feat: add support for dynamic theme switching

[javier-godoy]

Summary by CodeRabbit

• New Features

  • Dynamic theme switching with three theme options (including smooth transitions and hover-based preloading).
  • Theme selector added to the demo footer for easy access.

• Style

  • Footer alignment improved; select control visuals adjusted.
  • Fix to select overlay to prevent stale closing state when switching themes.

• Tests

  • Demo app initializes a default theme at startup.

[coderabbitai]

Walkthrough

Adds a new public enum DynamicTheme implementing runtime theme selection (LUMO, AURA, BASE) with initialization, prepare, and apply lifecycle methods; integrates a theme selector into TabbedDemo; adjusts footer/select styles; and updates AppShell configuration to initialize the dynamic theme when supported.

Changes

Cohort / File(s)	Summary
Core Theme Management src/main/java/com/flowingcode/vaadin/addons/demo/DynamicTheme.java	New public enum defining LUMO, AURA, BASE with href and bgColor, Lombok getters, feature/version checks (isFeatureSupported, isFeatureInitialized, getCurrent), and lifecycle APIs: initialize(AppShellSettings), prepare(Component), apply(HasElement). Implements stylesheet injection, mouseover preloading, session-backed current theme, and client-side link toggling (with view transition fallback).
UI Integration src/main/java/com/flowingcode/vaadin/addons/demo/TabbedDemo.java	Added @CssImport for vaadin-select overlay and a guarded Select<DynamicTheme> theme selector in the footer wired to call apply when the feature is initialized.
Styling Updates src/main/resources/META-INF/resources/frontend/styles/commons-demo/shared-styles.css, src/main/resources/META-INF/resources/frontend/styles/commons-demo/vaadin-select-overlay.css	Centered items in .demo-footer, adjusted vaadin-select-value-button mask/padding; added rule to disable vaadin-select-overlay animation when switching themes to avoid a stuck closing state.
AppShell / Tests src/test/java/com/flowingcode/vaadin/addons/demo/AppShellConfiguratorImpl.java	Removed @Theme usage and added configurePage(AppShellSettings) to initialize DynamicTheme.LUMO when DynamicTheme.isFeatureSupported() is true.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Suggested reviewers

• mlopezFC
• paodb

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 63.64% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding a new DynamicTheme enum with public methods to support runtime theme switching between LUMO, AURA, and BASE themes.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch theme-switch

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[coderabbitai]

Actionable comments posted: 2

🤖 Fix all issues with AI agents

In `@src/main/java/com/flowingcode/vaadin/addons/demo/DynamicTheme.java`:
- Around line 70-73: The calls to VaadinSession.getCurrent() in
isFeatureInitialized(), getCurrent(), and initialize() can be null and cause
NPEs; update each method to first retrieve VaadinSession session =
VaadinSession.getCurrent() and guard against null (e.g., return false from
isFeatureInitialized(), return null or throw a clear IllegalStateException from
getCurrent(), and no-op or delay initialization in initialize()) before
accessing session.getAttribute(...) or session.setAttribute(...), preserving
existing behavior when session is present and adding a clear, defensive early
return when it's absent.
- Around line 166-178: The injected JS in component.getElement().executeJs calls
document.startViewTransition and then accesses properties on link without
verifying link exists, which can throw in non-Chromium browsers or when the
stylesheet isn't present; update the script to first check that
document.startViewTransition is a function and fall back to executing the
transition callback directly if unavailable, and add a null check for link
(e.g., if (link) { ... }) before reading or writing link.rel or link.disabled
when iterating over the href list (note the passed href parameter $0), so the
code safely handles missing <link> elements and browsers without
startViewTransition support.

🧹 Nitpick comments (2)

src/main/java/com/flowingcode/vaadin/addons/demo/DynamicTheme.java (1)

107-116: Consider using theme.getHref() instead of hardcoded paths.

The enum already defines href for each theme. Using theme.getHref() would be more consistent and DRY.

♻️ Proposed refactor

-    switch (theme) {
-      case AURA:
-        settings.addLink(Position.APPEND, "stylesheet", "aura/aura.css");
-        break;
-      case LUMO:
-        settings.addLink(Position.APPEND, "stylesheet", "lumo/lumo.css");
-        break;
-      default:
-        break;
+    if (theme.getHref() != null) {
+      settings.addLink(Position.APPEND, "stylesheet", theme.getHref());
     }

src/main/java/com/flowingcode/vaadin/addons/demo/TabbedDemo.java (1)

132-142: Consider null-safety for value change handler.

While Select typically won't fire change events with null values when properly configured, adding a defensive check prevents potential NPEs.

🛡️ Proposed defensive check

-      themeSelect.addValueChangeListener(ev -> ev.getValue().apply(this));
+      themeSelect.addValueChangeListener(ev -> {
+        DynamicTheme theme = ev.getValue();
+        if (theme != null) {
+          theme.apply(this);
+        }
+      });

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud