local function surface()
    while turtle.detect() do
        turtle.up()
    end
end

local function getBelowName()
    present,tile = turtle.inspectDown()
    if present then
        return tile.name
    end
end

local function getBelowNameRaw(name)
    name = name or getBelowName()
    return string.sub(name,string.find(name,":")+1,#name)
end

local function getItemSlotName(id)
    turtle.select(id)
    slot = turtle.getItemDetail()
    return slot.name
end

deniedblocks = {"minecraft:dirt","minecraft:cobblestone","minecraft:stone"}

print("Starting...")

while true do
    surface()
    turtle.forward()
	if turtle.detectDown() then
		blockbelow = getBelowName()
	else
		blockbelow = "minecraft:air"
	end
    while getBelowNameRaw(blockbelow) ~= "minecraft:bedrock" do
        if blockbelow == "minecraft:lava" or blockbelow == "minecraft:flowing_lava" then
        	turtle.select(1)
        	turtle.place()
        	turtle.refuel()
        	print("Refueled. Fuel level now " .. turtle.getFuelLevel())
        else
            turtle.digDown()
		end
        for i=1,16,1 do
            if turtle.getItemCount(i) > 0 then
                slotname = getItemSlotName(i)
                for j=1,#deniedblocks,1 do
                    if slotname == deniedblocks[j] then
                        print("Slot " .. i .. " has denied block (" .. slotname .. "). Ejecting...")
                        turtle.dropUp()
                    end
                end
            end
        end
        turtle.down()
    end
    print("Layer done!")
end