local tArgs = { ... }
if #tArgs ~= 1 then
    print( "Usage: tunnel <length>" )
    return
end

-- Mine in a quarry pattern until we hit something we can't dig
local length = tonumber( tArgs[1] )
if length < 1 then
    print( "Tunnel length must be positive" )
    return
end

local depth = 0
local collected = 0
local xPos = 0
local yPos = 0
local zPos = 0
local xDir = 0
local zDir = 0
local goTo -- Filled in further down

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

    if (bFull) then
        returnSupplies(false)
    end
end

local function unload( _bKeepOneFuelStack )
	print( "Unloading items..." )
	for n=1,16 do
		local nCount = turtle.getItemCount(n)
		if nCount > 0 then
			turtle.select(n)
			local bDrop = true
			if _bKeepOneFuelStack and turtle.refuel(0) then
				bDrop = false
				_bKeepOneFuelStack = false
			end
			if bDrop then
				turtle.drop()
				unloaded = unloaded + nCount
			end
		end
	end
	collected = 0
	turtle.select(1)
end

local function returnSupplies(stop)
	local x,y,z,xd,zd = xPos,yPos,zPos,xDir,zDir
	print( "Returning to surface..." )
	goTo( 0,0,0,0,-1 )

	local fuelNeeded = 2*(x+y+z) + 1
	if not refuel( fuelNeeded ) or not stop then
		unload( true )
		print( "Waiting for fuel" )
		while not refuel( fuelNeeded ) do
			os.pullEvent( "turtle_inventory" )
		end
	else
		unload( true )
	end

	print( "Resuming mining..." )
	goTo( x,y,z,xd,zd )
end

local function tryDig()
    while turtle.detect() do
        if turtle.dig() then
            collect()
            sleep(0.5)
        else
            return false
        end
    end
    return true
end

local function tryDigUp()
    while turtle.detectUp() do
        if turtle.digUp() then
            collect()
            sleep(0.5)
        else
            return false
        end
    end
    return true
end

local function tryDigDown()
    while turtle.detectDown() do
        if turtle.digDown() then
            collect()
            sleep(0.5)
        else
            return false
        end
    end
    return true
end

local 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.he(1)
        return false
    end

    if not tryRefuel() then
        print( "Add more fuel to continue." )
        while not tryRefuel() do
            os.pullEvent( "turtle_inventory" )
        end
        print( "Resuming Tunnel." )
    end
end

local function tryUp()
    refuel()
    while not turtle.up() do
        if turtle.detectUp() then
            if not tryDigUp() then
                return false
            end
        elseif turtle.attackUp() then
            collect()
        else
            sleep( 0.5 )
        end
    end
    return true
end

local function tryDown()
    refuel()
    while not turtle.down() do
        if turtle.detectDown() then
            if not tryDigDown() then
                return false
            end
        elseif turtle.attackDown() then
            collect()
        else
            sleep( 0.5 )
        end
    end
    return true
end

local function tryForward()
    refuel()
    while not turtle.forward() do
        if turtle.detect() then
            if not tryDig() then
                return false
            end
        elseif turtle.attack() then
            collect()
        else
            sleep( 0.5 )
        end
    end
    return true
end

function goTo( x, y, z, xd, zd )
	while depth > y do
		if turtle.up() then
			depth = depth - 1
		elseif turtle.digUp() or turtle.attackUp() then
			collect()
		else
			sleep( 0.5 )
		end
	end

	if xPos > x then
		while xDir ~= -1 do
			turnLeft()
		end
		while xPos > x do
			if turtle.forward() then
				xPos = xPos - 1
			elseif turtle.dig() or turtle.attack() then
				collect()
			else
				sleep( 0.5 )
			end
		end
	elseif xPos < x then
		while xDir ~= 1 do
			turnLeft()
		end
		while xPos < x do
			if turtle.forward() then
				xPos = xPos + 1
			elseif turtle.dig() or turtle.attack() then
				collect()
			else
				sleep( 0.5 )
			end
		end
	end

	if zPos > z then
		while zDir ~= -1 do
			turnLeft()
		end
		while zPos > z do
			if turtle.forward() then
				zPos = zPos - 1
			elseif turtle.dig() or turtle.attack() then
				collect()
			else
				sleep( 0.5 )
			end
		end
	elseif zPos < z then
		while zDir ~= 1 do
			turnLeft()
		end
		while zPos < z do
			if turtle.forward() then
				zPos = zPos + 1
			elseif turtle.dig() or turtle.attack() then
				collect()
			else
				sleep( 0.5 )
			end
		end
	end

	while depth < y do
		if turtle.down() then
			depth = depth + 1
		elseif turtle.digDown() or turtle.attackDown() then
			collect()
		else
			sleep( 0.5 )
		end
	end

	while zDir ~= zd or xDir ~= xd do
		turnLeft()
	end
end

print( "Tunnelling..." )

for n=1,length do
    turtle.placeDown()
    tryDigUp()
    turtle.turnLeft()
    xDir, zDir = -zDir, xDir
    tryDig()
    tryUp()
    yPos = yPos + 1
    tryDig()
    turtle.turnRight()
    xDir, zDir = zDir, -xDir
    turtle.turnRight()
    xDir, zDir = zDir, -xDir
    tryDig()
    tryDown()
    yPos = yPos - 1
    tryDig()
    turtle.turnLeft()
    xDir, zDir = -zDir, xDir

    if n<length then
        tryDig()
        if not tryForward() then
            print( "Aborting Tunnel." )
            returnSupplies(true)
            goTo(0, 0, 0, 0, 0)
            break
        end
    else
        print( "Tunnel complete." )
        returnSupplies(true)
        goTo(0, 0, 0, 0, 0)
    end

end

print( "Tunnel complete." )
print( "Mined "..collected.." items total." )