ComputerCraft: 'Fell' excavates up for trees

--v1.1 by GraySloth 2013-Mar-14, new cc1.5 version. will probably not change much,
--here is a video demonstration of my scripts, it is almost good. http://youtu.be/9vhl7dSENs8
--based on the excavate program but goes up instead of down, great for jungle and ExtrabiomesXL trees
local tArgs = { ... }
if #tArgs ~= 1 then
    print( "Usage: fell <diameter>" )
    return
end

-- the "timber" variable will prevent it from going up forever, by making it return once it has gone up two levels without digging up or forward
local size = tonumber( tArgs[1] )
if size < 1 then
    print( "fell diameter must be positive" )
    return
end

local depth = 0
local unloaded = 0
local collected = 0
local timber = 0

local xPos,zPos = 0,0
local xDir,zDir = 0,1

local goTo -- Filled in further down
local refuel -- Filled in further down

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()
    local x,y,z,xd,zd = xPos,depth,zPos,xDir,zDir
    print( "Returning to ground level..." )
    goTo( 0,0,0,0,-1 )

    local fuelNeeded = 2*(x+y+z) + 1
    if not refuel( fuelNeeded ) then
        unload( true )
        print( "Waiting for fuel" )
        while not refuel( fuelNeeded ) do
            sleep(1)
        end
    else
        unload( true )
    end

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

local function collect()
    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 nTotalItems > collected then
        collected = nTotalItems
        if math.fmod(collected + unloaded, 50) == 0 then
            print( "Chopped "..(collected + unloaded).." items." )
        end
    end

    if bFull then
        print( "No empty slots left." )
        return false
    end
    return true
end

function refuel( ammount )
    local fuelLevel = turtle.getFuelLevel()
    print( fuelLevel )
    if fuelLevel == "unlimited" then
        return true
    end

    local needed = ammount or (xPos + zPos + depth + 1)
    if turtle.getFuelLevel() < needed then
        print( needed )
        local fueled = false
        for n=1,16 do
            if turtle.getItemCount(n) > 0 then
                turtle.select(n)
                if turtle.refuel(1) then
                    print( fuelLevel )
                    while turtle.getItemCount(n) > 0 and turtle.getFuelLevel() < needed do
                        turtle.refuel(1)
                        print( fuelLevel )
                    end
                    if turtle.getFuelLevel() >= needed then
                        turtle.select(1)
                        return true
                    end
                end
            end
        end
        turtle.select(1)
        return false
    end

    return true
end

local function tryForwards()
    if not refuel() then
        print( "Not enough Fuel" )
        returnSupplies()
    end

    while not turtle.forward() do
        if turtle.detect() then
            if turtle.dig() then
                timber = 0
                if not collect() then
                    returnSupplies()
                end
            else
                return false
            end
        elseif turtle.attack() then
            if not collect() then
                returnSupplies()
            end
        else
            sleep( 0.5 )
        end
    end

    xPos = xPos + xDir
    zPos = zPos + zDir
    return true
end

local function tryUp()
    if not refuel() then
        print( "Not enough Fuel" )
        returnSupplies()
    end

    while not turtle.up() do
        if turtle.detectUp() then
            if turtle.digUp() then
                timber = 0
                if not collect() then
                    returnSupplies()
                end
            else
                return false
            end
        elseif turtle.attackUp() then
            if not collect() then
                returnSupplies()
            end
        else
            sleep( 0.5 )
        end
    end


    depth = depth + 1
    if math.fmod( depth, 10 ) == 0 then
        print( "Ascended "..depth.." metres." )
    end

    timber = timber + 1
    if timber > 2 then
        return false
    end

    return true
end

local function turnLeft()
    turtle.turnLeft()
    xDir, zDir = -zDir, xDir
end

local function turnRight()
    turtle.turnRight()
    xDir, zDir = zDir, -xDir
end

function goTo( x, y, z, xd, zd )
    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

    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.up() then
            depth = depth + 1
        elseif turtle.digUp() or turtle.attackUp() then
            collect()
        else
            sleep( 0.5 )
        end
    end

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

if not refuel() then
    print( "Out of Fuel" )
    return
end

print( "Chopping..." )

local reseal = false
turtle.select(1)
if turtle.digUp() then
    reseal = true
end

local alternate = 0
local done = false
while not done do
    for n=1,size do
        for m=1,size-1 do
            if not tryForwards() then
                done = true
                break
            end
        end
        if done then
            break
        end
        if n<size then
            if math.fmod(n + alternate,2) == 0 then
                turnLeft()
                if not tryForwards() then
                    done = true
                    break
                end
                turnLeft()
            else
                turnRight()
                if not tryForwards() then
                    done = true
                    break
                end
                turnRight()
            end
        end
    end
    if done then
        break
    end

    if size > 1 then
        if math.fmod(size,2) == 0 then
            turnRight()
        else
            if alternate == 0 then
                turnLeft()
            else
                turnRight()
            end
            alternate = 1 - alternate
        end
    end

    if not tryUp() then
        done = true
        break
    end
end

print( "Returning to ground level..." )

-- Return to where we started
goTo( 0,0,0,0,-1 )
unload( false )
goTo( 0,0,0,0,1 )

-- Seal the hole
if reseal then
    turtle.placeUp()
end

print( "Chopped "..(collected + unloaded).." items total." )