wood = 0
nextColDir  = "up"
nextRowDir = "right"

function digTunnel(length)
	for i = 1, length, 1 do
		for k = 1, 4, 1 do
			if not digSide(nextColDir) then
				return false
			end
			swapColDirection()
			turn(nextRowDir)
			swapRowDirection()
			for j = 1, 3, 1 do
				if not digCenter(nextColDir) then
					return false
				end
				swapColDirection()
			end
			if not digSide(nextColDir) then
				return false
			end
			swapColDirection()
			turn(nextRowDir)
		end
		if not addSupports() then
			return false
		end
	end
	return true
end

function addSupports()
	success = true
	turn(nextRowDir)
	forward()
	turn(nextRowDir)
	forward()
	turn(nextRowDir)
	success = placeBeams(nextColDir)
	swapColDirection()
	turn(nextRowDir)
	turn(nextRowDir)
	swapRowDirection()
	forward()
	if nextColDir == "up" then
		digDown()
		success = placeWood("down")
		up()
		up()
		success = placeWood("up")
	elseif nextColDir == "down" then
		success = placeWood("up")
		down()
		down()
		digDown()
		success = placeWood("down")
	end
	swapColDirection()
	forward()
	success = placeBeams(nextColDir)
	swapColDirection()
	turn(nextRowDir)
	swapRowDirection()
	forward()
	turn(nextRowDir)
	forward()
	swapRowDirection()
	turn(nextRowDir)
	return success
end

function  placeBeams(direction)
	success = true
	if direction == "up" then
		digDown()
		sucess = placeWood("down")
		sucess = placeWood("front")
		up()
		sucess = placeWood("front")
		up()
		sucess = placeWood("front")
		sucess = placeWood("up")
	elseif direction == "down" then
		sucess = placeWood("up")
		sucess = placeWood("front")
		down()
		sucess = placeWood("front")
		down()
		digDown()
		sucess = placeWood("front")
		sucess = placeWood("down")
	end
	return success
end

function turn(direction)
	if direction == "right" then
		turtle.turnRight()
	elseif direction == "left" then
		turtle.turnLeft()
	end
end

function swapRowDirection()
	if nextRowDir == "right" then
		nextRowDir = "left"
	else
		nextRowDir = "right"
	end
end

function swapColDirection()
	if nextColDir == "up" then
		nextColDir = "down"
	else
		nextColDir = "up"
	end
end

function digSide(direction)
	success = true
	dig()
	forward()
	if direction == "up" then
		digDown()
		success = placeWood("down")
		for i = 1, 2, 1 do
			digUp()
			up()
		end
		digUp()
		success = placeWood("up")
	else
		digUp()
		success = placeWood("up")
		for i = 1, 2, 1 do
			digDown()
			down()
		end
		digDown()
		success = placeWood("down")
	end
	return success
end

function digCenter(direction)
	success = true
	dig()
	forward()
	if direction == "up" then
		digUp()
		up()
		digUp()
		up()
		digUp()
	else
		digUp()
		for i = 1, 2, 1 do
			digDown()
			down()
		end
	end
	return success
end

function placeWood(direction)
	if wood  > 0 then
		wood = wood - 1
	else
		wood = findWood()
		if wood == 0 then
			print("Out of wood! Please refill!")
			return false
		end
	end
	if direction == "front" then
		return turtle.place()
	elseif direction == "up" then
		return turtle.placeUp()
	elseif direction == "down" then
		return turtle.placeDown()
	end
end

function findWood()
	for i = 1, 15, 1 do
		turtle.select(i)
		if turtle.compareTo(16) then
			return turtle.getItemCount(i)
		end
	end
	return 0
end

function digUp()
	while turtle.detectUp() do
		turtle.digUp()
	end
end

function dig()
	while turtle.detect() do
		turtle.dig()
	end
end

function digDown()
	while turtle.detectDown() do
		turtle.digDown()
	end
end

function forward()
	done = false
	while not done do
		dig()
		done = turtle.forward()
	end
end

function up()
	done = false
	while not done do
		digUp()
		done = turtle.up()
	end
end

function down()
	done = false
	while not done do
		digDown()
		done = turtle.down()
	end
end