term.clear()
term.setCursorPos(1,1)

local collected = 0
local turn = 0

function collect()
	collected = collected+1
	if math.fmod(collected, 25) == 0 then
		print("Mined "..collected.." items.")
	end
end

function dig()
	if turtle.detectDown() then
		turtle.digDown()
		collect()
		sleep(0.5)
	else
		return false
	end
	return true
end

function select()
	for i = 1,4 do
		if turtle.getItemCount(i) > 0 then
			turtle.select(i)
			return true
		else
			return false
		end
	end
end

function place()
	if not turtle.detectDown() then
		if select() then
			turtle.placeDown()
		else
			print("No more blocks")

			local function blocks()
				for s = 1, 4 do
					if turtle.getItemCount(s) > 0 then
						return true
					else
						return false
					end
				end
			end

			while true do
				if blocks() then
					turtle.placeDown()
					break
				end
			end
		end
	else
		dig()
	end
end

function forward()
	refuel()
	if turtle.detect() then
		turn()
	else
		turtle.forward()
		sleep(0.5)
	end
end

function turn()
	if turtle.detect() then
		if turn == 0 then
			turtle.turnLeft()
			turtle.forward()
			turtle.turnLeft()
			turn = 1
		elseif turn == 1 then
			turtle.turnRight()
			turtle.forward()
			turtle.turnRight()
			turn = 0
		end
	end
end

function refuel()
	local fuelLevel = turtle.getFuelLevel()
	if fuelLevel == "unlimited" or fuelLevel > 0 then
		return
	end

	local function tryRefuel()
		for n=1,16 do
			if turtle.getItemCount(n) > 0 then
				turtle.select(n)
				if turtle.refuel(1) then
					turtle.select(1)
					return true
				end
			end
		end
		turtle.select(1)
		return false
	end

	if not tryRefuel() then
		print( "Add more fuel to continue." )
		while not tryRefuel() do
			sleep(1)
		end
		print( "Resuming Tunnel." )
	end
end

local function  init()
	while true do
		sleep(0)
		place()
		forward()
	end
end

init()