Move variable files to to variables folder

lib/variables/variable-string.hpp

@@ -0,0 +1,42 @@
+#pragma once
+#include "variable.hpp"
+
+#include <string>
+#include <obs.hpp>
+
+namespace advss {
+
+// Helper class which automatically resolves variables contained in strings
+// when reading its value as a std::string
+
+class StringVariable {
+public:
+	EXPORT StringVariable() : _value(""){};
+	EXPORT StringVariable(std::string str) : _value(std::move(str)){};
+	EXPORT StringVariable(const char *str) : _value(str){};
+	EXPORT operator std::string() const;
+	EXPORT operator QVariant() const;
+	EXPORT void operator=(std::string);
+	EXPORT void operator=(const char *value);
+	EXPORT const char *c_str();
+	EXPORT const char *c_str() const;
+	EXPORT bool empty() const;
+
+	EXPORT const std::string &UnresolvedValue() const { return _value; }
+
+	EXPORT void Load(obs_data_t *obj, const char *name);
+	EXPORT void Save(obs_data_t *obj, const char *name) const;
+
+private:
+	void Resolve() const;
+
+	std::string _value = "";
+	mutable std::string _resolvedValue = "";
+	mutable std::chrono::high_resolution_clock::time_point _lastResolve{};
+};
+
+std::string SubstitueVariables(std::string str);
+
+} // namespace advss
+
+Q_DECLARE_METATYPE(advss::StringVariable);