First implementation of graph vehicles

vehicle/graph/graph_lua.h

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+/*
+This Source Code Form is subject to the
+terms of the Mozilla Public License, v.
+2.0. If a copy of the MPL was not
+distributed with this file, You can
+obtain one at
+http://mozilla.org/MPL/2.0/.
+*/
+
+#pragma once
+
+#include "vehicle/graph/graph_types.h"
+
+#include <cstdint>
+#include <functional>
+#include <string>
+#include <vector>
+
+struct lua_State;
+
+// lua function blocks of the vehicle graph. each vehicle gets a lua state of its own, separate from the scenery's
+// one, and each block an environment of its own within it. scripts run in lua 5.1 (luajit) with a restricted set of
+// libraries: no files, operating system, modules, ffi or bytecode loading. the jit compiler is turned off for these
+// states, so the instruction budget which stops endless loops works reliably
+namespace vgraph
+{
+
+// messages of the lua blocks (print, errors). the simulator directs them to its log, the command line tools to the console
+using log_sink = std::function<void(std::string const &)>;
+void set_log_sink(log_sink Sink);
+void log_message(std::string const &Message);
+
+// whether this build of the simulator can run lua blocks (WITH_LUA)
+bool lua_available();
+
+// interface of a lua block, read from its script:
+// block "name" { inputs = { a = "bool" }, outputs = { q = "float" }, params = { k = 1.0 }, state = { ... }, rate = 20,
+//                update = function(self, i, o, dt) ... end }
+struct lua_block_definition
+{
+	std::string name;
+	std::vector<port_def> ports; // inputs then outputs, each sorted by key so the order doesn't depend on the lua hash
+	std::vector<param_def> params; // numeric parameters of the script as "lua.<key>", with the script's values as defaults
+	double rate{0.0}; // updates per second; 0 updates the block in every step
+};
+
+// runs the script in a temporary state and reads the block interface. returns false with the reason on failure
+bool parse_lua_block(std::string const &Script, std::string const &Chunkname, lua_block_definition &Definition, std::string &Error);
+
+// lua state shared by the lua blocks of one vehicle
+class lua_host
+{
+public:
+	lua_host();
+	~lua_host();
+	lua_host(lua_host const &) = delete;
+	lua_host &operator=(lua_host const &) = delete;
+
+	lua_State *state() const
+	{
+		return m_state;
+	}
+	// runs the script of a block in a new environment and returns the registry reference of the block definition table,
+	// or a negative value with the reason on failure. the environment's random generator is seeded from the node id
+	int load_block(std::string const &Script, std::string const &Nodeid, std::string &Error);
+	// calls the function placed on the stack below its arguments, within the instruction budget. returns false with the reason on failure
+	bool call(int Arguments, std::string &Error);
+	void release(int Reference);
+
+private:
+	lua_State *m_state{nullptr};
+};
+
+// random generator used by math.random of the lua blocks; the external editor uses the same one, so previews match
+struct block_random
+{
+	std::uint64_t state;
+
+	explicit block_random(std::uint64_t Seed);
+	double next(); // [0, 1)
+	static std::uint64_t seed_from(std::string const &Text);
+};
+
+} // namespace vgraph