12.ndc

init, lines := read_file("input/12").split_once("\n\n");
_, init := init.split_once(": ");

rules := %{:"."};
for line in lines.lines() {
  from, to := line.split_once(" => ");
  rules[from] = to;
}

fn evolve(cur,idx0) {
  idx0 += 1;
  // Pad with ... 
  cur := "..." ++ cur ++ "...";
  len := cur.len();
  new := "";
  for i in 2..(len-2) {
    slice := cur.slice(i-2,5);
    new.append(rules[slice]);
  }

  ok := true;
  trim := 0;
  for c in new {
    if c == "." and ok {
      trim += 1;
    } else {
      ok = false;
    }
  }
  l := new.len();

  idx0 - trim, new.slice(trim, l - trim)
}

fn score(idx0, cur) {
  idx := 0 - idx0;
  ans := 0;
  for c in cur {
    if c == "#" {
      ans += idx;
    }
    idx += 1;
  }
  ans
}
cur := init;
idx0 := 0;
print("0", cur);
i := 0;
a := [];
target := 50000000000;
while i < target {
  idx0, cur = evolve(cur, idx0);
  // print(i, idx0, score(idx0, cur), cur);
  a.push(score(idx0, cur));
  i += 1;

  if a.len() >= 2 and a[-1] - a[-2] == 96 {
    rem := target - i;
    print(score(idx0 - rem, cur));
    assert(false);
  }
}