add StateMachine

include/td/common/StateMachine.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include <memory>
+
+namespace td {
+
+template <typename TDerived, typename TReturn, typename... TArgs>
+class StateMachine {
+  public:
+	class State {
+	  public:
+		State(TDerived& a_StateMachine) : m_StateMachine(a_StateMachine) {}
+		virtual ~State() {}
+
+		virtual TReturn Update(TArgs... args) = 0;
+
+	  protected:
+		TDerived& m_StateMachine;
+	};
+
+	StateMachine() {}
+	virtual ~StateMachine() {}
+
+	TReturn Update(TArgs... args) {
+		assert(m_State);
+		return m_State->Update(args...);
+	}
+
+	template <typename T, typename... Args>
+	void ChangeState(Args&&... args) {
+		m_State = std::make_unique<T>(static_cast<TDerived&>(*this), args...);
+	}
+
+  private:
+	std::unique_ptr<State> m_State;
+};
+
+
+}  // namespace td