Move theme detection into Application

* Add function to Application to quickly determine if in light or dark theme
* Add kpxcApp symbol
* Explicitly define main function for GUI tests to improve performance and use custom Application.

src/gui/Application.cpp

@@ -18,8 +18,14 @@
  */
 
 #include "Application.h"
-#include "MainWindow.h"
+
+#include "autotype/AutoType.h"
 #include "core/Config.h"
+#include "core/Global.h"
+#include "gui/MainWindow.h"
+#include "gui/osutils/OSUtils.h"
+#include "gui/styles/dark/DarkStyle.h"
+#include "gui/styles/light/LightStyle.h"
 
 #include <QFileInfo>
 #include <QFileOpenEvent>
@@ -28,9 +34,6 @@
 #include <QStandardPaths>
 #include <QtNetwork/QLocalSocket>
 
-#include "autotype/AutoType.h"
-#include "core/Global.h"
-
 #if defined(Q_OS_WIN) || (defined(Q_OS_UNIX) && !defined(Q_OS_MACOS))
 #include "core/OSEventFilter.h"
 #endif
@@ -65,6 +68,26 @@ Application::Application(int& argc, char** argv)
     registerUnixSignals();
 #endif
 
+    QString appTheme = config()->get("GUI/ApplicationTheme").toString();
+    if (appTheme == "auto") {
+        if (osUtils->isDarkMode()) {
+            setStyle(new DarkStyle);
+            m_darkTheme = true;
+        } else {
+            setStyle(new LightStyle);
+        }
+    } else if (appTheme == "light") {
+        setStyle(new LightStyle);
+    } else if (appTheme == "dark") {
+        setStyle(new DarkStyle);
+        m_darkTheme = true;
+    } else {
+        // Classic mode, only check for dark theme when not on Windows
+#ifndef Q_OS_WIN
+        m_darkTheme = osUtils->isDarkMode();
+#endif
+    }
+
     QString userName = qgetenv("USER");
     if (userName.isEmpty()) {
         userName = qgetenv("USERNAME");
@@ -281,3 +304,8 @@ bool Application::sendFileNamesToRunningInstance(const QStringList& fileNames)
     const bool disconnected = client.waitForDisconnected(WaitTimeoutMSec);
     return writeOk && disconnected;
 }
+
+bool Application::isDarkTheme() const
+{
+    return m_darkTheme;
+}