diff --git a/Telegram/SourceFiles/apiwrap.h b/Telegram/SourceFiles/apiwrap.h
index e787c1d7b5..31695e9bc9 100644
--- a/Telegram/SourceFiles/apiwrap.h
+++ b/Telegram/SourceFiles/apiwrap.h
@@ -11,7 +11,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "base/timer.h"
 #include "base/flat_map.h"
 #include "base/flat_set.h"
-#include "core/single_timer.h"
 #include "mtproto/sender.h"
 #include "chat_helpers/stickers.h"
 #include "data/data_messages.h"
diff --git a/Telegram/SourceFiles/app.cpp b/Telegram/SourceFiles/app.cpp
index 97fd21d2f0..53623537c6 100644
--- a/Telegram/SourceFiles/app.cpp
+++ b/Telegram/SourceFiles/app.cpp
@@ -810,7 +810,7 @@ namespace App {
 		setLaunchState(QuitRequested);
 
 		if (auto window = App::wnd()) {
-			if (!Sandbox::isSavingSession()) {
+			if (!Core::App().isSavingSession()) {
 				window->hide();
 			}
 		}
diff --git a/Telegram/SourceFiles/application.cpp b/Telegram/SourceFiles/application.cpp
index 4485cc7368..417e0b9b77 100644
--- a/Telegram/SourceFiles/application.cpp
+++ b/Telegram/SourceFiles/application.cpp
@@ -510,39 +510,8 @@ void Application::closeApplication() {
 	_updateChecker = nullptr;
 }
 
-inline Application *application() {
-	return qobject_cast<Application*>(QApplication::instance());
-}
-
 namespace Sandbox {
 
-QRect availableGeometry() {
-	if (auto a = application()) {
-		return a->desktop()->availableGeometry();
-	}
-	return QDesktopWidget().availableGeometry();
-}
-
-QRect screenGeometry(const QPoint &p) {
-	if (auto a = application()) {
-		return a->desktop()->screenGeometry(p);
-	}
-	return QDesktopWidget().screenGeometry(p);
-}
-
-void setActiveWindow(QWidget *window) {
-	if (auto a = application()) {
-		a->setActiveWindow(window);
-	}
-}
-
-bool isSavingSession() {
-	if (auto a = application()) {
-		return a->isSavingSession();
-	}
-	return false;
-}
-
 void execExternal(const QString &cmd) {
 	DEBUG_LOG(("Application Info: executing external command '%1'").arg(cmd));
 	if (cmd == "show") {
@@ -554,23 +523,7 @@ void execExternal(const QString &cmd) {
 	}
 }
 
-void adjustSingleTimers() {
-	if (auto a = application()) {
-		a->adjustSingleTimers();
-	}
-	base::Timer::Adjust();
-	base::ConcurrentTimerEnvironment::Adjust();
-}
-
-void connect(const char *signal, QObject *object, const char *method) {
-	if (auto a = application()) {
-		a->connect(a, signal, object, method);
-	}
-}
-
 void launch() {
-	Assert(application() != 0);
-
 	const auto dpi = Application::primaryScreen()->logicalDotsPerInch();
 	LOG(("Primary screen DPI: %1").arg(dpi));
 	if (dpi <= 108) {
@@ -587,7 +540,7 @@ void launch() {
 		cSetScreenScale(300); // 300%: 288 DPI (264-inf)
 	}
 
-	auto devicePixelRatio = application()->devicePixelRatio();
+	auto devicePixelRatio = Core::App().devicePixelRatio();
 	if (devicePixelRatio > 1.) {
 		if ((cPlatform() != dbipMac && cPlatform() != dbipMacOld) || (devicePixelRatio != 2.)) {
 			LOG(("Found non-trivial Device Pixel Ratio: %1").arg(devicePixelRatio));
@@ -601,13 +554,7 @@ void launch() {
 		cSetScreenScale(kInterfaceScaleDefault);
 	}
 
-	application()->createMessenger();
-}
-
-void refreshGlobalProxy() {
-	if (const auto instance = application()) {
-		instance->refreshGlobalProxy();
-	}
+	Core::App().createMessenger();
 }
 
 } // namespace Sandbox
diff --git a/Telegram/SourceFiles/application.h b/Telegram/SourceFiles/application.h
index 97683f4ec8..3e82601f45 100644
--- a/Telegram/SourceFiles/application.h
+++ b/Telegram/SourceFiles/application.h
@@ -40,9 +40,6 @@ public:
 
 	~Application();
 
-signals:
-	void adjustSingleTimers();
-
 // Single instance application
 public slots:
 	void socketConnected();
@@ -115,19 +112,7 @@ inline Application &App() {
 
 namespace Sandbox {
 
-QRect availableGeometry();
-QRect screenGeometry(const QPoint &p);
-void setActiveWindow(QWidget *window);
-bool isSavingSession();
-
 void execExternal(const QString &cmd);
-
-void adjustSingleTimers();
-
-void refreshGlobalProxy();
-
-void connect(const char *signal, QObject *object, const char *method);
-
 void launch();
 
 } // namespace Sandbox
diff --git a/Telegram/SourceFiles/boxes/about_box.cpp b/Telegram/SourceFiles/boxes/about_box.cpp
index 2551546f5b..fe0093fb2c 100644
--- a/Telegram/SourceFiles/boxes/about_box.cpp
+++ b/Telegram/SourceFiles/boxes/about_box.cpp
@@ -11,7 +11,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "mainwidget.h"
 #include "mainwindow.h"
 #include "boxes/confirm_box.h"
-#include "application.h"
 #include "ui/widgets/buttons.h"
 #include "ui/widgets/labels.h"
 #include "styles/style_boxes.h"
@@ -70,7 +69,7 @@ void AboutBox::showVersionHistory() {
 		}
 		url = url.arg(qsl("talpha%1_%2").arg(cRealAlphaVersion()).arg(Core::countAlphaVersionSignature(cRealAlphaVersion())));
 
-		Application::clipboard()->setText(url);
+		QApplication::clipboard()->setText(url);
 
 		Ui::show(Box<InformBox>("The link to the current private alpha version of Telegram Desktop was copied to the clipboard."));
 	} else {
diff --git a/Telegram/SourceFiles/boxes/peers/edit_peer_info_box.cpp b/Telegram/SourceFiles/boxes/peers/edit_peer_info_box.cpp
index 9e3f4f85e8..878820f98f 100644
--- a/Telegram/SourceFiles/boxes/peers/edit_peer_info_box.cpp
+++ b/Telegram/SourceFiles/boxes/peers/edit_peer_info_box.cpp
@@ -33,7 +33,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "mainwidget.h"
 #include "messenger.h"
 #include "apiwrap.h"
-#include "application.h"
 #include "auth_session.h"
 #include "observer_peer.h"
 #include "styles/style_boxes.h"
@@ -742,7 +741,7 @@ object_ptr<Ui::RpWidget> Controller::createInviteLinkEdit() {
 	_controls.inviteLink->setContextCopyText(QString());
 	_controls.inviteLink->setBreakEverywhere(true);
 	_controls.inviteLink->setClickHandlerFilter([=](auto&&...) {
-		Application::clipboard()->setText(inviteLinkText());
+		QApplication::clipboard()->setText(inviteLinkText());
 		Ui::Toast::Show(lang(lng_group_invite_copied));
 		return false;
 	});
diff --git a/Telegram/SourceFiles/boxes/username_box.cpp b/Telegram/SourceFiles/boxes/username_box.cpp
index bc8af847ad..def070a560 100644
--- a/Telegram/SourceFiles/boxes/username_box.cpp
+++ b/Telegram/SourceFiles/boxes/username_box.cpp
@@ -8,7 +8,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "boxes/username_box.h"
 
 #include "lang/lang_keys.h"
-#include "application.h"
 #include "mainwidget.h"
 #include "mainwindow.h"
 #include "ui/widgets/buttons.h"
@@ -166,7 +165,7 @@ void UsernameBox::changed() {
 }
 
 void UsernameBox::linkClick() {
-	Application::clipboard()->setText(Messenger::Instance().createInternalLinkFull(getName()));
+	QApplication::clipboard()->setText(Messenger::Instance().createInternalLinkFull(getName()));
 	Ui::Toast::Show(lang(lng_username_copied));
 }
 
@@ -180,7 +179,7 @@ bool UsernameBox::onUpdateFail(const RPCError &error) {
 
 	_saveRequestId = 0;
 	const auto self = Auth().user();
-	const auto err = error.type();
+	const auto &err = error.type();
 	if (err == qstr("USERNAME_NOT_MODIFIED") || _sentUsername == self->username) {
 		self->setName(
 			TextUtilities::SingleLine(self->firstName),
diff --git a/Telegram/SourceFiles/config.h b/Telegram/SourceFiles/config.h
index bbf97ebeb9..d2ee936576 100644
--- a/Telegram/SourceFiles/config.h
+++ b/Telegram/SourceFiles/config.h
@@ -26,8 +26,6 @@ enum {
 
 	MTPKillFileSessionTimeout = 5000, // how much time without upload / download causes additional session kill
 
-	MTPChannelGetDifferenceLimit = 100,
-
 	MaxSelectedItems = 100,
 
 	MaxPhoneCodeLength = 4, // max length of country phone code
@@ -80,8 +78,6 @@ enum {
 	ServiceUserId = 777000,
 	WebPageUserId = 701000,
 
-	CacheBackgroundTimeout = 3000, // cache background scaled image after 3s
-
 	UpdateDelayConstPart = 8 * 3600, // 8 hour min time between update check requests
 	UpdateDelayRandPart = 8 * 3600, // 8 hour max - min time between update check requests
 
@@ -246,32 +242,6 @@ inline const QString &cTempDir() {
 	return res;
 }
 
-enum {
-	DialogsFirstLoad = 20, // first dialogs part size requested
-	DialogsPerPage = 500, // next dialogs part size
-
-    UseBigFilesFrom = 10 * 1024 * 1024, // mtp big files methods used for files greater than 10mb
-
-	UploadPartSize = 32 * 1024, // 32kb for photo
-    DocumentMaxPartsCount = 3000, // no more than 3000 parts
-    DocumentUploadPartSize0 = 32 * 1024, // 32kb for tiny document ( < 1mb )
-    DocumentUploadPartSize1 = 64 * 1024, // 64kb for little document ( <= 32mb )
-    DocumentUploadPartSize2 = 128 * 1024, // 128kb for small document ( <= 375mb )
-    DocumentUploadPartSize3 = 256 * 1024, // 256kb for medium document ( <= 750mb )
-    DocumentUploadPartSize4 = 512 * 1024, // 512kb for large document ( <= 1500mb )
-    UploadRequestInterval = 500, // one part each half second, if not uploaded faster
-
-	MaxPhotosInMemory = 50, // try to clear some memory after 50 photos are created
-	NoUpdatesTimeout = 60 * 1000, // if nothing is received in 1 min we ping
-	NoUpdatesAfterSleepTimeout = 60 * 1000, // if nothing is received in 1 min when was a sleepmode we ping
-	WaitForSkippedTimeout = 1000, // 1s wait for skipped seq or pts in updates
-	WaitForChannelGetDifference = 1000, // 1s wait after show channel history before sending getChannelDifference
-
-	IdleMsecs = 60 * 1000, // after 60secs without user input we think we are idle
-
-	SendViewsTimeout = 1000, // send views each second
-};
-
 inline const QRegularExpression &cRussianLetters() {
 	static QRegularExpression regexp(QString::fromUtf8("[а-яА-ЯёЁ]"));
 	return regexp;
diff --git a/Telegram/SourceFiles/core/crash_report_window.cpp b/Telegram/SourceFiles/core/crash_report_window.cpp
index d13a164a9e..dfb09ea63c 100644
--- a/Telegram/SourceFiles/core/crash_report_window.cpp
+++ b/Telegram/SourceFiles/core/crash_report_window.cpp
@@ -806,7 +806,7 @@ void LastCrashedWindow::onNetworkSettingsSaved(
 	proxy.user = username;
 	proxy.password = password;
 
-	Sandbox::refreshGlobalProxy();
+	Core::App().refreshGlobalProxy();
 
 	if (_updaterData
 		&& ((_updaterData->state == UpdatingCheck)
diff --git a/Telegram/SourceFiles/core/single_timer.cpp b/Telegram/SourceFiles/core/single_timer.cpp
deleted file mode 100644
index 81eeaad175..0000000000
--- a/Telegram/SourceFiles/core/single_timer.cpp
+++ /dev/null
@@ -1,59 +0,0 @@
-/*
-This file is part of Telegram Desktop,
-the official desktop application for the Telegram messaging service.
-
-For license and copyright information please follow this link:
-https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
-*/
-#include "core/single_timer.h"
-
-#include "application.h"
-
-SingleTimer::SingleTimer(QObject *parent) : QTimer(parent) {
-	QTimer::setSingleShot(true);
-	Sandbox::connect(SIGNAL(adjustSingleTimers()), this, SLOT(adjust()));
-}
-
-void SingleTimer::setTimeoutHandler(Fn<void()> handler) {
-	if (_handler && !handler) {
-		disconnect(this, SIGNAL(timeout()), this, SLOT(onTimeout()));
-	} else if (handler && !_handler) {
-		connect(this, SIGNAL(timeout()), this, SLOT(onTimeout()));
-	}
-	_handler = std::move(handler);
-}
-
-void SingleTimer::adjust() {
-	auto n = getms(true);
-	if (isActive()) {
-		if (n >= _finishing) {
-			start(0);
-		} else {
-			start(_finishing - n);
-		}
-	}
-}
-
-void SingleTimer::onTimeout() {
-	if (_handler) {
-		_handler();
-	}
-}
-
-void SingleTimer::start(int msec) {
-	_finishing = getms(true) + (msec < 0 ? 0 : msec);
-	QTimer::start(msec);
-}
-
-void SingleTimer::startIfNotActive(int msec) {
-	if (isActive()) {
-		int remains = remainingTime();
-		if (remains > msec) {
-			start(msec);
-		} else if (!remains) {
-			start(1);
-		}
-	} else {
-		start(msec);
-	}
-}
diff --git a/Telegram/SourceFiles/core/single_timer.h b/Telegram/SourceFiles/core/single_timer.h
deleted file mode 100644
index 6b72b2fee4..0000000000
--- a/Telegram/SourceFiles/core/single_timer.h
+++ /dev/null
@@ -1,33 +0,0 @@
-/*
-This file is part of Telegram Desktop,
-the official desktop application for the Telegram messaging service.
-
-For license and copyright information please follow this link:
-https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
-*/
-#pragma once
-
-class SingleTimer : public QTimer { // single shot timer with check
-	Q_OBJECT
-
-public:
-	SingleTimer(QObject *parent = nullptr);
-
-	void setSingleShot(bool); // is not available
-	void start(); // is not available
-
-	void setTimeoutHandler(Fn<void()> handler);
-
-public slots:
-	void start(int msec);
-	void startIfNotActive(int msec);
-
-private slots:
-	void adjust();
-	void onTimeout();
-
-private:
-	TimeMs _finishing = 0;
-	Fn<void()> _handler;
-
-};
diff --git a/Telegram/SourceFiles/core/utils.cpp b/Telegram/SourceFiles/core/utils.cpp
index 9c3c285b4b..e010ac2ae8 100644
--- a/Telegram/SourceFiles/core/utils.cpp
+++ b/Telegram/SourceFiles/core/utils.cpp
@@ -8,7 +8,8 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "core/utils.h"
 
