refactor: more comments and minor optimizations

.github/workflows/release.yml

@@ -44,4 +44,3 @@ jobs:
         if: startsWith(github.ref, 'refs/tags/')
         with:
           files: wallpaper-carousel-linux-x64.tar.gz
-          generate_release_notes: true

src/config.h

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-08-05 01:34:52
- * @LastEditTime: 2026-01-15 03:40:25
+ * @LastEditTime: 2026-01-15 07:18:46
  * @Description: Configuration manager.
  */
 #ifndef CONFIG_H
@@ -11,6 +11,26 @@
 #include <QString>
 #include <QStringList>
 
+// Config entries:
+//
+// wallpaper.paths          array       image paths
+// wallpaper.dirs           array       directories to search for images.
+//                                      all images in these directories will be added.
+//                                      NOT recursive.
+// wallpaper.excludes       array       exclude patterns
+//
+// action.confirm           string      command to execute on confirm
+//
+// style.aspect_ratio       number      (width / height) of each image
+// style.image_width        number      width of each image
+// style.image_focus_width  number      width of focused image
+// style.window_width       number      fixed window width
+// style.window_height      number      fixed window height
+// style.no_loading_screen  boolean     disable loading screen and load images while updating UI in batches
+//
+// sort.type                string      sorting type: "none", "name", "date", "size"
+// sort.reverse             boolean     whether to reverse the sorting order
+
 class Config : public QObject {
     Q_OBJECT
 
@@ -23,33 +43,33 @@ class Config : public QObject {
     };
 
     struct WallpaperConfigItems {
-        QStringList paths;
+        QStringList paths;     // "wallpaper.paths"
-        QStringList dirs;
+        QStringList dirs;      // "wallpaper.dirs"
-        QStringList excludes;
+        QStringList excludes;  // "wallpaper.excludes"
     };
 
     struct ActionConfigItems {
-        QString confirm;
+        QString confirm;  // "action.confirm"
     };
 
     struct StyleConfigItems {
-        double aspectRatio   = 1.6;
+        double aspectRatio   = 1.6;    // "style.aspect_ratio"
-        int imageWidth       = 320;
+        int imageWidth       = 320;    // "style.image_width"
-        int imageFocusWidth  = 480;
+        int imageFocusWidth  = 480;    // "style.image_focus_width"
-        int windowWidth      = 750;
+        int windowWidth      = 750;    // "style.window_width"
-        int windowHeight     = 500;
+        int windowHeight     = 500;    // "style.window_height"
-        bool noLoadingScreen = false;
+        bool noLoadingScreen = false;  // "style.no_loading_screen"
     };
 
     struct SortConfigItems {
-        SortType type = SortType::Name;
+        SortType type = SortType::Name;  // "sort.type"
-        bool reverse  = false;
+        bool reverse  = false;           // "sort.reverse"
     };
 
     Config(
-        const QString& configDir,
+        const QString& configDir,  // Fixed, usually "~/.config/wallpaper-carousel"
         const QStringList& searchDirs = {},
-        const QString& configPath     = "",
+        const QString& configPath     = "",  // Override the default config path
         QObject* parent               = nullptr);
 
     ~Config();

src/image_item.cpp

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-11-30 20:32:27
- * @LastEditTime: 2026-01-15 00:48:24
+ * @LastEditTime: 2026-01-15 07:09:29
  * @Description: Image item widget for displaying an image.
  */
 #include "image_item.h"
@@ -16,6 +16,7 @@ ImageData* ImageData::create(const QString& p, const int initWidth, const int in
     ImageData* data = new ImageData(p);
     data->image     = new QImage();
 
+    // Use QImageReader for better performance
     QImageReader reader(p);
     if (!reader.canRead()) {
         warn(QString("Failed to load image from path: %1").arg(p));
@@ -26,6 +27,7 @@ ImageData* ImageData::create(const QString& p, const int initWidth, const int in
     const QSize targetSize(initWidth, initHeight);
     const QSize originalSize = reader.size();
 
+    // Scale the image to fit the target size while maintaining aspect ratio
     if (originalSize.isValid()) {
         double widthRatio  = (double)targetSize.width() / originalSize.width();
         double heightRatio = (double)targetSize.height() / originalSize.height();
@@ -41,6 +43,7 @@ ImageData* ImageData::create(const QString& p, const int initWidth, const int in
         return nullptr;
     }
 
