
                nodeToBrowse.ResultMask = (uint)BrowseResultMask.All;

                ReferenceDescriptionCollection references = Browse(session, nodeToBrowse, throwOnError);

                while (references != null && references.Count > 0)
                {
                    // should never be more than one supertype.
                    supertypes.Add(references[0]);

                    // only follow references within this server.
                    if (references[0].NodeId.IsAbsolute)
                    {
                        break;
                    }

                    // get the references for the next level up.
                    nodeToBrowse.NodeId = (NodeId)references[0].NodeId;
                    references = Browse(session, nodeToBrowse, throwOnError);
                }

                // return complete list.
                return supertypes;
            }
            catch (Exception exception)
            {
                if (throwOnError)
                {
                    throw new ServiceResultException(exception, StatusCodes.BadUnexpectedError);
                }

                return null;
            }
        }

        /// <summary>
        /// Returns the node ids for a set of relative paths.
        /// </summary>
        /// <param name="session">An open session with the server to use.</param>
        /// <param name="startNodeId">The starting node for the relative paths.</param>
        /// <param name="namespacesUris">The namespace URIs referenced by the relative paths.</param>
        /// <param name="relativePaths">The relative paths.</param>
        /// <returns>A collection of local nodes.</returns>
        public static List<NodeId> TranslateBrowsePaths(
            Session session,
            NodeId startNodeId,
            NamespaceTable namespacesUris,
            params string[] relativePaths)
        {
            // build the list of browse paths to follow by parsing the relative paths.
            BrowsePathCollection browsePaths = new BrowsePathCollection();

            if (relativePaths != null)
            {
                for (int ii = 0; ii < relativePaths.Length; ii++)
                {
                    BrowsePath browsePath = new BrowsePath();

                    // The relative paths used indexes in the namespacesUris table. These must be 
                    // converted to indexes used by the server. An error occurs if the relative path
                    // refers to a namespaceUri that the server does not recognize.

                    // The relative paths may refer to ReferenceType by their BrowseName. The TypeTree object
                    // allows the parser to look up the server's NodeId for the ReferenceType.

                    browsePath.RelativePath = RelativePath.Parse(
                        relativePaths[ii],
                        session.TypeTree,
                        namespacesUris,
                        session.NamespaceUris);

                    browsePath.StartingNode = startNodeId;

                    browsePaths.Add(browsePath);
                }
            }

            // make the call to the server.
            BrowsePathResultCollection results;
            DiagnosticInfoCollection diagnosticInfos;

            ResponseHeader responseHeader = session.TranslateBrowsePathsToNodeIds(
                null,
                browsePaths,
                out results,
                out diagnosticInfos);

            // ensure that the server returned valid results.
            Session.ValidateResponse(results, browsePaths);
            Session.ValidateDiagnosticInfos(diagnosticInfos, browsePaths);

            // collect the list of node ids found.
            List<NodeId> nodes = new List<NodeId>();

            for (int ii = 0; ii < results.Count; ii++)
            {
                // check if the start node actually exists.
                if (StatusCode.IsBad(results[ii].StatusCode))
                {
                    nodes.Add(null);
                    continue;
                }

                // an empty list is returned if no node was found.
                if (results[ii].Targets.Count == 0)
                {
                    nodes.Add(null);
                    continue;
                }

                // Multiple matches are possible, however, the node that matches the type model is the
                // one we are interested in here. The rest can be ignored.
                BrowsePathTarget target = results[ii].Targets[0];

                if (target.RemainingPathIndex != UInt32.MaxValue)
                {
                    nodes.Add(null);
                    continue;
                }

                // The targetId is an ExpandedNodeId because it could be node in another server. 
                // The ToNodeId function is used to convert a local NodeId stored in a ExpandedNodeId to a NodeId.
                nodes.Add(ExpandedNodeId.ToNodeId(target.TargetId, session.NamespaceUris));
            }

            // return whatever was found.
            return nodes;
        }
        #endregion

