diff --git a/CircularProgressBar.cpp b/CircularProgressBar.cpp
index bc0d332..7b88f61 100644
--- a/CircularProgressBar.cpp
+++ b/CircularProgressBar.cpp
@@ -10,30 +10,26 @@ CircularProgressBar::CircularProgressBar(QWidget *parent)
     setFixedSize(220, 220);
 }
 
-void CircularProgressBar::setValue(int value)
-{
-    int clampedValue = qBound(0, value, m_maximum);
-    if (clampedValue != m_value) {
+void CircularProgressBar::setValue(const int value) {
+  if (const int clampedValue = qBound(0, value, m_maximum); clampedValue != m_value) {
         m_value = clampedValue;
         update();
     }
 }
 
-void CircularProgressBar::setMaximum(int maximum)
-{
+void CircularProgressBar::setMaximum(int maximum){
     m_maximum = maximum;
     update();
 }
 
-void CircularProgressBar::paintEvent(QPaintEvent *event)
-{
+void CircularProgressBar::paintEvent(QPaintEvent *event){
     Q_UNUSED(event)
 
     QPainter painter(this);
     painter.setRenderHint(QPainter::Antialiasing);
 
-    int side = qMin(width(), height());
-    QRect rect((width() - side) / 2 + 20, (height() - side) / 2 + 20,
+    const int side = qMin(width(), height());
+    const QRect rect((width() - side) / 2 + 20, (height() - side) / 2 + 20,
                side - 40, side - 40);
 
     // Background circle
@@ -48,19 +44,17 @@ void CircularProgressBar::paintEvent(QPaintEvent *event)
         progressPen.setCapStyle(Qt::RoundCap);
         painter.setPen(progressPen);
 
-        int angle = (360 * m_value) / m_maximum;
+        const int angle = (360 * m_value) / m_maximum;
         painter.drawArc(rect, 90 * 16, -angle * 16);
     }
 }
 
-void CircularProgressBar::resizeEvent(QResizeEvent *event)
-{
+void CircularProgressBar::resizeEvent(QResizeEvent *event){
     QWidget::resizeEvent(event);
     updateChildPositions();
 }
 
-void CircularProgressBar::updateChildPositions()
-{
+void CircularProgressBar::updateChildPositions() const {
     const auto children = findChildren<QWidget*>(QString(), Qt::FindDirectChildrenOnly);
     for (QWidget *child : children) {
         child->resize(width(), 40);
diff --git a/CircularProgressBar.h b/CircularProgressBar.h
index 5e174f8..812b781 100644
--- a/CircularProgressBar.h
+++ b/CircularProgressBar.h
@@ -3,8 +3,7 @@
 
 #include <QWidget>
 
-class CircularProgressBar : public QWidget
-{
+class CircularProgressBar final : public QWidget {
     Q_OBJECT
 
 public:
@@ -12,8 +11,8 @@ public:
 
     void setValue(int value);
     void setMaximum(int maximum);
-    int value() const { return m_value; }
-    int maximum() const { return m_maximum; }
+    [[nodiscard]] int value() const { return m_value; }
+    [[nodiscard]] int maximum() const { return m_maximum; }
 
 protected:
     void paintEvent(QPaintEvent *event) override;
@@ -23,7 +22,7 @@ private:
     int m_value;
     int m_maximum;
 
-    void updateChildPositions();
+    void updateChildPositions() const;
 };
 
 #endif // CIRCULARPROGRESSBAR_H
diff --git a/KeyboardShortcuts.cpp b/KeyboardShortcuts.cpp
index d9bab28..4fb6f02 100644
--- a/KeyboardShortcuts.cpp
+++ b/KeyboardShortcuts.cpp
@@ -1,11 +1,10 @@
 #include "KeyboardShortcuts.h"
 #include <QWidget>
 
-KeyboardShortcuts::KeyboardShortcuts(QWidget *parent)
-    : QObject(parent)
-{
-    setupShortcuts(parent);
+KeyboardShortcuts::KeyboardShortcuts(QWidget *parent) : QObject(parent) {
+  setupShortcuts(parent);
 }
+KeyboardShortcuts::~KeyboardShortcuts() = default;
 
 void KeyboardShortcuts::setupShortcuts(QWidget *parent)
 {
diff --git a/KeyboardShortcuts.h b/KeyboardShortcuts.h
index b9dab73..172a0be 100644
--- a/KeyboardShortcuts.h
+++ b/KeyboardShortcuts.h
@@ -1,7 +1,6 @@
 #ifndef KEYBOARDSHORTCUTS_H
 #define KEYBOARDSHORTCUTS_H
 