+    // Crop to target size if necessary
     if (data->image->size() != targetSize) {
         int x        = (data->image->width() - targetSize.width()) / 2;
         int y        = (data->image->height() - targetSize.height()) / 2;

src/image_item.h

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-11-30 20:31:15
- * @LastEditTime: 2026-01-14 23:32:58
+ * @LastEditTime: 2026-01-15 07:10:21
  * @Description: Image item widget for displaying an image.
  */
 #ifndef IMAGE_ITEM_H
@@ -13,6 +13,9 @@
 #include <QLabel>
 #include <QPropertyAnimation>
 
+class ImageData;
+class ImageItem;
+
 /**
  * @brief Data structure to hold image information
  *        and can be safely created and passed between threads.
@@ -26,6 +29,7 @@ class ImageData {
 
     ~ImageData() { releaseImage(); }
 
+    // Optimization: release image data as soon as they are no longer needed
     void releaseImage() { delete image, image = nullptr; }
 
     [[nodiscard]] const QImage& getImage() const { return *image; }
@@ -67,6 +71,12 @@ class ImageItem : public QLabel {
 
     [[nodiscard]] qint64 getFileSize() const { return m_data->getFileInfo().size(); }
 
+    /**
+     * @brief Set focus state by scaling the image label
+     *
+     * @param focus whether to focus
+     * @param animate whether to animate the transition
+     */
     void setFocus(bool focus = true, bool animate = true);
 
   protected:

src/images_carousel.cpp

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-08-05 01:22:53
- * @LastEditTime: 2026-01-15 05:11:52
+ * @LastEditTime: 2026-01-15 07:24:52
  * @Description: Animated carousel widget for displaying and selecting images.
  */
 #include "images_carousel.h"
@@ -50,11 +50,6 @@ ImagesCarousel::ImagesCarousel(const Config::StyleConfigItems& styleConfig,
             this,
             &ImagesCarousel::_onImagesLoaded);
 
-    connect(this,
-            &ImagesCarousel::stopped,
-            this,
-            &ImagesCarousel::_onImagesLoaded);
-
     // Auto focus when scrolling
     m_scrollDebounceTimer = new QTimer(this);
     m_scrollDebounceTimer->setSingleShot(true);
@@ -78,6 +73,12 @@ ImagesCarousel::ImagesCarousel(const Config::StyleConfigItems& styleConfig,
 }
 
 void ImagesCarousel::_onImagesLoaded() {
+    // reset stop sign
+    {
+        // No need to lock m_countMutex here, but just for safety
+        QMutexLocker locker(&m_stopSignMutex);
+        m_stopSign = false;
+    }
     m_animationEnabled = true;
     if (!m_noLoadingScreen) {
         _enableUIUpdates(true);
@@ -86,19 +87,17 @@ void ImagesCarousel::_onImagesLoaded() {
         m_imageInsertQueueTimer->deleteLater();
         m_imageInsertQueueTimer = nullptr;
     }
-    if (m_initialImagesLoaded) {
+    // No images loaded
-        // No images loaded
+    if (!getLoadedImagesCount()) {
-        if (!getLoadedImagesCount()) {
+        return;
-            return;
+    }
-        }
+    // Focus the first image
-        // Focus the first image
+    if (m_currentIndex < 0) {
-        if (m_currentIndex < 0) {
+        m_currentIndex = 0;
-            m_currentIndex = 0;
+        // Ensure the layout events are processed before focusing
-            // Ensure the layout events are processed
+        QTimer::singleShot(0, this, [this]() {
-            QTimer::singleShot(0, this, [this]() {
+            focusCurrImage();
-                focusCurrImage();
+        });
-            });
-        }
     }
 
     // exit(1);  // for debug
@@ -156,7 +155,7 @@ void ImagesCarousel::_insertImageQueue(ImageData* data) {
     }
     {
         QMutexLocker locker(&m_imageInsertQueueMutex);
-        m_imageInsertQueue.enqueue(const_cast<ImageData*>(data));
+        m_imageInsertQueue.enqueue(data);
     }
 }
 
