sugarcanebot

function refuel()
    if turtle.getFuelLevel() < 10 then
        turtle.select(1)
        turtle.refuel(1)
    end
end

function harvest_row()
    for i=1, 128 do
        refuel()
        turtle.dig()
        turtle.forward()
        turtle.digDown()
    end
end

function harvest_section()
    harvest_row()
    turtle.forward()
    turtle.turnLeft()
    turtle.forward()
    turtle.turnLeft()
    harvest_row()
    turtle.forward()
end

while true do
    while turtle.detectDown() do
        print("Waiting for piston retraction")
        sleep(1)
    end
    turtle.select(1)
    while turtle.getItemCount() < 16 do
        turtle.suckUp(16 - turtle.getItemCount())
    end
    harvest_section()
    refuel()
    for v=2, 16 do
        turtle.select(v)
        turtle.dropDown()
    end
    turtle.turnLeft()
    turtle.forward()
    turtle.turnLeft()
end