#!/usr/bin/env bash
# Elementary cellular automatons (rule X) in pure Bash (zero dependencies)
# Usage: echo 'state' | elem rule# [iterations]
# Created by Luxferre in 2026, released into public domain

D2B=({0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1})
RULENO="$1"
if ((RULENO > 255 || RULENO < 0)); then
  echo "Invalid rule number!"
  exit 1
fi
rule="${D2B[RULENO]}"

ITERS="$2"
if [[ -z "$ITERS" ]]; then # get the iteration count dynamically
  shopt -s checkwinsize # enable checking the terminal size
  :|: # trigger the WINCH signal to get the size
  ITERS=$((LINES - 1)) # the row count is now in LINES
fi
[[ -z "$RENDER_CHAR" ]] && RENDER_CHAR='#'

# read and process the state
IFS= read -r state
state="${state//[[:space:]]/0}"
state="${state//[^0]/1}"
slen=$((${#state} - 1)) # length + 4 (temporary padding) - 5

for ((i=0; i<ITERS; ++i)); do
  state="0${state}0" # pad the current state from both sides
  newstate=''
  for ((k=0; k<slen; ++k)); do
    vidx=$((2#${state:k:3}))
    newstate="${newstate}${rule:$vidx:1}"    
  done
  state="$newstate"
  newstate="${newstate//0/ }"
  printf '%s\n' "${newstate//1/$RENDER_CHAR}"
done