@@ -166,14 +165,15 @@ int ImagesCarousel::_insertImage(ImageData* data) {
         emit imageLoaded(getLoadedImagesCount());
         {
             QMutexLocker countLocker(&m_countMutex);
-            if (++m_loadedImagesCount >= m_addedImagesCount) {
+            if (++m_processedImagesCount >= m_addedImagesCount) {
-                QMutexLocker stopSignLocker(&m_stopSignMutex);
+                {
-                if (m_stopSign) {
+                    QMutexLocker stopSignLocker(&m_stopSignMutex);
-                    // if all stopped
+                    if (m_stopSign) {
-                    emit stopped();
+                        // if all stopped
-                } else {
+                        emit stopped();
-                    emit loadingCompleted(m_loadedImagesCount);
+                    }
                 }
+                emit loadingCompleted(m_processedImagesCount);
             }
         }
         return;
@@ -241,6 +241,7 @@ void ImagesCarousel::_processImageInsertQueue() {
     int currPos = m_currentIndex;
     for (ImageData* data : batch) {
         int pos = _insertImage(data);
+        // Keep the focusing index correct
         if (pos >= 0 && pos <= currPos) {
             currPos++;
         }
@@ -276,6 +277,7 @@ void ImageLoader::run() {
                                   Qt::QueuedConnection,
                                   Q_ARG(ImageData*, data));
     });
+    // We need to call _insertImageQueue even if stopped to increase the loaded count
     {
         QMutexLocker stopSignLocker(&m_carousel->m_stopSignMutex);
         if (m_carousel->m_stopSign) return;

src/images_carousel.h

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-08-05 01:22:53
- * @LastEditTime: 2026-01-15 03:42:17
+ * @LastEditTime: 2026-01-15 07:06:46
  * @Description: Animated carousel widget for displaying and selecting images.
  */
 #ifndef IMAGES_CAROUSEL_H
@@ -20,8 +20,57 @@
 #include "config.h"
 #include "image_item.h"
 
-class ImageData;
+// Two different image loading strategies:
-class ImageItem;
+// - With loading screen: load all images directly
+//   1. appendImages called -> increace m_addedImagesCount & spawn all ImageLoader
+//      threads
+//   2. Each ImageLoader calls _insertImageQueue with queued connection
+//   3. _insertImageQueue calls _insertImage directly
+// - Without loading screen: queue loaded images and insert them in batches
+//   1. appendImages called -> increace m_addedImagesCount & spawn all ImageLoader
+//      threads and a timer m_imageInsertQueueTimer, disable UI updates
+//   2. Each ImageLoader calls _insertImageQueue with queued connection
+//   3. _insertImageQueue enqueues the ImageData
+//   4. m_imageInsertQueueTimer calls _processImageInsertQueue every
+//      s_processBatchTimeout ms
+//   5. _processImageInsertQueue processes up to s_processBatchSize items from the
+//      queue and calls _insertImage for each
+//
+// The stop logic is identical:
+// - Force stop
+//   1. Set m_stopSign to true
+//   2. ImageLoader::run checks m_stopSign and returns early if true
+//      and calls _insertImageQueue using queued connection, but passing a
+//      nullptr as parameter
+//   3. The callstack from _insertImageQueue to _insertImage is same as above
+//   4. _insertImage ignores nullptr and just increases m_processedImagesCount
+//   5. when m_processedImagesCount >= m_addedImagesCount, emit stopped()
+//   6. Call ImagesCarousel::_onImagesLoaded
+// - Normal completion
+//   1. Same as above until _insertImage, but m_stopSign is false and ImageLoader::run
+//      passes valid ImageData pointer to _insertImageQueue
+//   2. When m_processedImagesCount >= m_addedImagesCount, emit loadingCompleted()
+//   3. Call ImagesCarousel::_onImagesLoaded
+//
+// 3 different ways to change focusing image:
+// - focusNextImage / focusPrevImage: directly change m_currentIndex and call
+//   focusCurrImage
+//   These can be triggered by different events, e.g. key press, button click, etc.
+// - Auto focus on scroll: debounce scroll events and calculate the nearest image
+//   index to focus, then change m_currentIndex and call focusCurrImage
+// - Initial focus: set m_currentIndex to 0 and call focusCurrImage
+//
+// Note:
+// - All methods and slots of ImageCarousel should be called from the main thread.
+// - ImageCarousel::m_addedImagesCount and ImageCarousel::m_processedImagesCount
+//   should be identical after loading is finished, regardless of whether loading is
+//   forcedly stopped or completed normally.
+// - ImageCarousel::getLoadedImagesCount() returns the number of images currently
+//   displayed in the carousel, which may be less than m_addedImagesCount if loading
+//   is not yet completed or some images failed to load.
+// - The current implementation actually supports dynamic addition of images during runtime,
+//   but the UI does not provide such functionality yet and thus it is not tested :)
+
 class ImageLoader;
 class ImagesCarousel;
 class ImagesCarouselScrollArea;
@@ -56,11 +105,19 @@ class ImagesCarousel : public QWidget {
                             QWidget* parent = nullptr);
     ~ImagesCarousel();
 
