Minecraft Turtle: Spiral miner (Robust)

    --[[
    2015 (c) psychedelixx
    Minecraft Turtle: Spiral miner (Robust)
    2015-01-04

    Mines in a spiralform (spin me right round baby) and stays on the level it started.

    Robust API:
    http://computercraft.info/wiki/Robust_Turtle_API

    Usage:
        - use turtle and type "label set <name>"
          (to give your turtle an unique name so it remembers its programs)
        - type "pastebin get 7Ckr8y7s spiral"
        - type "spiral <limit> [<fillGround 0|1 default 0> <factor default 1.5> <useTesseract 0|1 default 0>]"
    - place chests in slot 16
    ]]
torchesAvailable = false
chestsAvailable = false
torchSlot = 15
factor = 1.5
useTesseract = false

function move()
    slot = 1
    while not turtle.detectDown() and fillGround == 1 do
        turtle.select(slot)
        turtle.placeDown()

        if slot < 13 then
            slot = slot+1
        else
            print("no items to fill ground")
            fillGround = 0
            break
        end
    end

    t.dig()
    t.forward()
    t.digUp()

    empty = 0
    for slot = 1, 13 do
        if turtle.getItemCount(slot) == 0 then
            empty = 1
            break
        end
    end

    --[[ if turtle is full, turn around, place chest, move items into it, turn around and continue ]]--
    if empty == 0 then
        t.turnAround()

        if not chestsAvailable then
            print("Please put chests in slot 15 and press enter to continue")
            read()
        end

        turtle.select(14)
        turtle.place()

        for slot = 1, 13 do
                turtle.select(slot)
                turtle.drop()
        end

        if useTesseract then
            os.sleep(0.5)
            turtle.select(14)
            turtle.dig()
        end

        if turtle.getItemCount(14) > 0 then
                chestsAvailable = true
        else
                chestsAvailable = false
        end

        t.turnAround()
    end
end

local args = { ... }
if #args < 1 then
    print("")
    print("spiral <limit> [<fillGround 0|1 default 0> <factor default 1.5> <useTesseract 0|1 default 0]")
    print("place chests/tesseract in slot 14")
    print("place torches in slots 15 and 16")

    error()
end

if #args >= 1 then
    limit  = tonumber(args[1])
    fillGround = 0
end
if #args >= 2 then
    fillGround = tonumber(args[2])
end
if #args >= 3 then
    factor= tonumber(args[3])
end
if #args >= 4 then
    if tonumber(args[4]) > 0 then
        useTesseract = true
    else
        useTesseract = false
    end
end

if turtle.getFuelLevel() < 0.75*limit*limit + limit then
    print("I need " .. (0.75*limit*limit + limit) - turtle.getFuelLevel() .. " more fuel!")
else
    print("======== 2015 (c) psychedelixx ========")
    print("Let's go!")
    print("Mining a spiral...")

    if turtle.getItemCount(15)+turtle.getItemCount(16) > 0 then
        torchesAvailable = true
    else
        print("")
        print("Warning: no torches found in slot 15 and 16. Press enter to continue")
        read()
        torchesAvailable = false
    end

    if turtle.getItemCount(14) > 0 then
        chestsAvailable = true
    else
        print("")
        print("Warning: no chests found in slot 14. Press enter to continue")
        read()
        chestsAvailable = false
    end

    if turtle.getItemCount(15) > 0 then
        torchesAvailable = true
        torchSlot = 15
    elseif turtle.getItemCount(16) > 0 then
        torchesAvailable = true
        torchSlot = 16
    else
        torchesAvailable = false
    end

    if turtle.getItemCount(14) > 0 then
        chestsAvailable = true
    else
        chestsAvailable = false
    end

    x = 0

    repeat
        x = x + 1
        y = math.ceil(x*factor)

        for i = 1, y do
            move()
            if i%7 == 0 and y-i > 5 and torchesAvailable and turtle.detectDown() then
                t.turnAround()
                turtle.select(torchSlot)

                turtle.place()
                t.turnAround()

                if torchSlot == 15 and turtle.getItemCount(torchSlot) == 0 then
                    torchSlot = 16
                elseif torchSlot == 16 and turtle.getItemCount(torchSlot) == 0 then
                    torchSlot = 15
                end

                if turtle.getItemCount(15) + turtle.getItemCount(16) > 0 then
                    torchesAvailable = true
                else
                    torchesAvailable = false
                end
            end
        end

        if torchesAvailable then
            t.dig()
            turtle.select(torchSlot)
            turtle.place()
        end

        t.right()

        print (y .. " / " .. limit .. "... fuel: " .. turtle.getFuelLevel())
    until y >= limit
    print("Done")
end