local util = require("util")
---- INIT ----
script.on_init(function()
	storage.entities = {}
	storage.power_entities = {}
end)
script.on_configuration_changed(function()
	storage.power_entities = {} -- ensures this field exists, but keeps old value
	storage.entities = {}
end)

---- ON EVENT ----
script.on_event({defines.events.on_robot_built_entity, defines.events.on_built_entity}, function(event)
	if event.entity.name == "artillery-turret" or event.entity.name == "flamethrower-turret" then
		event.entity.disabled_by_script = true
		local id = event.entity.unit_number
		storage.entities[id] = event.entity
		storage.power_entities[id] = event.entity.surface.create_entity{
			name = event.entity.name.."-power",
			position = event.entity.position,
			force = event.entity.force,
			direction = event.entity.direction,
			destructible = false} end end)

script.on_event({defines.events.on_entity_died, defines.events.on_robot_pre_mined, defines.events.on_pre_player_mined_item, defines.events.on_space_platform_pre_mined}, function(event)
	local id = event.entity.unit_number
    if storage.power_entities[id] then
		storage.power_entities[id].destroy()
		storage.power_entities[id] = nil
		storage.entities[id] = nil
	end end)

local refresh_rate = 20 -- how often to check whether an out-of-power turret should be re-enabled
local energy_per_shot = util.parse_energy("8kJ") -- set to whatever you want

script.on_event(defines.events.on_script_trigger_effect, function (event)
	if event.effect_id ~= "turret-consume-energy" then return end
	local turret = event.cause_entity -- or should it be event.source_entity?
	local id = turret.unit_number
	local interface = storage.power_entities[id]
	if interface.energy >= energy_per_shot then
		interface.energy = interface.energy - energy_per_shot
	else
		turret.disabled_by_script = true  end end)
		
script.on_nth_tick(refresh_rate, function(event)
    for id, interface in pairs(storage.power_entities) do
		local turret = storage.entities[id]
		if not turret.valid then
			interface.destroy()
			storage.power_entities[id] = nil
			storage.entities[id] = nil
		elseif turret.disabled_by_script and interface.energy >= energy_per_shot then
			interface.energy = interface.energy - energy_per_shot 
			turret.disabled_by_script = false end end end)