day13.coconut

def parse_fold(line):
  tokens = line.strip().split()
  assert tokens |> len == 3
  assert (tokens[0], tokens[1]) == ('fold', 'along')
  axis, value = tokens[2].split('=')
  return (axis, value |> int)

with open('./inputs/day13.txt') as infile:
  # parse points
  points = []
  line = infile.readline().strip()
  while line != '':
    points.append(line.split(',') |> map$(int)..>tuple)
    line = infile.readline().strip()
  
  folds = infile.readlines() |> map$(parse_fold)..>list

def fold_point(along_axis, axis_value, (px, py)):
  match along_axis:
    case 'x':
      # point disappears
      if px == axis_value:
        return None
      nx = axis_value - (px - axis_value) if px > axis_value else px
      return (nx, py)
    case 'y':
      if py == axis_value:
        return None
      ny = axis_value - (py - axis_value) if py > axis_value else py
      return (px, ny)

part1_ans = None
remaining_points = set(points)
for along_axis, axis_value in folds:
  new_points = remaining_points |> map$(fold_point$(along_axis, axis_value)) |> filter$(p -> p is not None) |> set
  if part1_ans is None:
    part1_ans = new_points |> len
  remaining_points = new_points
print(f'part 1 = {part1_ans}')

max_x = remaining_points |> map$(.[0])..>max
max_y = remaining_points |> map$(.[1])..>max

grid = range(max_y+1) |> map$(_->range(max_x+1)|>map$(_->'⬛')..>list)..>list

for point in remaining_points:
  x, y = point
  grid[y][x] = '🟥'

# just eyeball the result
print('part 2 (grid):')
print(grid |> map$(''.join) |> '\n'.join)