Move project save write planning to app core

src/app_core/document_canvas.h

@@ -103,6 +103,21 @@ struct DocumentCanvasProjectSaveTargetPlan {
     std::string timelapse_path;
 };
 
+enum class DocumentCanvasProjectSaveWriteAction {
+    write_direct_to_target,
+    write_temporary_then_swap,
+};
+
+struct DocumentCanvasProjectSaveWritePlan {
+    DocumentCanvasProjectSaveWriteAction action = DocumentCanvasProjectSaveWriteAction::write_direct_to_target;
+    std::string write_path;
+    std::string target_path;
+    std::string temporary_path;
+    bool target_exists = false;
+    bool uses_temporary = false;
+    bool falls_back_to_direct_on_temporary_open_failure = false;
+};
+
 class DocumentCanvasClearServices {
 public:
     virtual ~DocumentCanvasClearServices() = default;
@@ -350,6 +365,38 @@ plan_document_canvas_project_save_target(
     return pp::foundation::Result<DocumentCanvasProjectSaveTargetPlan>::success(std::move(plan));
 }
 
+[[nodiscard]] inline pp::foundation::Result<DocumentCanvasProjectSaveWritePlan>
+plan_document_canvas_project_save_write(
+    const DocumentCanvasProjectSaveTargetPlan& target,
+    bool target_exists)
+{
+    if (target.target_path.empty()) {
+        return pp::foundation::Result<DocumentCanvasProjectSaveWritePlan>::failure(
+            pp::foundation::Status::invalid_argument("project save write target path must not be empty"));
+    }
+
+    DocumentCanvasProjectSaveWritePlan plan;
+    plan.target_exists = target_exists;
+    plan.target_path = target.target_path;
+    plan.temporary_path = target.temporary_path;
+
+    if (!target_exists) {
+        plan.write_path = target.target_path;
+        return pp::foundation::Result<DocumentCanvasProjectSaveWritePlan>::success(std::move(plan));
+    }
+
+    if (target.temporary_path.empty()) {
+        return pp::foundation::Result<DocumentCanvasProjectSaveWritePlan>::failure(
+            pp::foundation::Status::invalid_argument("project save temporary path must not be empty"));
+    }
+
+    plan.action = DocumentCanvasProjectSaveWriteAction::write_temporary_then_swap;
+    plan.write_path = target.temporary_path;
+    plan.uses_temporary = true;
+    plan.falls_back_to_direct_on_temporary_open_failure = true;
+    return pp::foundation::Result<DocumentCanvasProjectSaveWritePlan>::success(std::move(plan));
+}
+
 [[nodiscard]] inline pp::foundation::Result<DocumentCanvasClearPlan> plan_document_canvas_clear(
     bool has_canvas,
     float r = 0.0F,