[traffxml] Add traff_storage

Signed-off-by: mvglasow <michael -at- vonglasow.com>

traffxml/traff_storage.hpp

@@ -0,0 +1,77 @@
+#pragma once
+
+#include <mutex>
+
+#include <pugixml.hpp>
+
+/*
+ * TODO combine this header and its CPP file with editor/editor_storage.hpp and its CPP counterpart,
+ * give it an appropriate namespace and place it where both editor and traffic can use it.
+ * `traff_storage` is essentially copied from `editor_storage` with just a few modifications:
+ *  - namespace
+ *  - instead of relying on a hardcoded file name, `LocalStorage` is initialized with a file name
+ *  - log output, variable names and comments changed to be use case neutral (no API changes)
+ *  - refactoring: no global `using namespace` (no API changes)
+ * Apart from the first two points, this file can serve as a drop-in replacement for `editor_storage`.
+ * Traffic uses only `LocalStorage`, the rest has been kept to ease migration to a unified storage
+ * component.
+ */
+
+namespace traffxml
+{
+/**
+ * @brief Storage interface for XML data.
+ */
+class StorageBase
+{
+public:
+  virtual ~StorageBase() = default;
+
+  virtual bool Save(pugi::xml_document const & doc) = 0;
+  virtual bool Load(pugi::xml_document & doc) = 0;
+  virtual bool Reset() = 0;
+};
+
+/**
+ * @brief Class which saves/loads XML data to/from local file.
+ * @note this class IS thread-safe.
+ */
+class LocalStorage : public StorageBase
+{
+public:
+  /**
+   * @brief Constructs a `LocalStorage` instance.
+   * @param fileName The file name and path where the file in question will be persisted. It is
+   * interpreted relative to the platform-specific path; absolute paths are not supported as some
+   * platforms restrict applications’ access to files outside their designated path.
+   */
+  LocalStorage(std::string & fileName)
+    : m_fileName(fileName)
+  {}
+
+  // StorageBase overrides:
+  bool Save(pugi::xml_document const & doc) override;
+  bool Load(pugi::xml_document & doc) override;
+  bool Reset() override;
+
+private:
+  std::string m_fileName;
+  std::mutex m_mutex;
+};
+
+/**
+ * @brief Class which saves/loads data to/from xml_document class instance.
+ * @note this class is NOT thread-safe.
+ */
+class InMemoryStorage : public StorageBase
+{
+public:
+  // StorageBase overrides:
+  bool Save(pugi::xml_document const & doc) override;
+  bool Load(pugi::xml_document & doc) override;
+  bool Reset() override;
+
+private:
+  pugi::xml_document m_doc;
+};
+}  // namespace traffxml