        #region Events
        /// <summary>
        /// Finds the type of the event for the notification.
        /// </summary>
        /// <param name="monitoredItem">The monitored item.</param>
        /// <param name="notification">The notification.</param>
        /// <returns>The NodeId of the EventType.</returns>
        public static NodeId FindEventType(MonitoredItem monitoredItem, EventFieldList notification)
        {
            EventFilter filter = monitoredItem.Status.Filter as EventFilter;

            if (filter != null)
            {
                for (int ii = 0; ii < filter.SelectClauses.Count; ii++)
                {
                    SimpleAttributeOperand clause = filter.SelectClauses[ii];

                    if (clause.BrowsePath.Count == 1 && clause.BrowsePath[0] == BrowseNames.EventType)
                    {
                        return notification.EventFields[ii].Value as NodeId;
                    }
                }
            }

            return null;
        }

        /// <summary>
        /// Constructs an event object from a notification.
        /// </summary>
        /// <param name="session">The session.</param>
        /// <param name="monitoredItem">The monitored item that produced the notification.</param>
        /// <param name="notification">The notification.</param>
        /// <param name="knownEventTypes">The known event types.</param>
        /// <param name="eventTypeMappings">Mapping between event types and known event types.</param>
        /// <returns>
        /// The event object. Null if the notification is not a valid event type.
        /// </returns>
        public static BaseEventState ConstructEvent(
            Session session,
            MonitoredItem monitoredItem,
            EventFieldList notification,
            Dictionary<NodeId, Type> knownEventTypes,
            Dictionary<NodeId, NodeId> eventTypeMappings)
        {
            // find the event type.
            NodeId eventTypeId = FindEventType(monitoredItem, notification);

            if (eventTypeId == null)
            {
                return null;
            }

            // look up the known event type.
            Type knownType = null;
            NodeId knownTypeId = null;

            if (eventTypeMappings.TryGetValue(eventTypeId, out knownTypeId))
            {
                knownType = knownEventTypes[knownTypeId];
            }

            // try again.
            if (knownType == null)
            {
                if (knownEventTypes.TryGetValue(eventTypeId, out knownType))
                {
                    knownTypeId = eventTypeId;
                    eventTypeMappings.Add(eventTypeId, eventTypeId);
                }
            }

            // try mapping it to a known type.
            if (knownType == null)
            {
                // browse for the supertypes of the event type.
                ReferenceDescriptionCollection supertypes = ClientUtils.BrowseSuperTypes(session, eventTypeId, false);

                // can't do anything with unknown types.
                if (supertypes == null)
                {
                    return null;
                }

                // find the first supertype that matches a known event type.
                for (int ii = 0; ii < supertypes.Count; ii++)
                {
                    NodeId superTypeId = (NodeId)supertypes[ii].NodeId;

                    if (knownEventTypes.TryGetValue(superTypeId, out knownType))
                    {
                        knownTypeId = superTypeId;
                        eventTypeMappings.Add(eventTypeId, superTypeId);
                    }

                    if (knownTypeId != null)
                    {
                        break;
                    }
                }

                // can't do anything with unknown types.
                if (knownTypeId == null)
                {
                    return null;
                }
            }

            // construct the event based on the known event type.
            BaseEventState e = (BaseEventState)Activator.CreateInstance(knownType, new object[] { (NodeState)null });

            // get the filter which defines the contents of the notification.
            EventFilter filter = monitoredItem.Status.Filter as EventFilter;

            // initialize the event with the values in the notification.
            e.Update(session.SystemContext, filter.SelectClauses, notification);

            // save the orginal notification.
            e.Handle = notification;

            return e;
        }
        #endregion

        #region Type Model Browsing
        /// <summary>
        /// Collects the instance declarations for a type.
        /// </summary>
        public static List<InstanceDeclaration> CollectInstanceDeclarationsForType(Session session, NodeId typeId)
        {
            return CollectInstanceDeclarationsForType(session, typeId, true);
        }

        /// <summary>
        /// Collects the instance declarations for a type.
        /// </summary>
        public static List<InstanceDeclaration> CollectInstanceDeclarationsForType(Session session, NodeId typeId, bool includeSupertypes)
        {
            // process the types starting from the top of the tree.
            List<InstanceDeclaration> instances = new List<InstanceDeclaration>();
            Dictionary<string, InstanceDeclaration> map = new Dictionary<string, InstanceDeclaration>();