 #include "base/qthelp_url.h"
-#include "application.h"
+#include "base/timer.h"
+#include "base/concurrent_timer.h"
 #include "platform/platform_specific.h"
 
 extern "C" {
@@ -84,7 +85,7 @@ std::atomic<int> GlobalAtomicRequestId = 0;
 }
 
 TimeId LocalUnixtime() {
-	return (TimeId)time(NULL);
+	return (TimeId)time(nullptr);
 }
 
 void unixtimeInit() {
@@ -173,24 +174,24 @@ namespace {
 	int _ffmpegLockManager(void **mutex, AVLockOp op) {
 		switch (op) {
 		case AV_LOCK_CREATE: {
-			Assert(*mutex == 0);
+			Assert(*mutex == nullptr);
 			*mutex = reinterpret_cast<void*>(new QMutex());
 		} break;
 
 		case AV_LOCK_OBTAIN: {
-			Assert(*mutex != 0);
+			Assert(*mutex != nullptr);
 			reinterpret_cast<QMutex*>(*mutex)->lock();
 		} break;
 
 		case AV_LOCK_RELEASE: {
-			Assert(*mutex != 0);
+			Assert(*mutex != nullptr);
 			reinterpret_cast<QMutex*>(*mutex)->unlock();
 		}; break;
 
 		case AV_LOCK_DESTROY: {
-			Assert(*mutex != 0);
+			Assert(*mutex != nullptr);
 			delete reinterpret_cast<QMutex*>(*mutex);
-			*mutex = 0;
+			*mutex = nullptr;
 		} break;
 		}
 		return 0;
@@ -428,7 +429,8 @@ namespace ThirdParty {
 
 bool checkms() {
 	if (crl::adjust_time()) {
-		Sandbox::adjustSingleTimers();
+		base::Timer::Adjust();
+		base::ConcurrentTimerEnvironment::Adjust();
 		return true;
 	}
 	return false;
diff --git a/Telegram/SourceFiles/data/data_pts_waiter.cpp b/Telegram/SourceFiles/data/data_pts_waiter.cpp
index 4ae9c6a819..9ffb5f642c 100644
--- a/Telegram/SourceFiles/data/data_pts_waiter.cpp
+++ b/Telegram/SourceFiles/data/data_pts_waiter.cpp
@@ -139,7 +139,8 @@ bool PtsWaiter::updateAndApply(ChannelData *channel, int32 pts, int32 count) {
 	return true;
 }
 
-bool PtsWaiter::check(ChannelData *channel, int32 pts, int32 count) { // return false if need to save that update and apply later
+// Return false if need to save that update and apply later.
+bool PtsWaiter::check(ChannelData *channel, int32 pts, int32 count) {
 	if (!inited()) {
 		init(pts);
 		return true;
@@ -153,7 +154,7 @@ bool PtsWaiter::check(ChannelData *channel, int32 pts, int32 count) { // return
 	} else if (_last < _count) {
 		setWaitingForSkipped(channel, 1);
 	} else {
-		setWaitingForSkipped(channel, WaitForSkippedTimeout);
+		setWaitingForSkipped(channel, kWaitForSkippedTimeout);
 	}
 	return !count;
 }
diff --git a/Telegram/SourceFiles/data/data_pts_waiter.h b/Telegram/SourceFiles/data/data_pts_waiter.h
index 7714704749..9d45c0be42 100644
--- a/Telegram/SourceFiles/data/data_pts_waiter.h
+++ b/Telegram/SourceFiles/data/data_pts_waiter.h
@@ -15,6 +15,10 @@ enum PtsSkippedQueue {
 class PtsWaiter {
 public:
 	PtsWaiter() = default;
+
+	// 1s wait for skipped seq or pts in updates.
+	static constexpr auto kWaitForSkippedTimeout = 1000;
+
 	void init(int32 pts) {
 		_good = _last = _count = pts;
 		clearSkippedUpdates();
diff --git a/Telegram/SourceFiles/dialogs/dialogs_widget.cpp b/Telegram/SourceFiles/dialogs/dialogs_widget.cpp
index efd816da11..a5a8a52d74 100644
--- a/Telegram/SourceFiles/dialogs/dialogs_widget.cpp
+++ b/Telegram/SourceFiles/dialogs/dialogs_widget.cpp
@@ -41,6 +41,9 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 
 namespace {
 
+constexpr auto kDialogsFirstLoad = 20;
+constexpr auto kDialogsPerPage = 500;
+
 QString SwitchToChooseFromQuery() {
 	return qsl("from:");
 }
@@ -877,7 +880,7 @@ void DialogsWidget::loadDialogs() {
 	}
 
 	const auto firstLoad = !_dialogsOffsetDate;
-	const auto loadCount = firstLoad ? DialogsFirstLoad : DialogsPerPage;
+	const auto loadCount = firstLoad ? kDialogsFirstLoad : kDialogsPerPage;
 	const auto flags = MTPmessages_GetDialogs::Flag::f_exclude_pinned;
 	const auto feedId = 0;
 	const auto hash = 0;
diff --git a/Telegram/SourceFiles/facades.h b/Telegram/SourceFiles/facades.h
index 7469866a35..821d61be94 100644
--- a/Telegram/SourceFiles/facades.h
+++ b/Telegram/SourceFiles/facades.h
@@ -182,8 +182,6 @@ void WorkingDirReady();
 void WriteInstallBetaVersionsSetting();
 void WriteDebugModeSetting();
 
-void MainThreadTaskAdded();
-
 void start();
 bool started();
 void finish();
diff --git a/Telegram/SourceFiles/history/history_inner_widget.h b/Telegram/SourceFiles/history/history_inner_widget.h
index 75877a1680..17c5874425 100644
--- a/Telegram/SourceFiles/history/history_inner_widget.h
+++ b/Telegram/SourceFiles/history/history_inner_widget.h
@@ -39,7 +39,7 @@ class HistoryInner
 	: public Ui::RpWidget
 	, public Ui::AbstractTooltipShower
 	, private base::Subscriber {
-	// The Q_OBJECT meta info is used for qobject_cast to HistoryInner!
+	// The Q_OBJECT meta info is used for qobject_cast!
 	Q_OBJECT
 
 public:
diff --git a/Telegram/SourceFiles/history/history_widget.cpp b/Telegram/SourceFiles/history/history_widget.cpp
index 25d3b29543..958de686cd 100644
--- a/Telegram/SourceFiles/history/history_widget.cpp
+++ b/Telegram/SourceFiles/history/history_widget.cpp
@@ -176,6 +176,7 @@ HistoryWidget::HistoryWidget(
 	QWidget *parent,
 	not_null<Window::Controller*> controller)
 : Window::AbstractSectionWidget(parent, controller)
+, _updateEditTimeLeftDisplay([=] { updateField(); })
 , _fieldBarCancel(this, st::historyReplyCancel)
 , _previewTimer([=] { requestPreview(); })
 , _topBar(this, controller)
@@ -360,8 +361,6 @@ HistoryWidget::HistoryWidget(
 		ActivateWindow(this->controller());
 	});
 
-	connect(&_updateEditTimeLeftDisplay, SIGNAL(timeout()), this, SLOT(updateField()));
-
 	subscribe(Adaptive::Changed(), [this] { update(); });
 	Auth().data().itemRemoved(
 	) | rpl::start_with_next(
@@ -6425,7 +6424,7 @@ void HistoryWidget::paintEditHeader(Painter &p, const QRect &rect, int left, int
 
 	// Restart timer only if we are sure that we've painted the whole timer.
 	if (rect.contains(myrtlrect(left, top, width() - left, st::normalFont->height)) && updateIn > 0) {
-		_updateEditTimeLeftDisplay.start(updateIn);
+		_updateEditTimeLeftDisplay.callOnce(updateIn);
 	}
 
 	if (!editTimeLeftText.isEmpty()) {
diff --git a/Telegram/SourceFiles/history/history_widget.h b/Telegram/SourceFiles/history/history_widget.h
index 62bf01413e..c8fa56e670 100644
--- a/Telegram/SourceFiles/history/history_widget.h
+++ b/Telegram/SourceFiles/history/history_widget.h
@@ -11,7 +11,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "mainwidget.h"
 #include "chat_helpers/field_autocomplete.h"
 #include "window/section_widget.h"
-#include "core/single_timer.h"
 #include "ui/widgets/input_fields.h"
 #include "ui/rp_widget.h"
 #include "base/flags.h"
@@ -358,14 +357,13 @@ private slots:
 
 	void onModerateKeyActivate(int index, bool *outHandled);
 
-	void updateField();
-
 private:
 	using TabbedPanel = ChatHelpers::TabbedPanel;
 	using TabbedSelector = ChatHelpers::TabbedSelector;
 	using DragState = Storage::MimeDataState;
 
 	void initTabbedSelector();
+	void updateField();
 
 	void send(Qt::KeyboardModifiers modifiers = Qt::KeyboardModifiers());
 	void handlePendingHistoryUpdate();
@@ -516,7 +514,7 @@ private:
 
 	HistoryItem *_replyEditMsg = nullptr;
 	Text _replyEditMsgText;
-	mutable SingleTimer _updateEditTimeLeftDisplay;
+	mutable base::Timer _updateEditTimeLeftDisplay;
 
 	object_ptr<Ui::IconButton> _fieldBarCancel;
 	void updateReplyEditTexts(bool force = false);
diff --git a/Telegram/SourceFiles/info/profile/info_profile_actions.cpp b/Telegram/SourceFiles/info/profile/info_profile_actions.cpp
index 9f53d47c2b..ed27dfbf1a 100644
--- a/Telegram/SourceFiles/info/profile/info_profile_actions.cpp
+++ b/Telegram/SourceFiles/info/profile/info_profile_actions.cpp
@@ -40,7 +40,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "auth_session.h"
 #include "messenger.h"
 #include "apiwrap.h"
-#include "application.h"
 #include "styles/style_info.h"
 #include "styles/style_boxes.h"
 
@@ -293,7 +292,7 @@ object_ptr<Ui::RpWidget> DetailsFiller::setupInfo() {
 			auto link = Messenger::Instance().createInternalLinkFull(
 				peer->userName());
 			if (!link.isEmpty()) {
-				Application::clipboard()->setText(link);
+				QApplication::clipboard()->setText(link);
 				Ui::Toast::Show(lang(lng_username_copied));
 			}
 			return false;
diff --git a/Telegram/SourceFiles/mainwidget.cpp b/Telegram/SourceFiles/mainwidget.cpp
index 9176352cf7..a8629e00b0 100644
--- a/Telegram/SourceFiles/mainwidget.cpp
+++ b/Telegram/SourceFiles/mainwidget.cpp
@@ -100,6 +100,23 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 
 namespace {
 
+constexpr auto kChannelGetDifferenceLimit = 100;
+
+// 1s wait after show channel history before sending getChannelDifference.
+constexpr auto kWaitForChannelGetDifference = TimeMs(1000);
+
+// If nothing is received in 1 min we ping.
+constexpr auto kNoUpdatesTimeout = 60 * 1000;
+
+// If nothing is received in 1 min when was a sleepmode we ping.
+constexpr auto kNoUpdatesAfterSleepTimeout = 60 * TimeMs(1000);
+
+// Send channel views each second.
+constexpr auto kSendViewsTimeout = TimeMs(1000);
+
+// Cache background scaled image after 3s.
+constexpr auto kCacheBackgroundTimeout = 3000;
+
 bool IsForceLogoutNotification(const MTPDupdateServiceNotification &data) {
 	return qs(data.vtype).startsWith(qstr("AUTH_KEY_DROP_"));
 }
@@ -239,7 +256,16 @@ MainWidget::MainWidget(
 	this,
 	_controller,
 	Media::Player::Panel::Layout::OnlyPlaylist)
-, _playerPanel(this, _controller, Media::Player::Panel::Layout::Full) {
+, _playerPanel(this, _controller, Media::Player::Panel::Layout::Full)
+, _noUpdatesTimer([=] { sendPing(); })
+, _byPtsTimer([=] { getDifferenceByPts(); })
+, _bySeqTimer([=] { getDifference(); })
+, _byMinChannelTimer([=] { getDifference(); })
+, _onlineTimer([=] { updateOnline(); })
+, _idleFinishTimer([=] { checkIdleFinish(); })
+, _failDifferenceTimer([=] { getDifferenceAfterFail(); })
+, _cacheBackgroundTimer([=] { cacheBackground(); })
+, _viewsIncrementTimer([=] { viewsIncrement(); }) {
 	Messenger::Instance().mtp()->setUpdatesHandler(rpcDone(&MainWidget::updateReceived));
 	Messenger::Instance().mtp()->setGlobalFailHandler(rpcFail(&MainWidget::updateFail));
 
@@ -256,13 +282,6 @@ MainWidget::MainWidget(
 	connect(_dialogs, SIGNAL(cancelled()), this, SLOT(dialogsCancelled()));
 	connect(this, SIGNAL(dialogsUpdated()), _dialogs, SLOT(onListScroll()));
 	connect(_history, SIGNAL(cancelled()), _dialogs, SLOT(activate()));
-	connect(&noUpdatesTimer, SIGNAL(timeout()), this, SLOT(mtpPing()));
-	connect(&_onlineTimer, SIGNAL(timeout()), this, SLOT(updateOnline()));
-	connect(&_idleFinishTimer, SIGNAL(timeout()), this, SLOT(checkIdleFinish()));
-	connect(&_bySeqTimer, SIGNAL(timeout()), this, SLOT(getDifference()));
-	connect(&_byPtsTimer, SIGNAL(timeout()), this, SLOT(onGetDifferenceTimeByPts()));
-	connect(&_byMinChannelTimer, SIGNAL(timeout()), this, SLOT(getDifference()));
-	connect(&_failDifferenceTimer, SIGNAL(timeout()), this, SLOT(onGetDifferenceTimeAfterFail()));
 	subscribe(Media::Player::Updated(), [this](const AudioMsgId &audioId) {
 		if (audioId.type() != AudioMsgId::Type::Video) {
 			handleAudioUpdate(audioId);
@@ -310,15 +329,12 @@ MainWidget::MainWidget(
 
 	QCoreApplication::instance()->installEventFilter(this);
 
-	connect(&_viewsIncrementTimer, SIGNAL(timeout()), this, SLOT(onViewsIncrement()));
-
 	using Update = Window::Theme::BackgroundUpdate;
 	subscribe(Window::Theme::Background(), [this](const Update &update) {
 		if (update.type == Update::Type::New || update.type == Update::Type::Changed) {
 			clearCachedBackground();
 		}
 	});
-	connect(&_cacheBackgroundTimer, SIGNAL(timeout()), this, SLOT(onCacheBackground()));
 
 	_playerPanel->setPinCallback([this] { switchToFixedPlayer(); });
 	_playerPanel->setCloseCallback([this] { closeBothPlayers(); });
@@ -925,7 +941,7 @@ bool MainWidget::sendMessageFail(const RPCError &error) {
 	return false;
 }
 
