feat(app): add tick info/result and system diagnosis

modules/app/private/application.cpp

@@ -9,10 +9,16 @@ void Application::game_loop()
 	{
 		for (auto &system : m_systems)
 		{
-			if (system->tick())
-			{
-				return;
+			const auto &last_tick = system->get_last_tick_result();
+			const auto now = std::chrono::steady_clock::now();
+
+			system->tick(
+			    TickInfo {
+			        .delta_time = now - last_tick.end_time,
+			        .budget = std::chrono::milliseconds { 10 },
+			        .start_time = now,
 			    }
+			);
 		}
 
 		for (auto &system : m_systems_to_be_registered)

modules/app/public/system.hpp

@@ -1,7 +1,89 @@
 #pragma once
 
+#include <chrono>
+
 namespace lt::app {
 
+/** Information required to tick a system.
+ * @note May be used across an entire application-frame (consisting of multiple systems ticking)
+ */
+struct TickInfo
+{
+	using Timepoint_T = std::chrono::time_point<std::chrono::steady_clock>;
+
+	using Duration_T = std::chrono::duration<double>;
+
+	/** Duration since previous tick's end_time to current tick's start_time. */
+	Duration_T delta_time {};
+
+	/** Maximum duration the system is expected to finish ticking in.
+	 *
+	 * if end_time - start_time > budget -> the system exceeded its ticking budget.
+	 * else end_time - start_time < budget -> the system ticked properly.
+	 *
+	 * In other words, end_time is expected to be less than start_time + budget.
+	 */
+	Duration_T budget {};
+
+	/** Exact time which ticking started. */
+	Timepoint_T start_time;
+};
+
+/** Information about how a system's tick performed */
+struct TickResult
+{
+	using Timepoint_T = std::chrono::time_point<std::chrono::steady_clock>;
+
+	using Duration_T = std::chrono::duration<double>;
+
+	/** The info supplied to the system for ticking. */
+	TickInfo info;
+
+	/** Equivalent to end_time - info.start_time. */
+	Duration_T duration {};
+
+	/** Exact time which ticking ended. */
+	Timepoint_T end_time;
+};
+
+
+struct SystemDiagnosis
+{
+	enum class Severity : uint8_t
+	{
+		verbose,
+		info,
+		warning,
+		error,
+		fatal,
+	};
+
+	std::string message;
+
+	std::string code;
+
+	Severity severity;
+};
+
+class SystemStats
+{
+public:
+	void push_diagnosis(SystemDiagnosis &&diagnosis)
+	{
+		auto diag = m_diagnosis.emplace_back(std::move(diagnosis));
+
+		log_dbg("message: {}", diag.message);
+	}
+
+	[[nodiscard]] auto empty_diagnosis() const -> bool
+	{
+		return m_diagnosis.empty();
+	}
+
+private:
+	std::vector<SystemDiagnosis> m_diagnosis;
+};
+
 class ISystem
 {
 public:
@@ -21,7 +103,9 @@ public:
 
 	virtual void on_unregister() = 0;
 
-	virtual auto tick() -> bool = 0;
+	virtual void tick(TickInfo tick) = 0;
+
+	[[nodiscard]] virtual auto get_last_tick_result() const -> const TickResult & = 0;
 };
 
 } // namespace lt::app