-    static constexpr int s_debounceInterval    = 200;
+    static constexpr int s_debounceInterval  = 200;  // ms
-    static constexpr int s_animationDuration   = 300;
+    static constexpr int s_animationDuration = 300;  // ms
+
     static constexpr int s_processBatchTimeout = 50;  // ms
     static constexpr int s_processBatchSize    = 30;  // items
 
+    /**
+     * @brief Get the Current Image Path
+     *
+     * @return QString
+     *
+     * @note This method should be always called from the main thread.
+     */
     [[nodiscard]] QString getCurrentImagePath() const {
         if (m_currentIndex >= 0 && m_currentIndex < getLoadedImagesCount()) {
             auto item = getImageItemAt(m_currentIndex);
@@ -71,11 +128,25 @@ class ImagesCarousel : public QWidget {
         return "";
     }
 
-    // Should always be called in the main thread
+    /**
+     * @brief Get count of loaded images
+     *
+     * @return qsizetype
+     *
+     * @note This method should be always called from the main thread.
+     */
     [[nodiscard]] qsizetype getLoadedImagesCount() const {
         return m_imagesLayout->count();
     }
 
+    /**
+     * @brief Get the Image object at index
+     *
+     * @param index
+     * @return ImageItem*
+     *
+     * @note This method should be always called from the main thread.
+     */
     [[nodiscard]] ImageItem* getImageItemAt(int index) const {
         if (index < 0 || index >= getLoadedImagesCount()) {
             return nullptr;
@@ -86,6 +157,11 @@ class ImagesCarousel : public QWidget {
                 ->widget());
     }
 
+    /**
+     * @brief Get count of added images
+     *
+     * @return qsizetype
+     */
     [[nodiscard]] qsizetype getAddedImagesCount() {
         QMutexLocker locker(&m_countMutex);
         return m_addedImagesCount;
@@ -110,8 +186,7 @@ class ImagesCarousel : public QWidget {
   private slots:
     void _onScrollBarValueChanged(int value);
     void _onItemClicked(const QString& path);
-    void _onImagesLoaded();
+    void _onImagesLoaded();  // Called when loading is completed or stopped
-
     void _processImageInsertQueue();
 
   public:
@@ -131,10 +206,10 @@ class ImagesCarousel : public QWidget {
     ImagesCarouselScrollArea* m_scrollArea = nullptr;
 
     // Items and counters
-    int m_loadedImagesCount = 0;  // increase when _insertImage is called OR ImageLoader::run() is called with m_stopSign as true
+    int m_processedImagesCount = 0;  // increase when _insertImage is called OR ImageLoader::run() is called with m_stopSign as true
-    int m_addedImagesCount  = 0;  // increase when appendImages called
+    int m_addedImagesCount     = 0;  // increase when appendImages called
-    QMutex m_countMutex;          // for m_loadedImagesCount and m_addedImagesCount
+    QMutex m_countMutex;             // for m_processedImagesCount and m_addedImagesCount
-    int m_currentIndex = -1;      // initially no focus
+    int m_currentIndex = -1;         // initially no focus
 
     // Threading
     QQueue<ImageData*> m_imageInsertQueue;
@@ -154,9 +229,6 @@ class ImagesCarousel : public QWidget {
     QMutex m_stopSignMutex;
     bool m_stopSign = false;
 