-void MainWidget::onCacheBackground() {
+void MainWidget::cacheBackground() {
 	if (Window::Theme::Background()->color()) {
 		return;
 	} else if (Window::Theme::Background()->tile()) {
@@ -1025,7 +1041,7 @@ void MainWidget::itemEdited(not_null<HistoryItem*> item) {
 
 void MainWidget::checkLastUpdate(bool afterSleep) {
 	auto n = getms(true);
-	if (_lastUpdateTime && n > _lastUpdateTime + (afterSleep ? NoUpdatesAfterSleepTimeout : NoUpdatesTimeout)) {
+	if (_lastUpdateTime && n > _lastUpdateTime + (afterSleep ? kNoUpdatesAfterSleepTimeout : kNoUpdatesTimeout)) {
 		_lastUpdateTime = n;
 		MTP::ping();
 	}
@@ -1399,7 +1415,7 @@ bool MainWidget::isIdle() const {
 
 void MainWidget::clearCachedBackground() {
 	_cachedBackground = QPixmap();
-	_cacheBackgroundTimer.stop();
+	_cacheBackgroundTimer.cancel();
 	update();
 }
 
@@ -1411,7 +1427,7 @@ QPixmap MainWidget::cachedBackground(const QRect &forRect, int &x, int &y) {
 	}
 	if (_willCacheFor != forRect || !_cacheBackgroundTimer.isActive()) {
 		_willCacheFor = forRect;
-		_cacheBackgroundTimer.start(CacheBackgroundTimeout);
+		_cacheBackgroundTimer.callOnce(kCacheBackgroundTimeout);
 	}
 	return QPixmap();
 }
@@ -1562,12 +1578,12 @@ void MainWidget::scheduleViewIncrement(HistoryItem *item) {
 	auto j = _viewsToIncrement.find(peer);
 	if (j == _viewsToIncrement.cend()) {
 		j = _viewsToIncrement.insert(peer, ViewsIncrementMap());
-		_viewsIncrementTimer.start(SendViewsTimeout);
+		_viewsIncrementTimer.callOnce(kSendViewsTimeout);
 	}
 	j.value().insert(item->id, true);
 }
 
-void MainWidget::onViewsIncrement() {
+void MainWidget::viewsIncrement() {
 	for (auto i = _viewsToIncrement.begin(); i != _viewsToIncrement.cend();) {
 		if (_viewsIncrementRequests.contains(i.key())) {
 			++i;
@@ -1603,7 +1619,7 @@ void MainWidget::viewsIncrementDone(QVector<MTPint> ids, const MTPVector<MTPint>
 		}
 	}
 	if (!_viewsToIncrement.isEmpty() && !_viewsIncrementTimer.isActive()) {
-		_viewsIncrementTimer.start(SendViewsTimeout);
+		_viewsIncrementTimer.callOnce(kSendViewsTimeout);
 	}
 }
 
@@ -1617,7 +1633,7 @@ bool MainWidget::viewsIncrementFail(const RPCError &error, mtpRequestId req) {
 		}
 	}
 	if (!_viewsToIncrement.isEmpty() && !_viewsIncrementTimer.isActive()) {
-		_viewsIncrementTimer.start(SendViewsTimeout);
+		_viewsIncrementTimer.callOnce(kSendViewsTimeout);
 	}
 	return false;
 }
@@ -1775,7 +1791,7 @@ void MainWidget::ui_showPeerHistory(
 		if (nowActivePeer && nowActivePeer != wasActivePeer) {
 			if (const auto channel = nowActivePeer->asChannel()) {
 				channel->ptsWaitingForShortPoll(
-					WaitForChannelGetDifference);
+					kWaitForChannelGetDifference);
 			}
 			_viewsIncremented.remove(nowActivePeer);
 		}
@@ -2787,7 +2803,7 @@ void MainWidget::keyPressEvent(QKeyEvent *e) {
 
 bool MainWidget::eventFilter(QObject *o, QEvent *e) {
 	if (e->type() == QEvent::FocusIn) {
-		if (auto widget = qobject_cast<QWidget*>(o)) {
+		if (const auto widget = qobject_cast<QWidget*>(o)) {
 			if (_history == widget || _history->isAncestorOf(widget)
 				|| (_mainSection && (_mainSection == widget || _mainSection->isAncestorOf(widget)))
 				|| (_thirdSection && (_thirdSection == widget || _thirdSection->isAncestorOf(widget)))) {
@@ -2928,7 +2944,9 @@ void MainWidget::updSetState(int32 pts, int32 date, int32 qts, int32 seq) {
 	}
 	if (seq && seq != updSeq) {
 		updSeq = seq;
-		if (_bySeqTimer.isActive()) _bySeqTimer.stop();
+		if (_bySeqTimer.isActive()) {
+			_bySeqTimer.cancel();
+		}
 		for (QMap<int32, MTPUpdates>::iterator i = _bySeqUpdates.begin(); i != _bySeqUpdates.end();) {
 			int32 s = i.key();
 			if (s <= seq + 1) {
@@ -2938,7 +2956,9 @@ void MainWidget::updSetState(int32 pts, int32 date, int32 qts, int32 seq) {
 					return feedUpdates(v);
 				}
 			} else {
-				if (!_bySeqTimer.isActive()) _bySeqTimer.start(WaitForSkippedTimeout);
+				if (!_bySeqTimer.isActive()) {
+					_bySeqTimer.callOnce(PtsWaiter::kWaitForSkippedTimeout);
+				}
 				break;
 			}
 		}
@@ -3008,7 +3028,9 @@ void MainWidget::gotChannelDifference(
 		MTP_LOG(0, ("getChannelDifference { good - after not final channelDifference was received }%1").arg(cTestMode() ? " TESTMODE" : ""));
 		getChannelDifference(channel);
 	} else if (_controller->activeChatCurrent().peer() == channel) {
-		channel->ptsWaitingForShortPoll(timeout ? (timeout * 1000) : WaitForChannelGetDifference);
+		channel->ptsWaitingForShortPoll(timeout
+			? (timeout * TimeMs(1000))
+			: kWaitForChannelGetDifference);
 	}
 }
 
@@ -3037,7 +3059,7 @@ void MainWidget::gotState(const MTPupdates_State &state) {
 	updSetState(d.vpts.v, d.vdate.v, d.vqts.v, d.vseq.v);
 
 	_lastUpdateTime = getms(true);
-	noUpdatesTimer.start(NoUpdatesTimeout);
+	_noUpdatesTimer.callOnce(kNoUpdatesTimeout);
 	_ptsWaiter.setRequesting(false);
 
 	_dialogs->loadDialogs();
@@ -3053,7 +3075,7 @@ void MainWidget::gotDifference(const MTPupdates_Difference &difference) {
 		updSetState(_ptsWaiter.current(), d.vdate.v, updQts, d.vseq.v);
 
 		_lastUpdateTime = getms(true);
-		noUpdatesTimer.start(NoUpdatesTimeout);
+		_noUpdatesTimer.callOnce(kNoUpdatesTimeout);
 
 		_ptsWaiter.setRequesting(false);
 	} break;
@@ -3125,7 +3147,7 @@ bool MainWidget::getDifferenceTimeChanged(ChannelData *channel, int32 ms, Channe
 
 void MainWidget::ptsWaiterStartTimerFor(ChannelData *channel, int32 ms) {
 	if (getDifferenceTimeChanged(channel, ms, _channelGetDifferenceTimeByPts, _getDifferenceTimeByPts)) {
-		onGetDifferenceTimeByPts();
+		getDifferenceByPts();
 	}
 }
 
@@ -3140,7 +3162,7 @@ void MainWidget::failDifferenceStartTimerFor(ChannelData *channel) {
 			: i.value();
 	}();
 	if (getDifferenceTimeChanged(channel, timeout * 1000, _channelGetDifferenceTimeAfterFail, _getDifferenceTimeAfterFail)) {
-		onGetDifferenceTimeAfterFail();
+		getDifferenceAfterFail();
 	}
 	if (timeout < 64) timeout *= 2;
 }
@@ -3174,11 +3196,11 @@ bool MainWidget::failDifference(const RPCError &error) {
 	if (MTP::isDefaultHandledError(error)) return false;
 
 	LOG(("RPC Error in getDifference: %1 %2: %3").arg(error.code()).arg(error.type()).arg(error.description()));
-	failDifferenceStartTimerFor(0);
+	failDifferenceStartTimerFor(nullptr);
 	return true;
 }
 
-void MainWidget::onGetDifferenceTimeByPts() {
+void MainWidget::getDifferenceByPts() {
 	auto now = getms(true), wait = 0LL;
 	if (_getDifferenceTimeByPts) {
 		if (_getDifferenceTimeByPts > now) {
@@ -3197,13 +3219,13 @@ void MainWidget::onGetDifferenceTimeByPts() {
 		}
 	}
 	if (wait) {
-		_byPtsTimer.start(wait);
+		_byPtsTimer.callOnce(wait);
 	} else {
-		_byPtsTimer.stop();
+		_byPtsTimer.cancel();
 	}
 }
 
-void MainWidget::onGetDifferenceTimeAfterFail() {
+void MainWidget::getDifferenceAfterFail() {
 	auto now = getms(true), wait = 0LL;
 	if (_getDifferenceTimeAfterFail) {
 		if (_getDifferenceTimeAfterFail > now) {
@@ -3224,9 +3246,9 @@ void MainWidget::onGetDifferenceTimeAfterFail() {
 		}
 	}
 	if (wait) {
-		_failDifferenceTimer.start(wait);
+		_failDifferenceTimer.callOnce(wait);
 	} else {
-		_failDifferenceTimer.stop();
+		_failDifferenceTimer.cancel();
 	}
 }
 
@@ -3238,14 +3260,22 @@ void MainWidget::getDifference() {
 	if (requestingDifference()) return;
 
 	_bySeqUpdates.clear();
-	_bySeqTimer.stop();
+	_bySeqTimer.cancel();
 
-	noUpdatesTimer.stop();
+	_noUpdatesTimer.cancel();
 	_getDifferenceTimeAfterFail = 0;
 
 	_ptsWaiter.setRequesting(true);
 
-	MTP::send(MTPupdates_GetDifference(MTP_flags(0), MTP_int(_ptsWaiter.current()), MTPint(), MTP_int(updDate), MTP_int(updQts)), rpcDone(&MainWidget::gotDifference), rpcFail(&MainWidget::failDifference));
+	MTP::send(
+		MTPupdates_GetDifference(
+			MTP_flags(0),
+			MTP_int(_ptsWaiter.current()),
+			MTPint(),
+			MTP_int(updDate),
+			MTP_int(updQts)),
+		rpcDone(&MainWidget::gotDifference),
+		rpcFail(&MainWidget::failDifference));
 }
 
 void MainWidget::getChannelDifference(ChannelData *channel, ChannelDifferenceRequest from) {
@@ -3270,10 +3300,18 @@ void MainWidget::getChannelDifference(ChannelData *channel, ChannelDifferenceReq
 			flags = 0; // No force flag when requesting for short poll.
 		}
 	}
-	MTP::send(MTPupdates_GetChannelDifference(MTP_flags(flags), channel->inputChannel, filter, MTP_int(channel->pts()), MTP_int(MTPChannelGetDifferenceLimit)), rpcDone(&MainWidget::gotChannelDifference, channel), rpcFail(&MainWidget::failChannelDifference, channel));
+	MTP::send(
+		MTPupdates_GetChannelDifference(
+			MTP_flags(flags),
+			channel->inputChannel,
+			filter,
+			MTP_int(channel->pts()),
+			MTP_int(kChannelGetDifferenceLimit)),
+		rpcDone(&MainWidget::gotChannelDifference, channel),
+		rpcFail(&MainWidget::failChannelDifference, channel));
 }
 
-void MainWidget::mtpPing() {
+void MainWidget::sendPing() {
 	MTP::ping();
 }
 
@@ -3470,7 +3508,7 @@ void MainWidget::incrementSticker(DocumentData *sticker) {
 		it->stickers.removeAt(index);
 		for (auto i = it->emoji.begin(); i != it->emoji.end();) {
 			if (const auto index = i->indexOf(sticker); index >= 0) {
-				removedFromEmoji.push_back(i.key());
+				removedFromEmoji.emplace_back(i.key());
 				i->removeAt(index);
 				if (i->isEmpty()) {
 					i = it->emoji.erase(i);
@@ -3620,7 +3658,7 @@ void MainWidget::updateOnline(bool gotOtherOffline) {
 			isOnline = false;
 			if (!_isIdle) {
 				_isIdle = true;
-				_idleFinishTimer.start(900);
+				_idleFinishTimer.callOnce(900);
 			}
 		} else {
 			updateIn = qMin(updateIn, int(Global::OfflineIdleTimeout() - idle));
@@ -3652,7 +3690,7 @@ void MainWidget::updateOnline(bool gotOtherOffline) {
 	} else if (isOnline) {
 		updateIn = qMin(updateIn, int(_lastSetOnline + Global::OnlineUpdatePeriod() - ms));
 	}
-	_onlineTimer.start(updateIn);
+	_onlineTimer.callOnce(updateIn);
 }
 
 void MainWidget::saveDraftToCloud() {
@@ -3703,14 +3741,13 @@ void MainWidget::writeDrafts(History *history) {
 }
 
 void MainWidget::checkIdleFinish() {
-	if (this != App::main()) return;
 	if (psIdleTime() < Global::OfflineIdleTimeout()) {
-		_idleFinishTimer.stop();
+		_idleFinishTimer.cancel();
 		_isIdle = false;
 		updateOnline();
-		if (App::wnd()) App::wnd()->checkHistoryActivation();
+		App::wnd()->checkHistoryActivation();
 	} else {
-		_idleFinishTimer.start(900);
+		_idleFinishTimer.callOnce(900);
 	}
 }
 
@@ -3734,7 +3771,7 @@ void MainWidget::updateReceived(const mtpPrime *from, const mtpPrime *end) {
 			updates.read(from, end);
 
 			_lastUpdateTime = getms(true);
-			noUpdatesTimer.start(NoUpdatesTimeout);
+			_noUpdatesTimer.callOnce(kNoUpdatesTimeout);
 			if (!requestingDifference()
 				|| HasForceLogoutNotification(updates)) {
 				feedUpdates(updates);
@@ -3860,7 +3897,8 @@ void MainWidget::feedUpdates(const MTPUpdates &updates, uint64 randomId) {
 			}
 			if (d.vseq.v > updSeq + 1) {
 				_bySeqUpdates.insert(d.vseq.v, updates);
-				return _bySeqTimer.start(WaitForSkippedTimeout);
+				_bySeqTimer.callOnce(PtsWaiter::kWaitForSkippedTimeout);
+				return;
 			}
 		}
 
@@ -3879,7 +3917,8 @@ void MainWidget::feedUpdates(const MTPUpdates &updates, uint64 randomId) {
 			}
 			if (d.vseq_start.v > updSeq + 1) {
 				_bySeqUpdates.insert(d.vseq_start.v, updates);
-				return _bySeqTimer.start(WaitForSkippedTimeout);
+				_bySeqTimer.callOnce(PtsWaiter::kWaitForSkippedTimeout);
+				return;
 			}
 		}
 