-#include <QObject>
 #include <QShortcut>
 
 class KeyboardShortcuts : public QObject
@@ -10,7 +9,7 @@ class KeyboardShortcuts : public QObject
 
 public:
     explicit KeyboardShortcuts(QWidget *parent = nullptr);
-    ~KeyboardShortcuts() = default;
+    ~KeyboardShortcuts() override;
 
 signals:
     void startPauseRequested();
@@ -22,11 +21,11 @@ signals:
 private:
     void setupShortcuts(QWidget *parent);
 
-    QShortcut *m_startShortcut;
-    QShortcut *m_pauseShortcut;
-    QShortcut *m_resetShortcut;
-    QShortcut *m_settingsShortcut;
-    QShortcut *m_skipShortcut;
+    QShortcut *m_startShortcut{};
+    QShortcut *m_pauseShortcut{};
+    QShortcut *m_resetShortcut{};
+    QShortcut *m_settingsShortcut{};
+    QShortcut *m_skipShortcut{};
 };
 
 #endif // KEYBOARDSHORTCUTS_H
diff --git a/NotificationManager.cpp b/NotificationManager.cpp
index fdba42c..6ac9b3f 100644
--- a/NotificationManager.cpp
+++ b/NotificationManager.cpp
@@ -4,12 +4,9 @@
 #include <QMessageBox>
 
 NotificationManager::NotificationManager(QWidget *parent)
-    : QObject(parent)
-    , m_parent(parent)
-    , m_trayManager(nullptr)
-    , m_notificationsEnabled(true)
-{
-}
+    : QObject(parent), m_parent(parent), m_trayManager(nullptr),
+      m_notificationsEnabled(true) {}
+NotificationManager::~NotificationManager() {}
 
 void NotificationManager::setSystemTrayManager(SystemTrayManager *trayManager)
 {
@@ -21,8 +18,7 @@ void NotificationManager::setNotificationsEnabled(bool enabled)
     m_notificationsEnabled = enabled;
 }
 
-void NotificationManager::showNotification(const QString &message)
-{
+void NotificationManager::showNotification(const QString &message) const {
     if (!m_notificationsEnabled) return;
 
     if (m_trayManager && m_trayManager->isVisible()) {
diff --git a/NotificationManager.h b/NotificationManager.h
index 1aafc63..8c19773 100644
--- a/NotificationManager.h
+++ b/NotificationManager.h
@@ -13,11 +13,11 @@ class NotificationManager : public QObject
 
 public:
     explicit NotificationManager(QWidget *parent = nullptr);
-    ~NotificationManager() = default;
+    ~NotificationManager() override;
 
     void setSystemTrayManager(SystemTrayManager *trayManager);
     void setNotificationsEnabled(bool enabled);
-    void showNotification(const QString &message);
+    void showNotification(const QString &message) const;
 
 private:
     QWidget *m_parent;
diff --git a/PomodoroTimer.cpp b/PomodoroTimer.cpp
index d326bd0..e5b1d00 100644
--- a/PomodoroTimer.cpp
+++ b/PomodoroTimer.cpp
@@ -8,10 +8,8 @@
 #include "TimerState.h"
 
 #include <QApplication>
-#include <QCloseEvent>
 #include <QDateTime>
 #include <QFont>
-#include <QHBoxLayout>
 #include <QKeyEvent>
 #include <QSettings>
 #include <QVBoxLayout>
@@ -104,8 +102,8 @@ void PomodoroTimer::createButtons()
     m_statsButton = new QPushButton("Statistics", m_mainFrame);
 
