add building_lib.replace

build.lua

@@ -75,8 +75,10 @@ function building_lib.build(mapblock_pos, playername, building_name, rotation, c
 		end
 	end)
 
-	placement.place(placement, mapblock_pos, building_def, rotation, callback)
-	building_lib.fire_event("placed", mapblock_pos, playername, building_def, rotation, size)
+	placement.place(placement, mapblock_pos, building_def, rotation, function()
+		callback()
+		building_lib.fire_event("placed", mapblock_pos, playername, building_def, rotation, size)
+	end)
 	return true
 end
 

build.spec.lua

@@ -10,6 +10,7 @@ building_lib.register_building("building_lib:dummy_v2", {
 mtt.register("build", function(callback)
     local mapblock_pos = {x=0, y=0, z=0}
     local building_name = "building_lib:dummy"
+    local new_building_name = "building_lib:dummy_v2"
     local rotation = 0
     local playername = "singleplayer"
 
@@ -41,6 +42,20 @@ mtt.register("build", function(callback)
     assert(info.size.y == 1)
     assert(info.size.z == 1)
 
+    -- try to replace
+    success, err = building_lib.can_replace(mapblock_pos, playername, new_building_name)
+    assert(not err)
+    assert(success)
+
+    -- replace
+    callback_called = false
+    success, err = building_lib.replace(mapblock_pos, playername, new_building_name, function()
+        callback_called = true
+    end)
+    assert(not err)
+    assert(success)
+    assert(callback_called)
+
     -- try to remove
     success, err = building_lib.can_remove(mapblock_pos)
     assert(not err)

init.lua

@@ -22,6 +22,7 @@ dofile(MP .. "/autoplace.lua")
 dofile(MP .. "/autoplace_tool.lua")
 dofile(MP .. "/remove.lua")
 dofile(MP .. "/remove_tool.lua")
+dofile(MP .. "/replace.lua")
 dofile(MP .. "/chat.lua")
 dofile(MP .. "/events.lua")
 dofile(MP .. "/hacks.lua")

readme.md

@@ -10,6 +10,13 @@ local success, message = building_lib.can_build(mapblock_pos, playername, buildi
 -- build it there
 local success, message = building_lib.build(mapblock_pos, playername, building_name, rotation, callback)
 
+-- check if it can be replaced
+-- NOTE: conditions are not checked on replace, just the size
+local success, err = building_lib.can_replace(mapblock_pos, playername, new_building_name)
+
+-- replace with a building of the same size
+local success, err = building_lib.replace(mapblock_pos, playername, new_building_name, callback)
+
 -- check if it can be removed
 local success, message = building_lib.can_remove(mapblock_pos)
 

replace.lua

@@ -0,0 +1,57 @@
+
+function building_lib.can_replace(mapblock_pos, _, building_name)
+    local new_building_def = building_lib.get_building(building_name)
+	if not new_building_def then
+		return false, "New building not found: '" .. building_name .. "'"
+	end
+
+    local info = building_lib.get_placed_building_info(mapblock_pos)
+	if not info then
+		return false, "no building found"
+	end
+
+    local old_building_def = building_lib.get_building(info.name)
+	if not old_building_def then
+		return false, "Old building not found: '" .. info.name .. "'"
+	end
+
+    local success, message = building_lib.can_remove(mapblock_pos)
+	if not success then
+		return false, message
+	end
+
+    local new_placement = building_lib.get_placement(new_building_def.placement)
+	if not info then
+		return false, "placement not found"
+	end
+
+    local old_size = info.size
+    local new_size = new_placement.get_size(new_placement, mapblock_pos, new_building_def, info.rotation)
+
+    if not vector.equals(old_size, new_size) then
+        return false, "replacement size does not match"
+    end
+
+    return true
+end
+
+function building_lib.replace(mapblock_pos, playername, new_building_name, callback)
+    callback = callback or function() end
+
+	local success, message = building_lib.can_replace(mapblock_pos, playername, new_building_name)
+	if not success then
+		return false, message
+	end
+
+    local info = building_lib.get_placed_building_info(mapblock_pos)
+    local rotation = info.rotation or 0
+
+    -- remove old building
+    success, message = building_lib.remove(mapblock_pos, playername)
+	if not success then
+		return false, message
+	end
+
+    -- place new building
+    return building_lib.build(mapblock_pos, playername, new_building_name, rotation, callback)
+end