public int Exec(ref Guid pguidCmdGroup, uint nCmdID, uint nCmdexecopt, IntPtr pvaIn, IntPtr pvaOut)
        {
            if (pguidCmdGroup == VSConstants.VSStd2K)
            {
                if (nCmdID == (uint)VSConstants.VSStd2KCmdID.INSERTSNIPPET || nCmdID == (uint)VSConstants.VSStd2KCmdID.SURROUNDWITH)
                {
                    IVsTextManager2 textManager = (IVsTextManager2)this.serviceProvider.GetService(typeof(SVsTextManager));
                    IVsExpansionManager expansionManager;
                    if (VSConstants.S_OK == textManager.GetExpansionManager(out expansionManager))
                    {
                        expansionManager.InvokeInsertionUI(
                            vsTextView,
                            this,
                            GuidList.guidSpringLanguage,
                            new string[] { "Expansion" },
                            1,
                            0,
                            null,
                            0,
                            1,
                            "Insert Snippet",
                            string.Empty);
                    }

                    return VSConstants.S_OK;
                }

                if (this.expansionSession != null)
                {
                    // Handle VS Expansion (Code Snippets) keys
                    if ((nCmdID == (uint)VSConstants.VSStd2KCmdID.TAB))
                    {
                        if (expansionSession.GoToNextExpansionField(0) == VSConstants.S_OK)
                            return VSConstants.S_OK;
                    }
                    else if ((nCmdID == (uint)VSConstants.VSStd2KCmdID.BACKTAB))
                    {
                        if (expansionSession.GoToPreviousExpansionField() == VSConstants.S_OK)
                            return VSConstants.S_OK;
                    }
                    else if ((nCmdID == (uint)VSConstants.VSStd2KCmdID.RETURN || nCmdID == (uint)VSConstants.VSStd2KCmdID.CANCEL))
                    {
                        if (expansionSession.EndCurrentExpansion(0) == VSConstants.S_OK)
                        {
                            expansionSession = null;

                            return VSConstants.S_OK;
                        }
                    }
                }

                // Handle Edit.ListMembers or Edit.CompleteWord commands
                if ((nCmdID == (uint)VSConstants.VSStd2KCmdID.SHOWMEMBERLIST ||
                    nCmdID == (uint)VSConstants.VSStd2KCmdID.COMPLETEWORD))
                {
                    if (completionSession != null)
                    {
                        completionSession.Dismiss();
                    }

                    ShowCompletion();

                    return VSConstants.S_OK;
                }

                // Handle Enter/Tab commit keys
                if (completionSession != null && (nCmdID == (uint)VSConstants.VSStd2KCmdID.RETURN || nCmdID == (uint)VSConstants.VSStd2KCmdID.TAB))
                {
                    if (completionSession.SelectedCompletionSet.SelectionStatus.IsSelected)
                    {
                        completionSession.Commit();
                    }
                    else
                    {
                        completionSession.Dismiss();
                    }

                    return VSConstants.S_OK;
                }

                // Handle Code Snippets after pressing the Tab key without completion
                if (completionSession == null && (nCmdID == (uint)VSConstants.VSStd2KCmdID.TAB))
                {
                    IVsTextManager2 expansionManager = (IVsTextManager2)this.serviceProvider.GetService(typeof(SVsTextManager));
                    SnippetsEnumerable snippetsEnumerator = new SnippetsEnumerable(expansionManager, GuidList.guidSpringLanguage);

                    SnapshotPoint currentPoint = (this.textView.Caret.Position.BufferPosition) - 1;
                    ITextStructureNavigator navigator = this.textStructureNavigatorSelectorService.GetTextStructureNavigator(this.textView.TextBuffer);
                    TextExtent extent = navigator.GetExtentOfWord(currentPoint);
                    string shortcut = this.textView.TextSnapshot.GetText(extent.Span);

                    // Search a snippet that matched the token text
                    VsExpansion expansion = snippetsEnumerator.FirstOrDefault(e => e.title == shortcut);
                    if (expansion.title != null)
                    {
                        // Set the location where the snippet will be inserted
                        int startLine, startColumn, endLine, endColumn;

                        this.vsTextView.GetCaretPos(out startLine, out endColumn);
                        startColumn = endColumn - expansion.title.Length;
                        endLine = startLine;

                        // Insert the snippet
                        InsertCodeExpansion(expansion, startLine, startColumn, endLine, endColumn);

                        return VSConstants.S_OK;
                    }
                }

                // Hanlde other keys
                if ((nCmdID == (uint)VSConstants.VSStd2KCmdID.TYPECHAR))
                {
                    char typedChar = (char)(ushort)Marshal.GetObjectForNativeVariant(pvaIn);

                    if (completionSession == null)
                    {
                        // Handle trigger keys
                        // Check if the typed char is a trigger
                        if (IsTriggerKey(typedChar))
                        {
                            var result = this.nextCommandTarget.Exec(pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut);

                            ShowCompletion();

                            return result;
                        }
                    }
                    else
                    {
                        // Handle commit keys
                        // Check if the typed char is a commit key
                        if (IsCommitKey(typedChar))
                        {
                            SpringCompletion selectedCompletion = completionSession.SelectedCompletionSet.SelectionStatus.Completion as SpringCompletion;
                            if (completionSession.SelectedCompletionSet.SelectionStatus.IsSelected &&
                                selectedCompletion != null && selectedCompletion.Type != null &&
                                selectedCompletion.Type.Value == SpringCompletionType.Namespace)
                            {
                                completionSession.Commit();
                            }
                            else
                            {
                                completionSession.Dismiss();
                            }

                            var result = this.nextCommandTarget.Exec(pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut);

                            // Check we should trigger completion after comitting the previous session (for example, after typing dot '.')
                            if (IsTriggerKey(typedChar))
                            {
                                ShowCompletion();
                            }

                            return result;
                        }
                        else
                        {
                            var result = this.nextCommandTarget.Exec(pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut);
                            completionSession.Filter();
                            return result;
                        }
                    }
                }

                // redo the filter if there is a deletion
                if (nCmdID == (uint)VSConstants.VSStd2KCmdID.BACKSPACE ||
                    nCmdID == (uint)VSConstants.VSStd2KCmdID.DELETE)
                {
                    var result = this.nextCommandTarget.Exec(pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut);

                    if (completionSession != null && !completionSession.IsDismissed)
                    {
                        completionSession.Filter();
                    }

                    return result;
                }
            }

            // we haven't handled this command so pass it onto the next target
            return this.nextCommandTarget.Exec(pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut);
        }
        private IEnumerable<SpringCompletion> GetSnippetsCompletions()
        {
            List<SpringCompletion> completions = new List<SpringCompletion>();

            IVsTextManager2 expansionManager = (IVsTextManager2)this.serviceProvider.GetService(typeof(SVsTextManager));
            SnippetsEnumerable snippetsEnumerator = new SnippetsEnumerable(expansionManager, GuidList.guidSpringLanguage);
            completions.AddRange(snippetsEnumerator.Select(vsExpansion => new SpringCompletion(this.glyphService, vsExpansion)));

            completions.Sort();
            return completions;
        }