--coal in slot2, cobble in 1
--BmGxztNt

width = 14-1

junk_blocks = "minecraft:cobblestone  minecraft:dirt  minecraft:gravel  chisel:limestone  chisel:marble"

function buildWall(func)
    if turtle.getItemCount(1) > 1 then
        return func()
    end
    return true
end

function clearLava(func)
    if turtle.getItemCount(1) > 1 then
        return func()
    end
    return true
end

turtle.turnLeft()
while true do

	--refueling
	turtle.select(2)
	while turtle.getFuelLevel() < 256 do
		if turtle.getItemCount(2) > 1 then
			turtle.refuel(1)
		end
		sleep(0.5)
	end
	turtle.select(1)

	--clear inventory
	local lastSlot = 3
	local slot = 3
	for slot = 16, 3, -1 do
		if turtle.getItemCount(slot) > 0 then
			lastSlot = slot
			break
		end
	end
	while slot < lastSlot do
		turtle.select(slot)
		data = turtle.getItemDetail(slot)
		if turtle.compareTo(1) or (data and junk_blocks:find(data.name)) then
			turtle.drop()
			turtle.select(lastSlot)
			turtle.transferTo(slot)
			lastSlot = lastSlot - 1
			slot = slot - 1
		end
		slot = slot + 1
	end
	while turtle.getItemCount(16) > 0 do
		sleep(1)
	end
	turtle.select(1)

	--tunnel bore
	for x = 1, width do
		turtle.digDown()
		buildWall(turtle.placeDown)
        clearLava(turtle.placeUp)
		turtle.digUp()
		repeat turtle.dig() until turtle.forward()
	end

	turtle.digDown()
	buildWall(turtle.placeDown)
    clearLava(turtle.placeUp)
	turtle.digUp()

	turtle.dig()
	buildWall(turtle.place)
	repeat turtle.digUp() until turtle.up()
	turtle.dig()
	buildWall(turtle.place)
	repeat turtle.digUp() until turtle.up()
	turtle.dig()
	buildWall(turtle.place)
	repeat turtle.digUp() until turtle.up()
	turtle.dig()
	buildWall(turtle.place)

	turtle.turnRight()
	turtle.turnRight()

	for x = 1, width do
		repeat turtle.digUp() until buildWall(turtle.placeUp)
        clearLava(turtle.placeDown)
		turtle.digDown()
		repeat turtle.dig() until turtle.forward()
	end

	repeat turtle.digUp() until buildWall(turtle.placeUp)
    clearLava(turtle.placeDown)
	turtle.digDown()

	turtle.dig()
	buildWall(turtle.place)
	repeat turtle.digDown() until turtle.down()
	turtle.dig()
	buildWall(turtle.place)
	repeat turtle.digDown() until turtle.down()
	turtle.dig()
	buildWall(turtle.place)
	repeat turtle.digDown() until turtle.down()
	turtle.dig()
	buildWall(turtle.place)

	turtle.turnLeft()
	repeat turtle.dig() until turtle.forward()
	turtle.turnLeft()
end