@@ -4019,7 +4058,7 @@ void MainWidget::feedUpdate(const MTPUpdate &update) {
 			}
 
 			if (!_byMinChannelTimer.isActive()) { // getDifference after timeout
-				_byMinChannelTimer.start(WaitForSkippedTimeout);
+				_byMinChannelTimer.callOnce(PtsWaiter::kWaitForSkippedTimeout);
 			}
 			return;
 		}
@@ -4068,7 +4107,7 @@ void MainWidget::feedUpdate(const MTPUpdate &update) {
 		if (!channel) {
 			if (!_byMinChannelTimer.isActive()) {
 				// getDifference after timeout.
-				_byMinChannelTimer.start(WaitForSkippedTimeout);
+				_byMinChannelTimer.callOnce(PtsWaiter::kWaitForSkippedTimeout);
 			}
 			return;
 		}
@@ -4615,13 +4654,13 @@ void MainWidget::feedUpdate(const MTPUpdate &update) {
 					auto &v = set.vdocuments.v;
 					it->stickers.clear();
 					it->stickers.reserve(v.size());
-					for (int i = 0, l = v.size(); i < l; ++i) {
-						const auto doc = Auth().data().document(v.at(i));
-						if (!doc->sticker()) continue;
+					for (const auto &item : v) {
+						const auto document = Auth().data().document(item);
+						if (!document->sticker()) continue;
 
-						it->stickers.push_back(doc);
-						if (doc->sticker()->set.type() != mtpc_inputStickerSetID) {
-							doc->sticker()->set = inputSet;
+						it->stickers.push_back(document);
+						if (document->sticker()->set.type() != mtpc_inputStickerSetID) {
+							document->sticker()->set = inputSet;
 						}
 					}
 					it->emoji.clear();
@@ -4678,11 +4717,11 @@ void MainWidget::feedUpdate(const MTPUpdate &update) {
 			auto &order = d.vorder.v;
 			auto &sets = Auth().data().stickerSets();
 			Stickers::Order result;
-			for (int i = 0, l = order.size(); i < l; ++i) {
-				if (sets.constFind(order.at(i).v) == sets.cend()) {
+			for (const auto &item : order) {
+				if (sets.constFind(item.v) == sets.cend()) {
 					break;
 				}
-				result.push_back(order.at(i).v);
+				result.push_back(item.v);
 			}
 			if (result.size() != Auth().data().stickerSetsOrder().size() || result.size() != order.size()) {
 				Auth().data().setLastStickersUpdate(0);
diff --git a/Telegram/SourceFiles/mainwidget.h b/Telegram/SourceFiles/mainwidget.h
index dab9e9ec59..5a67724a90 100644
--- a/Telegram/SourceFiles/mainwidget.h
+++ b/Telegram/SourceFiles/mainwidget.h
@@ -7,7 +7,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 */
 #pragma once
 
-#include "core/single_timer.h"
+#include "base/timer.h"
 #include "base/weak_ptr.h"
 #include "ui/rp_widget.h"
 #include "media/player/media_player_float.h"
@@ -257,11 +257,14 @@ public:
 
 	void feedChannelDifference(const MTPDupdates_channelDifference &data);
 
-	// Mayde public for ApiWrap, while it is still here.
+	// Made public for ApiWrap, while it is still here.
 	// Better would be for this to be moved to ApiWrap.
 	bool requestingDifference() const {
 		return _ptsWaiter.requesting();
 	}
+	void getDifference();
+	void updateOnline(bool gotOtherOffline = false);
+	void checkIdleFinish();
 
 	bool contentOverlapped(const QRect &globalRect);
 
@@ -307,18 +310,6 @@ public slots:
 
 	void dialogsCancelled();
 
-	void getDifference();
-	void onGetDifferenceTimeByPts();
-	void onGetDifferenceTimeAfterFail();
-	void mtpPing();
-
-	void updateOnline(bool gotOtherOffline = false);
-	void checkIdleFinish();
-
-	void onCacheBackground();
-
-	void onViewsIncrement();
-
 protected:
 	void paintEvent(QPaintEvent *e) override;
 	void resizeEvent(QResizeEvent *e) override;
@@ -343,6 +334,11 @@ private:
 		UserData *from;
 	};
 
+	void viewsIncrement();
+	void sendPing();
+	void getDifferenceByPts();
+	void getDifferenceAfterFail();
+
 	void animationCallback();
 	void handleAdaptiveLayoutUpdate();
 	void updateWindowAdaptiveLayout();
@@ -429,6 +425,7 @@ private:
 	void showAll();
 	void clearHider(not_null<Window::HistoryHider*> instance);
 
+	void cacheBackground();
 	void clearCachedBackground();
 
 	not_null<Media::Player::FloatDelegate*> floatPlayerDelegate();
@@ -510,7 +507,7 @@ private:
 	int32 updDate = 0;
 	int32 updQts = -1;
 	int32 updSeq = 0;
-	SingleTimer noUpdatesTimer;
+	base::Timer _noUpdatesTimer;
 
 	PtsWaiter _ptsWaiter;
 
@@ -518,22 +515,23 @@ private:
 	TimeMs _getDifferenceTimeByPts = 0;
 	TimeMs _getDifferenceTimeAfterFail = 0;
 
-	SingleTimer _byPtsTimer;
+	base::Timer _byPtsTimer;
 
 	QMap<int32, MTPUpdates> _bySeqUpdates;
-	SingleTimer _bySeqTimer;
+	base::Timer _bySeqTimer;
 
-	SingleTimer _byMinChannelTimer;
+	base::Timer _byMinChannelTimer;
 
 	mtpRequestId _onlineRequest = 0;
-	SingleTimer _onlineTimer, _idleFinishTimer;
+	base::Timer _onlineTimer;
+	base::Timer _idleFinishTimer;
 	bool _lastWasOnline = false;
 	TimeMs _lastSetOnline = 0;
 	bool _isIdle = false;
 
 	int32 _failDifferenceTimeout = 1; // growing timeout for getDifference calls, if it fails
 	QMap<ChannelData*, int32> _channelFailDifferenceTimeout; // growing timeout for getChannelDifference calls, if it fails
-	SingleTimer _failDifferenceTimer;
+	base::Timer _failDifferenceTimer;
 
 	TimeMs _lastUpdateTime = 0;
 	bool _handlingChannelDifference = false;
@@ -542,7 +540,7 @@ private:
 	QRect _cachedFor, _willCacheFor;
 	int _cachedX = 0;
 	int _cachedY = 0;
-	SingleTimer _cacheBackgroundTimer;
+	base::Timer _cacheBackgroundTimer;
 
 	PhotoData *_deletingPhoto = nullptr;
 
@@ -550,7 +548,7 @@ private:
 	QMap<PeerData*, ViewsIncrementMap> _viewsIncremented, _viewsToIncrement;
 	QMap<PeerData*, mtpRequestId> _viewsIncrementRequests;
 	QMap<mtpRequestId, PeerData*> _viewsIncrementByRequest;
-	SingleTimer _viewsIncrementTimer;
+	base::Timer _viewsIncrementTimer;
 
 	struct SettingBackground;
 	std::unique_ptr<SettingBackground> _background;
diff --git a/Telegram/SourceFiles/mainwindow.cpp b/Telegram/SourceFiles/mainwindow.cpp
index 4416617331..1e90896d1b 100644
--- a/Telegram/SourceFiles/mainwindow.cpp
+++ b/Telegram/SourceFiles/mainwindow.cpp
@@ -714,7 +714,7 @@ void MainWindow::toggleDisplayNotifyFromTray() {
 }
 
 void MainWindow::closeEvent(QCloseEvent *e) {
-	if (Sandbox::isSavingSession()) {
+	if (Core::App().isSavingSession()) {
 		e->accept();
 		App::quit();
 	} else {
diff --git a/Telegram/SourceFiles/mainwindow.h b/Telegram/SourceFiles/mainwindow.h
index 6a53d208a6..99a19c5f68 100644
--- a/Telegram/SourceFiles/mainwindow.h
+++ b/Telegram/SourceFiles/mainwindow.h
@@ -9,7 +9,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 
 #include "platform/platform_specific.h"
 #include "platform/platform_main_window.h"
-#include "core/single_timer.h"
 #include "base/unique_qptr.h"
 
 class MainWidget;
diff --git a/Telegram/SourceFiles/mediaview.cpp b/Telegram/SourceFiles/mediaview.cpp
index 51d7db50e5..f33e161f8a 100644
--- a/Telegram/SourceFiles/mediaview.cpp
+++ b/Telegram/SourceFiles/mediaview.cpp
@@ -906,7 +906,7 @@ void MediaView::onSaveAs() {
 			}));
 	}
 	activateWindow();
-	Sandbox::setActiveWindow(this);
+	Core::App().setActiveWindow(this);
 	setFocus();
 }
 
@@ -1777,7 +1777,7 @@ void MediaView::displayFinished() {
 		show();
 		psShowOverAll(this);
 		activateWindow();
-		Sandbox::setActiveWindow(this);
+		Core::App().setActiveWindow(this);
 		setFocus();
 	}
 }
diff --git a/Telegram/SourceFiles/messenger.cpp b/Telegram/SourceFiles/messenger.cpp
index aa6521b50a..fb847268de 100644
--- a/Telegram/SourceFiles/messenger.cpp
+++ b/Telegram/SourceFiles/messenger.cpp
@@ -79,6 +79,7 @@ struct Messenger::Private {
 Messenger::Messenger(not_null<Core::Launcher*> launcher)
 : QObject()
 , _launcher(launcher)
+, _killDownloadSessionsTimer([=] { killDownloadSessions(); })
 , _private(std::make_unique<Private>())
 , _databases(std::make_unique<Storage::Databases>())
 , _langpack(std::make_unique<Lang::Instance>())
@@ -95,7 +96,7 @@ Messenger::Messenger(not_null<Core::Launcher*> launcher)
 
 	ThirdParty::start();
 	Global::start();
-	Sandbox::refreshGlobalProxy(); // Depends on Global::started().
+	Core::App().refreshGlobalProxy(); // Depends on Global::started().
 
 	startLocalStorage();
 
@@ -110,7 +111,7 @@ Messenger::Messenger(not_null<Core::Launcher*> launcher)
 	}
 
 	_translator = std::make_unique<Lang::Translator>();
-	QCoreApplication::instance()->installTranslator(_translator.get());
+	qApp->installTranslator(_translator.get());
 
 	style::startManager();
 	anim::startManager();
@@ -120,12 +121,10 @@ Messenger::Messenger(not_null<Core::Launcher*> launcher)
 
 	DEBUG_LOG(("Application Info: inited..."));
 
-	QCoreApplication::instance()->installNativeEventFilter(psNativeEventFilter());
+	QApplication::instance()->installNativeEventFilter(psNativeEventFilter());
 
 	cChangeTimeFormat(QLocale::system().timeFormat(QLocale::ShortFormat));
 
-	connect(&killDownloadSessionsTimer, SIGNAL(timeout()), this, SLOT(killDownloadSessions()));
-
 	DEBUG_LOG(("Application Info: starting app..."));
 
 	// Create mime database, so it won't be slow later.
@@ -138,8 +137,12 @@ Messenger::Messenger(not_null<Core::Launcher*> launcher)
 	_mediaView = std::make_unique<MediaView>();
 	_window->setGeometry(currentGeometry);
 
-	QCoreApplication::instance()->installEventFilter(this);
-	Sandbox::connect(SIGNAL(applicationStateChanged(Qt::ApplicationState)), this, SLOT(onAppStateChanged(Qt::ApplicationState)));
+	qApp->installEventFilter(this);
+	connect(
+		qApp,
+		SIGNAL(applicationStateChanged(Qt::ApplicationState)),
+		this,
+		SLOT(onAppStateChanged(Qt::ApplicationState)));
 
 	DEBUG_LOG(("Application Info: window created..."));
 
@@ -252,13 +255,13 @@ bool Messenger::eventFilter(QObject *object, QEvent *e) {
 	} break;
 
 	case QEvent::ApplicationActivate: {
-		if (object == QCoreApplication::instance()) {
+		if (object == qApp) {
 			psUserActionDone();
 		}
 	} break;
 
 	case QEvent::FileOpen: {
-		if (object == QCoreApplication::instance()) {
+		if (object == qApp) {
 			auto url = QString::fromUtf8(static_cast<QFileOpenEvent*>(e)->url().toEncoded().trimmed());
 			if (url.startsWith(qstr("tg://"), Qt::CaseInsensitive)) {
 				cSetStartUrl(url.mid(0, 8192));
@@ -289,7 +292,7 @@ void Messenger::setCurrentProxy(
 			: ProxyData()));
 	Global::SetSelectedProxy(proxy);
 	Global::SetProxySettings(settings);
-	Sandbox::refreshGlobalProxy();
+	Core::App().refreshGlobalProxy();
 	if (_mtproto) {
 		_mtproto->restart();
 		if (previousKey != key(proxy)) {
@@ -527,13 +530,18 @@ void Messenger::destroyMtpKeys(MTP::AuthKeysList &&keys) {
 	destroyConfig.mainDcId = MTP::Instance::Config::kNoneMainDc;
 	destroyConfig.keys = std::move(keys);
 	_mtprotoForKeysDestroy = std::make_unique<MTP::Instance>(_dcOptions.get(), MTP::Instance::Mode::KeysDestroyer, std::move(destroyConfig));
-	connect(_mtprotoForKeysDestroy.get(), SIGNAL(allKeysDestroyed()), this, SLOT(onAllKeysDestroyed()));
+	connect(
+		_mtprotoForKeysDestroy.get(),
+		&MTP::Instance::allKeysDestroyed,
+		[=] { allKeysDestroyed(); });
 }
 
-void Messenger::onAllKeysDestroyed() {
+void Messenger::allKeysDestroyed() {
 	LOG(("MTP Info: all keys scheduled for destroy are destroyed."));
-	_mtprotoForKeysDestroy.reset();
-	Local::writeMtpData();
+	crl::on_main(this, [=] {
+		_mtprotoForKeysDestroy = nullptr;
+		Local::writeMtpData();
+	});
 }
 
 void Messenger::suggestMainDcId(MTP::DcId mainDcId) {
@@ -601,18 +609,19 @@ void Messenger::startLocalStorage() {
 }
 
 void Messenger::killDownloadSessionsStart(MTP::DcId dcId) {
-	if (killDownloadSessionTimes.constFind(dcId) == killDownloadSessionTimes.cend()) {
-		killDownloadSessionTimes.insert(dcId, getms() + MTPAckSendWaiting + MTPKillFileSessionTimeout);
+	if (!_killDownloadSessionTimes.contains(dcId)) {
+		_killDownloadSessionTimes.emplace(dcId, getms() + MTPAckSendWaiting + MTPKillFileSessionTimeout);
 	}
-	if (!killDownloadSessionsTimer.isActive()) {
-		killDownloadSessionsTimer.start(MTPAckSendWaiting + MTPKillFileSessionTimeout + 5);
+	if (!_killDownloadSessionsTimer.isActive()) {
+		_killDownloadSessionsTimer.callOnce(MTPAckSendWaiting + MTPKillFileSessionTimeout + 5);
 	}
 }
 
 void Messenger::killDownloadSessionsStop(MTP::DcId dcId) {
-	killDownloadSessionTimes.remove(dcId);
-	if (killDownloadSessionTimes.isEmpty() && killDownloadSessionsTimer.isActive()) {
-		killDownloadSessionsTimer.stop();
+	_killDownloadSessionTimes.erase(dcId);
+	if (_killDownloadSessionTimes.empty()
+		&& _killDownloadSessionsTimer.isActive()) {
+		_killDownloadSessionsTimer.cancel();
 	}
 }
 