            // get the supertypes.
            if (includeSupertypes)
            {
                ReferenceDescriptionCollection supertypes = ClientUtils.BrowseSuperTypes(session, typeId, false);

                if (supertypes != null)
                {
                    for (int ii = supertypes.Count - 1; ii >= 0; ii--)
                    {
                        CollectInstanceDeclarations(session, (NodeId)supertypes[ii].NodeId, null, instances, map);
                    }
                }
            }

            // collect the fields for the selected type.
            CollectInstanceDeclarations(session, typeId, null, instances, map);

            // return the complete list.
            return instances;
        }

        /// <summary>
        /// Collects the fields for the instance node.
        /// </summary>
        private static void CollectInstanceDeclarations(
            Session session,
            NodeId typeId,
            InstanceDeclaration parent,
            List<InstanceDeclaration> instances,
            IDictionary<string, InstanceDeclaration> map)
        {
            // find the children.
            BrowseDescription nodeToBrowse = new BrowseDescription();

            if (parent == null)
            {
                nodeToBrowse.NodeId = typeId;
            }
            else
            {
                nodeToBrowse.NodeId = parent.NodeId;
            }

            nodeToBrowse.BrowseDirection = BrowseDirection.Forward;
            nodeToBrowse.ReferenceTypeId = ReferenceTypeIds.HasChild;
            nodeToBrowse.IncludeSubtypes = true;
            nodeToBrowse.NodeClassMask = (uint)(NodeClass.Object | NodeClass.Variable | NodeClass.Method);
            nodeToBrowse.ResultMask = (uint)BrowseResultMask.All;

            // ignore any browsing errors.
            ReferenceDescriptionCollection references = ClientUtils.Browse(session, nodeToBrowse, false);

            if (references == null)
            {
                return;
            }

            // process the children.
            List<NodeId> nodeIds = new List<NodeId>();
            List<InstanceDeclaration> children = new List<InstanceDeclaration>();

            for (int ii = 0; ii < references.Count; ii++)
            {
                ReferenceDescription reference = references[ii];

                if (reference.NodeId.IsAbsolute)
                {
                    continue;
                }

                // create a new declaration.
                InstanceDeclaration child = new InstanceDeclaration();

                child.RootTypeId = typeId;
                child.NodeId = (NodeId)reference.NodeId;
                child.BrowseName = reference.BrowseName;
                child.NodeClass = reference.NodeClass;

                if (!LocalizedText.IsNullOrEmpty(reference.DisplayName))
                {
                    child.DisplayName = reference.DisplayName.Text;
                }
                else
                {
                    child.DisplayName = reference.BrowseName.Name;
                }

                if (parent != null)
                {
                    child.BrowsePath = new QualifiedNameCollection(parent.BrowsePath);
                    child.BrowsePathDisplayText = Utils.Format("{0}/{1}", parent.BrowsePathDisplayText, reference.BrowseName);
                    child.DisplayPath = Utils.Format("{0}/{1}", parent.DisplayPath, reference.DisplayName);
                }
                else
                {
                    child.BrowsePath = new QualifiedNameCollection();
                    child.BrowsePathDisplayText = Utils.Format("{0}", reference.BrowseName);
                    child.DisplayPath = Utils.Format("{0}", reference.DisplayName);
                }

                child.BrowsePath.Add(reference.BrowseName);

                // check if reading an overridden declaration.
                InstanceDeclaration overriden = null;

                if (map.TryGetValue(child.BrowsePathDisplayText, out overriden))
                {
                    child.OverriddenDeclaration = overriden;
                }

                map[child.BrowsePathDisplayText] = child;

                // add to list.
                children.Add(child);
                nodeIds.Add(child.NodeId);
            }

            // check if nothing more to do.
            if (children.Count == 0)
            {
                return;
            }

