dig.lua

turtle.refuel(1)
local range = math.floor(math.sqrt(turtle.getFuelLevel()))
local steps = 0
local turn = false
local badb = {"minecraft:air", "minecraft:water", "minecraft:lava"}
function isBad(name)
    for i = 1, table.getn(badb), 1 do
        if badb[i] == name then
            return true
        end
    end
    return false
end
while turtle.getFuelLevel() > 0 do
    while turtle.dig() do
    end
    turtle.digDown()
    turtle.forward()
    local success, meta, err = turtle.inspectUp()
    if not success or isBad(meta.name) then
        turtle.placeUp()
    end
    steps = steps + 1
    if steps < range then
        turtle.turnLeft()
        success, meta = turtle.inspect()
        if not success or isBad(meta.name) then
            turtle.place()
        end
        turtle.turnRight()
    end
    if steps > (range * range) - range then
        turtle.turnRight()
        success, meta = turtle.inspect()
        if not success or isBad(meta.name) then
            turtle.place()
        end
        turtle.turnLeft()
    end
    if steps % range == 0 then
        success, meta = turtle.inspect()
        if not success or isBad(meta.name) then
            turtle.place()
        end
        if turn then
            turtle.turnLeft()
        else
            turtle.turnRight()
        end
        while turtle.dig() do
        end
        turtle.digDown()
        turtle.forward()
        if turn then
            turtle.turnLeft()
        else
            turtle.turnRight()
        end
        turn = not turn
     end
end