Add ModMetadata API (#5131)

* mod can create a ModMetadata object where store its values and retrieve it.
* Modmetadata object can only be fetched at mod loading
* Save when modified using same time as map interval or at server stop
* add helper function to get mod storage path
* ModMetadata has exactly same calls than all every other Metadata

src/mods.h

@@ -28,6 +28,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include <map>
 #include <json/json.h>
 #include "config.h"
+#include "metadata.h"
 
 #define MODNAME_ALLOWED_CHARS "abcdefghijklmnopqrstuvwxyz0123456789_"
 
@@ -205,4 +206,24 @@ struct ModStoreModDetails {
 	bool valid;
 };
 
+class ModMetadata: public Metadata
+{
+public:
+	ModMetadata(const std::string &mod_name);
+	~ModMetadata() {}
+
+	virtual void clear();
+
+	bool save(const std::string &root_path);
+	bool load(const std::string &root_path);
+
+	bool isModified() const { return m_modified; }
+	const std::string &getModName() const { return m_mod_name; }
+
+	virtual bool setString(const std::string &name, const std::string &var);
+private:
+	std::string m_mod_name;
+	bool m_modified;
+};
+
 #endif