            // find the modelling rules.
            List<NodeId> modellingRules = FindTargetOfReference(session, nodeIds, Opc.Ua.ReferenceTypeIds.HasModellingRule, false);

            if (modellingRules != null)
            {
                for (int ii = 0; ii < nodeIds.Count; ii++)
                {
                    children[ii].ModellingRule = modellingRules[ii];

                    // if the modelling rule is null then the instance is not part of the type declaration.
                    if (NodeId.IsNull(modellingRules[ii]))
                    {
                        map.Remove(children[ii].BrowsePathDisplayText);
                    }
                }
            }

            // update the descriptions.
            UpdateInstanceDescriptions(session, children, false);

            // recusively collect instance declarations for the tree below.
            for (int ii = 0; ii < children.Count; ii++)
            {
                if (!NodeId.IsNull(children[ii].ModellingRule))
                {
                    instances.Add(children[ii]);
                    CollectInstanceDeclarations(session, typeId, children[ii], instances, map);
                }
            }
        }

        /// <summary>
        /// Finds the targets for the specified reference.
        /// </summary>
        private static List<NodeId> FindTargetOfReference(Session session, List<NodeId> nodeIds, NodeId referenceTypeId, bool throwOnError)
        {
            try
            {
                // construct browse request.
                BrowseDescriptionCollection nodesToBrowse = new BrowseDescriptionCollection();

                for (int ii = 0; ii < nodeIds.Count; ii++)
                {
                    BrowseDescription nodeToBrowse = new BrowseDescription();
                    nodeToBrowse.NodeId = nodeIds[ii];
                    nodeToBrowse.BrowseDirection = BrowseDirection.Forward;
                    nodeToBrowse.ReferenceTypeId = referenceTypeId;
                    nodeToBrowse.IncludeSubtypes = false;
                    nodeToBrowse.NodeClassMask = 0;
                    nodeToBrowse.ResultMask = (uint)BrowseResultMask.None;
                    nodesToBrowse.Add(nodeToBrowse);
                }

                // start the browse operation.
                BrowseResultCollection results = null;
                DiagnosticInfoCollection diagnosticInfos = null;

                session.Browse(
                    null,
                    null,
                    1,
                    nodesToBrowse,
                    out results,
                    out diagnosticInfos);

                ClientBase.ValidateResponse(results, nodesToBrowse);
                ClientBase.ValidateDiagnosticInfos(diagnosticInfos, nodesToBrowse);

                List<NodeId> targetIds = new List<NodeId>();
                ByteStringCollection continuationPoints = new ByteStringCollection();

                for (int ii = 0; ii < nodeIds.Count; ii++)
                {
                    targetIds.Add(null);

                    // check for error.
                    if (StatusCode.IsBad(results[ii].StatusCode))
                    {
                        continue;
                    }

                    // check for continuation point.
                    if (results[ii].ContinuationPoint != null && results[ii].ContinuationPoint.Length > 0)
                    {
                        continuationPoints.Add(results[ii].ContinuationPoint);
                    }

                    // get the node id.
                    if (results[ii].References.Count > 0)
                    {
                        if (NodeId.IsNull(results[ii].References[0].NodeId) || results[ii].References[0].NodeId.IsAbsolute)
                        {
                            continue;
                        }

                        targetIds[ii] = (NodeId)results[ii].References[0].NodeId;
                    }
                }

                // release continuation points.
                if (continuationPoints.Count > 0)
                {
                    session.BrowseNext(
                        null,
                        true,
                        continuationPoints,
                        out results,
                        out diagnosticInfos);

                    ClientBase.ValidateResponse(results, nodesToBrowse);
                    ClientBase.ValidateDiagnosticInfos(diagnosticInfos, nodesToBrowse);
                }

