Use a full user data object for MapObject references

Based on a templated helper class, MapObject references in Lua scripts are now
full user data objects. Using the '__index' member of their metatable, a
library is associated with it so that member functions can be called directly
on the object.

Reviewed-by: Yohann Ferreira
Reviewed-by: Erik Schilling

4 files changed, 94 insertions, 53 deletions

diff --git a/example/serverdata/scripts/npcs/merchant.lua b/example/serverdata/scripts/npcs/merchant.lua
index 23035b11..c3bd36a0 100644
--- a/example/serverdata/scripts/npcs/merchant.lua
+++ b/example/serverdata/scripts/npcs/merchant.lua
@@ -48,6 +48,7 @@ function Merchant(npc, ch, buy_sell_table)
   else
       table.insert (choice_table, "Can you make me a price for what I have?")
   end
+  table.insert (choice_table, "Tell me about the objects on this map")
   table.insert (choice_table, "Nevermind...")
 
   local v = do_choice(npc, ch, choice_table)
@@ -94,6 +95,15 @@ function Merchant(npc, ch, buy_sell_table)
         end
     end
 
+  elseif v == 3 then
+
+    local objects = mana.map_get_objects()
+    do_message(npc, ch, "There are " .. #objects .. " objects on this map, their names are:")
+    for i=1,#objects do
+        do_message(npc, ch, tostring(i) .. ": " .. objects[i]:name())
+    end
+
   end
+
   do_message(npc, ch, "See you later!")
 end
diff --git a/src/scripting/lua.cpp b/src/scripting/lua.cpp
index c7053b3c..63149792 100644
--- a/src/scripting/lua.cpp
+++ b/src/scripting/lua.cpp
@@ -2500,31 +2500,17 @@ static int map_get_objects(lua_State *s)
 static int map_object_get_property(lua_State *s)
 {
     const char *key = luaL_checkstring(s, 2);
-    if (!lua_islightuserdata(s, 1))
-    {
-        raiseScriptError(s, "map_object_get_property called with invalid"
-                            "object handle");
-        return 0;
-    }
-    MapObject *obj = static_cast<MapObject *>(lua_touserdata(s, 1));
-    if (obj)
+    MapObject *obj = LuaMapObject::check(s, 1);
+
+    std::string property = obj->getProperty(key);
+    if (!property.empty())
     {
-        std::string property = obj->getProperty(key);
-        if (!property.empty())
-        {
-            lua_pushstring(s, property.c_str());
-            return 1;
-        }
-        else
-        {
-            // scripts can check for nil
-            return 0;
-        }
+        lua_pushstring(s, property.c_str());
+        return 1;
     }
     else
     {
-        raiseScriptError(s, "map_object_get_property called with invalid"
-                            "object handle");
+        // scripts can check for nil
         return 0;
     }
 }
@@ -2535,13 +2521,7 @@ static int map_object_get_property(lua_State *s)
  */
 static int map_object_get_bounds(lua_State *s)
 {
-    if (!lua_islightuserdata(s, 1))
-    {
-        raiseScriptError(s, "map_object_get_bounds called with invalid"
-                            "object handle");
-        return 0;
-    }
-    MapObject *obj = static_cast<MapObject *>(lua_touserdata(s, 1));
+    MapObject *obj = LuaMapObject::check(s, 1);
     const Rectangle &bounds = obj->getBounds();
     lua_pushinteger(s, bounds.x);
     lua_pushinteger(s, bounds.y);
@@ -2556,13 +2536,7 @@ static int map_object_get_bounds(lua_State *s)
  */
 static int map_object_get_name(lua_State *s)
 {
-    if (!lua_islightuserdata(s, 1))
-    {
-        raiseScriptError(s, "map_object_get_name called with invalid"
-                            "object handle");
-        return 0;
-    }
-    MapObject *obj = static_cast<MapObject *>(lua_touserdata(s, 1));
+    MapObject *obj = LuaMapObject::check(s, 1);
     lua_pushstring(s, obj->getName().c_str());
     return 1;
 }
@@ -2573,13 +2547,7 @@ static int map_object_get_name(lua_State *s)
  */
 static int map_object_get_type(lua_State *s)
 {
-    if (!lua_islightuserdata(s, 1))
-    {
-        raiseScriptError(s, "map_object_get_type called with invalid"
-                            "object handle");
-        return 0;
-    }
-    MapObject *obj = static_cast<MapObject *>(lua_touserdata(s, 1));
+    MapObject *obj = LuaMapObject::check(s, 1);
     lua_pushstring(s, obj->getType().c_str());
     return 1;
 }
@@ -2718,16 +2686,22 @@ LuaScript::LuaScript():
         { "log",                             &log                             },
         { "get_distance",                    &get_distance                    },
         { "map_get_objects",                 &map_get_objects                 },
-        { "map_object_get_property",         &map_object_get_property         },
-        { "map_object_get_bounds",           &map_object_get_bounds           },
-        { "map_object_get_name",             &map_object_get_name             },
-        { "map_object_get_type",             &map_object_get_type             },
         { "announce",                        &announce                        },
         { NULL, NULL }
     };
     luaL_register(mState, "mana", callbacks);
     lua_pop(mState, 1);                     // pop the 'mana' table
 