     // Set button sizes
-    const QSize mainButtonSize(MAIN_BUTTON_WIDTH, MAIN_BUTTON_HEIGHT);
-    const QSize smallButtonSize(SMALL_BUTTON_WIDTH, SMALL_BUTTON_HEIGHT);
+    constexpr QSize mainButtonSize(MAIN_BUTTON_WIDTH, MAIN_BUTTON_HEIGHT);
+    constexpr QSize smallButtonSize(SMALL_BUTTON_WIDTH, SMALL_BUTTON_HEIGHT);
 
     m_startButton->setFixedSize(mainButtonSize);
     m_pauseButton->setFixedSize(mainButtonSize);
@@ -165,8 +163,7 @@ void PomodoroTimer::createLayouts()
     setLayout(frameLayout);
 }
 
-void PomodoroTimer::applyStyles()
-{
+void PomodoroTimer::applyStyles() const {
     QFont timeFont = m_timeLabel->font();
     timeFont.setPointSize(TIME_FONT_SIZE);
     timeFont.setBold(true);
@@ -325,13 +322,14 @@ void PomodoroTimer::updateTimerState(TimerState newState)
     m_currentState = newState;
 }
 
-QString PomodoroTimer::formatTime(int seconds) const
-{
-    const int minutes = seconds / 60;
-    const int secs = seconds % 60;
-    return QString("%1:%2").arg(minutes, 2, 10, QChar('0'))
-                          .arg(secs, 2, 10, QChar('0'));
+QString PomodoroTimer::formatTime(int seconds) {
+  const int minutes = seconds / 60;
+  const int secs = seconds % 60;
+  return QString("%1:%2")
+      .arg(minutes, 2, 10, QChar('0'))
+      .arg(secs, 2, 10, QChar('0'));
 }
+void PomodoroTimer::needsDisplayUpdate() {}
 
 void PomodoroTimer::updateDisplay()
 {
@@ -350,16 +348,14 @@ void PomodoroTimer::updateDisplay()
                                 currentSession, SESSIONS_BEFORE_LONG_BREAK);
 }
 
-void PomodoroTimer::updateSessionCounter()
-{
+void PomodoroTimer::updateSessionCounter() const {
     const int currentSession = (m_completedSessions % SESSIONS_BEFORE_LONG_BREAK) + 1;
     m_sessionLabel->setText(QString("Session %1 of %2")
                            .arg(currentSession)
                            .arg(SESSIONS_BEFORE_LONG_BREAK));
 }
 
-void PomodoroTimer::updateButtonStates()
-{
+void PomodoroTimer::updateButtonStates() const {
     m_startButton->setEnabled(!m_isRunning);
     m_pauseButton->setEnabled(m_isRunning);
 
@@ -377,21 +373,22 @@ void PomodoroTimer::updateButtonStates()
     }
 }
 
-void PomodoroTimer::updateWindowTitle()
-{
-    const QString timeRemaining = formatTime(m_currentTime);
-    const QString emoji = TimerStateHelper::getStateEmoji(m_currentState);
+void PomodoroTimer::updateWindowTitle() {
+  const QString timeRemaining = formatTime(m_currentTime);
+  const QString emoji = TimerStateHelper::getStateEmoji(m_currentState);
 
-    QString title;
-    if (m_isRunning) {
-        const QString stateText = (m_currentState == TimerState::Work) ? "Focus" : "Break";
-        title = QString("%1 %2: %3").arg(emoji, stateText, timeRemaining);
-    } else {
-        title = "🍅 Pomodoro Timer";
-    }
+  QString title;
+  if (m_isRunning) {
+    const QString stateText =
+        (m_currentState == TimerState::Work) ? "Focus" : "Break";
+    title = QString("%1 %2: %3").arg(emoji, stateText, timeRemaining);
+  } else {
+    title = "🍅 Pomodoro Timer";
+  }
 
-    setWindowTitle(title);
+  setWindowTitle(title);
 }
+void PomodoroTimer::updateTrayTooltip() {}
 
 void PomodoroTimer::onShowSettings()
 {
@@ -459,8 +456,7 @@ void PomodoroTimer::loadSettings()
     m_totalBreakTime = settings.value("totalBreakTime", 0).toInt();
 }
 
-void PomodoroTimer::saveSettings()
-{
+void PomodoroTimer::saveSettings() const {
     QSettings settings;
     settings.setValue("workDuration", m_workDuration);
     settings.setValue("shortBreakDuration", m_shortBreakDuration);
diff --git a/PomodoroTimer.h b/PomodoroTimer.h
index 88e01a9..234379a 100644
--- a/PomodoroTimer.h
+++ b/PomodoroTimer.h
@@ -1,7 +1,6 @@
 #ifndef POMODOROTIMER_H
 #define POMODOROTIMER_H
 
