part2_weird_error.pi

main =>
  G = read_file_lines(),
  H = G.len,
  W = G[1].len,
  Max = 0,
  foreach (I in 1..W)
    Max := max(Max, go([{I,1,south}])),
    Max := max(Max, go([{I,H,north}])),
    Max := max(Max, go([{1,I,east}])),
    Max := max(Max, go([{W,I,west}])),
  end,
  println(Max).

go(Beams) = R =>
  Energised = new_set(),
  Seen = new_set(),
  while (Beams.len > 0)
    {X,Y,Dir} = Beams.head,
    Beams := Beams.tail,
    if not(Seen.has_key({X,Y,Dir})) then
      Energised.put({X,Y}),
      Seen.put({X,Y,Dir}),
      New_beams = [{I,J,New_dir} : {I,J,New_dir} in step_beam(G[Y,X],X,Y,Dir), I >= 1, I <= W, J >= 1, J <=W],
      foreach (Beam in New_beams)
        Beams := [Beam|Beams]
      end,
    end,
  end,

  % foreach(J in 1..H)
  %   foreach(I in 1..W)
  %     if Energised.has_key({I,J}) then
  %       print("#"),
  %     else
  %       print(G[J,I]),
  %     end,
  %   end,
  %   nl,
  % end,
  R = Energised.size.

step_beam('.',X,Y,Dir) = [inc(X,Y,Dir)].
step_beam('|',X,Y,north) = [inc(X,Y,north)].
step_beam('|',X,Y,south) = [inc(X,Y,south)].
step_beam('|',X,Y,_) = [inc(X,Y,north),inc(X,Y,south)].
step_beam('-',X,Y,east) = [inc(X,Y,east)].
step_beam('-',X,Y,west) = [inc(X,Y,west)].
step_beam('-',X,Y,_) = [inc(X,Y,west),inc(X,Y,east)].
step_beam('/',X,Y,east) = [{X,Y-1,north}].
step_beam('/',X,Y,west) = [{X,Y+1,south}].
step_beam('/',X,Y,north) = [{X+1,Y,east}].
step_beam('/',X,Y,south) = [{X-1,Y,west}].
step_beam('\\',X,Y,east) = [inc(X,Y,south)].
step_beam('\\',X,Y,west) = [inc(X,Y,north)].
step_beam('\\',X,Y,north) = [inc(X,Y,west)].
step_beam('\\',X,Y,south) = [inc(X,Y,east)].

inc(X,Y,north) = {X,Y-1,north}.
inc(X,Y,east) = {X+1,Y,east}.
inc(X,Y,south) = {X,Y+1,south}.
inc(X,Y,west) = {X-1,Y,west}.