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term.setBackgroundColor(colors.black)
term.clear()

local w, h = term.getSize()
local grid = {}

-- initialize grid
for y = 1, h do
    grid[y] = {}
    for x = 1, w do
        grid[y][x] = false -- false = closed ▣, true = open []
    end
end

local function drawGrid()
    for y = 1, h do
        term.setCursorPos(1, y)
        for x = 1, w do
            if grid[y][x] then
                term.write("[]")  -- open
            else
                term.write("▣ ")  -- closed
            end
        end
    end
end

-- carve a random sweeping path
local function carve()
    local col = math.random(1, w)
    for row = 1, h do
        grid[row][col] = true
        local r = math.random(3)
        if r == 1 and col > 1 then
            col = col - 1
        elseif r == 3 and col < w then
            col = col + 1
        end
    end
end

-- randomly re-close cells
local function fade()
    for y = 1, h do
        for x = 1, w do
            if math.random(120) < 2 then
                grid[y][x] = false
            end
        end
    end
end

while true do
    carve()
    fade()
    drawGrid()
    sleep(0.07)
end