-    // Flags
-    bool m_initialImagesLoaded = true;
-
   signals:
     void imageFocused(const QString& path, const int index, const int count);
 

src/logger.cpp

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-08-07 01:12:37
- * @LastEditTime: 2026-01-15 04:07:40
+ * @LastEditTime: 2026-01-15 06:26:35
  * @Description: Implementation of logger.
  */
 #include "logger.h"
@@ -23,6 +23,7 @@ static QTextStream* s_logStream = nullptr;
 static bool s_isColored         = false;
 static QMutex s_logMutex;
 
+// Check if the output stream supports colored output
 static bool checkIsColored(FILE* stream) {
     if (!stream || !isatty(fileno(stream))) {
         return false;
@@ -35,6 +36,7 @@ static bool checkIsColored(FILE* stream) {
     return true;
 }
 
+// Custom message handler
 static void messageOutput(QtMsgType type, const QMessageLogContext& context, const QString& msg) {
     Q_UNUSED(context);
 
@@ -126,3 +128,5 @@ void GeneralLogger::warn(const QString& msg) {
 void GeneralLogger::critical(const QString& msg) {
     qCCritical(logMain).noquote() << msg;
 }
+
+// No fatal because qCFatal does not exist before Qt 6.5

src/logger.h

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-08-05 10:43:31
- * @LastEditTime: 2026-01-15 04:07:46
+ * @LastEditTime: 2026-01-15 06:25:57
  * @Description: A simple thread-safe logger.
  */
 #ifndef GENERAL_LOGGER_H
@@ -27,10 +27,24 @@ void critical(const QString& msg);
 
 class Logger {
   public:
+    /**
+     * @brief Initialize the logger and set the output stream.
+     *
+     * @param stream
+     */
     static void init(FILE* stream = stderr);
 
+    /**
+     * @brief Set the log level.
+     *
+     * @param level
+     */
     static void setLogLevel(QtMsgType level);
 
+    /**
+     * @brief Suppress all log output.
+     *
+     */
     static void quiet();
 };
 

src/main.cpp

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-08-05 00:37:58
- * @LastEditTime: 2026-01-15 03:41:55
+ * @LastEditTime: 2026-01-15 05:58:06
  * @Description: Argument parser and entry point.
  */
 #include <QApplication>
@@ -16,21 +16,32 @@
 #include "utils.h"
 #include "version.h"
 
+/**
+ * @brief A static & single-instance class to handle application options.
+ *
+ */
 static class AppOptions {
     QCommandLineParser parser{};
 
+    // The following 3 functions handle specific command line options
+    // and mark doReturn as true to indicate that the application should exit
+    // after parsing arguments.
+
+    // -v --version
     void printVersion() {
         QTextStream out(stdout);
         out << APP_NAME << " version " << APP_VERSION << Qt::endl;
         doReturn = true;
     }
 
+    // -h --help
     void printHelp() {
         QTextStream out(stdout);
         out << parser.helpText() << Qt::endl;
         doReturn = true;
     }
 
+    // Print error message and help
     void printError() {
         if (!errorText.isEmpty()) {
             QTextStream out(stderr);
@@ -44,7 +55,7 @@ static class AppOptions {
     QString configPath = "";
     QStringList appendDirs;
     QString errorText = "";
-    bool doReturn     = false;
+    bool doReturn     = false;  ///< Indicates whether the application should exit after parsing arguments.
 
     void parseArgs(QApplication* a) {
         parser.setApplicationDescription("A small wallpaper utility made with Qt");
@@ -64,6 +75,9 @@ static class AppOptions {
         QCommandLineOption configFileOption(QStringList() << "c" << "config-file", "Specify a custom configuration file", "file");
         parser.addOption(configFileOption);
 
+        // Not parser.process(a->arguments()) because we want to handle exit logics ourselves.
+        // parser.process(...) will do something like exit(...) that will terminate
+        // the application brutally and produce unwanted warnings.
         if (!parser.parse(a->arguments())) {
             errorText = parser.errorText();
             doReturn  = true;
@@ -85,6 +99,7 @@ static class AppOptions {
         } else if (parser.isSet(quietOption)) {
             Logger::quiet();
         } else {
+            // Default to INFO level
             Logger::setLogLevel(QtInfoMsg);
         }
 