                //return complete list.
                return targetIds;
            }
            catch (Exception exception)
            {
                if (throwOnError)
                {
                    throw new ServiceResultException(exception, StatusCodes.BadUnexpectedError);
                }

                return null;
            }
        }

        /// <summary>
        /// Finds the targets for the specified reference.
        /// </summary>
        private static void UpdateInstanceDescriptions(Session session, List<InstanceDeclaration> instances, bool throwOnError)
        {
            try
            {
                ReadValueIdCollection nodesToRead = new ReadValueIdCollection();

                for (int ii = 0; ii < instances.Count; ii++)
                {
                    ReadValueId nodeToRead = new ReadValueId();
                    nodeToRead.NodeId = instances[ii].NodeId;
                    nodeToRead.AttributeId = Attributes.Description;
                    nodesToRead.Add(nodeToRead);

                    nodeToRead = new ReadValueId();
                    nodeToRead.NodeId = instances[ii].NodeId;
                    nodeToRead.AttributeId = Attributes.DataType;
                    nodesToRead.Add(nodeToRead);

                    nodeToRead = new ReadValueId();
                    nodeToRead.NodeId = instances[ii].NodeId;
                    nodeToRead.AttributeId = Attributes.ValueRank;
                    nodesToRead.Add(nodeToRead);
                }

                // start the browse operation.
                DataValueCollection results = null;
                DiagnosticInfoCollection diagnosticInfos = null;

                session.Read(
                    null,
                    0,
                    TimestampsToReturn.Neither,
                    nodesToRead,
                    out results,
                    out diagnosticInfos);

                ClientBase.ValidateResponse(results, nodesToRead);
                ClientBase.ValidateDiagnosticInfos(diagnosticInfos, nodesToRead);

                // update the instances.
                for (int ii = 0; ii < nodesToRead.Count; ii += 3)
                {
                    InstanceDeclaration instance = instances[ii / 3];

                    instance.Description = results[ii].GetValue<LocalizedText>(LocalizedText.Null).Text;
                    instance.DataType = results[ii + 1].GetValue<NodeId>(NodeId.Null);
                    instance.ValueRank = results[ii + 2].GetValue<int>(ValueRanks.Any);

                    if (!NodeId.IsNull(instance.DataType))
                    {
                        instance.BuiltInType = DataTypes.GetBuiltInType(instance.DataType, session.TypeTree);
                        instance.DataTypeDisplayText = session.NodeCache.GetDisplayText(instance.DataType);

                        if (instance.ValueRank >= 0)
                        {
                            instance.DataTypeDisplayText += "[]";
                        }
                    }
                }
            }
            catch (Exception exception)
            {
                if (throwOnError)
                {
                    throw new ServiceResultException(exception, StatusCodes.BadUnexpectedError);
                }
            }
        }
        #endregion

        #region Private Methods
        /// <summary>
        /// Collects the fields for the type.
        /// </summary>
        /// <param name="session">The session.</param>
        /// <param name="typeId">The type id.</param>
        /// <param name="fields">The fields.</param>
        /// <param name="fieldNodeIds">The node id for the declaration of the field.</param>
        private static void CollectFieldsForType(Session session, NodeId typeId, SimpleAttributeOperandCollection fields, List<NodeId> fieldNodeIds)
        {
            // get the supertypes.
            ReferenceDescriptionCollection supertypes = ClientUtils.BrowseSuperTypes(session, typeId, false);

            if (supertypes == null)
            {
                return;
            }

            // process the types starting from the top of the tree.
            Dictionary<NodeId, QualifiedNameCollection> foundNodes = new Dictionary<NodeId, QualifiedNameCollection>();
            QualifiedNameCollection parentPath = new QualifiedNameCollection();

            for (int ii = supertypes.Count - 1; ii >= 0; ii--)
            {
                CollectFields(session, (NodeId)supertypes[ii].NodeId, parentPath, fields, fieldNodeIds, foundNodes);
            }

            // collect the fields for the selected type.
            CollectFields(session, typeId, parentPath, fields, fieldNodeIds, foundNodes);
        }

        /// <summary>
        /// Collects the fields for the instance.
        /// </summary>
        /// <param name="session">The session.</param>
        /// <param name="instanceId">The instance id.</param>
        /// <param name="fields">The fields.</param>
        /// <param name="fieldNodeIds">The node id for the declaration of the field.</param>
        private static void CollectFieldsForInstance(Session session, NodeId instanceId, SimpleAttributeOperandCollection fields, List<NodeId> fieldNodeIds)
        {
            Dictionary<NodeId, QualifiedNameCollection> foundNodes = new Dictionary<NodeId, QualifiedNameCollection>();
            QualifiedNameCollection parentPath = new QualifiedNameCollection();
            CollectFields(session, instanceId, parentPath, fields, fieldNodeIds, foundNodes);
        }

