input_file = "input.txt"

# -1 is floor
# 0 is empty seat
# 1 is occupied seat

# Map represents each cell with [current_state,next_state]
# Would a dictionary be better ?
seating_map = []


def load_map():
    with open(input_file) as text_map:
        line = text_map.readline().strip("\n")

        while line:
            seating_map.append([])
            for character in line:
                # Set every seat to occupied as its the first iteration anyway
                seating_map[-1].append([1 if character == 'L' else -1, 1])

            line = text_map.readline().strip("\n")


def run_adjacent_seats():
    """
    Run the cellular automata with the following rules :
        If empty and adjacent are empty, seat
        If seated and 4 or more neighbours, become empty
        If floor, pass
    """
    load_map()

    game_stable = False
    occupied_seats = 0
    iteration = 0

    while not game_stable:

        for i in range(len(seating_map)):
            for j in range(len(seating_map[0])):
                current_cell = seating_map[i][j]
                if current_cell[0] < 0:
                    continue

                seated_neighbours = 0

                for cell_position in [(i+di, j+dj) for di in [-1, 0, 1] for dj in [-1, 0, 1]]:
                    if cell_position != (i, j) and \
                       0 <= cell_position[0] < len(seating_map) and 0 <= cell_position[1] < len(seating_map[0]):

                        seated_neighbours += 1 if seating_map[cell_position[0]][cell_position[1]][0] > 0 else 0

                if current_cell[0] == 0 and seated_neighbours == 0:
                    current_cell[1] = 1
                elif current_cell[0] == 1 and seated_neighbours >= 4:
                    current_cell[1] = 0

        game_stable = True
        occupied_seats = 0

        # Should be integrated to the first loop to speed things up
        for i in range(len(seating_map)):
            for j in range(len(seating_map[0])):
                current_cell = seating_map[i][j]
                if current_cell[0] < 0:
                    continue

                if game_stable and current_cell[0] != current_cell[1]:
                    game_stable = False

                current_cell[0] = current_cell[1]
                occupied_seats += current_cell[0]

        iteration += 1

    print(f"The number of occupied seats when stabilized is {occupied_seats}")


run_adjacent_seats()