Scan rework, car fix & multislot fix

- only scanning for forces with connected players
- only scanning on init, updating with entities when they are built/removed
- no alerts for cars without guns
- added multislot behaviour

control.lua

@@ -1,6 +1,18 @@
 --control.lua
 --This mod scans the map for cars and gun-turrets and places alerts when they are low on ammo.
 
+--util functions
+
+function table_is_empty(table)
+    for _,_ in pairs(table) do
+        return false
+    end
+    return true
+end
+
+
+--local functions
+
 local get_ammo_flags = {
 	--Applies mode to inventory, calculates and returns respective inventory flags
 	["added"] = function (inventory,player_threshold)
@@ -55,25 +67,83 @@ local get_ammo_flags = {
 	end
 }
 
+local function add_entity_to_list(event)
+	--Whenever an ammo-turret or car type entity is built, add it to the global table.
+	local index = event.created_entity.surface.name.."_"..event.created_entity.force.name
+	if global.ammo_entities[index] then
+		table.insert(global.ammo_entities[index], event.created_entity)
+	end
+end
 
-script.on_init(function (event)
+local function remove_entity_from_list(event)
+	--Whenever an ammo-turret or car type entity dies / is mined, remove it from the global table.
+	local index = event.entity.surface.name.."_"..event.entity.force.name
+	if global.ammo_entities[index] then
+		for i,entity in pairs(global.ammo_entities[index]) do
+			if (entity == event.entity) then
+				table.remove(global.ammo_entities[index], i)
+				break
+			end
+		end
+	end
+end
+
+local function add_force_to_list(event)
+	--Whenever a player of an unscanned force joins the game or a force is created, add all ammo-turret or car type entities of that force to the global table.
+	local player, force
+	if event.player_index then
+		player = game.get_player(event.player_index)
+		force = player.force
+	elseif event.force then
+		force = event.force
+		if force.connected_players then
+			player = force.connected_players[1]
+		end
+	end
+
+	if player and force and not global.ammo_entities[player.surface.name.."_"..force.name] then
+		for _,surface in pairs(game.surfaces) do
+			global.ammo_entities[surface.name.."_"..force.name] = surface.find_entities_filtered{type = {"ammo-turret","car"}, force = force, to_be_deconstructed = false}
+		end
+	end
+end
+
+local function remove_force_from_list(event)
+	--Whenever the last player of a force leaves the game or forces are merged, remove all entities of that force from the global table.
+	local force
+	local param = {}
+	if event.player_index and event.force then
+		param.player_index = event.player_index
+		add_force_to_list(param)
+		force = event.force
+	elseif event.player_index then
+		force = game.get_player(event.player_index).force
+	elseif event.force then
+		force = event.force
+	elseif event.source and event.destination then
+		param.force = event.destination
+		add_force_to_list(param)
+		force = source
+	end
+
+	if force and not force.connected_players then
+		for surface_name,_ in pairs(game.surfaces) do
+			global.ammo_entities[surface_name.."_"..force.name] = nil
+		end
+	end
+end
+
+local function init_list()
 	-- index init
 	global.ammo_entities = {}
-end)
-
-script.on_configuration_changed(function (event)
-	-- index init fix
-	global.ammo_entities = {}
-end)
-
-script.on_nth_tick(3600, function (event)
-	--Every minute the surface is rescanned for car and ammo-turret type entities. This is stored in a global table. 
-	for index,surface in pairs(game.surfaces) do
-		global.ammo_entities[index] = surface.find_entities_filtered{type = {"ammo-turret","car"}}
+	local param = {}
+	for _,force in pairs(game.forces) do
+		param.force = force
+		add_force_to_list(param)
 	end
-end)
+end
 
-script.on_nth_tick(600, function (event)
+local function generate_alerts()
 	--Every 10 seconds recheck and give alerts to players for car and ammo-turret entities on the same force as them.
 	for _,player in pairs(game.connected_players) do
 		
@@ -81,7 +151,7 @@ script.on_nth_tick(600, function (event)
 		local car_enabled = player.mod_settings["gun-turret-alerts-car-enabled"].value
 		local mode = player.mod_settings["gun-turret-alerts-mode"].value
 		local player_threshold = player.mod_settings["gun-turret-alerts-threshold"].value
-		local ammo_entities = global.ammo_entities[player.surface.name]
+		local ammo_entities = global.ammo_entities[player.surface.name.."_"..player.force.name]
 
 		if ammo_entities then
 			for _,entity in pairs(ammo_entities) do
@@ -91,7 +161,7 @@ script.on_nth_tick(600, function (event)
 					local inventory
 					if turret_enabled and entity.type == "ammo-turret" then
 						inventory = entity.get_inventory(defines.inventory.turret_ammo)
-					elseif car_enabled and entity.type == "car" --[[and entity.prototype.guns]] then
+					elseif car_enabled and entity.type == "car" and not table_is_empty(entity.prototype.guns) then
 						inventory = entity.get_inventory(defines.inventory.car_ammo)
 					end
 
@@ -117,4 +187,26 @@ script.on_nth_tick(600, function (event)
 			end
 		end
 	end
-end)
+end
+
+
+-- Event handlers
+
+script.on_init(init_list)
+script.on_configuration_changed(init_list)
+
+script.on_event(defines.events.on_player_joined_game, add_force_to_list)
+script.on_event(defines.events.on_player_left_game, remove_force_from_list)
+script.on_event(defines.events.on_player_changed_force, remove_force_from_list)
+
+script.on_event(defines.events.on_force_created, add_force_to_list)
+script.on_event(defines.events.on_forces_merged, remove_force_from_list)
+
+script.on_event(defines.events.on_built_entity, add_entity_to_list, {{filter="type", type = "ammo-turret"},{filter="type", type = "car"}})
+script.on_event(defines.events.on_robot_built_entity, add_entity_to_list, {{filter="type", type = "ammo-turret"},{filter="type", type = "car"}})
+
+script.on_event(defines.events.on_player_mined_entity, remove_entity_from_list, {{filter="type", type = "ammo-turret"},{filter="type", type = "car"}})
+script.on_event(defines.events.on_robot_mined_entity, remove_entity_from_list, {{filter="type", type = "ammo-turret"},{filter="type", type = "car"}})
+script.on_event(defines.events.on_entity_died, remove_entity_from_list, {{filter="type", type = "ammo-turret"},{filter="type", type = "car"}})
+
+script.on_nth_tick(600, generate_alerts)