3x3improved

if not turtle then
    printError("Requires a Turtle")
    return
end

local tArgs = { ... }
if #tArgs ~= 1 then
    local programName = arg[0] or fs.getName(shell.getRunningProgram())
    print("Usage: " .. programName .. " <length>")
    return
end

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

local collected = 0

local function collect()
    collected = collected + 1
    if math.fmod(collected, 25) == 0 then
        print("Mined " .. collected .. " items.")
    end
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.select(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 tryMove(moveFunc, digFunc, attackFunc)
    refuel()
    while not moveFunc() do
        if turtle.detect() then
            if not digFunc() then
                return false
            end
        elseif attackFunc and attackFunc() then
            collect()
        else
            sleep(0.5)
        end
    end
    return true
end

local function digLayer()
    -- Dig the 3x3 layer
    tryDigUp() -- Top center
    tryDigDown() -- Bottom center
    turtle.turnLeft()
    tryDig() -- Left center
    tryMove(turtle.up, tryDig, turtle.attack) -- Top left
    tryDig()
    turtle.turnRight()
    turtle.turnRight()
    tryDig() -- Top right
    tryMove(turtle.down, tryDig, turtle.attack)
    tryDig() -- Bottom right
    tryMove(turtle.down, tryDig, turtle.attack)
    tryDig() -- Bottom left
    turtle.turnLeft()
    turtle.turnLeft()
    tryDig() -- Left bottom
    turtle.turnRight()
    tryMove(turtle.up, tryDig, turtle.attack) -- Return to center
end

print("Tunnelling...")

for n = 1, length do
    digLayer()
    if n < length then
        if not tryMove(turtle.forward, tryDig, turtle.attack) then
            print("Aborting Tunnel.")
            break
        end
    else
        print("Tunnel complete.")
    end
end

-- Return to start
local depth = length
turtle.turnLeft()
turtle.turnLeft()
while depth > 0 do
    if not tryMove(turtle.forward, tryDig, turtle.attack) then
        print("Unable to return to start.")
        break
    end
    depth = depth - 1
end
turtle.turnRight()
turtle.turnRight()

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