@@ -113,6 +128,7 @@ static class AppOptions {
 } s_options;
 
 static QString getConfigDir() {
+    // This will be ~/.config/AppName, where AppName is the name of executable target in CMakeLists.txt
     auto configDir = QStandardPaths::writableLocation(QStandardPaths::AppConfigLocation);
     if (configDir.isEmpty()) {
         configDir = QDir::homePath() + QDir::separator() + ".config" + QDir::separator() + APP_NAME;

src/main_window.cpp

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-08-05 00:37:58
- * @LastEditTime: 2026-01-15 05:30:06
+ * @LastEditTime: 2026-01-15 07:25:41
  * @Description: MainWindow implementation.
  */
 #include "main_window.h"
@@ -15,14 +15,10 @@
 #include "./ui_main_window.h"
 #include "images_carousel.h"
 #include "logger.h"
+#include "utils.h"
 
 using namespace GeneralLogger;
 
-static QString splitNameFromPath(const QString& path) {
-    QFileInfo fileInfo(path);
-    return fileInfo.fileName();
-}
-
 MainWindow::MainWindow(const Config& config, QWidget* parent)
     : QMainWindow(parent), ui(new Ui::MainWindow), m_config(config) {
     ui->setupUi(this);
@@ -85,6 +81,7 @@ void MainWindow::_setupUI() {
 }
 
 void MainWindow::keyPressEvent(QKeyEvent* event) {
+    // Same effects as clicking the confirm/cancel buttons
     if (event->key() == Qt::Key_Escape) {
         _onCancelPressed();
         return;
@@ -136,6 +133,8 @@ void MainWindow::keyPressEvent(QKeyEvent* event) {
     }
 }
 
+// Stop loading images and call onStopped when loading is really stopped
+// emit stop() -> ImagesCarousel::onStop() -> ImagesCarousel::stopped() -> call onStopped
 void MainWindow::_stopLoadingAndQuit(const std::function<void()>& onStopped) {
     if (m_state != Loading) {
         return;
@@ -170,8 +169,7 @@ void MainWindow::_onCancelPressed() {
                 debug("Stopping loading and displaying loaded images...");
                 _stopLoadingAndQuit([this]() {
                     debug("Loading stopped.");
-                    _onLoadingCompleted(m_carousel->getLoadedImagesCount());
+                    // and do nothing
-                    m_carousel->focusCurrImage();
                 });
             }
             break;
@@ -190,13 +188,13 @@ void MainWindow::_onConfirmPressed() {
             // case loading screen is disabled, confirm the selection
             if (m_config.getStyleConfig().noLoadingScreen) {
                 debug("Stopping loading and confirming selection...");
-                connect(
+                // Save current path because the stopping process may take some time
-                    m_carousel,
+                const QString currentPath = m_carousel->getCurrentImagePath();
-                    &ImagesCarousel::stopped,
+                debug("Loading stopped. Confirming selection...");
-                    this,
+                _stopLoadingAndQuit([this, currentPath]() {
-                    &MainWindow::onConfirm);
+                    close();
-                m_state = Stopping;
+                    _runConfirmAction(currentPath);
-                emit stop();
+                });
             }
             break;
         case Ready:
@@ -213,6 +211,7 @@ void MainWindow::wheelEvent(QWheelEvent* event) {
         event->ignore();
         return;
     }
+    // angleDelta().x() is handled by QScrollArea
     if (event->angleDelta().y() > 0) {
         m_carousel->focusPrevImage();
     } else if (event->angleDelta().y() < 0) {
@@ -226,7 +225,7 @@ void MainWindow::closeEvent(QCloseEvent* event) {
     if (m_state == Loading) {
         event->ignore();
         _stopLoadingAndQuit([this]() {
-            debug("Quitting app.");
+            debug("Quitting app...");
             close();
         });
     } else {
@@ -236,12 +235,16 @@ void MainWindow::closeEvent(QCloseEvent* event) {
 
