Route layer merge through app core

src/app_layout.cpp

@@ -167,6 +167,8 @@ void execute_document_canvas_clear_plan(App& app, const pp::app::DocumentCanvasC
         LOG("Canvas clear failed: %s", status.message);
 }
 
+void execute_document_layer_merge_plan(App& app, const pp::app::DocumentLayerMergePlan& plan);
+
 bool apply_document_export_menu_plan(App& app, pp::app::DocumentExportMenuKind kind)
 {
     class LegacyDocumentExportMenuServices final : public pp::app::DocumentExportMenuServices {
@@ -605,8 +607,21 @@ public:
 
     void merge_with_lower_layer(int from_index, int to_index) override
     {
-        if (app_.layers)
-            app_.layers->merge(from_index, to_index, true);
+        const int layer_count = app_.canvas && app_.canvas->m_canvas
+            ? static_cast<int>(app_.canvas->m_canvas->m_layers.size())
+            : 0;
+        const int animation_duration = Canvas::I
+            ? Canvas::I->anim_duration()
+            : 0;
+        const auto plan = pp::app::plan_document_layer_merge(
+            layer_count,
+            from_index,
+            to_index,
+            animation_duration);
+        if (!plan)
+            return;
+
+        execute_document_layer_merge_plan(app_, plan.value());
     }
 
     void show_merge_animated_not_supported() override
@@ -618,6 +633,23 @@ private:
     App& app_;
 };
 
+class LegacyDocumentLayerMergeServices final : public pp::app::DocumentLayerMergeServices {
+public:
+    explicit LegacyDocumentLayerMergeServices(App& app) noexcept
+        : app_(app)
+    {
+    }
+
+    void merge_layers(int from_index, int to_index, bool create_history) override
+    {
+        if (app_.layers)
+            app_.layers->merge(from_index, to_index, create_history);
+    }
+
+private:
+    App& app_;
+};
+
 class LegacyDocumentLayerOperationServices final : public pp::app::DocumentLayerOperationServices {
 public:
     LegacyDocumentLayerOperationServices(
@@ -786,6 +818,14 @@ void execute_document_layer_menu_plan(App& app, const pp::app::DocumentLayerMenu
         LOG("Layer menu action failed: %s", status.message);
 }
 
+void execute_document_layer_merge_plan(App& app, const pp::app::DocumentLayerMergePlan& plan)
+{
+    LegacyDocumentLayerMergeServices services(app);
+    const auto status = pp::app::execute_document_layer_merge_plan(plan, services);
+    if (!status.ok())
+        LOG("Layer merge failed: %s", status.message);
+}
+
 void execute_document_layer_operation_plan(
     App& app,
     const pp::app::DocumentLayerOperationPlan& plan,