CC Tunnel

-- definitions

function checkLavaAndFuel()
    local fuelLimit = turtle.getFuelLimit()
    if turtle.getFuelLevel() < fuelLimit - 1000 then
        turtle.select(15)
        if turtle.place() then
            if not turtle.refuel() then
                -- we picked up something other than lava (water, etc.)
                turtle.place()
            end
        end
    end
end

function autoRefuel()
    checkLavaAndFuel()
    local fuelLimit = turtle.getFuelLimit()
    while turtle.getFuelLevel() < 80 do
        turtle.select(16)
        if turtle.refuel(0) then
            -- we can refuel using slot 16
            turtle.refuel(1)
        end
    end
end

function isFull()
    if turtle.getItemCount(12) > 0 then
        return true
    else
        return false
    end
end

-- start
pos_x = 0

while not isFull() do
    autoRefuel()
    while turtle.detect() do
        turtle.dig()
    end
    turtle.forward()
    pos_x = pos_x + 1
    while turtle.detectUp() do
        turtle.digUp()
    end
end

turtle.turnLeft()
turtle.turnLeft()

while pos_x > 0 do
    autoRefuel()
    while turtle.detect() do
        turtle.dig()
    end
    turtle.forward()
    pos_x = pos_x - 1
    while turtle.detectUp() do
        turtle.digUp()
    end
end

turtle.turnLeft()
turtle.turnLeft()

for i=1, 14 do
    turtle.select(i)
    turtle.dropDown()
end