Add basic files and settings followed by PR JabRef#9263

- Add "Use System Preference" option under General -> Appearance -> Visual Theme
- Add flags to store whether user chose this option
- Add SystemThemeDetector.java for auto detect system theme(to do)

Author: EthanYifanJu

src/main/java/org/jabref/gui/preferences/general/GeneralTabViewModel.java

@@ -54,6 +54,9 @@ public class GeneralTabViewModel implements PreferenceTabViewModel {
     private final ReadOnlyListProperty<ThemeTypes> themesListProperty =
             new ReadOnlyListWrapper<>(FXCollections.observableArrayList(ThemeTypes.values()));
     private final ObjectProperty<ThemeTypes> selectedThemeProperty = new SimpleObjectProperty<>();
+
+    private final BooleanProperty flagWhenAutomaticButtonSelected = new SimpleBooleanProperty();
+
     private final StringProperty customPathToThemeProperty = new SimpleStringProperty();
 
     private final BooleanProperty fontOverrideProperty = new SimpleBooleanProperty();
@@ -125,8 +128,16 @@ public void setValues() {
         // The light theme is in fact the absence of any theme modifying 'base.css'. Another embedded theme like
         // 'dark.css', stored in the classpath, can be introduced in {@link org.jabref.gui.theme.Theme}.
         switch (workspacePreferences.getTheme().getType()) {
-            case DEFAULT -> selectedThemeProperty.setValue(ThemeTypes.LIGHT);
-            case EMBEDDED -> selectedThemeProperty.setValue(ThemeTypes.DARK);
+            case DEFAULT -> {
+                selectedThemeProperty.setValue(ThemeTypes.LIGHT);
+                if(workspacePreferences.automaticThemeDetectionFlag().getValue())
+                    selectedThemeProperty.setValue(ThemeTypes.SYNC);
+            }
+            case EMBEDDED -> {
+                selectedThemeProperty.setValue(ThemeTypes.DARK);
+                if(workspacePreferences.automaticThemeDetectionFlag().getValue())
+                    selectedThemeProperty.setValue(ThemeTypes.SYNC);
+            }
             case CUSTOM -> {
                 selectedThemeProperty.setValue(ThemeTypes.CUSTOM);
                 customPathToThemeProperty.setValue(workspacePreferences.getTheme().getName());
@@ -166,8 +177,19 @@ public void storeSettings() {
         workspacePreferences.setMainFontSize(Integer.parseInt(fontSizeProperty.getValue()));
 
         switch (selectedThemeProperty.get()) {
-            case LIGHT -> workspacePreferences.setTheme(Theme.light());
-            case DARK -> workspacePreferences.setTheme(Theme.dark());
+            case LIGHT -> {
+                workspacePreferences.setTheme(Theme.light());
+                workspacePreferences.setAutomaticThemeDetectionFlag(flagWhenAutomaticButtonSelected.getValue());
+            }
+            case DARK -> {
+                workspacePreferences.setTheme(Theme.dark());
+                workspacePreferences.setAutomaticThemeDetectionFlag(flagWhenAutomaticButtonSelected.getValue());
+            }
+            case SYNC -> {
+                workspacePreferences.setTheme(Theme.dark());
+                flagWhenAutomaticButtonSelected.setValue(true);
+                workspacePreferences.setAutomaticThemeDetectionFlag(flagWhenAutomaticButtonSelected.getValue());
+            }
             case CUSTOM -> workspacePreferences.setTheme(Theme.custom(customPathToThemeProperty.getValue()));
         }
 

src/main/java/org/jabref/gui/theme/SystemThemeDetector.java

@@ -0,0 +1,5 @@
+package org.jabref.gui.theme;
+
+public class SystemThemeDetector {
+
+}

src/main/java/org/jabref/gui/theme/ThemeTypes.java

@@ -6,6 +6,7 @@ public enum ThemeTypes {
 
         LIGHT(Localization.lang("Light")),
         DARK(Localization.lang("Dark")),
+        SYNC(Localization.lang("Use System Preference")),
         CUSTOM(Localization.lang("Custom..."));
 
         private final String displayName;

src/main/java/org/jabref/preferences/JabRefPreferences.java

@@ -417,6 +417,9 @@ public class JabRefPreferences implements PreferencesService {
     // Helper string
     private static final String USER_HOME = System.getProperty("user.home");
 
