local fmt = require "fmt"
require "table2"

local rows, cols = 0, 0  --  extent of input configuration
local rx, cx = 0, 0      --  grid extent (includes border)
local mn = {}            --  offsets of Moore neighborhood

local function gprint(grid)
    print(string.rep("__", cols))
    print()
    for r = 1, rows do
        for c = 1, cols do fmt.write(" %s", grid[r * cx + c + 1]) end
        print()
    end
end

local function step(dst, src)
    for r = 1, rows do
        for c = 1, cols do
            local x = r * cx + c + 1
            dst[x] = src[x]
            if dst[x] == "H" then
                dst[x] = "t"
            elseif dst[x] == "t" then
                dst[x] = "."
            elseif dst[x] == "." then
                local nn = 0
                for mn as n do
                    if src[x + n] == "H" then nn += 1 end
                end
                if nn == 1 or nn == 2 then dst[x] = "H" end
            end
        end
    end
end

local nl = os.platform == "windows" ? "\r\n" : "\n"
local src_rows = io.contents("ww.config"):rstrip():split(nl)
rows = #src_rows
for src_rows as r do
    if #r > cols then cols = #r end
end
rx = rows + 2
cx = cols + 2
mn = {-cx - 1, -cx, -cx + 1, -1, 1, cx - 1, cx, cx + 1}

--  Allocate two grids and copy input into first grid.
local odd  = table.rep(rx * cx, " ")
local even = table.rep(rx * cx, " ")

local ri = 0
for src_rows as r do
    for i = 0, #r - 1 do
        odd[(ri + 1) * cx + 2 + i] = r[i + 1]
    end
    ri += 1
end

--  Run.
while true do
    gprint(odd)
    step(even, odd)
    io.read() --  wait for enter to be pressed

    gprint(even)
    step(odd, even)
    io.read() --  ditto
end