 void MainWindow::onConfirm() {
     close();
-    const auto path = m_carousel->getCurrentImagePath();
+    _runConfirmAction(m_carousel->getCurrentImagePath());
+}
+
+void MainWindow::_runConfirmAction(const QString& path) {
     if (path.isEmpty()) {
         warn("No image selected");
         return;
     }
     info(QString("Selected image: %1").arg(path));
+    // Output the selected path to stdout
     QTextStream out(stdout);
     out << path << Qt::endl;
     const auto cmdOrig = m_config.getActionConfig().confirm;
@@ -270,11 +273,13 @@ void MainWindow::_onLoadingStarted(const qsizetype amount) {
         return;
     }
     m_loadingIndicator->setMaximum(amount);
+    // Change to loading indicator view
     ui->stackedWidget->setCurrentIndex(m_loadingIndicatorIndex);
 }
 
 void MainWindow::_onLoadingCompleted(const qsizetype amount) {
     info(QString("Loading completed, loaded %1 images").arg(amount));
+    // Change to carousel view
     ui->stackedWidget->setCurrentIndex(m_carouselIndex);
     m_state = Ready;
 }

src/main_window.h

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-08-05 00:37:58
- * @LastEditTime: 2025-12-01 00:37:35
+ * @LastEditTime: 2026-01-15 06:16:07
  * @Description: MainWindow implementation.
  */
 #ifndef MAINWINDOW_H
@@ -39,6 +39,7 @@ class MainWindow : public QMainWindow {
   private:
     void _setupUI();
     void _stopLoadingAndQuit(const std::function<void()>& onStopped = nullptr);
+    void _runConfirmAction(const QString& path = "");
 
   private slots:
     void _onImageFocused(const QString& path, const int index, const int count);
@@ -56,6 +57,10 @@ class MainWindow : public QMainWindow {
         Ready,
     } m_state = Init;
 
+    // Init -> Loading -> Ready -> (Quit)
+    // Init -> Loading -> Stopping -> Ready -> (Quit)   (with loading screen)
+    // Init -> Loading -> Stopping -> (Quit)            (without loading screen)
+
     Ui::MainWindow* ui;
     ImagesCarousel* m_carousel           = nullptr;
     LoadingIndicator* m_loadingIndicator = nullptr;

src/utils.h

@@ -1,7 +1,7 @@
 /*
  * @Author: Uyanide pywang0608@foxmail.com
  * @Date: 2025-11-30 20:59:57
- * @LastEditTime: 2026-01-15 03:11:08
+ * @LastEditTime: 2026-01-15 06:00:51
  * @Description: THE utils header that every project needs :)
  */
 
@@ -15,6 +15,11 @@
 #include <QStandardPaths>
 #include <utility>
 
+/**
+ * @brief Defer execution of a callable until the end of the current scope.
+ *
+ * @tparam Callable
+ */
 template <typename Callable>
 class Defer {
     Callable m_func;
@@ -31,16 +36,34 @@ class Defer {
     }
 };
 
+/**
+ * @brief Check if a file exists, is a regular file, and is readable.
+ *
+ * @param path
+ */
 inline bool checkFile(const QString& path) {
     QFileInfo checkFile(path);
+    // According to Qt docs, "exists() returns true if the symlink points to an existing target, otherwise it returns false."
+    // So no need to separately check for isSymbolicLink() or isSymLink().
     return checkFile.exists() && checkFile.isFile() && checkFile.isReadable();
 }
 
+/**
+ * @brief Check if a directory exists, is a directory, and is readable.
+ *
+ * @param path
+ */
 inline bool checkDir(const QString& path) {
     QFileInfo checkFile(path);
     return checkFile.exists() && checkFile.isDir() && checkFile.isReadable();
 }
 
+/**
+ * @brief Expand environment variables and ~ in a given path.
+ *
+ * @param path Input path
+ * @return QString Expanded path
+ */
 inline QString expandPath(const QString& path) {
     QString expandedPath = path;
 
@@ -66,6 +89,25 @@ inline QString expandPath(const QString& path) {
     return QDir::cleanPath(expandedPath);
 }
 
+/**
+ * @brief Split the file name from a given path.
+ *
+ * @param path
+ * @return QString
+ */
+static QString splitNameFromPath(const QString& path) {
+    QFileInfo fileInfo(path);
+    return fileInfo.fileName();
+}
+
+/**
+ * @brief In addition to checking if the file exists and is readable,
+ *        also checks if the file has a valid image extension.
+ *
+ * @param filePath
+ * @return true
+ * @return false
+ */
 inline bool checkImageFile(const QString& filePath) {
     static const QStringList validExtensions = {
         ".jpg",