Set up basic deterministic lockstep

src/game_server/NetworkProtocol.h

@@ -1,15 +1,77 @@
 #pragma once
 
 #include "../external/nlohmann/json.hpp"
+#include <Eigen/Dense>
+#include <cstdint>
+#include <map>
 #include <string>
+#include <vector>
 
 namespace FRG {
 
-inline constexpr int kGameProtocolVersion = 1;
+inline constexpr int kGameProtocolVersion = 2;
+inline constexpr std::int64_t kSimulationTickMs = 100;
+inline constexpr std::uint32_t kDefaultInputDelayTicks = 2;
 
-std::string makeStateMessage(const nlohmann::json& state);
-bool parseStateMessage(
-	const std::string& message, nlohmann::json& state,
-	std::string& error);
+struct InitialStateMessage {
+	nlohmann::json state;
+	std::string assignedPlayerId;
+	std::uint64_t snapshotTick = 0;
+	std::int64_t tickMs = kSimulationTickMs;
+	std::uint32_t inputDelayTicks = kDefaultInputDelayTicks;
+	std::string compatibilityFingerprint;
+};
+
+struct DestinationInputMessage {
+	std::uint64_t clientSequence = 0;
+	Eigen::Vector3f target = Eigen::Vector3f::Zero();
+};
+
+struct ScheduledDestinationCommand {
+	std::uint64_t commandSequence = 0;
+	std::string playerId;
+	Eigen::Vector3f target = Eigen::Vector3f::Zero();
+};
+
+struct TickMessage {
+	std::uint64_t tickId = 0;
+	std::vector<ScheduledDestinationCommand> commands;
+	std::string stateHash;
+};
+
+class LockstepTimeline {
+public:
+	explicit LockstepTimeline(
+		std::uint32_t inputDelayTicks = kDefaultInputDelayTicks)
+		: inputDelayTicks_(inputDelayTicks) {}
+
+	std::uint64_t currentTick() const { return currentTick_; }
+	std::uint64_t schedule(
+		const std::string& playerId, const Eigen::Vector3f& target);
+	TickMessage advance();
+
+private:
+	std::uint32_t inputDelayTicks_;
+	std::uint64_t currentTick_ = 0;
+	std::uint64_t nextCommandSequence_ = 1;
+	std::map<std::uint64_t, std::vector<ScheduledDestinationCommand>> pending_;
+};
+
+std::string makeInitialStateMessage(const InitialStateMessage& message);
+bool parseInitialStateMessage(
+	const std::string& text, InitialStateMessage& message, std::string& error);
+std::string makeDestinationInputMessage(const DestinationInputMessage& message);
+bool parseDestinationInputMessage(
+	const std::string& text, DestinationInputMessage& message, std::string& error);
+std::string makeTickMessage(const TickMessage& message);
+bool parseTickMessage(
+	const std::string& text, TickMessage& message, std::string& error);
+std::string makeErrorMessage(const std::string& code, const std::string& detail);
+bool parseErrorMessage(
+	const std::string& text, std::string& code, std::string& detail);
+
+// Stable for the same executable/content build. Persistence-only wall-clock
+// fields are removed before hashing.
+std::string canonicalStateHash(nlohmann::json state);
 
 } // namespace FRG