UC23: Fix signal best practice violations in dashboard

src/main/java/com/example/usecase23/UseCase23View.java

@@ -139,8 +139,8 @@ private Component createViewEvents() {
         bindData(chart, newYorkSeries, newYorkTimelineSignal);
         bindData(chart, tokyoSeries, tokyoTimelineSignal);
 
-        Signal.effect(chart, () -> xAxis.setCategories(timelineCategoriesSignal
-                .get().stream().map(Signal::get).toArray(String[]::new)));
+        Signal.effect(chart, () -> xAxis.setCategories(
+                timelineCategoriesSignal.getValues().toArray(String[]::new)));
 
         conf.addSeries(berlinSeries);
         conf.addSeries(londonSeries);
@@ -165,12 +165,8 @@ private Component createViewEvents() {
 
     private static void bindData(Chart chart, ListSeries series,
             ListSignal<Number> signal) {
-        Signal.effect(chart, () -> {
-            series.setData(signal.get().stream().map(Signal::get)
-                    .toArray(Number[]::new));
-            // TODO issue of getting the values from ListSignal instead of
-            // Signal<Number>
-        });
+        Signal.effect(chart,
+                () -> series.setData(signal.getValues().toArray(Number[]::new)));
     }
 
     private Component createServiceHealth() {
@@ -309,7 +305,7 @@ private String getStatusDisplayName(ServiceHealth serviceHealth) {
      * Callback invoked by the scheduler service with new dashboard data. This
      * method only updates signals - no UI access or chart drawing.
      */
-    private void onDataUpdate(DashboardData data) {
+    void onDataUpdate(DashboardData data) {
         // Update highlight card signals
         currentUsersSignal.set(data.currentUsers());
         viewEventsSignal.set(data.viewEvents());
@@ -389,10 +385,13 @@ private HighlightCard(String title, ValueSignal<Number> signal,
                     signal.peek().doubleValue(), signal.peek().doubleValue()));
 
             // update previous value when the main signal changes
+            // Uses runWithoutTransaction since we must track previous state
+            // No infinite loop risk: effect depends on signal, not changeSignal
             Signal.effect(this, () -> {
                 double current = signal.get().doubleValue();
                 double previous = changeSignal.peek().current();
-                changeSignal.set(new Change(previous, current));
+                Signal.runWithoutTransaction(
+                        () -> changeSignal.set(new Change(previous, current)));
             });
 
             // Computed signal for percentage change
@@ -415,8 +414,8 @@ private HighlightCard(String title, ValueSignal<Number> signal,
             valueSpan.bindText(signal.map(format::apply));
 
             Span percentageSpan = new Span();
-            percentageSpan.bindText(prefixSignal
-                    .map(prefix -> prefix + percentageSignal.get()));
+            percentageSpan.bindText(Signal.computed(
+                    () -> prefixSignal.get() + percentageSignal.get()));
 
             Icon icon = new Icon(iconSignal);
             icon.setSize("10px");

src/test/java/com/example/usecase23/UseCase23ViewTest.java

@@ -1,5 +1,7 @@
 package com.example.usecase23;
 
+import java.util.List;
+
 import org.junit.jupiter.api.Test;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.security.test.context.support.WithMockUser;
@@ -9,6 +11,7 @@
 import com.vaadin.flow.component.board.Board;
 import com.vaadin.flow.component.grid.Grid;
 import com.vaadin.flow.component.html.H2;
+import com.vaadin.flow.component.html.Span;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -47,4 +50,55 @@ void serviceHealthGridRendered() {
         // Grid for service health should be present
         assertTrue($view(Grid.class).all().size() >= 1);
     }
+
+    @Test
+    void highlightCardUpdatesValueOnDataUpdate() {
+        navigate(UseCase23View.class);
+        runPendingSignalsTasks();
+
+        UseCase23View view = $view(UseCase23View.class).first();
+
+        // Push data update with known values
+        view.onDataUpdate(createTestData(42, 1500, 3.5, 99));
+        runPendingSignalsTasks();
+
+        // "Current users" card should show "42"
+        assertTrue($view(Span.class).all().stream()
+                .anyMatch(s -> "42".equals(s.getText())),
+                "Expected a Span with text '42' for current users");
+    }
+
+    @Test
+    void highlightCardShowsPercentageChangeAfterTwoUpdates() {
+        navigate(UseCase23View.class);
+        runPendingSignalsTasks();
+
+        UseCase23View view = $view(UseCase23View.class).first();
+
+        // First update: baseline
+        view.onDataUpdate(createTestData(100, 1000, 2.0, 50));
+        runPendingSignalsTasks();
+
+        // Second update: double the users (100 → 200 = +100%)
+        view.onDataUpdate(createTestData(200, 1000, 2.0, 50));
+        runPendingSignalsTasks();
+
+        // Should show "+100.0" in the percentage badge
+        assertTrue($view(Span.class).all().stream().anyMatch(
+                s -> s.getText() != null && s.getText().contains("+100.0")),
+                "Expected percentage badge showing +100.0");
+    }
+
+    private DashboardData createTestData(int users, int views,
+            double conversion, double custom) {
+        return new DashboardData(users, views, conversion, custom,
+                new DashboardData.TimelineData("12:00", 10, 20, 30, 40),
+                List.of(new ServiceHealth(ServiceHealth.Status.OK,
+                        "Münster", 100, 200),
+                        new ServiceHealth(ServiceHealth.Status.EXCELLENT,
+                                "Cluj-Napoca", 150, 250),
+                        new ServiceHealth(ServiceHealth.Status.FAILING,
+                                "Ciudad Victoria", 50, 75)),
+                List.of(10.0, 20.0, 30.0, 15.0, 25.0, 35.0));
+    }
 }