--[[
2016 (c) psychedelixx
Minecraft Spiralstairs (robust)
2016-10-14

Mines a spiral stairs (downwards left)

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 0gCW6AMP spiralstairs"
    - type "spiralstairs <size>"
- place stairs in slot 14
- place chests in slot 15
- place torches in slot 16
]]
stairsSlot = 14
chestSlot = 15
torchSlot = 16

function placeChestIfFull()
    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.up()
        t.turnAround()
        t.dig()

        if turtle.getItemCount(chestSlot) == 0 then
            print("Please put chests in slot 15 and press enter to continue")
            read()
        end

        turtle.select(chestSlot)
        turtle.place()

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

        t.turnAround()
        t.down()
    end
end

local args = { ... }

if #args ~= 1 then
    print("Usage: spiralstairs <size>")
    print("place stairs in slot 14")
    print("place chests in slot 15")
    print("place torches in slot 16")
    error()
end

function placeTorchIfNeeded(x)

    if (x+1)%13 == 0 and turtle.getItemCount(torchSlot) > 0 then
        oldSlot = turtle.getSelectedSlot()

        t.left()
        t.place(torchSlot)
        t.right()

        turtle.select(oldSlot)
    end
end

print("======== 2016 (c) psychedelixx ========")
print("Let's go!")
print("Mining spiral stairs...")

if turtle.getItemCount(chestSlot) == 0 then
    print("")
    print("Warning: no chests found in slot 15. Press enter to continue")
    read()
end

if turtle.getItemCount(torchSlot) == 0 then
    print("")
    print("Warning: no torches found in slot 16. Press enter to continue")
    read()
end

x = 0
done = false

repeat
    t.dig()
    t.forward()
    placeChestIfFull()

    t.digUp()
    t.up()
    t.placeDown(stairsSlot)

    x = x + 1

    placeTorchIfNeeded(x)

    if x%(tonumber(args[1])-1) == 0 then
        t.right()
    end
until done