-- definition
function doRefuel(amount)
    local fuelLevel = turtle.getFuelLevel()
    if fuelLevel == "unlimited" then
        return true
    end

    local needed = amount or (xPos + zPos + depth + 2)
    if turtle.getFuelLevel() < needed then
        local fueled = false
        for n = 1, 16 do
            if turtle.getItemCount(n) > 0 then
                turtle.select(n)
                if turtle.refuel(1) then
                    while turtle.getItemCount(n) > 0 and turtle.getFuelLevel() < needed do
                        turtle.refuel(1)
                    end
                    if turtle.getFuelLevel() >= needed then
                        turtle.select(1)
                        return true
                    end
                end
            end
        end
        turtle.select(1)
        return false
    end

    return true
end

-- export
return { doRefuel = doRefuel }