madness

--Define variables
local colourList = {}
local coloursUsed = {}
local coloursUnused  = {}
local dir = 1
local x = 1
local y = 1
local w = 1
local h = 1
local grid = {}
local sequential = true
local step = 1

--Miscellaneous helper functions to simplify code later
--Generate either -1 or 1
local function randomSign()
        local k = math.random(2)
        return (k * 2 - 3)
end
--Turn integers from 1 to 16 into their colour vaues without needing to perform exponents.
local function colourSwitch(c)
        if c == 1 then return 1
        elseif c == 2 then return 2
        elseif c == 3 then return 4
        elseif c == 4 then return 8
        elseif c == 5 then return 16
        elseif c == 6 then return 32
        elseif c == 7 then return 64
        elseif c == 8 then return 128
        elseif c == 9 then return 256
        elseif c == 10 then return 512
        elseif c == 11 then return 1024
        elseif c == 12 then return 2048
        elseif c == 13 then return 4096
        elseif c == 14 then return 8192
        elseif c == 15 then return 16384
        elseif c == 16 then return 32768
        end
end

--Helper functions for creating a ruleset.

local function initColourLists()
        for i=1,16 do colourList[i] = {} end
        coloursUsed = {16}
        coloursUnused = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
end
local function chooseColours()
        local n = math.random(15)
        local choicesLeft = table.getn(coloursUnused)
        local choice = 1

        --Choose colours randomly from the list of unchosen colours
        for i=1,n do
                choice = math.random(choicesLeft)
                coloursUsed[i+1] = table.remove(coloursUnused, choice)
                choicesLeft = choicesLeft - 1
        end

        --Set up colourList linkage
        for i=1,n do
                colourList[coloursUsed[i]][2] = coloursUsed[i+1]
        end
        colourList[coloursUsed[n]][2] = coloursUsed[1]
end
local function chooseDirections()
        local n = table.getn(coloursUsed)
        local total = 0
        local s = 0

        --Randomise the direction for all colours used.
        for i, c in ipairs(coloursUsed) do
                s = randomSign()
                colourList[c][1] = s
                total = total + s
        end

        --If all colours turn in the same direction, switch the direction of one used colour.
        if math.abs(total) == n then
                colourList[coloursUsed[1]][1] = - colourList[coloursUsed[1]][1]
        end
end

--Function to create the play-space and position the ant/
local function initGrid()
        for i=1,w do
                grid[i] = {}
                for j=1,h do
                        grid[i][j] = 16
                end
        end

        x = math.ceil(w/2)
        y = math.ceil(h/2)
        dir = math.random(4)
end

--Step function for ant movement.  Returns true until the ant leaves the grid.
local function move()
        --Move the ant
        if dir == 1 then x = x + 1
        elseif dir == 2 then y = y + 1
        elseif dir == 3 then x = x - 1
        elseif dir == 4 then y = y - 1
        end

        --If out of bounds, return false to end the program
        if x<1 or x>w or y<1 or y>h then
                return false
        end

        --Change colour of new position and direction
        local c = grid[x][y]
        grid[x][y] = colourList[c][2]
        dir = dir + colourList[c][1]

        --Correct directions outside of possible values
        if dir == 0 then dir = 4
        elseif dir == 5 then dir = 1
        end

        return true
end

--Function to generate a ruleset and play it out.
function play(monitorSide, sequential, step)
        local m = peripheral.wrap(monitorSide)
        if not m.isColor() then error("Advanced monitor required.") end
        m.setTextScale(0.5)
        w, h = m.getSize()
        if sequential ~= false then sequential = true end
        step = tonumber(step) or 1

        --randomise background colour
        --standard can be set by replacing math.random(16) with an integer from 1 to 16
        m.setBackgroundColour(colourSwitch(math.random(16)))
        m.clear()

        --initialize variables and choose generator ruleset
        initColourLists()
        initGrid()
        chooseColours()
        chooseDirections()
        local i = 0

        --play out the ruleset
        while move() do
                m.setCursorPos(x, y)
                m.setBackgroundColour(colourSwitch(grid[x][y]))
                m.write(" ")
                i = i + 1

                --leave breaks so that the program yields and to allow stopping by right-click
                if sequential and i == step then
                        i = 0
                        os.startTimer(0.1)
                        local e = os.pullEvent()
                        if e == 'monitor_touch' then return true end
                end
        end
end


--The part of the program that runs it if not used as an API
local tArgs = {...}
local side = tArgs[1] or "top"
if tArgs[2] == 'false' then sequential = false end
if tArgs[3] ~= nil then step = tonumber(tArgs[3]) end

while true do
        play(side, sequential, step)
        os.pullEvent('monitor_touch')
end