AdventOfCode2018, day 23

class Cart:
    STATES = [-1, 0, 1]

    MOVEMENT_INSTRUCTIONS = {'^': 3, 'v': 1, '<': 2,
                             '>': 0}

    def __init__(self, pos, sign, raw_map):
        self.raw_map = raw_map
        map_width = len(raw_map.split('\n')[0]) + 1

        self.directions = [1, map_width, -1, -map_width]
        self.pos = pos
        self.state = 0
        self.direction = self.MOVEMENT_INSTRUCTIONS[sign]

    def intersect(self):
        state = self.state % 3
        self.direction = (self.direction + self.STATES[state] + 4) % 4
        self.state = (state + 1) % 3

    def move(self):
        self.pos += self.directions[self.direction]
        track = self.raw_map[self.pos]
        if track in ['\\', '/']:
            self.corner(track)
        elif track == '+':
            self.intersect()

    def corner(self, track):
        if track == '/':
            if self.direction == 0:
                self.direction = 3
            elif self.direction == 1:
                self.direction = 2
            elif self.direction == 2:
                self.direction = 1
            elif self.direction == 3:
                self.direction = 0
            else:
                print(self.direction)
                raise ValueError
        else:
            if self.direction == 2:
                self.direction = 3
            elif self.direction == 3:
                self.direction = 2
            elif self.direction == 1:
                self.direction = 0
            elif self.direction == 0:
                self.direction = 1
            else:
                print(self.direction)
                print(track)
                raise ValueError


def find_solutions(raw_map, return_on_first_collision=False):
    carts = {}
    map_width = len(raw_map.split('\n')[0]) + 1
    for pos, c in enumerate(raw_map):
        if c in '<>^v':
            carts[pos] = Cart(pos, c, raw_map)
    # MAP_RAW = [c for c in MAP_RAW if c != '\n']
    round_counter = 0
    collision = 0
    while len(carts) > 1:
        current_carts = sorted(carts.keys())
        for cart_pos in current_carts:
            try:
                cart = carts[cart_pos]
            except KeyError:
                continue
            cart.move()
            del carts[cart_pos]
            new_pos = cart.pos
            if new_pos in carts:
                collision += 1
                if collision == 1:
                    first_collision_coordinates = (
                        new_pos % map_width, new_pos // map_width)
                    print('First collision : {},{}'.format(
                        *first_collision_coordinates
                        )
                          )
                    if return_on_first_collision:
                        return first_collision_coordinates
                del carts[new_pos]
            else:
                carts[new_pos] = cart
        round_counter += 1
    try:
        try:
            remaining_cart = carts.keys()[0]
        except TypeError:  # Python3 .keys() is not a list
            remaining_cart = list(carts.keys())[0]
        remaining_cart_coordinates = (remaining_cart % map_width,
                                      remaining_cart // map_width)
        print('Last remaining cart: {},{}'.format(*remaining_cart_coordinates))
        return remaining_cart_coordinates
    except IndexError:
        print('No carts left after the last collision!')
        return None


if __name__ == '__main__':
    from input_day13 import raw

    #
    MAP_RAW = raw
    map = [[c for c in line] for line in MAP_RAW.split('\n') if line]

    test_map_part1 = r"""/->-\
|   |  /----\
| /-+--+-\  |
| | |  | v  |
\-+-/  \-+--/
  \------/   """

    test_map_part2 = r"""/>-<\
|   |
| /<+-\
| | | v
\>+</ |
  |   ^
  \<->/"""
    assert find_solutions(test_map_part1, return_on_first_collision=True) == (7, 3)
    assert find_solutions(test_map_part2) == (6, 4)
    find_solutions(MAP_RAW)