singleton: add reloadable Singleton type

src/core/singleton.cpp

@@ -0,0 +1,64 @@
+#include "singleton.hpp"
+
+#include <qlogging.h>
+#include <qmap.h>
+#include <qobject.h>
+#include <qqmlcontext.h>
+#include <qqmlengine.h>
+#include <qurl.h>
+
+#include "reload.hpp"
+
+void Singleton::componentComplete() {
+	auto* context = QQmlEngine::contextForObject(this);
+
+	if (context == nullptr) {
+		qWarning() << "not registering singleton not created in the qml context:" << this;
+		return;
+	}
+
+	auto url = context->baseUrl();
+
+	if (this->parent() != nullptr || context->contextObject() != this) {
+		qWarning() << "tried to register singleton" << this
+		           << "which is not the root component of its file" << url;
+		return;
+	}
+
+	SingletonRegistry::instance()->install(url, this);
+	this->ReloadPropagator::componentComplete();
+}
+
+SingletonRegistry::~SingletonRegistry() {
+	delete this->previousRegistry;
+	delete this->currentRegistry;
+}
+
+void SingletonRegistry::install(const QUrl& url, Singleton* singleton) {
+	QObject* old = nullptr;
+
+	if (this->previousRegistry != nullptr) {
+		old = this->previousRegistry->value(url);
+	}
+
+	if (this->currentRegistry == nullptr) {
+		this->currentRegistry = new QMap<QUrl, QObject*>();
+	}
+
+	this->currentRegistry->insert(url, singleton);
+	singleton->onReload(old);
+}
+
+void SingletonRegistry::flip() {
+	delete this->previousRegistry;
+	this->previousRegistry = this->currentRegistry;
+	this->currentRegistry = nullptr;
+}
+
+SingletonRegistry* SingletonRegistry::instance() {
+	static SingletonRegistry* instance = nullptr; // NOLINT
+	if (instance == nullptr) {
+		instance = new SingletonRegistry();
+	}
+	return instance;
+}