        /// <summary>
        /// Collects the fields for the instance node.
        /// </summary>
        /// <param name="session">The session.</param>
        /// <param name="nodeId">The node id.</param>
        /// <param name="parentPath">The parent path.</param>
        /// <param name="fields">The event fields.</param>
        /// <param name="fieldNodeIds">The node id for the declaration of the field.</param>
        /// <param name="foundNodes">The table of found nodes.</param>
        private static void CollectFields(
            Session session,
            NodeId nodeId,
            QualifiedNameCollection parentPath,
            SimpleAttributeOperandCollection fields,
            List<NodeId> fieldNodeIds,
            Dictionary<NodeId, QualifiedNameCollection> foundNodes)
        {
            // find all of the children of the field.
            BrowseDescription nodeToBrowse = new BrowseDescription();

            nodeToBrowse.NodeId = nodeId;
            nodeToBrowse.BrowseDirection = BrowseDirection.Forward;
            nodeToBrowse.ReferenceTypeId = ReferenceTypeIds.Aggregates;
            nodeToBrowse.IncludeSubtypes = true;
            nodeToBrowse.NodeClassMask = (uint)(NodeClass.Object | NodeClass.Variable);
            nodeToBrowse.ResultMask = (uint)BrowseResultMask.All;

            ReferenceDescriptionCollection children = ClientUtils.Browse(session, nodeToBrowse, false);

            if (children == null)
            {
                return;
            }

            // process the children.
            for (int ii = 0; ii < children.Count; ii++)
            {
                ReferenceDescription child = children[ii];

                if (child.NodeId.IsAbsolute)
                {
                    continue;
                }

                // construct browse path.
                QualifiedNameCollection browsePath = new QualifiedNameCollection(parentPath);
                browsePath.Add(child.BrowseName);

                // check if the browse path is already in the list.
                int index = ContainsPath(fields, browsePath);

                if (index < 0)
                {
                    SimpleAttributeOperand field = new SimpleAttributeOperand();

                    field.TypeDefinitionId = ObjectTypeIds.BaseEventType;
                    field.BrowsePath = browsePath;
                    field.AttributeId = (child.NodeClass == NodeClass.Variable) ? Attributes.Value : Attributes.NodeId;

                    fields.Add(field);
                    fieldNodeIds.Add((NodeId)child.NodeId);
                }

                // recusively find all of the children.
                NodeId targetId = (NodeId)child.NodeId;

                // need to guard against loops.
                if (!foundNodes.ContainsKey(targetId))
                {
                    foundNodes.Add(targetId, browsePath);
                    CollectFields(session, (NodeId)child.NodeId, browsePath, fields, fieldNodeIds, foundNodes);
                }
            }
        }

        /// <summary>
        /// Determines whether the specified select clause contains the browse path.
        /// </summary>
        /// <param name="selectClause">The select clause.</param>
        /// <param name="browsePath">The browse path.</param>
        /// <returns>
        /// 	<c>true</c> if the specified select clause contains path; otherwise, <c>false</c>.
        /// </returns>
        private static int ContainsPath(SimpleAttributeOperandCollection selectClause, QualifiedNameCollection browsePath)
        {
            for (int ii = 0; ii < selectClause.Count; ii++)
            {
                SimpleAttributeOperand field = selectClause[ii];

                if (field.BrowsePath.Count != browsePath.Count)
                {
                    continue;
                }

                bool match = true;

                for (int jj = 0; jj < field.BrowsePath.Count; jj++)
                {
                    if (field.BrowsePath[jj] != browsePath[jj])
                    {
                        match = false;
                        break;
                    }
                }

                if (match)
                {
                    return ii;
                }
            }

            return -1;
        }
        #endregion

    }
}
