Add a generic lua function binding, alongside properties

src/lua/bridge.cpp

@@ -110,16 +110,32 @@ static auto new_property_module(lua_State* state) -> int {
   return 1;
 }
 
+template <class... Ts>
+inline constexpr bool always_false_v = false;
+
 auto Bridge::AddPropertyModule(
     const std::string& name,
-    std::vector<std::pair<std::string, std::shared_ptr<Property>>> props)
-    -> void {
+    std::vector<std::pair<std::string,
+                          std::variant<LuaFunction, std::shared_ptr<Property>>>>
+        props) -> void {
   // Create the module (or retrieve it if one with this name already exists)
   luaL_requiref(&state_, name.c_str(), new_property_module, true);
 
   for (const auto& prop : props) {
     lua_pushstring(&state_, prop.first.c_str());
-    bindings_.Register(&state_, prop.second.get());
+    std::visit(
+        [&](auto&& arg) {
+          using T = std::decay_t<decltype(arg)>;
+          if constexpr (std::is_same_v<T, LuaFunction>) {
+            bindings_.Register(&state_, arg);
+          } else if constexpr (std::is_same_v<T, std::shared_ptr<Property>>) {
+            bindings_.Register(&state_, arg.get());
+          } else {
+            static_assert(always_false_v<T>, "missing case");
+          }
+        },
+        prop.second);
+
     lua_settable(&state_, -3);  // metatable.propname = property
   }
 

src/lua/include/bridge.hpp

@@ -24,7 +24,10 @@ class Bridge {
 
   auto AddPropertyModule(
       const std::string&,
-      std::vector<std::pair<std::string, std::shared_ptr<Property>>>) -> void;
+      std::vector<
+          std::pair<std::string,
+                    std::variant<LuaFunction, std::shared_ptr<Property>>>>)
+      -> void;
 
   system_fsm::ServiceLocator& services() { return services_; }
   PropertyBindings& bindings() { return bindings_; }

src/lua/include/property.hpp

@@ -16,6 +16,7 @@
 namespace lua {
 
 using LuaValue = std::variant<std::monostate, int, float, bool, std::string>;
+using LuaFunction = std::function<int(lua_State*)>;
 
 class Property {
  public:
@@ -42,6 +43,12 @@ class PropertyBindings {
   PropertyBindings(lua_State&);
 
   auto Register(lua_State*, Property*) -> void;
+  auto Register(lua_State*, LuaFunction) -> void;
+
+  auto GetFunction(size_t i) -> const LuaFunction&;
+
+ private:
+  std::vector<LuaFunction> functions_;
 };
 
 }  // namespace lua

src/lua/property.cpp

@@ -5,10 +5,12 @@
  */
 
 #include "property.hpp"
+#include <sys/_stdint.h>
 
 #include <memory>
 #include <string>
 
+#include "lauxlib.h"
 #include "lua.h"
 #include "lua.hpp"
 #include "lvgl.h"
@@ -16,11 +18,13 @@
 
 namespace lua {
 
-static const char kMetatableName[] = "property";
+static const char kPropertyMetatable[] = "property";
+static const char kFunctionMetatable[] = "function";
 static const char kBindingsTable[] = "bindings";
+static const char kBinderKey[] = "binder";
 
 static auto check_property(lua_State* state) -> Property* {
-  void* data = luaL_checkudata(state, 1, kMetatableName);
+  void* data = luaL_checkudata(state, 1, kPropertyMetatable);
   luaL_argcheck(state, data != NULL, 1, "`property` expected");
   return *reinterpret_cast<Property**>(data);
 }
@@ -71,9 +75,25 @@ static const struct luaL_Reg kPropertyBindingFuncs[] = {{"get", property_get},
                                                         {"bind", property_bind},
                                                         {NULL, NULL}};
 
+static auto generic_function_cb(lua_State* state) -> int {
+  lua_pushstring(state, kBinderKey);
+  lua_gettable(state, LUA_REGISTRYINDEX);
+  PropertyBindings* binder =
+      reinterpret_cast<PropertyBindings*>(lua_touserdata(state, -1));
+
+  size_t* index =
+      reinterpret_cast<size_t*>(luaL_checkudata(state, 1, kFunctionMetatable));
+  const LuaFunction& fn = binder->GetFunction(*index);
+  return std::invoke(fn, state);
+}
+
 PropertyBindings::PropertyBindings(lua_State& s) {
+  lua_pushstring(&s, kBinderKey);
+  lua_pushlightuserdata(&s, this);
+  lua_settable(&s, LUA_REGISTRYINDEX);
+
   // Create the metatable responsible for the Property API.
-  luaL_newmetatable(&s, kMetatableName);
+  luaL_newmetatable(&s, kPropertyMetatable);
 
   lua_pushliteral(&s, "__index");
   lua_pushvalue(&s, -2);
@@ -94,16 +114,38 @@ PropertyBindings::PropertyBindings(lua_State& s) {
   lua_setmetatable(&s, -2);  // setmetatable(bindings, meta)
 
   lua_settable(&s, LUA_REGISTRYINDEX);  // REGISTRY[kBindingsTable] = bindings
+
+  // Create the metatable for C++ functions.
+  luaL_newmetatable(&s, kFunctionMetatable);
+
+  lua_pushliteral(&s, "__call");
+  lua_pushcfunction(&s, generic_function_cb);
+  lua_settable(&s, -3);  // metatable.__call = metatable
+
+  lua_pop(&s, 1);  // Clean up the function metatable
 }
 
 auto PropertyBindings::Register(lua_State* s, Property* prop) -> void {
   Property** data =
-      reinterpret_cast<Property**>(lua_newuserdata(s, sizeof(Property*)));
+      reinterpret_cast<Property**>(lua_newuserdata(s, sizeof(uintptr_t)));
   *data = prop;
 
-  luaL_setmetatable(s, kMetatableName);
+  luaL_setmetatable(s, kPropertyMetatable);
 }
 
+auto PropertyBindings::Register(lua_State* s, LuaFunction fn) -> void {
+  size_t* index = reinterpret_cast<size_t*>(lua_newuserdata(s, sizeof(size_t)));
+  *index = functions_.size();
+  functions_.push_back(fn);
+
+  luaL_setmetatable(s, kFunctionMetatable);
+}
+
+auto PropertyBindings::GetFunction(size_t i) -> const LuaFunction& {
+  assert(i < functions_.size());
+  return functions_[i];
+};
+
 template <class... Ts>
 inline constexpr bool always_false_v = false;