@@ -673,25 +682,25 @@ void Messenger::call_handleObservables() {
 
 void Messenger::killDownloadSessions() {
 	auto ms = getms(), left = static_cast<TimeMs>(MTPAckSendWaiting) + MTPKillFileSessionTimeout;
-	for (auto i = killDownloadSessionTimes.begin(); i != killDownloadSessionTimes.end(); ) {
-		if (i.value() <= ms) {
+	for (auto i = _killDownloadSessionTimes.begin(); i != _killDownloadSessionTimes.end(); ) {
+		if (i->second <= ms) {
 			for (int j = 0; j < MTP::kDownloadSessionsCount; ++j) {
-				MTP::stopSession(MTP::downloadDcId(i.key(), j));
+				MTP::stopSession(MTP::downloadDcId(i->first, j));
 			}
-			i = killDownloadSessionTimes.erase(i);
+			i = _killDownloadSessionTimes.erase(i);
 		} else {
-			if (i.value() - ms < left) {
-				left = i.value() - ms;
+			if (i->second - ms < left) {
+				left = i->second - ms;
 			}
 			++i;
 		}
 	}
-	if (!killDownloadSessionTimes.isEmpty()) {
-		killDownloadSessionsTimer.start(left);
+	if (!_killDownloadSessionTimes.empty()) {
+		_killDownloadSessionsTimer.callOnce(left);
 	}
 }
 
-void Messenger::onSwitchDebugMode() {
+void Messenger::switchDebugMode() {
 	if (Logs::DebugEnabled()) {
 		Logs::SetDebugEnabled(false);
 		Sandbox::WriteDebugModeSetting();
@@ -704,14 +713,14 @@ void Messenger::onSwitchDebugMode() {
 	}
 }
 
-void Messenger::onSwitchWorkMode() {
+void Messenger::switchWorkMode() {
 	Global::SetDialogsModeEnabled(!Global::DialogsModeEnabled());
 	Global::SetDialogsMode(Dialogs::Mode::All);
 	Local::writeUserSettings();
 	App::restart();
 }
 
-void Messenger::onSwitchTestMode() {
+void Messenger::switchTestMode() {
 	if (cTestMode()) {
 		QFile(cWorkingDir() + qsl("tdata/withtestmode")).remove();
 		cSetTestMode(false);
@@ -971,7 +980,7 @@ QWidget *Messenger::getFileDialogParent() {
 void Messenger::checkMediaViewActivation() {
 	if (_mediaView && !_mediaView->isHidden()) {
 		_mediaView->activateWindow();
-		Sandbox::setActiveWindow(_mediaView.get());
+		Core::App().setActiveWindow(_mediaView.get());
 		_mediaView->setFocus();
 	}
 }
@@ -1062,7 +1071,7 @@ void Messenger::unregisterLeaveSubscription(QWidget *widget) {
 
 void Messenger::QuitAttempt() {
 	auto prevents = false;
-	if (!Sandbox::isSavingSession() && AuthSession::Exists()) {
+	if (AuthSession::Exists() && !Core::App().isSavingSession()) {
 		if (Auth().api().isQuitPrevent()) {
 			prevents = true;
 		}
@@ -1073,7 +1082,7 @@ void Messenger::QuitAttempt() {
 	if (prevents) {
 		Instance().quitDelayed();
 	} else {
-		QCoreApplication::quit();
+		QApplication::quit();
 	}
 }
 
@@ -1085,7 +1094,7 @@ void Messenger::quitPreventFinished() {
 
 void Messenger::quitDelayed() {
 	if (!_private->quitTimer.isActive()) {
-		_private->quitTimer.setCallback([] { QCoreApplication::quit(); });
+		_private->quitTimer.setCallback([] { QApplication::quit(); });
 		_private->quitTimer.callOnce(kQuitPreventTimeoutMs);
 	}
 }
diff --git a/Telegram/SourceFiles/messenger.h b/Telegram/SourceFiles/messenger.h
index c4185b82fa..29fbd9820d 100644
--- a/Telegram/SourceFiles/messenger.h
+++ b/Telegram/SourceFiles/messenger.h
@@ -199,6 +199,10 @@ public:
 	void handleAppActivated();
 	void handleAppDeactivated();
 
+	void switchDebugMode();
+	void switchWorkMode();
+	void switchTestMode();
+
 	void call_handleUnreadCounterUpdate();
 	void call_handleDelayedPeerUpdates();
 	void call_handleObservables();
@@ -211,17 +215,13 @@ protected:
 	bool eventFilter(QObject *object, QEvent *event) override;
 
 public slots:
-	void onAllKeysDestroyed();
-
-	void onSwitchDebugMode();
-	void onSwitchWorkMode();
-	void onSwitchTestMode();
-
 	void killDownloadSessions();
 	void onAppStateChanged(Qt::ApplicationState state);
 
 private:
 	void destroyMtpKeys(MTP::AuthKeysList &&keys);
+	void allKeysDestroyed();
+
 	void startLocalStorage();
 	void startShortcuts();
 
@@ -238,8 +238,8 @@ private:
 
 	not_null<Core::Launcher*> _launcher;
 
-	QMap<MTP::DcId, TimeMs> killDownloadSessionTimes;
-	SingleTimer killDownloadSessionsTimer;
+	base::flat_map<MTP::DcId, TimeMs> _killDownloadSessionTimes;
+	base::Timer _killDownloadSessionsTimer;
 
 	// Some fields are just moved from the declaration.
 	struct Private;
diff --git a/Telegram/SourceFiles/mtproto/connection.h b/Telegram/SourceFiles/mtproto/connection.h
index feb2f61066..bed2668786 100644
--- a/Telegram/SourceFiles/mtproto/connection.h
+++ b/Telegram/SourceFiles/mtproto/connection.h
@@ -37,6 +37,7 @@ class RSAPublicKey;
 struct ConnectionOptions;
 
 class Thread : public QThread {
+	// The Q_OBJECT meta info is used for qobject_cast!
 	Q_OBJECT
 
 public:
diff --git a/Telegram/SourceFiles/mtproto/facade.h b/Telegram/SourceFiles/mtproto/facade.h
index 1cc586a793..16ed4c0f9f 100644
--- a/Telegram/SourceFiles/mtproto/facade.h
+++ b/Telegram/SourceFiles/mtproto/facade.h
@@ -7,7 +7,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 */
 #pragma once
 
-#include "core/single_timer.h"
 #include "mtproto/type_utils.h"
 #include "mtproto/mtp_instance.h"
 
diff --git a/Telegram/SourceFiles/mtproto/mtp_instance.cpp b/Telegram/SourceFiles/mtproto/mtp_instance.cpp
index 590fe3cb20..bc0ccd1e69 100644
--- a/Telegram/SourceFiles/mtproto/mtp_instance.cpp
+++ b/Telegram/SourceFiles/mtproto/mtp_instance.cpp
@@ -361,7 +361,7 @@ void Instance::Private::setGoodProxyDomain(
 	}
 	if (applyToProxy(Global::RefSelectedProxy())
 		&& (Global::ProxySettings() == ProxyData::Settings::Enabled)) {
-		Sandbox::refreshGlobalProxy();
+		Core::App().refreshGlobalProxy();
 	}
 }
 
diff --git a/Telegram/SourceFiles/mtproto/session.cpp b/Telegram/SourceFiles/mtproto/session.cpp
index 6f5ef367fe..ac52349066 100644
--- a/Telegram/SourceFiles/mtproto/session.cpp
+++ b/Telegram/SourceFiles/mtproto/session.cpp
@@ -122,13 +122,12 @@ void SessionData::clear(Instance *instance) {
 Session::Session(not_null<Instance*> instance, ShiftedDcId shiftedDcId) : QObject()
 , _instance(instance)
 , data(this)
-, dcWithShift(shiftedDcId) {
+, dcWithShift(shiftedDcId)
+, sender([=] { needToResumeAndSend(); }) {
 	connect(&timeouter, SIGNAL(timeout()), this, SLOT(checkRequestsByTimer()));
 	timeouter.start(1000);
 
 	refreshOptions();
-
-	connect(&sender, SIGNAL(timeout()), this, SLOT(needToResumeAndSend()));
 }
 
 void Session::start() {
@@ -247,10 +246,10 @@ void Session::sendAnything(qint64 msCanWait) {
 	if (msWait) {
 		DEBUG_LOG(("MTP Info: dcWithShift %1 can wait for %2ms from current %3").arg(dcWithShift).arg(msWait).arg(msSendCall));
 		msSendCall = ms;
-		sender.start(msWait);
+		sender.callOnce(msWait);
 	} else {
 		DEBUG_LOG(("MTP Info: dcWithShift %1 stopped send timer, can wait for %2ms from current %3").arg(dcWithShift).arg(msWait).arg(msSendCall));
-		sender.stop();
+		sender.cancel();
 		msSendCall = 0;
 		needToResumeAndSend();
 	}
diff --git a/Telegram/SourceFiles/mtproto/session.h b/Telegram/SourceFiles/mtproto/session.h
index ebecb03893..f2004ac596 100644
--- a/Telegram/SourceFiles/mtproto/session.h
+++ b/Telegram/SourceFiles/mtproto/session.h
@@ -7,7 +7,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 */
 #pragma once
 
-#include "core/single_timer.h"
+#include "base/timer.h"
 #include "mtproto/rpc_sender.h"
 
 namespace MTP {
@@ -394,7 +394,7 @@ private:
 	bool _ping = false;
 
 	QTimer timeouter;
-	SingleTimer sender;
+	base::Timer sender;
 
 };
 
diff --git a/Telegram/SourceFiles/passport/passport_panel_edit_scans.cpp b/Telegram/SourceFiles/passport/passport_panel_edit_scans.cpp
index f91d39ea0f..2628ce44d0 100644
--- a/Telegram/SourceFiles/passport/passport_panel_edit_scans.cpp
+++ b/Telegram/SourceFiles/passport/passport_panel_edit_scans.cpp
@@ -21,6 +21,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "lang/lang_keys.h"
 #include "boxes/abstract_box.h"
 #include "storage/storage_media_prepare.h"
+#include "storage/file_upload.h" // For Storage::kUseBigFilesFrom.
 #include "styles/style_boxes.h"
 #include "styles/style_passport.h"
 
@@ -31,7 +32,7 @@ constexpr auto kMaxDimensions = 2048;
 constexpr auto kMaxSize = 10 * 1024 * 1024;
 constexpr auto kJpegQuality = 89;
 
-static_assert(kMaxSize <= UseBigFilesFrom);
+static_assert(kMaxSize <= Storage::kUseBigFilesFrom);
 
 base::variant<ReadScanError, QByteArray> ProcessImage(QByteArray &&bytes) {
 	auto image = App::readImage(base::take(bytes));
diff --git a/Telegram/SourceFiles/platform/mac/main_window_mac.h b/Telegram/SourceFiles/platform/mac/main_window_mac.h
index 1c38821eb2..0597ff0864 100644
--- a/Telegram/SourceFiles/platform/mac/main_window_mac.h
+++ b/Telegram/SourceFiles/platform/mac/main_window_mac.h
@@ -14,7 +14,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 namespace Platform {
 
 class MainWindow : public Window::MainWindow {
-	// The Q_OBJECT meta info is used for qobject_cast to MainWindow!
+	// The Q_OBJECT meta info is used for qobject_cast!
 	Q_OBJECT
 
 public:
diff --git a/Telegram/SourceFiles/platform/mac/main_window_mac.mm b/Telegram/SourceFiles/platform/mac/main_window_mac.mm
index 0687965c71..0ea58ab8cf 100644
--- a/Telegram/SourceFiles/platform/mac/main_window_mac.mm
+++ b/Telegram/SourceFiles/platform/mac/main_window_mac.mm
@@ -10,7 +10,6 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "styles/style_window.h"
 #include "mainwindow.h"
 #include "mainwidget.h"
-#include "application.h"
 #include "messenger.h"
 #include "auth_session.h"
 #include "history/history.h"
@@ -70,7 +69,7 @@ public:
 	LayerCreationChecker(NSView * __weak view, Fn<void()> callback)
 	: _weakView(view)
 	, _callback(std::move(callback)) {
-		QCoreApplication::instance()->installEventFilter(this);
+		QApplication::instance()->installEventFilter(this);
 	}
 
 protected:
@@ -334,7 +333,7 @@ bool MainWindow::Private::clipboardHasText() {
 	auto currentChangeCount = static_cast<int>([_generalPasteboard changeCount]);
 	if (_generalPasteboardChangeCount != currentChangeCount) {
 		_generalPasteboardChangeCount = currentChangeCount;
-		_generalPasteboardHasText = !Application::clipboard()->text().isEmpty();
+		_generalPasteboardHasText = !QApplication::clipboard()->text().isEmpty();
 	}
 	return _generalPasteboardHasText;
 }
diff --git a/Telegram/SourceFiles/platform/win/main_window_win.cpp b/Telegram/SourceFiles/platform/win/main_window_win.cpp
index 18688de491..ea1937c388 100644
--- a/Telegram/SourceFiles/platform/win/main_window_win.cpp
+++ b/Telegram/SourceFiles/platform/win/main_window_win.cpp
@@ -179,7 +179,7 @@ public:
 			return false;
 		}
 
-		QRect avail(Sandbox::availableGeometry());
+		const auto avail = QApplication::desktop()->availableGeometry();
 		max_w = avail.width();
 		accumulate_max(max_w, st::windowMinWidth);
 		max_h = avail.height();
diff --git a/Telegram/SourceFiles/platform/win/notifications_manager_win.cpp b/Telegram/SourceFiles/platform/win/notifications_manager_win.cpp
index 236046e621..8935eee484 100644
--- a/Telegram/SourceFiles/platform/win/notifications_manager_win.cpp
+++ b/Telegram/SourceFiles/platform/win/notifications_manager_win.cpp
@@ -374,8 +374,8 @@ private:
 };
 
