Enable back button and introduce behavior

Signed-off-by: Danilo Aimini <82231674+AMZN-daimini@users.noreply.github.com>

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/PrefabFocusHandler.cpp

@@ -127,6 +127,11 @@ namespace AzToolsFramework::Prefab
         return m_instanceFocusPath;
     }
 
+    const int PrefabFocusHandler::GetPrefabFocusPathLength()
+    {
+        return m_instanceFocusVector.size();
+    }
+
     void PrefabFocusHandler::OnEntityStreamLoadSuccess()
     {
         // Focus on the root prefab (AZ::EntityId() will default to it)

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/PrefabFocusHandler.h

@@ -37,6 +37,7 @@ namespace AzToolsFramework::Prefab
         InstanceOptionalReference GetFocusedPrefabInstance() override;
         bool IsOwningPrefabBeingFocused(AZ::EntityId entityId) override;
         const AZ::IO::Path& GetPrefabFocusPath() override;
+        const int GetPrefabFocusPathLength() override;
 
         // EditorEntityContextNotificationBus...
         void OnEntityStreamLoadSuccess() override;

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/PrefabFocusInterface.h

@@ -43,10 +43,12 @@ namespace AzToolsFramework::Prefab
         //! @return true if the entity belongs to the focused instance or one of its descendants, false otherwise.
         virtual bool IsOwningPrefabBeingFocused(AZ::EntityId entityId) = 0;
 
-        //! Returns whether the entity belongs to the instance that is being focused on, or one of its descendants.
-        //! @param entityId The entityId of the queried entity.
-        //! @return true if the entity belongs to the focused instance or one of its descendants, false otherwise.
+        //! Returns the path from the root instance to the currently focused instance.
+        //! @return A path composed from the names of the container entities for the instance path.
         virtual const AZ::IO::Path& GetPrefabFocusPath() = 0;
+
+        //! Returns the size of the path to the currently focused instance.
+        virtual const int GetPrefabFocusPathLength() = 0;
     };
 
 } // namespace AzToolsFramework::Prefab

Code/Framework/AzToolsFramework/AzToolsFramework/UI/Prefab/PrefabViewportFocusPathHandler.cpp

@@ -34,8 +34,9 @@ namespace AzToolsFramework::Prefab
         m_breadcrumbsWidget = breadcrumbsWidget;
         m_backButton = backButton;
 
-        m_backButton->setEnabled(false);
+        m_backButton->setVisible(false);
 
+        // If a part of the path is clicked, focus on that instance
         connect(
             m_breadcrumbsWidget, &AzQtComponents::BreadCrumbs::linkClicked, this,
             [&](const QString&, int linkIndex)
@@ -43,12 +44,28 @@ namespace AzToolsFramework::Prefab
                 m_prefabFocusInterface->FocusOnPathIndex(linkIndex);
             }
         );
+
+        // The back button will allow user to go one level up
+        connect(m_backButton, &QToolButton::clicked, this,
+            [&]()
+            {
+                int length = m_prefabFocusInterface->GetPrefabFocusPathLength();
+
+                if (length > 1)
+                {
+                    m_prefabFocusInterface->FocusOnPathIndex(length - 2);
+                }
+            }
+        );
     }
 
     void PrefabViewportFocusPathHandler::OnPrefabFocusChanged()
     {
         // Push new Path
         m_breadcrumbsWidget->pushPath(m_prefabFocusInterface->GetPrefabFocusPath().c_str());
+
+        // Only show the back icon button if the path has more than one element
+        m_backButton->setVisible(m_prefabFocusInterface->GetPrefabFocusPathLength() > 1);
     }
 
 } // namespace AzToolsFramework::Prefab