control.lua

require "defines"

local spawn_belts = {}
local void_belts = {}
local belts
local spawn_item = "iron-ore"

remote.add_interface("spawnbelt", {
  setitem = function(item)
    spawn_item = item
  end
})

script.on_load(function(event)
  if global.belts ~= nil then
    belts = global.belts
    script.on_event(defines.events.on_tick, tick_belts)
  end
end)

script.on_event(defines.events.on_built_entity, function(event)
  if event.created_entity.name == "spawn-belt" 
  or event.created_entity.name == "void-belt" then
  
    if global.belts == nil then
      global.belts = {};
      belts = global.belts;
      script.on_event(defines.events.on_tick, tick_belts)
    end

    -- player = game.get_player(event.player_index);
    new_belt = {};
    new_belt["entity"] = event.created_entity;
    new_belt["item"] = spawn_item;
    -- new_belt["surface"] = player.surface;
    table.insert(belts, new_belt)
  end
end)

function tick_belts()
  for k, belt in ipairs(belts) do
    if belt.entity.valid ~= true then
      table.remove(belts, k)
      if #global.belts == 0 then
        belts = nil
        global.belts = nil
        script.on_event(defines.events.on_tick, nil)
      end
    else
      if belt.entity.name == "spawn-belt" then
        x = belt.entity.position.x;
        y = belt.entity.position.y;
        if belt.entity.direction == 0 then
          y = y + 1;
        elseif belt.entity.direction == 2 then
          x = x - 1;
        elseif belt.entity.direction == 4 then
          y = y - 1;
        elseif belt.entity.direction == 6 then
          x = x + 1;
        end
        
        chests = belt.entity.surface.find_entities_filtered({area = {{x,y},{x,y}}, type="container"});
        if #chests > 0 then
          chest = chests[1];
          inventory = chest.get_inventory(defines.inventory.chest);
          if inventory ~= nil
          and inventory.valid == true 
          and inventory.is_empty() == false 
          and inventory[1].valid == true
          and inventory[1].valid_for_read == true then
            belt.item = inventory[1].name;
          end
        end

        line1 = belt.entity.get_transport_line(1);
        if line1.can_insert_at_back() then
          line1.insert_at_back({name = belt.item});
        end
        line2 = belt.entity.get_transport_line(2);
        if line2.can_insert_at_back() then
          line2.insert_at_back({name = belt.item});
        end
      elseif belt.entity.name == "void-belt" then
        belt.entity.get_transport_line(1).clear();
        belt.entity.get_transport_line(2).clear();
      end
    end
  end
end