-- get arguments

local tArgs = { ... }
if #tArgs ~= 1 then
	print( "Usage: basicTunne; <Tunnel Length>" )
	return
end

local tunnelLength = tonumber( tArgs[1] )
if tunnelLength < 1 then
	print( "Tunnel Length must be positive!" )
	return
end

-- stolen collect function

local function collect()
	local bFull = true
	local nTotalItems = 0
	for n=1,16 do
		local nCount = turtle.getItemCount(n)
		if nCount == 0 then
			bFull = false
		end
		nTotalItems = nTotalItems + nCount
	end

	if nTotalItems > collected then
		collected = nTotalItems
		if math.fmod(collected + unloaded, 50) == 0 then
			print( "Mined "..(collected + unloaded).." items." )
		end
	end

	if bFull then
		print( "No empty slots left." )
		return false
	end
	return true
end

-- function to tunnel 1x3 directly in front

local function digInFront ()
	if turtle.detectUp() then
		if turtle.digUp() then
			if not collect() then
				error()
			end
		end
	end

	if turtle.detect() then
		if turtle.dig() then
			if not collect() then
				error()
			end
		end
	end

	if turtle.detectDown() then
		if turtle.digDown() then
			if not collect() then
				error()
			end
		end
	end
end

-- function to move x blocks in given direction (left / right) maintaining orientation
local function move(numToMove, orientation)
	local cleanNumToMove = tonumber( numToMove )

	if orientation == "left" then
		if turtle.turnLeft() then
			for i = 1, cleanNumToMove, 1 do
				turtle.forward()
			end
			turtle.turnRight()
		end
	end

	if orientation == "right" then
		if turtle.turnRight() then
			for i = 1, cleanNumToMove, 1 do
				turtle.forward()
			end
			turtle.turnLeft()
		end
	end

end

-- program start

local done = false

while not done do
	for n = 1, tunnelLength/2 do

		digInFront()
		move(1, "right")
		digInFront()
		move(1, "right")
		digInFront()

		turtle.forward()

		digInFront()
		move(1, "left")
		digInFront()
		move(1, "left")
		digInFront()
	end
	done = true
end