from lib import Grid2D, add2

CARTS = (
    ("^", Grid2D.N, "|"),
    ("v", Grid2D.S, "|"),
    (">", Grid2D.E, "-"),
    ("<", Grid2D.W, "-"),
)
TURNS = "lsr"
DIRS = [(-1, 0), (0, 1), (1, 0), (0, -1)]


def part_1(data):
    g = Grid2D(data)
    first_shown = False
    carts = []
    occupied = set()

    for c, d, r in CARTS:
        for cart in g.find(c):
            carts.append((cart, d, "l"))
            g[cart] = r
            occupied.add(cart)

    for _ in range(1, 100_000):
        carts = sorted(carts)

        ncarts = []
        i_to_skip = []
        for i in range(len(carts)):
            if i in i_to_skip:
                continue

            pos, dir, turn = carts[i]
            occupied.remove(pos)
            pos = add2(pos, dir)

            # detect collision and remove carts
            if pos in occupied:
                if first_shown is False:
                    print(f"{pos[1]},{pos[0]}")
                    first_shown = True
                # either from carts that haven't moved, yet
                for j in range(len(carts)):
                    jpos, _, _ = carts[j]
                    if jpos == pos:
                        i_to_skip.append(j)
                        break
                else:
                    # or from carts that have already moved
                    ncarts = list(filter(lambda c: c[0] != pos, ncarts))
                occupied.remove(pos)
                continue
            else:
                occupied.add(pos)

            if g[pos] == "+":
                if turn == "l":
                    dir = DIRS[(DIRS.index(dir) - 1) % len(DIRS)]
                elif turn == "r":
                    dir = DIRS[(DIRS.index(dir) + 1) % len(DIRS)]
                turn = TURNS[(TURNS.index(turn) + 1) % len(TURNS)]
            elif g[pos] == "/":
                if dir == g.E:
                    dir = g.N
                elif dir == g.W:
                    dir = g.S
                elif dir == g.N:
                    dir = g.E
                elif dir == g.S:
                    dir = g.W
                else:
                    assert False
            elif g[pos] == "\\":
                if dir == g.E:
                    dir = g.S
                elif dir == g.W:
                    dir = g.N
                elif dir == g.N:
                    dir = g.W
                elif dir == g.S:
                    dir = g.E
                else:
                    assert False

            ncarts.append((pos, dir, turn))
        carts = ncarts
        if len(carts) == 1:
            pos = carts[0][0]
            print(f"{pos[1]},{pos[0]}")
            return


def main():
    input_file = __file__.replace(".py", ".txt")
    with open(input_file) as f:
        data = f.read()
    part_1(data)


if __name__ == "__main__":
    main()