-#include <QWidget>
 #include <QTimer>
 #include <QLabel>
 #include <QPushButton>
@@ -61,11 +60,11 @@ private:
     void createLabels();
     void createButtons();
     void createLayouts();
-    void applyStyles();
+    void applyStyles() const;
 
     // Settings management
     void loadSettings();
-    void saveSettings();
+    void saveSettings() const;
 
     // Timer state management
     void resetTimerState();
@@ -73,14 +72,14 @@ private:
 
     // Display update methods - optimized to avoid unnecessary updates
     void updateDisplay();
-    void updateSessionCounter();
-    void updateButtonStates();
+    void updateSessionCounter() const;
+    void updateButtonStates() const;
     void updateWindowTitle();
-    void updateTrayTooltip();
+    static void updateTrayTooltip();
 
     // Utility methods
-    QString formatTime(int seconds) const;
-    bool needsDisplayUpdate() const;
+    static QString formatTime(int seconds);
+    static void needsDisplayUpdate();
 
     // UI elements - use raw pointers for Qt objects with parent ownership
     QTimer *m_timer;
diff --git a/SettingsDialog.cpp b/SettingsDialog.cpp
index 868bcdb..5be1f89 100644
--- a/SettingsDialog.cpp
+++ b/SettingsDialog.cpp
@@ -82,16 +82,15 @@ bool SettingsDialog::minimizeToTray() const { return m_minimizeToTrayCheck->isCh
 bool SettingsDialog::showNotifications() const { return m_showNotificationsCheck->isChecked(); }
 
 // Setters
-void SettingsDialog::setWorkDuration(int minutes) { m_workDurationSpin->setValue(minutes); }
-void SettingsDialog::setShortBreakDuration(int minutes) { m_shortBreakSpin->setValue(minutes); }
-void SettingsDialog::setLongBreakDuration(int minutes) { m_longBreakSpin->setValue(minutes); }
-void SettingsDialog::setAutoStartBreaks(bool enabled) { m_autoStartBreaksCheck->setChecked(enabled); }
-void SettingsDialog::setAutoStartWork(bool enabled) { m_autoStartWorkCheck->setChecked(enabled); }
-void SettingsDialog::setMinimizeToTray(bool enabled) { m_minimizeToTrayCheck->setChecked(enabled); }
-void SettingsDialog::setShowNotifications(bool enabled) { m_showNotificationsCheck->setChecked(enabled); }
+void SettingsDialog::setWorkDuration(int minutes) const { m_workDurationSpin->setValue(minutes); }
+void SettingsDialog::setShortBreakDuration(int minutes) const { m_shortBreakSpin->setValue(minutes); }
+void SettingsDialog::setLongBreakDuration(int minutes) const { m_longBreakSpin->setValue(minutes); }
+void SettingsDialog::setAutoStartBreaks(bool enabled) const { m_autoStartBreaksCheck->setChecked(enabled); }
+void SettingsDialog::setAutoStartWork(bool enabled) const { m_autoStartWorkCheck->setChecked(enabled); }
+void SettingsDialog::setMinimizeToTray(bool enabled) const { m_minimizeToTrayCheck->setChecked(enabled); }
+void SettingsDialog::setShowNotifications(bool enabled) const { m_showNotificationsCheck->setChecked(enabled); }
 
-void SettingsDialog::resetToDefaults()
-{
+void SettingsDialog::resetToDefaults() const {
     setWorkDuration(25);
     setShortBreakDuration(5);
     setLongBreakDuration(15);
diff --git a/SettingsDialog.h b/SettingsDialog.h
index e99b93e..5e5db88 100644
--- a/SettingsDialog.h
+++ b/SettingsDialog.h
@@ -26,19 +26,19 @@ public:
     bool showNotifications() const;
 
