1 files changed, 132 insertions, 0 deletions
diff --git a/api/logic/resources/Resource.h b/api/logic/resources/Resource.h
new file mode 100644
index 00000000..63e97b88
--- /dev/null
+++ b/api/logic/resources/Resource.h
@@ -0,0 +1,132 @@
+#pragma once
+
+#include <QString>
+#include <QMap>
+#include <QVariant>
+#include <functional>
+#include <memory>
+
+#include "ResourceObserver.h"
+#include "TypeMagic.h"
+
+#include "multimc_logic_export.h"
+
+class ResourceHandler;
+
+/** 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 Resource::Ptr! Copy and move constructors are disabled for a reason.
+ */
+class MULTIMC_LOGIC_EXPORT Resource : public std::enable_shared_from_this<Resource>
+{
+	// only allow creation from Resource::create and disallow passing around non-pointers
+	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::applyTo or Resource::then is called, or it is passed as
+	/// a placeholder to Resource::create itself.
+	static Ptr create(const QString &resource, Ptr placeholder = nullptr);
+
+	/// 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)
+	{
+		// Arg will be the functions argument with references and cv-qualifiers (const, volatile) removed
+		using Arg = TypeMagic::CleanType<typename TypeMagic::Function<Func>::Argument>;
+		// Ret will be the functions return type
+		using Ret = typename TypeMagic::Function<Func>::ReturnType;
+
+		// FunctionResourceObserver<ReturnType, ArgumentType, FunctionSignature>
+		return applyTo(new FunctionResourceObserver<Ret, 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>(); }
+
+	/// @internal Used by ResourceObserver and ResourceProxyModel
+	QVariant getResourceInternal(const int typeId) const;
+
+	/** Register a new ResourceHandler. T needs to inherit from ResourceHandler
+	 * Usage: Resource::registerHandler<MyResourceHandler>("myid");
+	 */
+	template<typename T>
+	static void registerHandler(const QString &id)
+	{
+		m_handlers.insert(id, [](const QString &res) { return std::make_shared<T>(res); });
+	}
+	/** Register a new resource transformer
+	 * Resource transformers are functions that are responsible for converting between different types,
+	 * for example converting from a QByteArray to a QPixmap. They are registered "externally" because not
+	 * all types might be available in this library, for example gui types like QPixmap.
+	 *
+	 * Usage: Resource::registerTransformer([](const InputType &type) { return OutputType(type); });
+	 *   This assumes that OutputType has a constructor that takes InputType as an argument. More
+	 *   complicated transformers can of course also be registered.
+	 *
+	 * When a ResourceObserver requests a type that's different from the actual resource type, a matching
+	 * transformer will be looked up from the list of transformers.
+	 * @note Only one-stage transforms will be performed (you can't registerTransformers for QString => int
+	 *       and int => float and expect QString to automatically be transformed into a float.
+	 */
+	template<typename Func>
+	static void registerTransformer(Func &&func)
+	{
+		using Out = typename TypeMagic::Function<Func>::ReturnType;
+		using In = TypeMagic::CleanType<typename TypeMagic::Function<Func>::Argument>;
+		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: // half private, implementation details
+	friend class ResourceHandler;
+	// the following three functions are called by ResourceHandlers
+	/** Notifies the observers. They will call Resource::getResourceInternal which will call ResourceHandler::result
+	 * or delegate to it's placeholder.
+	 */
+	void reportResult();
+	void reportFailure(const QString &reason);
+	void reportProgress(const int progress);
+
+	friend class ResourceObserver;
+	/// Removes observer from the list of observers so that we don't attempt to notify something that doesn't exist
+	void notifyObserverDeleted(ResourceObserver *observer);
+
+private: // truly private
+	QList<ResourceObserver *> m_observers;
+	std::shared_ptr<ResourceHandler> m_handler = nullptr;
+	Ptr m_placeholder = nullptr;
+	const QString m_resource;
+
+	static QString storageIdentifier(const QString &id, Ptr placeholder = nullptr);
+	QString storageIdentifier() const;
+
+	// 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;
+	// a list of resources so that we can reuse them
+	static QMap<QString, std::weak_ptr<Resource>> m_resources;
+};