control.lua

local function accepts_outside_entity(outside_entity, factory, interior, conn_specs)
  local inside_entity = nil
  local txControl, rxEntity
  if outside_entity.name == "relay-combinator" then
    inside_entity = interior.create_entity{
      name = "small-lamp", position = conn_specs.inside_pos,
      force = factory.force, direction = outside_entity.direction}

    outside_entity.direction = conn_specs.direction_out

    rxEntity = inside_entity
    txControl = outside_entity.get_or_create_control_behavior()
  elseif outside_entity.name == "small-lamp" then
    inside_entity = interior.create_entity{
      name = "relay-combinator", position = conn_specs.inside_pos,
      force = factory.force, direction = conn_specs.direction_in}

    txControl = inside_entity.get_or_create_control_behavior()
    rxEntity = outside_entity
  end
  if not inside_entity then return nil end
  outside_entity.rotatable = false
  outside_entity.destructible = false

  inside_entity.rotatable = false
  inside_entity.minable = false
  inside_entity.destructible = false

  local data = {
    outside = outside_entity, inside = inside_entity,
    txControl = txControl, rxEntity = rxEntity,
  }
  return data
end

local function on_update(data)
  if data.inside.valid and data.outside.valid
   then
    game.players[1].print("valid connection")
    return 60
  else
    game.players[1].print("invalid connection")
    return nil
  end
end

local function on_destroy(data)
  if data.inside.valid then
    data.inside.destroy()
  end
end

remote.add_interface("factorissimo_circuits",
	{
		accepts_outside_entity = accepts_outside_entity,
    on_update = on_update,
    on_destroy = on_destroy,
	}
)

remote.call(
  "factorissimo_connections",
  "register_connection_type",
  "relay-combinator", "factorissimo_circuits")

remote.call(
  "factorissimo_connections",
  "register_connection_type",
  "small-lamp", "factorissimo_circuits")