AutoRefueler

function fuelId()
    current = turtle.getSelectedSlot()
    for i = 1, 16 do
        turtle.select(i)
        if turtle.refuel(0) then
            turtle.select(current)
            return i
        end
    end
    return 0
end

function refuel()
    current_fuel = turtle.getFuelLevel()
    max_fuel = turtle.getFuelLimit()
    current = turtle.getSelectedSlot()
    if current_fuel > 1000 then
        return
    end
    fuel_id = fuelId()
    if fuel_id == 0 then
        return false
    end
    if current_fuel/max_fuel < 0.5 then
        turtle.select(fuel_id)
        turtle.refuel(1)
        turtle.select(current)
    end
    return true
end