fix(userInterface): remove function when expression is cleared

Author: bilyayeva

include/mathplotter/userInterface.hpp

@@ -20,6 +20,7 @@ namespace mathplotter {
         std::size_t rowIndex;
         std::string expression;
         sf::Color color;
+        bool shouldRemove{false};
     };
 
     class UserInterface {

src/application.cpp

@@ -144,22 +144,30 @@ namespace mathplotter {
                     )
                 };
 
-                if (renderer->IsValid()) {
-                    m_functionRenderers[submission->rowIndex] =
-                        std::move(renderer);
-
-                    m_userInterface.SetFunctionError(
-                        submission->rowIndex,
-                        false
-                    );
+                if (submission->shouldRemove) {
+                    if (submission->rowIndex < m_functionRenderers.size()) {
+                        m_functionRenderers[submission->rowIndex].reset();
+                    }
                 } else {
-                    m_functionRenderers[submission->rowIndex].reset();
-
-                    m_userInterface.SetFunctionError(
-                        submission->rowIndex,
-                        true
-                    );
+                    if (renderer->IsValid()) {
+                        m_functionRenderers[submission->rowIndex] =
+                            std::move(renderer);
+
+                        m_userInterface.SetFunctionError(
+                            submission->rowIndex,
+                            false
+                        );
+                    } else {
+                        m_functionRenderers[submission->rowIndex].reset();
+
+                        m_userInterface.SetFunctionError(
+                            submission->rowIndex,
+                            true
+                        );
+                    }
                 }
+
+                
             }
 
             // Render User Interface

src/userInterface.cpp

@@ -487,8 +487,19 @@ namespace mathplotter {
                     )
                 };
 
-                if (ImGui::IsItemEdited()) {
+                if (
+                    ImGui::IsItemEdited() &&
+                    m_functionRows[i].expression.empty()
+                ) {
                     m_functionRows[i].isSubmitted = false;
+                    m_functionRows[i].hasError = false;
+
+                    submission = FunctionSubmission{
+                        i,
+                        "",
+                        ToSfmlColor(m_functionRows[i].color),
+                        true
+                    };
                 }
 
                 if (