实现应用列表和SpkResource

SpkResource现有已知问题：首次使用不会完全进行所有任务。

inc/spkresource.h

@@ -2,13 +2,98 @@
 #pragma once
 
 #include <QObject>
+#include <QQueue>
+#include <QSemaphore>
+#include <QMap>
+#include <QNetworkReply>
+#include <QVariant>
+
+struct ResourceResult;
+class SpkResourceContext;
+class SpkPageBase;
 
 class SpkResource : public QObject
+{
+  Q_OBJECT
+  public:
+    enum class ResourceType { HomeImage, AppIcon, TagIcon, AppScreenshot, };
+    enum class ResourceStatus
     {
-    Q_OBJECT
-      public:
-        SpkResource(QObject *parent = nullptr);
-
-      private:
-
+      Ready, ///< The resource is ready to be read now and the file link is included
+      Deferred, ///< The resource is not in cache or outdated, and is being downloaded
+      Failed, ///< The requested resource can not be downloaded and thus can not be loaded.
     };
+
+  private:
+    struct ResourceTask
+    {
+      QString pkgName, path;
+      ResourceType type;
+      QVariant info;
+      int id;
+    };
+
+    static const QMap<ResourceType, QString> ResourceName;
+
+  public:
+    SpkResource(QObject *parent = nullptr);
+    ResourceResult
+    RequestResource(const int aId, const QString &aPkgName, ResourceType aType, const QString &aPath,
+                    const QVariant &aInfo = 0);
+    void PurgeCachedResource(const QString &aPkgName, SpkResource::ResourceType aType,
+                             const QVariant &aInfo);
+
+    inline QString GetCachePath(const ResourceTask &task);
+
+    /**
+     * @brief When the resource context was changed, the new context needs to acquire the resource
+     *        manager, so the resource manager can download resource for the new context.
+     *
+     *        A resource context, in Spark Store, is likely to be a "page" of the UI. AppList is
+     *        a page, Homepage is a page, AppDetails is a page. But each category is not a separated
+     *        context; they're all from AppList page.
+     * @param dest Pass a SpkResourceContext as the resource acquisition destination. Signals will
+     *             be connected in this function internally. When a resource was downloaded, this
+     *             object will be notified.
+     * @param clearQueue determines if the awaiting tasks needs to be cleared.
+     * @param stopOngoing determines if ongoing tasks needs to be terminated.
+     */
+    void Acquire(SpkPageBase *dest, bool stopOngoing, bool clearQueue = true);
+
+  public:
+    static SpkResource* Instance;
+    const int mMaximumConcurrent; ///< Maximum number of concurrent resource downloads
+    const QString mCacheDirectory;///< Where caches were stored
+
+  private slots:
+    void ResourceDownloaded();
+    void TryBeginAwaitingTasks();
+
+  private:
+    ResourceResult LocateCachedResource(const ResourceTask &task);
+
+  signals:
+    void AcquisitionFinish(int id, ResourceResult result);
+
+  private:
+    // Operations to mAwaitingRequests and mWorkingRequests must be all made synchronously.
+    // When connecting signal/slot pairs regarding operations to them, use QueuedConnection.
+    QQueue<ResourceTask> mAwaitingRequests;
+    QSemaphore *mRequestSemaphore;
+    QMap<QNetworkReply*, int> mWorkingRequests;
+};
+
+
+struct ResourceResult
+{
+  SpkResource::ResourceStatus status;
+  QByteArray data;
+};
+
+Q_DECLARE_METATYPE(ResourceResult);
+
+/**
+ * @brief SpkResourceContext is meant to be used by connecting signals from it. An object inheriting
+ *        it would be theoretically a resource context. A resource context can acquire a SpkResource
+ *        management object for downloading resources. More details at SpkResource::Acquire.
+ */