Structure tree parsing

PdfForQtLib/sources/pdfobjectutils.h

@@ -43,6 +43,54 @@ private:
     PDFObjectUtils() = delete;
 };
 
+/// Storage, which can mark objects (for example, when we want to mark already visited objects
+/// during parsing some complex structure, such as tree)
+class PDFMarkedObjectsContext
+{
+public:
+    inline explicit PDFMarkedObjectsContext() = default;
+
+    inline bool isMarked(PDFObjectReference reference) const { return m_markedReferences.count(reference); }
+    inline void mark(PDFObjectReference reference) { m_markedReferences.insert(reference); }
+    inline void unmark(PDFObjectReference reference) { m_markedReferences.erase(reference); }
+
+private:
+    std::set<PDFObjectReference> m_markedReferences;
+};
+
+/// Class for marking/unmarking objects functioning as guard. If not already marked, then
+/// during existence of this guard, object is marked and then it is unmarked. If it is
+/// already marked, then nothing happens and locked flag is set to false.
+class PDFMarkedObjectsLock
+{
+public:
+    explicit inline PDFMarkedObjectsLock(PDFMarkedObjectsContext* context, PDFObjectReference reference) :
+        m_context(context),
+        m_reference(reference),
+        m_locked(!context->isMarked(reference))
+    {
+        if (m_locked)
+        {
+            context->mark(reference);
+        }
+    }
+
+    inline ~PDFMarkedObjectsLock()
+    {
+        if (m_locked)
+        {
+            m_context->unmark(m_reference);
+        }
+    }
+
+    explicit operator bool() const { return m_locked; }
+
+private:
+    PDFMarkedObjectsContext* m_context;
+    PDFObjectReference m_reference;
+    bool m_locked;
+};
+
 } // namespace pdf
 
 #endif // PDFOBJECTUTILS_H