 Manager::Private::Private(Manager *instance, Type type)
-: _guarded(std::make_shared<Manager*>(instance))
-, _cachedUserpics(type) {
+: _cachedUserpics(type)
+, _guarded(std::make_shared<Manager*>(instance)) {
 }
 
 bool Manager::Private::init() {
diff --git a/Telegram/SourceFiles/settings/settings_codes.cpp b/Telegram/SourceFiles/settings/settings_codes.cpp
index b9ef596d56..2bcf8adfb8 100644
--- a/Telegram/SourceFiles/settings/settings_codes.cpp
+++ b/Telegram/SourceFiles/settings/settings_codes.cpp
@@ -34,7 +34,7 @@ auto GenerateCodes() {
 			: qsl("Do you want to enable DEBUG logs?\n\n"
 				"All network events will be logged.");
 		Ui::show(Box<ConfirmBox>(text, [] {
-			Messenger::Instance().onSwitchDebugMode();
+			Messenger::Instance().switchDebugMode();
 		}));
 	});
 	codes.emplace(qsl("viewlogs"), [] {
@@ -43,7 +43,7 @@ auto GenerateCodes() {
 	codes.emplace(qsl("testmode"), [] {
 		auto text = cTestMode() ? qsl("Do you want to disable TEST mode?") : qsl("Do you want to enable TEST mode?\n\nYou will be switched to test cloud.");
 		Ui::show(Box<ConfirmBox>(text, [] {
-			Messenger::Instance().onSwitchTestMode();
+			Messenger::Instance().switchTestMode();
 		}));
 	});
 	if (!Core::UpdaterDisabled()) {
@@ -71,7 +71,7 @@ auto GenerateCodes() {
 	codes.emplace(qsl("workmode"), [] {
 		auto text = Global::DialogsModeEnabled() ? qsl("Disable work mode?") : qsl("Enable work mode?");
 		Ui::show(Box<ConfirmBox>(text, [] {
-			Messenger::Instance().onSwitchWorkMode();
+			Messenger::Instance().switchWorkMode();
 		}));
 	});
 	codes.emplace(qsl("moderate"), [] {
diff --git a/Telegram/SourceFiles/storage/file_download.cpp b/Telegram/SourceFiles/storage/file_download.cpp
index 20f8dece37..fefdacb6c8 100644
--- a/Telegram/SourceFiles/storage/file_download.cpp
+++ b/Telegram/SourceFiles/storage/file_download.cpp
@@ -1440,18 +1440,18 @@ void WebLoadManager::onFailed(QNetworkReply *reply) {
 }
 
 void WebLoadManager::onProgress(qint64 already, qint64 size) {
-	QNetworkReply *reply = qobject_cast<QNetworkReply*>(QObject::sender());
+	const auto reply = qobject_cast<QNetworkReply*>(QObject::sender());
 	if (!reply) return;
 
-	Replies::iterator j = _replies.find(reply);
+	const auto j = _replies.find(reply);
 	if (j == _replies.cend()) { // handled already
 		return;
 	}
-	webFileLoaderPrivate *loader = j.value();
+	const auto loader = j.value();
 
-	WebReplyProcessResult result = WebReplyProcessProgress;
-	QVariant statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
-	int32 status = statusCode.isValid() ? statusCode.toInt() : 200;
+	auto result = WebReplyProcessProgress;
+	const auto statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
+	const auto status = statusCode.isValid() ? statusCode.toInt() : 200;
 	if (status != 200 && status != 206 && status != 416) {
 		if (status == 301 || status == 302) {
 			QString loc = reply->header(QNetworkRequest::LocationHeader).toString();
@@ -1490,20 +1490,19 @@ void WebLoadManager::onProgress(qint64 already, qint64 size) {
 }
 
 void WebLoadManager::onMeta() {
-	QNetworkReply *reply = qobject_cast<QNetworkReply*>(QObject::sender());
+	const auto reply = qobject_cast<QNetworkReply*>(QObject::sender());
 	if (!reply) return;
 
-	Replies::iterator j = _replies.find(reply);
+	const auto j = _replies.find(reply);
 	if (j == _replies.cend()) { // handled already
 		return;
 	}
-	webFileLoaderPrivate *loader = j.value();
+	const auto loader = j.value();
 
-	typedef QList<QNetworkReply::RawHeaderPair> Pairs;
-	Pairs pairs = reply->rawHeaderPairs();
-	for (Pairs::iterator i = pairs.begin(), e = pairs.end(); i != e; ++i) {
+	const auto pairs = reply->rawHeaderPairs();
+	for (auto i = pairs.begin(), e = pairs.end(); i != e; ++i) {
 		if (QString::fromUtf8(i->first).toLower() == "content-range") {
-			QRegularExpressionMatch m = QRegularExpression(qsl("/(\\d+)([^\\d]|$)")).match(QString::fromUtf8(i->second));
+			const auto m = QRegularExpression(qsl("/(\\d+)([^\\d]|$)")).match(QString::fromUtf8(i->second));
 			if (m.hasMatch()) {
 				loader->setProgress(qMax(qint64(loader->data().size()), loader->already()), m.captured(1).toLongLong());
 				if (!handleReplyResult(loader, WebReplyProcessProgress)) {
diff --git a/Telegram/SourceFiles/storage/file_upload.cpp b/Telegram/SourceFiles/storage/file_upload.cpp
index 932ff170a2..c5e45b7197 100644
--- a/Telegram/SourceFiles/storage/file_upload.cpp
+++ b/Telegram/SourceFiles/storage/file_upload.cpp
@@ -17,7 +17,28 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 namespace Storage {
 namespace {
 
-constexpr auto kMaxUploadFileParallelSize = MTP::kUploadSessionsCount * 512 * 1024; // max 512kb uploaded at the same time in each session
+// max 512kb uploaded at the same time in each session
+constexpr auto kMaxUploadFileParallelSize = MTP::kUploadSessionsCount * 512 * 1024;
+
+constexpr auto kDocumentMaxPartsCount = 3000;
+
+// 32kb for tiny document ( < 1mb )
+constexpr auto kDocumentUploadPartSize0 = 32 * 1024;
+
+// 64kb for little document ( <= 32mb )
+constexpr auto kDocumentUploadPartSize1 = 64 * 1024;
+
+// 128kb for small document ( <= 375mb )
+constexpr auto kDocumentUploadPartSize2 = 128 * 1024;
+
+// 256kb for medium document ( <= 750mb )
+constexpr auto kDocumentUploadPartSize3 = 256 * 1024;
+
+// 512kb for large document ( <= 1500mb )
+constexpr auto kDocumentUploadPartSize4 = 512 * 1024;
+
+// One part each half second, if not uploaded faster.
+constexpr auto kUploadRequestInterval = TimeMs(500);
 
 } // namespace
 
@@ -75,11 +96,11 @@ void Uploader::File::setDocSize(int32 size) {
 	docSize = size;
 	constexpr auto limit0 = 1024 * 1024;
 	constexpr auto limit1 = 32 * limit0;
-	if (docSize >= limit0 || !setPartSize(DocumentUploadPartSize0)) {
-		if (docSize > limit1 || !setPartSize(DocumentUploadPartSize1)) {
-			if (!setPartSize(DocumentUploadPartSize2)) {
-				if (!setPartSize(DocumentUploadPartSize3)) {
-					if (!setPartSize(DocumentUploadPartSize4)) {
+	if (docSize >= limit0 || !setPartSize(kDocumentUploadPartSize0)) {
+		if (docSize > limit1 || !setPartSize(kDocumentUploadPartSize1)) {
+			if (!setPartSize(kDocumentUploadPartSize2)) {
+				if (!setPartSize(kDocumentUploadPartSize3)) {
+					if (!setPartSize(kDocumentUploadPartSize4)) {
 						LOG(("Upload Error: bad doc size: %1").arg(docSize));
 					}
 				}
@@ -92,7 +113,7 @@ bool Uploader::File::setPartSize(uint32 partSize) {
 	docPartSize = partSize;
 	docPartsCount = (docSize / docPartSize)
 		+ ((docSize % docPartSize) ? 1 : 0);
-	return (docPartsCount <= DocumentMaxPartsCount);
+	return (docPartsCount <= kDocumentMaxPartsCount);
 }
 
 uint64 Uploader::File::id() const {
@@ -288,7 +309,7 @@ void Uploader::sendNext() {
 					QByteArray docMd5(32, Qt::Uninitialized);
 					hashMd5Hex(uploadingData.md5Hash.result(), docMd5.data());
 
-					const auto file = (uploadingData.docSize > UseBigFilesFrom)
+					const auto file = (uploadingData.docSize > kUseBigFilesFrom)
 						? MTP_inputFileBig(
 							MTP_long(uploadingData.id()),
 							MTP_int(uploadingData.docPartsCount),
@@ -347,7 +368,7 @@ void Uploader::sendNext() {
 				}
 			}
 			toSend = uploadingData.docFile->read(uploadingData.docPartSize);
-			if (uploadingData.docSize <= UseBigFilesFrom) {
+			if (uploadingData.docSize <= kUseBigFilesFrom) {
 				uploadingData.md5Hash.feed(toSend.constData(), toSend.size());
 			}
 		} else {
@@ -356,7 +377,7 @@ void Uploader::sendNext() {
 			toSend = content.mid(offset, uploadingData.docPartSize);
 			if ((uploadingData.type() == SendMediaType::File
 				|| uploadingData.type() == SendMediaType::Audio)
-				&& uploadingData.docSentParts <= UseBigFilesFrom) {
+				&& uploadingData.docSentParts <= kUseBigFilesFrom) {
 				uploadingData.md5Hash.feed(toSend.constData(), toSend.size());
 			}
 		}
@@ -367,7 +388,7 @@ void Uploader::sendNext() {
 			return;
 		}
 		mtpRequestId requestId;
-		if (uploadingData.docSize > UseBigFilesFrom) {
+		if (uploadingData.docSize > kUseBigFilesFrom) {
 			requestId = MTP::send(
 				MTPupload_SaveBigFilePart(
 					MTP_long(uploadingData.id()),
@@ -411,7 +432,7 @@ void Uploader::sendNext() {
 
 		parts.erase(part);
 	}
-	nextTimer.start(UploadRequestInterval);
+	nextTimer.start(kUploadRequestInterval);
 }
 
 void Uploader::cancel(const FullMsgId &msgId) {
diff --git a/Telegram/SourceFiles/storage/file_upload.h b/Telegram/SourceFiles/storage/file_upload.h
index 040687dd05..db474df8e5 100644
--- a/Telegram/SourceFiles/storage/file_upload.h
+++ b/Telegram/SourceFiles/storage/file_upload.h
@@ -12,6 +12,9 @@ struct SendMediaReady;
 
 namespace Storage {
 
+// MTP big files methods used for files greater than 10mb.
+constexpr auto kUseBigFilesFrom = 10 * 1024 * 1024;
+
 struct UploadedPhoto {
 	FullMsgId fullId;
 	bool silent = false;
diff --git a/Telegram/SourceFiles/storage/localimageloader.cpp b/Telegram/SourceFiles/storage/localimageloader.cpp
index f630904789..3f9e3b87ca 100644
--- a/Telegram/SourceFiles/storage/localimageloader.cpp
+++ b/Telegram/SourceFiles/storage/localimageloader.cpp
@@ -25,6 +25,9 @@ namespace {
 
 constexpr auto kThumbnailQuality = 87;
 constexpr auto kThumbnailSize = 320;
+constexpr auto kPhotoUploadPartSize = 32 * 1024;
+
+using Storage::ValidateThumbDimensions;
 
 struct PreparedFileThumbnail {
 	uint64 id = 0;
@@ -37,7 +40,7 @@ struct PreparedFileThumbnail {
 PreparedFileThumbnail PrepareFileThumbnail(QImage &&original) {
 	const auto width = original.width();
 	const auto height = original.height();
-	if (!Storage::ValidateThumbDimensions(width, height)) {
+	if (!ValidateThumbDimensions(width, height)) {
 		return {};
 	}
 	auto result = PreparedFileThumbnail();
@@ -133,7 +136,43 @@ MTPInputSingleMedia PrepareAlbumItemMedia(
 
 } // namespace
 
-using Storage::ValidateThumbDimensions;
+SendMediaReady::SendMediaReady(
+	SendMediaType type,
+	const QString &file,
+	const QString &filename,
+	int32 filesize,
+	const QByteArray &data,
+	const uint64 &id,
+	const uint64 &thumbId,
+	const QString &thumbExt,
+	const PeerId &peer,
+	const MTPPhoto &photo,
+	const PreparedPhotoThumbs &photoThumbs,
+	const MTPDocument &document,
+	const QByteArray &jpeg,
+	MsgId replyTo)
+: replyTo(replyTo)
+, type(type)
+, file(file)
+, filename(filename)
+, filesize(filesize)
+, data(data)
+, thumbExt(thumbExt)
+, id(id)
+, thumbId(thumbId)
+, peer(peer)
+, photo(photo)
+, document(document)
+, photoThumbs(photoThumbs) {
+	if (!jpeg.isEmpty()) {
+		int32 size = jpeg.size();
+		for (int32 i = 0, part = 0; i < size; i += kPhotoUploadPartSize, ++part) {
+			parts.insert(part, jpeg.mid(i, kPhotoUploadPartSize));
+		}
+		jpeg_md5.resize(32);
+		hashMd5Hex(jpeg.constData(), jpeg.size(), jpeg_md5.data());
+	}
+}
 
 SendMediaReady PreparePeerPhoto(PeerId peerId, QImage &&image) {
 	PreparedPhotoThumbs photoThumbs;
@@ -290,10 +329,8 @@ void TaskQueue::stop() {
 		_thread->quit();
 		DEBUG_LOG(("Waiting for taskThread to finish"));
 		_thread->wait();
-		delete _worker;
-		delete _thread;
-		_worker = 0;
-		_thread = 0;
+		delete base::take(_worker);
+		delete base::take(_thread);
 	}
 	_tasksToProcess.clear();
 	_tasksToFinish.clear();
@@ -399,6 +436,31 @@ FileLoadResult::FileLoadResult(
 , caption(caption) {
 }
 