+    static luaL_Reg const members_MapObject[] = {
+        { "property",                        &map_object_get_property         },
+        { "bounds",                          &map_object_get_bounds           },
+        { "name",                            &map_object_get_name             },
+        { "type",                            &map_object_get_type             },
+        { NULL, NULL }
+    };
+
+    LuaMapObject::registerType(mState, "MapObject", members_MapObject);
+
     // Make script object available to callback functions.
     lua_pushlightuserdata(mState, (void *)&registryKey);
     lua_pushlightuserdata(mState, this);
diff --git a/src/scripting/luautil.cpp b/src/scripting/luautil.cpp
index a7521426..b7680c6b 100644
--- a/src/scripting/luautil.cpp
+++ b/src/scripting/luautil.cpp
@@ -116,8 +116,3 @@ void push(lua_State *s, double val)
 {
     lua_pushnumber(s, val);
 }
-
-void push(lua_State *s, MapObject *val)
-{
-    lua_pushlightuserdata(s, val);
-}
diff --git a/src/scripting/luautil.h b/src/scripting/luautil.h
index ee3f1142..4f456ab6 100644
--- a/src/scripting/luautil.h
+++ b/src/scripting/luautil.h
@@ -44,19 +44,81 @@ void raiseScriptError(lua_State *s, const char *format, ...);
 
 void raiseWarning(lua_State *s, const char *format, ...);
 
+/**
+ * A helper class for pushing and checking custom Lua user data types.
+ */
+template <typename T>
+class LuaUserData
+{
+public:
+    /**
+     * Creates a metatable to be used for the user data associated with the
+     * type. Then, registers the \a members with a library named \a typeName,
+     * and sets the '__index' member of the metatable to this library.
+     */
+    static void registerType(lua_State *s,
+                             const char *typeName,
+                             const luaL_Reg *members)
+    {
+        mTypeName = typeName;
+
+        luaL_newmetatable(s, mTypeName);        // metatable
+        lua_pushstring(s, "__index");           // metatable, "__index"
+        luaL_register(s, typeName, members);    // metatable, "__index", {}
+        lua_rawset(s, -3);                      // metatable
+        lua_pop(s, 1);                          // -empty-
+    }
+
+    /**
+     * Pushes a userdata reference to the given object on the stack. Either by
+     * creating one, or reusing an existing one.
+     */
+    static int push(lua_State *L, T *object)
+    {
+        T **userData = static_cast<T**>(lua_newuserdata(L, sizeof(T*)));
+        *userData = object;
+
+        luaL_newmetatable(L, mTypeName);
+        lua_setmetatable(L, -2);
+
+        return 1;
+    }
+
+    /**
+     * Returns the argument at position \a narg when it is of the right type,
+     * and raises a Lua error otherwise.
+     */
+    static T *check(lua_State *L, int narg)
+    {
+        void *userData = luaL_checkudata(L, narg, mTypeName);
+        return *(static_cast<T**>(userData));
+    }
+
+private:
+    static const char *mTypeName;
+};
+
+template <typename T> const char * LuaUserData<T>::mTypeName;
+
+typedef LuaUserData<MapObject> LuaMapObject;
+
+
 NPC *getNPC(lua_State *s, int p);
 Character *getCharacter(lua_State *s, int p);
 Monster *getMonster(lua_State *s, int p);
 Being *getBeing(lua_State *s, int p);
 
-
 /* Polymorphic wrapper for pushing variables.
    Useful for templates.*/
 void push(lua_State *s, int val);
 void push(lua_State *s, const std::string &val);
 void push(lua_State *s, Thing *val);
 void push(lua_State *s, double val);
-void push(lua_State *s, MapObject *val);
+
+inline void push(lua_State *s, MapObject *val)
+{
+    LuaMapObject::push(s, val);
+}
 
 
 /*  Pushes an STL LIST */