Route layer merge through app core

src/app_core/document_layer.h

@@ -78,6 +78,12 @@ struct DocumentLayerMenuPlan {
     int to_index = 0;
 };
 
+struct DocumentLayerMergePlan {
+    int from_index = 0;
+    int to_index = 0;
+    bool create_history = true;
+};
+
 class DocumentLayerMenuServices {
 public:
     virtual ~DocumentLayerMenuServices() = default;
@@ -115,6 +121,13 @@ public:
     virtual void update_title() = 0;
 };
 
+class DocumentLayerMergeServices {
+public:
+    virtual ~DocumentLayerMergeServices() = default;
+
+    virtual void merge_layers(int from_index, int to_index, bool create_history) = 0;
+};
+
 [[nodiscard]] inline pp::foundation::Status validate_layer_index(
     int layer_count,
     int index) noexcept
@@ -447,6 +460,45 @@ public:
     return pp::foundation::Result<DocumentLayerMenuPlan>::success(std::move(plan));
 }
 
+[[nodiscard]] inline pp::foundation::Result<DocumentLayerMergePlan> plan_document_layer_merge(
+    int layer_count,
+    int from_index,
+    int to_index,
+    int animation_duration,
+    bool create_history = true)
+{
+    auto index_status = validate_layer_index(layer_count, from_index);
+    if (!index_status.ok()) {
+        return pp::foundation::Result<DocumentLayerMergePlan>::failure(index_status);
+    }
+
+    index_status = validate_layer_index(layer_count, to_index);
+    if (!index_status.ok()) {
+        return pp::foundation::Result<DocumentLayerMergePlan>::failure(index_status);
+    }
+
+    if (animation_duration < 0) {
+        return pp::foundation::Result<DocumentLayerMergePlan>::failure(
+            pp::foundation::Status::out_of_range("animation duration must not be negative"));
+    }
+
+    if (animation_duration > 1) {
+        return pp::foundation::Result<DocumentLayerMergePlan>::failure(
+            pp::foundation::Status::invalid_argument("animated layer merge is not supported"));
+    }
+
+    if (from_index <= to_index) {
+        return pp::foundation::Result<DocumentLayerMergePlan>::failure(
+            pp::foundation::Status::invalid_argument("layer merge source must be above the destination"));
+    }
+
+    DocumentLayerMergePlan plan;
+    plan.from_index = from_index;
+    plan.to_index = to_index;
+    plan.create_history = create_history;
+    return pp::foundation::Result<DocumentLayerMergePlan>::success(plan);
+}
+
 [[nodiscard]] inline pp::foundation::Status execute_document_layer_rename_plan(
     const DocumentLayerRenamePlan& plan,
     DocumentLayerRenameServices& services)
@@ -545,6 +597,19 @@ inline void execute_document_layer_operation_side_effects(
     return pp::foundation::Status::success();
 }
 
+[[nodiscard]] inline pp::foundation::Status execute_document_layer_merge_plan(
+    const DocumentLayerMergePlan& plan,
+    DocumentLayerMergeServices& services)
+{
+    if (plan.from_index <= plan.to_index) {
+        return pp::foundation::Status::invalid_argument(
+            "layer merge source must be above the destination");
+    }
+
+    services.merge_layers(plan.from_index, plan.to_index, plan.create_history);
+    return pp::foundation::Status::success();
+}
+
 [[nodiscard]] inline pp::foundation::Status execute_document_layer_menu_plan(
     const DocumentLayerMenuPlan& plan,
     DocumentLayerMenuServices& services)