+void FileLoadResult::setFileData(const QByteArray &filedata) {
+	if (filedata.isEmpty()) {
+		partssize = 0;
+	} else {
+		partssize = filedata.size();
+		for (int32 i = 0, part = 0; i < partssize; i += kPhotoUploadPartSize, ++part) {
+			fileparts.insert(part, filedata.mid(i, kPhotoUploadPartSize));
+		}
+		filemd5.resize(32);
+		hashMd5Hex(filedata.constData(), filedata.size(), filemd5.data());
+	}
+}
+
+void FileLoadResult::setThumbData(const QByteArray &thumbdata) {
+	if (!thumbdata.isEmpty()) {
+		int32 size = thumbdata.size();
+		for (int32 i = 0, part = 0; i < size; i += kPhotoUploadPartSize, ++part) {
+			thumbparts.insert(part, thumbdata.mid(i, kPhotoUploadPartSize));
+		}
+		thumbmd5.resize(32);
+		hashMd5Hex(thumbdata.constData(), thumbdata.size(), thumbmd5.data());
+	}
+}
+
+
 FileLoadTask::FileLoadTask(
 	const QString &filepath,
 	const QByteArray &content,
diff --git a/Telegram/SourceFiles/storage/localimageloader.h b/Telegram/SourceFiles/storage/localimageloader.h
index e1106dd99c..6faff9fde5 100644
--- a/Telegram/SourceFiles/storage/localimageloader.h
+++ b/Telegram/SourceFiles/storage/localimageloader.h
@@ -47,29 +47,22 @@ using SendMediaPrepareList = QList<SendMediaPrepare>;
 using UploadFileParts =  QMap<int, QByteArray>;
 struct SendMediaReady {
 	SendMediaReady() = default; // temp
-	SendMediaReady(SendMediaType type, const QString &file, const QString &filename, int32 filesize, const QByteArray &data, const uint64 &id, const uint64 &thumbId, const QString &thumbExt, const PeerId &peer, const MTPPhoto &photo, const PreparedPhotoThumbs &photoThumbs, const MTPDocument &document, const QByteArray &jpeg, MsgId replyTo)
-		: replyTo(replyTo)
-		, type(type)
-		, file(file)
-		, filename(filename)
-		, filesize(filesize)
-		, data(data)
-		, thumbExt(thumbExt)
-		, id(id)
-		, thumbId(thumbId)
-		, peer(peer)
-		, photo(photo)
-		, document(document)
-		, photoThumbs(photoThumbs) {
-		if (!jpeg.isEmpty()) {
-			int32 size = jpeg.size();
-			for (int32 i = 0, part = 0; i < size; i += UploadPartSize, ++part) {
-				parts.insert(part, jpeg.mid(i, UploadPartSize));
-			}
-			jpeg_md5.resize(32);
-			hashMd5Hex(jpeg.constData(), jpeg.size(), jpeg_md5.data());
-		}
-	}
+	SendMediaReady(
+		SendMediaType type,
+		const QString &file,
+		const QString &filename,
+		int32 filesize,
+		const QByteArray &data,
+		const uint64 &id,
+		const uint64 &thumbId,
+		const QString &thumbExt,
+		const PeerId &peer,
+		const MTPPhoto &photo,
+		const PreparedPhotoThumbs &photoThumbs,
+		const MTPDocument &document,
+		const QByteArray &jpeg,
+		MsgId replyTo);
+
 	MsgId replyTo;
 	SendMediaType type;
 	QString file, filename;
@@ -233,28 +226,9 @@ struct FileLoadResult {
 	PreparedPhotoThumbs photoThumbs;
 	TextWithTags caption;
 
-	void setFileData(const QByteArray &filedata) {
-		if (filedata.isEmpty()) {
-			partssize = 0;
-		} else {
-			partssize = filedata.size();
-			for (int32 i = 0, part = 0; i < partssize; i += UploadPartSize, ++part) {
-				fileparts.insert(part, filedata.mid(i, UploadPartSize));
-			}
-			filemd5.resize(32);
-			hashMd5Hex(filedata.constData(), filedata.size(), filemd5.data());
-		}
-	}
-	void setThumbData(const QByteArray &thumbdata) {
-		if (!thumbdata.isEmpty()) {
-			int32 size = thumbdata.size();
-			for (int32 i = 0, part = 0; i < size; i += UploadPartSize, ++part) {
-				thumbparts.insert(part, thumbdata.mid(i, UploadPartSize));
-			}
-			thumbmd5.resize(32);
-			hashMd5Hex(thumbdata.constData(), thumbdata.size(), thumbmd5.data());
-		}
-	}
+	void setFileData(const QByteArray &filedata);
+	void setThumbData(const QByteArray &thumbdata);
+
 };
 
 struct FileMediaInformation {
diff --git a/Telegram/SourceFiles/storage/localstorage.cpp b/Telegram/SourceFiles/storage/localstorage.cpp
index ce404b169e..a24b55dae7 100644
--- a/Telegram/SourceFiles/storage/localstorage.cpp
+++ b/Telegram/SourceFiles/storage/localstorage.cpp
@@ -1283,7 +1283,7 @@ bool _readSetting(quint32 blockId, QDataStream &stream, int version, ReadSetting
 		} else {
 			Global::SetProxiesList({});
 		}
-		Sandbox::refreshGlobalProxy();
+		Core::App().refreshGlobalProxy();
 	} break;
 
 	case dbiConnectionType: {
@@ -1383,7 +1383,7 @@ bool _readSetting(quint32 blockId, QDataStream &stream, int version, ReadSetting
 				Global::SetProxySettings(ProxyData::Settings::System);
 			}
 		}
-		Sandbox::refreshGlobalProxy();
+		Core::App().refreshGlobalProxy();
 	} break;
 
 	case dbiThemeKeyOld: {
diff --git a/Telegram/SourceFiles/ui/toast/toast_manager.cpp b/Telegram/SourceFiles/ui/toast/toast_manager.cpp
index cc6d5af934..346bdcb03b 100644
--- a/Telegram/SourceFiles/ui/toast/toast_manager.cpp
+++ b/Telegram/SourceFiles/ui/toast/toast_manager.cpp
@@ -20,8 +20,8 @@ NeverFreedPointer<QMap<QObject*, Manager*>> _managers;
 
 } // namespace
 
-Manager::Manager(QWidget *parent) : QObject(parent) {
-	connect(&_hideTimer, SIGNAL(timeout()), this, SLOT(onHideTimeout()));
+Manager::Manager(QWidget *parent) : QObject(parent)
+, _hideTimer([=] { hideByTimer(); }) {
 }
 
 bool Manager::eventFilter(QObject *o, QEvent *e) {
@@ -80,7 +80,7 @@ void Manager::addToast(std::unique_ptr<Instance> &&toast) {
 	}
 }
 
-void Manager::onHideTimeout() {
+void Manager::hideByTimer() {
 	auto now = getms(true);
 	for (auto i = _toastByHideTime.begin(); i != _toastByHideTime.cend();) {
 		if (i.key() <= now) {
@@ -114,9 +114,11 @@ void Manager::startNextHideTimer() {
 
 	auto ms = getms(true);
 	if (ms >= _toastByHideTime.firstKey()) {
-		QMetaObject::invokeMethod(this, SLOT("onHideTimeout"), Qt::QueuedConnection);
+		crl::on_main(this, [=] {
+			hideByTimer();
+		});
 	} else {
-		_hideTimer.start(_toastByHideTime.firstKey() - ms);
+		_hideTimer.callOnce(_toastByHideTime.firstKey() - ms);
 	}
 }
 
diff --git a/Telegram/SourceFiles/ui/toast/toast_manager.h b/Telegram/SourceFiles/ui/toast/toast_manager.h
index 01e273cd4b..ce4b795cfb 100644
--- a/Telegram/SourceFiles/ui/toast/toast_manager.h
+++ b/Telegram/SourceFiles/ui/toast/toast_manager.h
@@ -8,7 +8,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #pragma once
 
 #include "ui/toast/toast.h"
-#include "core/single_timer.h"
+#include "base/timer.h"
 
 namespace Ui {
 namespace Toast {
@@ -32,14 +32,14 @@ protected:
 	bool eventFilter(QObject *o, QEvent *e);
 
 private slots:
-	void onHideTimeout();
 	void onToastWidgetDestroyed(QObject *widget);
 
 private:
 	Manager(QWidget *parent);
 	void startNextHideTimer();
+	void hideByTimer();
 
-	SingleTimer _hideTimer;
+	base::Timer _hideTimer;
 	TimeMs _nextHide = 0;
 
 	QMultiMap<TimeMs, Instance*> _toastByHideTime;
diff --git a/Telegram/SourceFiles/ui/twidget.cpp b/Telegram/SourceFiles/ui/twidget.cpp
index 7f94c6d1da..0184bdf5cd 100644
--- a/Telegram/SourceFiles/ui/twidget.cpp
+++ b/Telegram/SourceFiles/ui/twidget.cpp
@@ -234,8 +234,7 @@ void ForceFullRepaint(not_null<QWidget*> widget) {
 }
 
 void PostponeCall(FnMut<void()> &&callable) {
-	const auto application = static_cast<Application*>(qApp);
-	application->postponeCall(std::move(callable));
+	Core::App().postponeCall(std::move(callable));
 }
 
 } // namespace Ui
diff --git a/Telegram/SourceFiles/ui/twidget.h b/Telegram/SourceFiles/ui/twidget.h
index c6051109f7..93853a446a 100644
--- a/Telegram/SourceFiles/ui/twidget.h
+++ b/Telegram/SourceFiles/ui/twidget.h
@@ -341,6 +341,7 @@ private:
 };
 
 class TWidget : public TWidgetHelper<QWidget> {
+	// The Q_OBJECT meta info is used for qobject_cast!
 	Q_OBJECT
 
 public:
diff --git a/Telegram/SourceFiles/ui/widgets/continuous_sliders.cpp b/Telegram/SourceFiles/ui/widgets/continuous_sliders.cpp
index afb736d1d8..27e6933a9a 100644
--- a/Telegram/SourceFiles/ui/widgets/continuous_sliders.cpp
+++ b/Telegram/SourceFiles/ui/widgets/continuous_sliders.cpp
@@ -7,6 +7,8 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 */
 #include "ui/widgets/continuous_sliders.h"
 
+#include "base/timer.h"
+
 namespace Ui {
 namespace {
 
@@ -29,14 +31,13 @@ void ContinuousSlider::setDisabled(bool disabled) {
 void ContinuousSlider::setMoveByWheel(bool move) {
 	if (move != moveByWheel()) {
 		if (move) {
-			_byWheelFinished = std::make_unique<SingleTimer>();
-			_byWheelFinished->setTimeoutHandler([this] {
+			_byWheelFinished = std::make_unique<base::Timer>([=] {
 				if (_changeFinishedCallback) {
 					_changeFinishedCallback(getCurrentValue());
 				}
 			});
 		} else {
-			_byWheelFinished.reset();
+			_byWheelFinished = nullptr;
 		}
 	}
 }
@@ -109,7 +110,7 @@ void ContinuousSlider::wheelEvent(QWheelEvent *e) {
 	if (_changeProgressCallback) {
 		_changeProgressCallback(finalValue);
 	}
-	_byWheelFinished->start(kByWheelFinishedTimeout);
+	_byWheelFinished->callOnce(kByWheelFinishedTimeout);
 }
 
 void ContinuousSlider::updateDownValueFromPos(const QPoint &pos) {
diff --git a/Telegram/SourceFiles/ui/widgets/continuous_sliders.h b/Telegram/SourceFiles/ui/widgets/continuous_sliders.h
index ceb7eab176..a32a0ac0c3 100644
--- a/Telegram/SourceFiles/ui/widgets/continuous_sliders.h
+++ b/Telegram/SourceFiles/ui/widgets/continuous_sliders.h
@@ -10,6 +10,10 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "styles/style_widgets.h"
 #include "ui/rp_widget.h"
 
+namespace base {
+class Timer;
+} // namespace base
+
 namespace Ui {
 
 class ContinuousSlider : public RpWidget {
@@ -87,7 +91,7 @@ private:
 	Direction _direction = Direction::Horizontal;
 	bool _disabled = false;
 
-	std::unique_ptr<SingleTimer> _byWheelFinished;
+	std::unique_ptr<base::Timer> _byWheelFinished;
 
 	Fn<float64(float64)> _adjustCallback;
 	Fn<void(float64)> _changeProgressCallback;
diff --git a/Telegram/SourceFiles/ui/widgets/dropdown_menu.cpp b/Telegram/SourceFiles/ui/widgets/dropdown_menu.cpp
index a309dd0796..de0c6ae52d 100644
--- a/Telegram/SourceFiles/ui/widgets/dropdown_menu.cpp
+++ b/Telegram/SourceFiles/ui/widgets/dropdown_menu.cpp
@@ -231,7 +231,7 @@ void DropdownMenu::hideFinish() {
 //
 //	auto menuTopLeft = mapFromGlobal(_menu->mapToGlobal(QPoint(0, 0)));
 //	auto w = p - QPoint(0, menuTopLeft.y());
-//	auto r = Sandbox::screenGeometry(p);
+//	auto r = QApplication::desktop()->screenGeometry(p);
 //	if (rtl()) {
 //		if (w.x() - width() < r.x() - _padding.left()) {
 //			if (_parent && w.x() + _parent->width() - _padding.left() - _padding.right() + width() - _padding.right() <= r.x() + r.width()) {
diff --git a/Telegram/SourceFiles/ui/widgets/input_fields.cpp b/Telegram/SourceFiles/ui/widgets/input_fields.cpp
index b0229b0433..fc9c312194 100644
--- a/Telegram/SourceFiles/ui/widgets/input_fields.cpp
+++ b/Telegram/SourceFiles/ui/widgets/input_fields.cpp
@@ -528,12 +528,12 @@ public:
 		setParent(QCoreApplication::instance());
 	}
 
-	void drawPrimitive(PrimitiveElement element, const QStyleOption *option, QPainter *painter, const QWidget *widget = 0) const {
+	void drawPrimitive(PrimitiveElement element, const QStyleOption *option, QPainter *painter, const QWidget *widget = nullptr) const override {
 	}
-	QRect subElementRect(SubElement r, const QStyleOption *opt, const QWidget *widget = 0) const {
+	QRect subElementRect(SubElement r, const QStyleOption *opt, const QWidget *widget = nullptr) const override {
 		switch (r) {
 			case SE_LineEditContents:
-				const InputClass *w = widget ? qobject_cast<const InputClass*>(widget) : 0;
+				const auto w = widget ? qobject_cast<const InputClass*>(widget) : nullptr;
 				return w ? w->getTextRect() : QCommonStyle::subElementRect(r, opt, widget);
 			break;
 		}
diff --git a/Telegram/SourceFiles/ui/widgets/input_fields.h b/Telegram/SourceFiles/ui/widgets/input_fields.h
index 11dac32def..9579896863 100644
--- a/Telegram/SourceFiles/ui/widgets/input_fields.h
+++ b/Telegram/SourceFiles/ui/widgets/input_fields.h
@@ -41,6 +41,7 @@ enum class InputSubmitSettings {
 };
 
 class FlatInput : public TWidgetHelper<QLineEdit>, private base::Subscriber {
+	// The Q_OBJECT meta info is used for qobject_cast!
 	Q_OBJECT
 
 public:
@@ -493,6 +494,7 @@ private:
 class MaskedInputField
 	: public RpWidgetWrap<QLineEdit>
 	, private base::Subscriber {
+	// The Q_OBJECT meta info is used for qobject_cast!
 	Q_OBJECT
 
 	using Parent = RpWidgetWrap<QLineEdit>;
diff --git a/Telegram/SourceFiles/ui/widgets/popup_menu.cpp b/Telegram/SourceFiles/ui/widgets/popup_menu.cpp
index 1ac1b367fd..09fa9558dd 100644
--- a/Telegram/SourceFiles/ui/widgets/popup_menu.cpp
+++ b/Telegram/SourceFiles/ui/widgets/popup_menu.cpp
@@ -447,7 +447,7 @@ void PopupMenu::showMenu(const QPoint &p, PopupMenu *parent, TriggeredSource sou
 
