mine-return

-- Attempt to refuel the turtle
local function attemptRefuel()
	if(turtle.getFuelLevel() >= 1) then
		return
	end

	local index = 1
	local hasRefueled = false
	while(index <= 16 and not hasRefueled) do
		turtle.select(index)
		if(turtle.refuel(0)) then
			turtle.refuel(1)
			hasRefueled = true
		end
		index = index + 1
	end
end

-- Move in a direction 1 or more times
local function move(direction, distance)
	local distance = tonumber(distance) or 1
	attemptRefuel()

	if(direction == "up") then
		turtle.up()
	elseif(direction == "down") then
		turtle.down()
	elseif(direction == "forward") then
		turtle.forward()
	elseif(direction == "back") then
		turtle.back()
	else
		print("Direction: " .. direction .. " not a valid movement")
		return false
	end

	if(distance > 1) then
		move(direction, distance - 1)
	end
	return true
end

-- Dig out a block and move into it
local function digMove(direction)
	if(direction == "up") then
		turtle.digUp()
		move("up")
	elseif(direction == "down") then
		turtle.digDown()
		move("down")
	elseif(direction == "forward") then
		turtle.dig()
		move("forward")
	elseif(direction == "back") then
		turtle.turnLeft()
		turtle.turnLeft()
		turtle.dig()
		turtle.turnLeft()
		turtle.turnLeft()
		move("back")
	else
		print("Direction: " .. direction .. " not a valid movement")
		return false
	end
	return true
end

-- Dig out a 3x3 vertical square
local function tunnelSquare()
	-- Dig out adjacent left and right blocks
	local function tunnelAdjacentLR()
		turtle.turnLeft()
		turtle.dig()
		turtle.turnLeft()
		turtle.turnLeft()
		turtle.dig()
		turtle.turnLeft()
	end

	digMove("forward")
	for i=1, 3 do
		tunnelAdjacentLR()
		if(i < 3) then
			digMove("up")
		end
	end
	move("down", 2)
end

-- Tunnel
local function tunnel(distance, tunnelFunc)
	-- Don't bother with tunnelling negative distances
	if(distance < 1) then
		return
	end

	-- Default to tunnelSquare
	local tunnelFunc = tunnelFunc or tunnelSquare

	-- Tunnel over a distance using specified tunneling function
	for i=1, distance do
		tunnelFunc()
	end
end

-- Display usage info
local function help()
	local name = "<name>"
	if(shell) then
		name = shell.getRunningProgram()
	end

	print("Usage: " .. name .. " <distance to tunnel >= 3> [shaft center spacing (-1 for no return)]")
end

-- Main
local function main(distance, spacing)
	local distance = tonumber(distance) or 0
	local spacing = tonumber(spacing) or 0

	-- Handle args
	if(not distance) then
		help()
		return
	elseif(distance < 3) then
		help()
		return
	end

	-- Initial tunneling distance
	tunnel(distance)

	-- Don't return if a negative spacing has been given
	if(spacing < 0) then
		return
	end

	-- Tunnel over to return shaft
	move("back")
	turtle.turnLeft()
	if(spacing > 0) then
		tunnel(spacing + 1)
		move("back")
	end

	-- Move to edge of return shaft
	turtle.turnLeft()
	move("forward")

	-- Tunnel/move back to start
	if(spacing == 0) then
		move("forward", distance - 2)
	else
		tunnel(distance - 2)
	end

	-- Spin back around
	turtle.turnLeft()
	turtle.turnLeft()
end

local arg = {...}
main(arg[1], arg[2])