Refactor theme manager to support arbitrary CSS modification at runtime

sampler/src/main/java/atlantafx/sampler/Launcher.java

@@ -51,7 +51,8 @@ public class Launcher extends Application {
         var scene = new Scene(root, 1200, 768);
 
         var tm = ThemeManager.getInstance();
-        tm.setTheme(scene, tm.getAvailableThemes().get(0));
+        tm.setScene(scene);
+        tm.setTheme(tm.getAvailableThemes().get(0));
         if (IS_DEV_MODE) { startCssFX(scene); }
 
         scene.getStylesheets().addAll(

sampler/src/main/java/atlantafx/sampler/page/general/ThemePage.java

@@ -62,7 +62,9 @@ public class ThemePage extends AbstractPage {
         selector.getItems().setAll(manager.getAvailableThemes());
         selector.getSelectionModel().selectedItemProperty().addListener((obs, old, val) -> {
             if (val != null && getScene() != null) {
-                ThemeManager.getInstance().setTheme(getScene(), val);
+                var tm = ThemeManager.getInstance();
+                tm.setTheme(val);
+                tm.reloadCustomCSS();
                 colorPalette.updateColorInfo(Duration.ofSeconds(1));
             }
         });

sampler/src/main/java/atlantafx/sampler/page/general/TypographyPage.java

@@ -69,7 +69,9 @@ public class TypographyPage extends AbstractPage {
 
         spinner.valueProperty().addListener((obs, old, val) -> {
             if (val != null && getScene() != null) {
-                ThemeManager.getInstance().setFontSize(getScene(), val);
+                var tm = ThemeManager.getInstance();
+                tm.setFontSize(val);
+                tm.reloadCustomCSS();
                 updateFontInfo(Duration.ofMillis(1000));
             }
         });

sampler/src/main/java/atlantafx/sampler/theme/ThemeManager.java

@@ -7,6 +7,7 @@ import atlantafx.base.theme.Theme;
 import atlantafx.sampler.Launcher;
 import atlantafx.sampler.Resources;
 import javafx.application.Application;
+import javafx.css.PseudoClass;
 import javafx.scene.Scene;
 
 import java.net.URI;
@@ -17,9 +18,25 @@ import static java.nio.charset.StandardCharsets.UTF_8;
 public final class ThemeManager {
 
     private static final String DUMMY_STYLESHEET = Resources.getResource("assets/styles/empty.css").toString();
+    private static final PseudoClass USER_CUSTOM = PseudoClass.getPseudoClass("user-custom");
+
+    // KEY           |  VALUE
+    // -fx-property  |  value;
+    private final Map<String, String> customCSSDeclarations = new LinkedHashMap<>();
+    // .foo          |  -fx-property: value;
+    private final Map<String, String> customCSSRules = new LinkedHashMap<>();
 
     private Theme currentTheme = null;
     private int currentFontSize = 14;
+    private Scene scene;
+
+    public Scene getScene() {
+        return scene;
+    }
+
+    public void setScene(Scene scene) {
+        this.scene = scene;
+    }
 
     public Theme getTheme() {
         return currentTheme;
@@ -33,7 +50,8 @@ public final class ThemeManager {
      * E.g. JavaFX ignores Ikonli -fx-icon-color and -fx-icon-size properties, but for an unknown
      * reason they won't be ignored when exactly the same stylesheet is set via {@link Scene#getStylesheets()}.
      */
-    public void setTheme(Scene scene, Theme theme) {
+    public void setTheme(Theme theme) {
+        Objects.requireNonNull(scene);
         Objects.requireNonNull(theme);
 
         Application.setUserAgentStylesheet(Objects.requireNonNull(theme.getUserAgentStylesheet()));
@@ -81,17 +99,59 @@ public final class ThemeManager {
         return currentFontSize;
     }
 
-    public void setFontSize(Scene scene, int fontSize) {
+    public void setFontSize(int fontSize) {
-        String css = String.format(".root { -fx-font-size: %dpx; } .ikonli-font-icon { -fx-icon-size: %dpx; }",
+        setCustomDeclaration("-fx-font-size", fontSize + "px");
-                                   fontSize,
+        setCustomRule(".ikonli-font-icon", String.format("-fx-icon-size: %dpx;", fontSize + 2));
-                                   fontSize + 2
+        currentFontSize = fontSize;
-        );
+    }
+
+    private void setCustomDeclaration(String property, String value) {
+        customCSSDeclarations.put(property, value);
+    }
+
+    private void setCustomRule(String selector, String rule) {
+        customCSSRules.put(selector, rule);
+    }
+
+    public void reloadCustomCSS() {
+        Objects.requireNonNull(scene);
+        StringBuilder css = new StringBuilder();
+
+        css.append(".root:");
+        css.append(USER_CUSTOM.getPseudoClassName());
+        css.append(" {\n");
+        customCSSDeclarations.forEach((k, v) -> {
+            css.append("\t");
+            css.append(k);
+            css.append(":\s");
+            css.append(v);
+            css.append(";\n");
+        });
+        css.append("}\n");
+
+        customCSSRules.forEach((k, v) -> {
+            css.append(".root:");
+            css.append(USER_CUSTOM.getPseudoClassName());
+            css.append(" ");
+            css.append(k);
+            css.append(" {");
+            css.append(v);
+            css.append("}\n");
+        });
+
+        System.out.println(css);
+
         scene.getStylesheets().removeIf(uri -> uri.startsWith("data:text/css"));
         scene.getStylesheets().add(
-                "data:text/css;base64," + Base64.getEncoder().encodeToString(css.getBytes(UTF_8))
+                "data:text/css;base64," + Base64.getEncoder().encodeToString(css.toString().getBytes(UTF_8))
         );
+        scene.getRoot().pseudoClassStateChanged(USER_CUSTOM, true);
+    }
 
-        currentFontSize = fontSize;
+    public void resetCustomCSS() {
+        customCSSDeclarations.clear();
+        customCSSRules.clear();
+        scene.getRoot().pseudoClassStateChanged(USER_CUSTOM, false);
     }
 
     public HighlightJSTheme getMatchingHighlightJSTheme(Theme theme) {