     // Setters
-    void setWorkDuration(int minutes);
-    void setShortBreakDuration(int minutes);
-    void setLongBreakDuration(int minutes);
-    void setAutoStartBreaks(bool enabled);
-    void setAutoStartWork(bool enabled);
-    void setMinimizeToTray(bool enabled);
-    void setShowNotifications(bool enabled);
+    void setWorkDuration(int minutes) const;
+    void setShortBreakDuration(int minutes) const;
+    void setLongBreakDuration(int minutes) const;
+    void setAutoStartBreaks(bool enabled) const;
+    void setAutoStartWork(bool enabled) const;
+    void setMinimizeToTray(bool enabled) const;
+    void setShowNotifications(bool enabled) const;
 
 signals:
     void settingsChanged();
 
 private slots:
-    void resetToDefaults();
+    void resetToDefaults() const;
 
 private:
     void setupUI();
diff --git a/StatisticsDialog.cpp b/StatisticsDialog.cpp
index 5ae020f..e9d51f0 100644
--- a/StatisticsDialog.cpp
+++ b/StatisticsDialog.cpp
@@ -1,18 +1,15 @@
 #include "StatisticsDialog.h"
 #include <QTabWidget>
-#include <QVBoxLayout>
 #include <QHBoxLayout>
 #include <QGridLayout>
 #include <QLabel>
 #include <QPushButton>
 #include <QTextEdit>
-#include <QScrollArea>
 #include <QPainter>
 #include <QSettings>
 #include <QDate>
 #include <QMessageBox>
 #include <QFileDialog>
-#include <QTextStream>
 #include <QApplication>
 
 #include "TimerState.h"
@@ -52,7 +49,7 @@ void StatisticsChart::paintEvent(QPaintEvent *event)
     }
 
     constexpr int LABEL_SKIP_INTERVAL = 3;
-    const int margin = 40;
+    constexpr int margin = 40;
     const int chartWidth = width() - 2 * margin;
     const int chartHeight = height() - 2 * margin;
 
@@ -305,8 +302,8 @@ void StatisticsDialog::setStatistics(int totalSessions, int totalWorkTime, int t
      .arg(m_totalWorkTime / 3600).arg((m_totalWorkTime % 3600) / 60)
      .arg(m_totalBreakTime / 3600).arg((m_totalBreakTime % 3600) / 60)
      .arg(m_totalSessions > 0 ? m_totalWorkTime / (m_totalSessions * 60) : 0)
-     .arg(m_totalBreakTime > 0 ? QString::number(double(m_totalWorkTime) / m_totalBreakTime, 'f', 2) : "N/A")
-     .arg(m_totalSessions > 0 ? QString::number(double(m_totalSessions) / 7, 'f', 1) : "0")
+     .arg(m_totalBreakTime > 0 ? QString::number(static_cast<double>(m_totalWorkTime) / m_totalBreakTime, 'f', 2) : "N/A")
+     .arg(m_totalSessions > 0 ? QString::number(static_cast<double>(m_totalSessions) / 7, 'f', 1) : "0")
      .arg(m_dailyWorkTime.value(QDate::currentDate(), 0))
      .arg(m_dailyWorkTime.value(QDate::currentDate().addDays(-1), 0))
      .arg(m_dailyWorkTime.value(QDate::currentDate(), 0)) // This week calculation can be improved
@@ -323,28 +320,27 @@ void StatisticsDialog::loadDailyStatistics()
     QDate today = QDate::currentDate();
     for (int i = 0; i < 30; ++i) {
         QDate date = today.addDays(-i);
-        QSettings settings;
-        QVariantMap dailyStats = settings.value("dailyStats").toMap();
+        QSettings settings1;
+        auto dailyStats = settings1.value("dailyStats").toMap();
 
         for (auto it = dailyStats.begin(); it != dailyStats.end(); ++it) {
-            QDate date = QDate::fromString(it.key(), "yyyy-MM-dd");
-            if (date.isValid()) {
+            QDate date1 = QDate::fromString(it.key(), "yyyy-MM-dd");
+            if (date1.isValid()) {
                 QVariantMap dayData = it.value().toMap();
-                m_dailyWorkTime[date] = dayData["workTime"].toInt();
-                m_dailySessions[date] = dayData["sessions"].toInt();
+                m_dailyWorkTime[date1] = dayData["workTime"].toInt();
+                m_dailySessions[date1] = dayData["sessions"].toInt();
             }
         }
 