+    // System default theme / Auto detect theme constant
+    private static final String AUTOMATIC_THEME_DETECTION = "automaticThemeDetection";
+
     // Indexes for Strings within stored custom export entries
     private static final int EXPORTER_NAME_INDEX = 0;
     private static final int EXPORTER_FILENAME_INDEX = 1;
@@ -787,6 +790,8 @@ private JabRefPreferences() {
 
         // set default theme
         defaults.put(FX_THEME, Theme.BASE_CSS);
+        // Set automatic theme detection OFF.
+        defaults.put(AUTOMATIC_THEME_DETECTION, Boolean.FALSE);
         setLanguageDependentDefaultValues();
     }
 
@@ -2086,7 +2091,8 @@ public WorkspacePreferences getWorkspacePreferences() {
                 getBoolean(OPEN_LAST_EDITED),
                 getBoolean(SHOW_ADVANCED_HINTS),
                 getBoolean(WARN_ABOUT_DUPLICATES_IN_INSPECTION),
-                getBoolean(CONFIRM_DELETE));
+                getBoolean(CONFIRM_DELETE),
+                getBoolean(AUTOMATIC_THEME_DETECTION));
 
         EasyBind.listen(workspacePreferences.languageProperty(), (obs, oldValue, newValue) -> {
             put(LANGUAGE, newValue.getId());
@@ -2102,7 +2108,7 @@ public WorkspacePreferences getWorkspacePreferences() {
         EasyBind.listen(workspacePreferences.showAdvancedHintsProperty(), (obs, oldValue, newValue) -> putBoolean(SHOW_ADVANCED_HINTS, newValue));
         EasyBind.listen(workspacePreferences.warnAboutDuplicatesInInspectionProperty(), (obs, oldValue, newValue) -> putBoolean(WARN_ABOUT_DUPLICATES_IN_INSPECTION, newValue));
         EasyBind.listen(workspacePreferences.confirmDeleteProperty(), (obs, oldValue, newValue) -> putBoolean(CONFIRM_DELETE, newValue));
-
+        EasyBind.listen(workspacePreferences.automaticThemeDetectionFlag(), (obs, oldValue, newValue) -> putBoolean(AUTOMATIC_THEME_DETECTION, newValue));
         return workspacePreferences;
     }
 

src/main/java/org/jabref/preferences/WorkspacePreferences.java

@@ -20,6 +20,7 @@ public class WorkspacePreferences {
     private final BooleanProperty showAdvancedHints;
     private final BooleanProperty warnAboutDuplicatesInInspection;
     private final BooleanProperty confirmDelete;
+    private final BooleanProperty automaticThemeDetectionFlag;
 
     public WorkspacePreferences(Language language,
                                 boolean shouldOverrideDefaultFontSize,
@@ -29,7 +30,8 @@ public WorkspacePreferences(Language language,
                                 boolean shouldOpenLastEdited,
                                 boolean showAdvancedHints,
                                 boolean warnAboutDuplicatesInInspection,
-                                boolean confirmDelete) {
+                                boolean confirmDelete,
+                                boolean automaticThemeDetectionFlag) {
         this.language = new SimpleObjectProperty<>(language);
         this.shouldOverrideDefaultFontSize = new SimpleBooleanProperty(shouldOverrideDefaultFontSize);
         this.mainFontSize = new SimpleIntegerProperty(mainFontSize);
@@ -39,6 +41,15 @@ public WorkspacePreferences(Language language,
         this.showAdvancedHints = new SimpleBooleanProperty(showAdvancedHints);
         this.warnAboutDuplicatesInInspection = new SimpleBooleanProperty(warnAboutDuplicatesInInspection);
         this.confirmDelete = new SimpleBooleanProperty(confirmDelete);
+        this.automaticThemeDetectionFlag = new SimpleBooleanProperty(automaticThemeDetectionFlag);
+    }
+
+    public BooleanProperty automaticThemeDetectionFlag() {
+        return automaticThemeDetectionFlag;
+    }
+
+    public void setAutomaticThemeDetectionFlag(boolean newValue) {
+        this.automaticThemeDetectionFlag.setValue(newValue);
     }
 
     public Language getLanguage() {