mine

local x = 20
local y = 20

function digForward(mode)
    if mode == 3 then
        while turtle.detect() do turtle.dig() end
        turtle.forward()
        while turtle.detectUp() do turtle.digUp() end
        while turtle.detectDown() do turtle.digDown() end
    end
end

function digLine(length, mode)
   for i = 1, length do digForward(mode) end
end

function newLine(side, mode)
    if side == true then
        turtle.turnRight()
        digForward(mode)
        turtle.turnRight()
    else
        turtle.turnLeft()
        digForward(mode)
        turtle.turnLeft()
    end
end

function digLayer(x, y, mode, side)
    local turn
    if side == "left" then turn = false else turn = true end
    for i = 1, y do
        digLine(x - 1, mode)
        if i ~= y then newLine(turn, mode) end
        turn = not turn
    end
end

digLayer(x, y, 3, "right")