         QString sessionKey = QString("dailyStats/sessions_%1").arg(date.toString("yyyy-MM-dd"));
-        int sessions = settings.value(sessionKey, 0).toInt();
+        int sessions = settings1.value(sessionKey, 0).toInt();
         if (sessions > 0) {
             m_dailySessions[date] = sessions;
         }
     }
 }
 
-void StatisticsDialog::updateOverview()
-{
+void StatisticsDialog::updateOverview() const {
     m_totalSessionsLabel->setText(QString::number(m_totalSessions));
 
     // Правильное форматирование времени
@@ -380,8 +376,7 @@ void StatisticsDialog::updateOverview()
     m_monthLabel->setText(TimerStateHelper::formatDuration(monthTotal * 60));
 }
 
-void StatisticsDialog::updateChart()
-{
+void StatisticsDialog::updateChart() const {
     QMap<QDate, int> chartData;
     QDate today = QDate::currentDate();
 
diff --git a/StatisticsDialog.h b/StatisticsDialog.h
index 95e2e00..6bd5c60 100644
--- a/StatisticsDialog.h
+++ b/StatisticsDialog.h
@@ -43,8 +43,8 @@ private:
     void setupChartTab();
     void setupDetailsTab();
     void loadDailyStatistics();
-    void updateOverview();
-    void updateChart();
+    void updateOverview() const;
+    void updateChart() const;
 
     // UI elements
     QTabWidget *m_tabWidget;
diff --git a/SystemTrayManager.cpp b/SystemTrayManager.cpp
index d650126..95a1f0c 100644
--- a/SystemTrayManager.cpp
+++ b/SystemTrayManager.cpp
@@ -3,23 +3,23 @@
 #include <QAction>
 
 SystemTrayManager::SystemTrayManager(QObject *parent)
-    : QObject(parent)
-    , m_trayIcon(nullptr)
-    , m_trayMenu(nullptr)
-{
-    if (!QSystemTrayIcon::isSystemTrayAvailable()) {
-        qWarning("System tray is not available on this system.");
-        return;
-    }
+    : QObject(parent), m_trayIcon(nullptr), m_trayMenu(nullptr) {
+  if (!QSystemTrayIcon::isSystemTrayAvailable()) {
+    qWarning("System tray is not available on this system.");
+    return;
+  }
 
-    m_trayIcon = new QSystemTrayIcon(this);
-    m_trayIcon->setIcon(qApp->windowIcon());
+  m_trayIcon = new QSystemTrayIcon(this);
+  m_trayIcon->setIcon(qApp->windowIcon());
 
-    setupTrayMenu();
+  setupTrayMenu();
 
-    connect(m_trayIcon, QOverload<QSystemTrayIcon::ActivationReason>::of(&QSystemTrayIcon::activated),
-            this, &SystemTrayManager::onTrayIconActivated);
+  connect(m_trayIcon,
+          QOverload<QSystemTrayIcon::ActivationReason>::of(
+              &QSystemTrayIcon::activated),
+          this, &SystemTrayManager::onTrayIconActivated);
 }
+SystemTrayManager::~SystemTrayManager() {}
 
 void SystemTrayManager::setupTrayMenu()
 {
diff --git a/SystemTrayManager.h b/SystemTrayManager.h
index 7eddab1..521330a 100644
--- a/SystemTrayManager.h
+++ b/SystemTrayManager.h
@@ -1,7 +1,6 @@
 #ifndef SYSTEMTRAYMANAGER_H
 #define SYSTEMTRAYMANAGER_H
 
-#include <QObject>
 #include <QSystemTrayIcon>
 #include <QMenu>
 #include "TimerState.h"
@@ -12,7 +11,7 @@ class SystemTrayManager : public QObject
 
 public:
     explicit SystemTrayManager(QObject *parent = nullptr);
-    ~SystemTrayManager() = default;
+    ~SystemTrayManager() override;
 
     void show();
     void hide();
diff --git a/main.cpp b/main.cpp
index 531c177..56af9f4 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,11 +1,9 @@
 #include <QApplication>
 #include <QScreen>
-#include <QIcon>
 #include <QPainter>
 #include <QPixmap>
 #include <QRadialGradient>
 #include <QPen>
-#include <QBrush>
 #include "PomodoroTimer.h"
 
 namespace {