itemWhitelist = {"coal","redstone","lapis","diamond","emerald","ore"}

function has(t,s)
	for i,k in pairs(t) do
		if s:find(k) then
			return true
		end
	end
	return false
end

function getName(sBelowAbove)
    if sBelowAbove == "below" then
        _,itemDetails = turtle.inspectDown()
    elseif sBelowAbove == "above" then
        _,itemDetails = turtle.inspectUp()
    else
        _,itemDetails = turtle.inspect()
    end
	if type(itemDetails) == "table" then
    	if itemDetails.name then
        	return itemDetails.name
    	else
        	return ""
		end
    end
end

function emptyJunk()
    for i=16,1,-1 do
        local itemDetails = turtle.getItemDetail(i)
		if type(itemDetails) == "table" then
        	if itemDetails.name then
            	if not has(itemWhitelist,itemDetails.name) then
                	print("Pruned " .. turtle.getItemCount(i) .. " " .. itemDetails.name)
                	turtle.select(i)
                	turtle.dropUp()
				end
            end
        end
    end
    turtle.select(1)
end

function digHole()
    local distanceDown = 0
    while true do
        turtle.digDown()
        if turtle.down() then
            distanceDown = distanceDown + 1
        else
            break
        end
        for i=1,4 do
        	turtle.dig()
			turtle.turnLeft()
        end
        emptyJunk()
    end
	print("Returning to surface")
    for i=distanceDown,1,-1 do
        turtle.up()
    end
end

s = 0
a = {...}
l = a[1]

for i=1,l do
	for j=1,l do
		digHole()
		turtle.forward()
		turtle.forward()
	end
	if s == 0 then
		turtle.turnLeft()
		turtle.forward()
		turtle.forward()
		turtle.turnLeft()
		s = 1
	else
		turtle.turnRight()
		turtle.forward()
		turtle.forward()
		turtle.turnRight()
		s = 0
	end
end

digHole()