Modded Tunnel

local tArgs = { ... }
-- Config for refueling itself
local refuelSelf = false

-- Various checks and balances. You can skip this part.
    -- check usage of arguments
    if #tArgs < 1 or #tArgs > 2 then
        print( "Usage: "..shell.getRunningProgram().." <length> [height]" )
        return
    end

    -- check if height argument was specified
    -- if not, default 3x3 tunnel will be dug out
    if not tArgs[2] then
        height = 3
    else
        height = tonumber(tArgs[2])
    end

    -- why would you run this on anything other than a turtle?
    if not turtle then
        print( "You must run this on a turtle." )
        return
    end

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

-- Various variables
local depth = 0
local collected = 0
local facing = 0
local currHeight = 0
local oldRight = turtle.turnRight()
local oldLeft = turtle.turnLeft()
local oldDig = turtle.dig()
local oldDigUp = turtle.digUp()
local oldDigDown = turtle.digDown()

-- Redefining some of the turtle functions
local function turtle.turnRight()
    facing = facing + 1
    if facing == 4 then
        facing = 0
    end
    return oldRight()
end

local function turtle.turnLeft()
    facing = facing - 1
    if facing == -4 then
        facing = 0
    end
    return oldLeft()
end

-- Refuel function
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 refuelSelf then
                    if turtle.refuel(1) then
                        turtle.select(1)
                        return true
                    end
                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

-- Return to base if full
local function rtb()
    local returnHeight = currHeight
    local returnFacing = facing
    while currHeight ~= 0 do
        turtle.down()
        currHeight = currHeight - 1
    end
    if facing < 0 then
        while facing ~= 0 do
            turtle.turnRight()
            facing = facing + 1
        end
    elseif facing > 0 then
        while facing ~= 0 do
            turtle.turnLeft()
            facing = facing - 1
        end
    end
    turtle.turnRight()
    turtle.turnRight()
    for i = 1, depth do
        refuel()
        turtle.forward()
    end
    for i = 1, 16 do
        turtle.select(i)
        turtle.drop()
    end
    turtle.turnRight()
    turtle.turnRight()
    for i = 1, depth do
        refuel()
        while not turtle.forward()
            turtle.dig()
        end
    end
    for i = 1, returnHeight do
        turtle.up()
    end
    if returnFacing < 0 then
        turtle.turnLeft()
    else
        turtle.turnRight()
    end
end

local function turtle.dig()
    for i = 1, 16 do
        if turtle.compare(i) then
            turtle.select(i)
            return oldDig()
        end
    end
    for i = 1, 16 do
        if turtle.getItemCount(i) < 64 then
            turtle.select(i)
            return oldDig()
        end
    end
    rtb()
end

local function turtle.digUp()
    for i = 1, 16 do
        if turtle.compareUp(i) then
            turtle.select(i)
            return oldDigUp()
        end
    end
    for i = 1, 16 do
        if turtle.getItemCount(i) < 64 then
            turtle.select(i)
            return oldDigUp()
        end
    end
    rtb()
end

local function turtle.digDown()
    for i = 1, 16 do
        if turtle.compareDown(i) then
            turtle.select(i)
            return oldDigDown()
        end
    end
    for i = 1, 16 do
        if turtle.getItemCount(i) < 64 then
            turtle.select(i)
            return oldDigDown()
        end
    end
    rtb()
end

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

-- Try digging something
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 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

-- Start tunneling
print( "Tunnelling..." )

for n=1,length do
    tryDigUp()
    turtle.turnLeft()
    tryDig()
    for i = 1, height do
        tryUp()
        currHeight = currHeight + 1
        tryDig()
    end
    turtle.turnRight()
    turtle.turnRight()
    tryDig()
    for i = 1, height do
        tryDown()
        currHeight = currHeight - 1
        tryDig()
    end
    turtle.turnLeft()

    if n<length then
        tryDig()
        if not tryForward() then
            print( "Aborting Tunnel." )
            break
        else
            depth = depth + 1
        end
    else
        print( "Tunnel complete." )
    end

end


print( "Returning to start..." )

-- Return to where we started
turtle.turnLeft()
turtle.turnLeft()
while depth > 0 do
    if turtle.forward() then
        depth = depth - 1
    else
        turtle.dig()
    end
end
-- Drop items into the chest
for i = 1, 16 do
    turtle.select(i)
    turtle.drop()
end
turtle.turnRight()
turtle.turnRight()


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