turtle cube

if turtle.getFuelLevel()==0 then
    print("No fuel!")
    return
end
local x,y,z,fx,fz=0,0,0,1,0
local size=2
local bottomLayer
local isFull
turtle.select(1)
function face(tfx,tfz)
    if tfx==-fz and tfz==fx then
        rt()
    end
    while tfx~=fx or tfz~=fz do
        lt()
    end
    return true
end
function goto(tx,ty,tz,txDir,tzDir)
    while y<ty do
        u()
    end
    while y>ty do
        d()
    end
    if x<tx then
        face(1,0)
        repeat
            f()
        until x==tx
    end
    if x>tx then
        face(-1,0)
        repeat
            f()
        until x==tx
    end
    if z<tz then
        face(0,1)
        repeat
            f()
        until z==tz
    end
    if z>tz then
        face(0,-1)
        repeat
            f()
        until z==tz
    end
    if txDir and tzDir then
        face(txDir,tzDir)
    end
end
function c()
    if turtle.getItemCount(16)>0 and not isFull then
        local ox,oy,oz,ofx,ofz=x,y,z,fx,fz
        isFull=true
        if ox==0 and oz==0 then
            f()
        end
        goto(0,0,0)
        for e=1,16 do
            turtle.select(e)
            turtle.refuel()
            turtle.dropDown()
        end
        turtle.select(1)
        goto(ox,0,oz)
        goto(ox,oy,oz,ofx,ofz)
        isFull=false
    end
end
function f()
    if turtle.detect() and not turtle.dig() then
        bottomLayer=y
        return
    end
    c()
    x=x+fx
    z=z+fz
    while not turtle.forward() do
        turtle.dig()
        sleep(0.5)
    end
end
function u()
    y=y+1
    repeat
        turtle.digUp()
    until turtle.up()
end
function d()
    if turtle.detectDown() and not turtle.digDown() then
        bottomLayer=y-1
    end
    c()
    repeat
    until turtle.down()
    y=y-1
end
function lt()
    fx,fz=fz,-fx
    return turtle.turnLeft()
end
function rt()
    fx,fz=-fz,fx
    return turtle.turnRight()
end
function layer()
    for i=0,size do
        for j=1,size do
            f()
            if bottomLayer and y==bottomLayer then
                return
            end
        end
        if i<size then
            if i%2==0 then
                rt()
                f()
                rt()
            else
                lt()
                f()
                lt()
            end
        end
    end
end
while true do
    goto(-size/2,size/2-1,-size/2,1,0)
    layer()
    for q=2,(bottomLayer and y-bottomLayer or size) do
        d()
        for w=1,4 do
            lt()
            for k=1,size do
                f()
            end
        end
    end
    if not bottomLayer then
        lt()
        lt()
        d()
    end
    if not bottomLayer then --bc d() could create it
        layer()
    end
    size=size+2
end