1 files changed, 116 insertions, 0 deletions
diff --git a/logic/resources/Resource.h b/logic/resources/Resource.h
new file mode 100644
index 00000000..d566b2a2
--- /dev/null
+++ b/logic/resources/Resource.h
@@ -0,0 +1,116 @@
+#pragma once
+
+#include <QString>
+#include <QMap>
+#include <QVariant>
+#include <functional>
+#include <memory>
+
+#include "ResourceObserver.h"
+
+class ResourceHandler;
+
+namespace Detail
+{
+template <typename T> struct Function : public Function<decltype(&T::operator())> {};
+template <typename Ret, typename Arg> struct Function<Ret(*)(Arg)> : public Function<Ret(Arg)> {};
+template <typename Ret, typename Arg> struct Function<Ret(Arg)>
+{
+	using ReturnType = Ret;
+	using Argument = Arg;
+};
+template <class C, typename Ret, typename Arg> struct Function<Ret(C::*)(Arg)> : public Function<Ret(Arg)> {};
+template <class C, typename Ret, typename Arg> struct Function<Ret(C::*)(Arg) const> : public Function<Ret(Arg)> {};
+template <typename F> struct Function<F&> : public Function<F> {};
+template <typename F> struct Function<F&&> : public Function<F> {};
+}
+
+/** Frontend class for resources
+ *
+ * Usage:
+ *	Resource::create("icon:noaccount")->applyTo(accountsAction);
+ *	Resource::create("web:http://asdf.com/image.png")->applyTo(imageLbl)->placeholder(Resource::create("icon:loading"));
+ *
+ * Memory management:
+ *	Resource caches ResourcePtrs using weak pointers, so while a resource is still existing
+ *	when a new resource is created the resources will be the same (including the same handler).
+ *
+ *	ResourceObservers keep a shared pointer to the resource, as does the Resource itself to it's
+ *	placeholder (if present). This means a resource stays valid while it's still used ("applied to" etc.)
+ *	by something. When nothing uses it anymore it gets deleted.
+ *
+ *	\note Always pass resource around using ResourcePtr! Copy and move constructors are disabled for a reason.
+ */
+class Resource : public std::enable_shared_from_this<Resource>
+{
+	explicit Resource(const QString &resource);
+	Resource(const Resource &) = delete;
+	Resource(Resource &&) = delete;
+public:
+	using Ptr = std::shared_ptr<Resource>;
+
+	~Resource();
+
+	/// The returned pointer needs to be stored until either Resource::then is called, or it is used as the argument to Resource::placeholder.
+	static Ptr create(const QString &resource);
+
+	/// This can e.g. be used to set a local icon as the placeholder while a slow (remote) icon is fetched
+	Ptr placeholder(Ptr other);
+
+	/// Use these functions to specify what should happen when e.g. the resource changes
+	Ptr applyTo(ResourceObserver *observer);
+	Ptr applyTo(QObject *target, const char *property = nullptr);
+	template<typename Func>
+	Ptr then(Func &&func)
+	{
+		using Arg = typename std::remove_cv<
+			typename std::remove_reference<typename Detail::Function<Func>::Argument>::type
+		>::type;
+		return applyTo(new FunctionResourceObserver<
+					   typename Detail::Function<Func>::ReturnType,
+					   Arg, Func
+					   >(std::forward<Func>(func)));
+	}
+
+	/// Retrieve the currently active resource. If it's type is different from T a conversion will be attempted.
+	template<typename T>
+	T getResource() const { return getResourceInternal(qMetaTypeId<T>()).template value<T>(); }
+	QVariant getResourceInternal(const int typeId) const;
+
+	template<typename T>
+	static void registerHandler(const QString &id)
+	{
+		m_handlers.insert(id, [](const QString &res) { return std::make_shared<T>(res); });
+	}
+	template<typename Func>
+	static void registerTransformer(Func &&func)
+	{
+		using Out = typename Detail::Function<Func>::ReturnType;
+		using In = typename std::remove_cv<typename std::remove_reference<typename Detail::Function<Func>::Argument>::type>::type;
+		static_assert(!std::is_same<Out, In>::value, "It does not make sense to transform a value to itself");
+		m_transfomers.insert(qMakePair(qMetaTypeId<In>(), qMetaTypeId<Out>()), [func](const QVariant &in)
+		{
+			return QVariant::fromValue<Out>(func(in.value<In>()));
+		});
+	}
+
+private:
+	friend class ResourceHandler;
+	void reportResult();
+	void reportFailure(const QString &reason);
+	void reportProgress(const int progress);
+
+	friend class ResourceObserver;
+	void notifyObserverDeleted(ResourceObserver *observer);
+
+private:
+	QList<ResourceObserver *> m_observers;
+	std::shared_ptr<ResourceHandler> m_handler = nullptr;
+	Ptr m_placeholder = nullptr;
+
+	// a list of resource handler factories, registered using registerHandler
+	static QMap<QString, std::function<std::shared_ptr<ResourceHandler>(const QString &)>> m_handlers;
+	// a list of resource transformers, registered using registerTransformer
+	static QMap<QPair<int, int>, std::function<QVariant(QVariant)>> m_transfomers;
+	static QMap<QString, std::weak_ptr<Resource>> m_resources;
+};