 	auto origin = PanelAnimation::Origin::TopLeft;
 	auto w = p - QPoint(0, _padding.top());
-	auto r = Sandbox::screenGeometry(p);
+	auto r = QApplication::desktop()->screenGeometry(p);
 	_useTransparency = Platform::TranslucentWindowsSupported(p);
 	setAttribute(Qt::WA_OpaquePaintEvent, !_useTransparency);
 	handleCompositingUpdate();
diff --git a/Telegram/SourceFiles/ui/widgets/scroll_area.cpp b/Telegram/SourceFiles/ui/widgets/scroll_area.cpp
index 718b14fb63..7c9e069b33 100644
--- a/Telegram/SourceFiles/ui/widgets/scroll_area.cpp
+++ b/Telegram/SourceFiles/ui/widgets/scroll_area.cpp
@@ -636,7 +636,7 @@ void ScrollArea::resizeEvent(QResizeEvent *e) {
 	_verticalBar->recountSize();
 	_topShadow->setGeometry(QRect(0, 0, width(), qAbs(_st.topsh)));
 	_bottomShadow->setGeometry(QRect(0, height() - qAbs(_st.bottomsh), width(), qAbs(_st.bottomsh)));
-	if (SplittedWidget *w = qobject_cast<SplittedWidget*>(widget())) {
+	if (const auto w = qobject_cast<SplittedWidget*>(widget())) {
 		w->resize(width() - w->otherWidth(), w->height());
 		if (!rtl()) {
 			_other->move(w->width(), w->y());
@@ -720,7 +720,7 @@ void ScrollArea::scrollToY(int toTop, int toBottom) {
 }
 
 void ScrollArea::doSetOwnedWidget(object_ptr<TWidget> w) {
-	auto splitted = qobject_cast<SplittedWidget*>(w.data());
+	const auto splitted = qobject_cast<SplittedWidget*>(w.data());
 	if (widget() && _touchEnabled) {
 		widget()->removeEventFilter(this);
 		if (!_widgetAcceptsTouch) widget()->setAttribute(Qt::WA_AcceptTouchEvents, false);
diff --git a/Telegram/SourceFiles/ui/widgets/scroll_area.h b/Telegram/SourceFiles/ui/widgets/scroll_area.h
index e4715c7bc2..9b8c69b008 100644
--- a/Telegram/SourceFiles/ui/widgets/scroll_area.h
+++ b/Telegram/SourceFiles/ui/widgets/scroll_area.h
@@ -110,6 +110,7 @@ private:
 };
 
 class SplittedWidget : public Ui::RpWidget {
+	// The Q_OBJECT meta info is used for qobject_cast!
 	Q_OBJECT
 
 public:
diff --git a/Telegram/SourceFiles/window/notifications_manager.cpp b/Telegram/SourceFiles/window/notifications_manager.cpp
index 479c6c9c42..93e13665e6 100644
--- a/Telegram/SourceFiles/window/notifications_manager.cpp
+++ b/Telegram/SourceFiles/window/notifications_manager.cpp
@@ -33,14 +33,12 @@ constexpr auto kMinimalAlertDelay = TimeMs(500);
 
 } // namespace
 
-System::System(AuthSession *session) : _authSession(session) {
+System::System(AuthSession *session)
+: _authSession(session)
+, _waitTimer([=] { showNext(); }) {
 	createManager();
 
-	_waitTimer.setTimeoutHandler([this] {
-		showNext();
-	});
-
-	subscribe(settingsChanged(), [this](ChangeType type) {
+	subscribe(settingsChanged(), [=](ChangeType type) {
 		if (type == ChangeType::DesktopEnabled) {
 			App::wnd()->updateTrayMenu();
 			clearAll();
@@ -124,7 +122,7 @@ void System::schedule(History *history, HistoryItem *item) {
 	}
 	if (haveSetting) {
 		if (!_waitTimer.isActive() || _waitTimer.remainingTime() > delay) {
-			_waitTimer.start(delay);
+			_waitTimer.callOnce(delay);
 		}
 	}
 }
@@ -150,7 +148,7 @@ void System::clearFromHistory(History *history) {
 	_waiters.remove(history);
 	_settingWaiters.remove(history);
 
-	_waitTimer.stop();
+	_waitTimer.cancel();
 	showNext();
 }
 
@@ -209,7 +207,7 @@ void System::checkDelayed() {
 			++i;
 		}
 	}
-	_waitTimer.stop();
+	_waitTimer.cancel();
 	showNext();
 }
 
@@ -259,7 +257,7 @@ void System::showNext() {
 
 	if (_waiters.isEmpty() || !Global::DesktopNotify() || Platform::Notifications::SkipToast()) {
 		if (nextAlert) {
-			_waitTimer.start(nextAlert - ms);
+			_waitTimer.callOnce(nextAlert - ms);
 		}
 		return;
 	}
@@ -306,7 +304,7 @@ void System::showNext() {
 					next = nextAlert;
 					nextAlert = 0;
 				}
-				_waitTimer.start(next - ms);
+				_waitTimer.callOnce(next - ms);
 				break;
 			} else {
 				auto forwardedItem = notifyItem->Has<HistoryMessageForwarded>() ? notifyItem : nullptr; // forwarded notify grouping
@@ -366,7 +364,7 @@ void System::showNext() {
 		}
 	}
 	if (nextAlert) {
-		_waitTimer.start(nextAlert - ms);
+		_waitTimer.callOnce(nextAlert - ms);
 	}
 }
 
diff --git a/Telegram/SourceFiles/window/notifications_manager.h b/Telegram/SourceFiles/window/notifications_manager.h
index 044b713311..7bd3af0fc2 100644
--- a/Telegram/SourceFiles/window/notifications_manager.h
+++ b/Telegram/SourceFiles/window/notifications_manager.h
@@ -7,6 +7,8 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 */
 #pragma once
 
+#include "base/timer.h"
+
 class AuthSession;
 
 namespace Platform {
@@ -96,7 +98,7 @@ private:
 	using Waiters = QMap<History*, Waiter>;
 	Waiters _waiters;
 	Waiters _settingWaiters;
-	SingleTimer _waitTimer;
+	base::Timer _waitTimer;
 
 	QMap<History*, QMap<TimeMs, PeerData*>> _whenAlerts;
 
diff --git a/Telegram/SourceFiles/window/notifications_manager_default.cpp b/Telegram/SourceFiles/window/notifications_manager_default.cpp
index 1912f3a9ce..75037fdc68 100644
--- a/Telegram/SourceFiles/window/notifications_manager_default.cpp
+++ b/Telegram/SourceFiles/window/notifications_manager_default.cpp
@@ -53,7 +53,9 @@ std::unique_ptr<Manager> Create(System *system) {
 	return std::make_unique<Manager>(system);
 }
 
-Manager::Manager(System *system) : Notifications::Manager(system) {
+Manager::Manager(System *system)
+: Notifications::Manager(system)
+, _inputCheckTimer([=] { checkLastInput(); }) {
 	subscribe(system->authSession()->downloader().taskFinished(), [this] {
 		for_const (auto &notification, _notifications) {
 			notification->updatePeerPhoto();
@@ -62,7 +64,6 @@ Manager::Manager(System *system) : Notifications::Manager(system) {
 	subscribe(system->settingsChanged(), [this](ChangeType change) {
 		settingsChanged(change);
 	});
-	_inputCheckTimer.setTimeoutHandler([this] { checkLastInput(); });
 }
 
 Manager::QueuedNotification::QueuedNotification(
@@ -144,7 +145,7 @@ void Manager::checkLastInput() {
 		}
 	}
 	if (waiting) {
-		_inputCheckTimer.start(300);
+		_inputCheckTimer.callOnce(300);
 	}
 }
 
@@ -494,15 +495,25 @@ void Background::paintEvent(QPaintEvent *e) {
 	p.fillRect(st::notifyBorderWidth, height() - st::notifyBorderWidth, width() - 2 * st::notifyBorderWidth, st::notifyBorderWidth, st::notifyBorder);
 }
 
-Notification::Notification(Manager *manager, History *history, PeerData *peer, PeerData *author, HistoryItem *msg, int forwardedCount, QPoint startPosition, int shift, Direction shiftDirection) : Widget(manager, startPosition, shift, shiftDirection)
+Notification::Notification(
+	Manager *manager,
+	History *history,
+	PeerData *peer,
+	PeerData *author,
+	HistoryItem *msg,
+	int forwardedCount,
+	QPoint startPosition,
+	int shift,
+	Direction shiftDirection)
+: Widget(manager, startPosition, shift, shiftDirection)
+#ifdef Q_OS_WIN
+, _started(GetTickCount())
+#endif // Q_OS_WIN
 , _history(history)
 , _peer(peer)
 , _author(author)
 , _item(msg)
 , _forwardedCount(forwardedCount)
-#ifdef Q_OS_WIN
-, _started(GetTickCount())
-#endif // Q_OS_WIN
 , _close(this, st::notifyClose)
 , _reply(this, langFactory(lng_notification_reply), st::defaultBoxButton) {
 	subscribe(Lang::Current().updated(), [this] { refreshLang(); });
diff --git a/Telegram/SourceFiles/window/notifications_manager_default.h b/Telegram/SourceFiles/window/notifications_manager_default.h
index d22defd93b..4c6c51aa6d 100644
--- a/Telegram/SourceFiles/window/notifications_manager_default.h
+++ b/Telegram/SourceFiles/window/notifications_manager_default.h
@@ -8,7 +8,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #pragma once
 
 #include "window/notifications_manager.h"
-#include "core/single_timer.h"
+#include "base/timer.h"
 
 namespace Ui {
 class IconButton;
@@ -79,7 +79,7 @@ private:
 	std::unique_ptr<HideAllButton> _hideAll;
 
 	bool _positionsOutdated = false;
-	SingleTimer _inputCheckTimer;
+	base::Timer _inputCheckTimer;
 
 	struct QueuedNotification {
 		QueuedNotification(not_null<HistoryItem*> item, int forwardedCount);
diff --git a/Telegram/SourceFiles/window/notifications_utilities.cpp b/Telegram/SourceFiles/window/notifications_utilities.cpp
index 18f9e61d01..24ae98b519 100644
--- a/Telegram/SourceFiles/window/notifications_utilities.cpp
+++ b/Telegram/SourceFiles/window/notifications_utilities.cpp
@@ -21,8 +21,9 @@ constexpr int kNotifyDeletePhotoAfterMs = 60000;
 
 } // namespace
 
-CachedUserpics::CachedUserpics(Type type) : _type(type) {
-	connect(&_clearTimer, SIGNAL(timeout()), this, SLOT(onClear()));
+CachedUserpics::CachedUserpics(Type type)
+: _type(type)
+, _clearTimer([=] { onClear(); }) {
 	QDir().mkpath(cWorkingDir() + qsl("tdata/temp"));
 }
 
@@ -87,7 +88,7 @@ void CachedUserpics::clearInMs(int ms) {
 			return;
 		}
 	}
-	_clearTimer.start(ms);
+	_clearTimer.callOnce(ms);
 }
 
 void CachedUserpics::onClear() {
diff --git a/Telegram/SourceFiles/window/notifications_utilities.h b/Telegram/SourceFiles/window/notifications_utilities.h
index 4ed6404ed3..a2be9338e3 100644
--- a/Telegram/SourceFiles/window/notifications_utilities.h
+++ b/Telegram/SourceFiles/window/notifications_utilities.h
@@ -8,7 +8,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #pragma once
 
 #include "window/notifications_manager.h"
-#include "core/single_timer.h"
+#include "base/timer.h"
 
 namespace Window {
 namespace Notifications {
@@ -42,7 +42,7 @@ private:
 	using Images = QMap<StorageKey, Image>;
 	Images _images;
 	bool _someSavedFlag = false;
-	SingleTimer _clearTimer;
+	base::Timer _clearTimer;
 
 };
 
diff --git a/Telegram/SourceFiles/window/themes/window_theme_warning.cpp b/Telegram/SourceFiles/window/themes/window_theme_warning.cpp
index 8aa89dd08d..610f8efa99 100644
--- a/Telegram/SourceFiles/window/themes/window_theme_warning.cpp
+++ b/Telegram/SourceFiles/window/themes/window_theme_warning.cpp
@@ -21,13 +21,14 @@ constexpr int kWaitBeforeRevertMs = 15999;
 
 } // namespace
 
-WarningWidget::WarningWidget(QWidget *parent) : TWidget(parent)
+WarningWidget::WarningWidget(QWidget *parent)
+: TWidget(parent)
+, _timer([=] { handleTimer(); })
 , _secondsLeft(kWaitBeforeRevertMs / 1000)
 , _keepChanges(this, langFactory(lng_theme_keep_changes), st::defaultBoxButton)
 , _revert(this, langFactory(lng_theme_revert), st::defaultBoxButton) {
 	_keepChanges->setClickedCallback([] { Window::Theme::KeepApplied(); });
 	_revert->setClickedCallback([] { Window::Theme::Revert(); });
-	_timer.setTimeoutHandler([this] { handleTimer(); });
 	updateText();
 }
 
@@ -52,7 +53,7 @@ void WarningWidget::paintEvent(QPaintEvent *e) {
 			_cache = QPixmap();
 			showChildren();
 			_started = getms(true);
-			_timer.start(100);
+			_timer.callOnce(100);
 		}
 		return;
 	}
@@ -100,7 +101,7 @@ void WarningWidget::setSecondsLeft(int secondsLeft) {
 			updateText();
 			update();
 		}
-		_timer.start(100);
+		_timer.callOnce(100);
 	}
 }
 
@@ -119,7 +120,7 @@ void WarningWidget::hideAnimated() {
 }
 
 void WarningWidget::startAnimation(bool hiding) {
-	_timer.stop();
+	_timer.cancel();
 	_hiding = hiding;
 	if (_cache.isNull()) {
 		showChildren();
diff --git a/Telegram/SourceFiles/window/themes/window_theme_warning.h b/Telegram/SourceFiles/window/themes/window_theme_warning.h
index 328460e0b9..165d40b19f 100644
--- a/Telegram/SourceFiles/window/themes/window_theme_warning.h
+++ b/Telegram/SourceFiles/window/themes/window_theme_warning.h
@@ -7,6 +7,8 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 */
 #pragma once
 
+#include "base/timer.h"
+
 namespace Ui {
 class RoundButton;
 } // namespace Ui
@@ -43,7 +45,7 @@ private:
 	QPixmap _cache;
 	QRect _inner, _outer;
 
-	SingleTimer _timer;
+	base::Timer _timer;
 	TimeMs _started = 0;
 	int _secondsLeft = 0;
 	QString _text;
diff --git a/Telegram/gyp/settings_win.gypi b/Telegram/gyp/settings_win.gypi
index ca308612eb..dff01287d3 100644
--- a/Telegram/gyp/settings_win.gypi
+++ b/Telegram/gyp/settings_win.gypi
@@ -30,6 +30,7 @@
             '/MP',     # Enable multi process build.
             '/EHsc',   # Catch C++ exceptions only, extern C functions never throw a C++ exception.
             '/w14834', # [[nodiscard]]
+            '/w15038', # wrong initialization order
           ],
           'TreatWChar_tAsBuiltInType': 'false',
         },
diff --git a/Telegram/gyp/telegram_sources.txt b/Telegram/gyp/telegram_sources.txt
index fa82c6e840..2a2d718b89 100644
--- a/Telegram/gyp/telegram_sources.txt
+++ b/Telegram/gyp/telegram_sources.txt
@@ -140,8 +140,6 @@
 <(src_loc)/core/mime_type.h
 <(src_loc)/core/shortcuts.cpp
 <(src_loc)/core/shortcuts.h
-<(src_loc)/core/single_timer.cpp
-<(src_loc)/core/single_timer.h
 <(src_loc)/core/update_checker.cpp
 <(src_loc)/core/update_checker.h
 <(src_loc)/core/utils.cpp