Introduce SelectedDeclarationService

It is a wrapper for an ISelectionService and the DeclarationFinder to remove the common duplication of code around getting the selected declaration from the code panes.

Author: MDoerner

Rubberduck.Main/Root/RubberduckIoCInstaller.cs

@@ -125,6 +125,10 @@ public void Install(IWindsorContainer container, IConfigurationStore store)
             RegisterParsingEngine(container);
             RegisterTypeLibApi(container);
 
+            container.Register(Component.For<ISelectedDeclarationService>()
+                .ImplementedBy<SelectedDeclarationService>()
+                .LifestyleSingleton());
+
             container.Register(Component.For<IRewritingManager>()
                 .ImplementedBy<RewritingManager>()
                 .LifestyleSingleton());

Rubberduck.Parsing/VBA/ISelectedDeclarationService.cs

@@ -0,0 +1,12 @@
+using Rubberduck.Parsing.Symbols;
+using Rubberduck.VBEditor;
+
+namespace Rubberduck.Parsing.VBA
+{
+    public interface ISelectedDeclarationService
+    {
+        Declaration SelectedDeclaration();
+        Declaration SelectedDeclaration(QualifiedModuleName module);
+        Declaration SelectedDeclaration(QualifiedSelection qualifiedSelection);
+    }
+}

Rubberduck.Parsing/VBA/SelectedDeclarationService.cs

@@ -0,0 +1,49 @@
+using Rubberduck.Parsing.Symbols;
+using Rubberduck.VBEditor;
+using Rubberduck.VBEditor.Utility;
+
+namespace Rubberduck.Parsing.VBA
+{
+    public class SelectedDeclarationService : ISelectedDeclarationService
+    {
+        private readonly ISelectionService _selectionService;
+        private readonly IDeclarationFinderProvider _declarationFinderProvider;
+
+        public SelectedDeclarationService(ISelectionService selectionService, IDeclarationFinderProvider declarationFinderProvider)
+        {
+            _selectionService = selectionService;
+            _declarationFinderProvider = declarationFinderProvider;
+        }
+
+        public Declaration SelectedDeclaration()
+        {
+            var selection = _selectionService.ActiveSelection();
+            return SelectedDeclaration(selection);
+        }
+
+        private Declaration SelectedDeclaration(QualifiedSelection? qualifiedSelection)
+        {
+            return qualifiedSelection.HasValue
+                ? SelectedDeclaration(qualifiedSelection.Value)
+                : null;
+        }
+
+        public Declaration SelectedDeclaration(QualifiedModuleName module)
+        {
+            var selection = _selectionService.Selection(module);
+            return SelectedDeclaration(module, selection);
+        }
+
+        private Declaration SelectedDeclaration(QualifiedModuleName module, Selection? selection)
+        {
+            return selection.HasValue
+                ? SelectedDeclaration(new QualifiedSelection(module, selection.Value))
+                : null;
+        }
+
+        public Declaration SelectedDeclaration(QualifiedSelection qualifiedSelection)
+        {
+            return _declarationFinderProvider.DeclarationFinder?.FindSelectedDeclaration(qualifiedSelection);
+        }
+    }
+}