#!/usr/bin/env python3

m = []

obstacles = set()
start = (-1,-1)

lx = ly = 0
with open('day06') as f:
    for y,l in enumerate(f):
        ly += 1
        lx = lx or len(l)
        for x,ll in enumerate(l):
            match ll:
                case '#': obstacles.add((y,x))
                case '^': start = (y,x)

lookup = {
    (-1, 0): ( 0, 1),
    ( 0, 1): ( 1, 0),
    ( 1, 0): ( 0,-1),
    ( 0,-1): (-1, 0)
}

# 1
def walk(pos, dir):
    visited = []
    visited.append((pos, dir))
    npos = (pos[0]+dir[0], pos[1]+dir[1])

    while True:
        while npos not in obstacles:
            pos = npos
            visited.append((pos,dir))
            npos = (pos[0]+dir[0], pos[1]+dir[1])

            if npos[0]==ly or npos[0]==-1: return visited
            if npos[1]==lx or npos[1]==-1: return visited

        dir = lookup[dir]
        npos = (pos[0]+dir[0], pos[1]+dir[1])

visited = walk(start, (-1,0))
vpos = set([v[0] for v in visited])
res1 = len(vpos)

# 2
def loop(pos, dir, sv, obstacles):
    while True:
        npos = (pos[0] + dir[0], pos[1] + dir[1])
        if npos[0]==ly or npos[0]==-1: return False
        if npos[1]==lx or npos[1]==-1: return False

        while npos not in obstacles:
            sv.add((pos,dir))

            pos = npos
            npos = (pos[0]+dir[0], pos[1]+dir[1])

            if (pos, dir) in sv:
                return True

            if npos[0]==ly or npos[0]==-1: return False
            if npos[1]==lx or npos[1]==-1: return False

        dir = lookup[dir]

done = set()
res2 = 0
for k,(pos,_) in enumerate(visited):
    if pos == start: continue
    if pos in obstacles: continue
    if pos in done: continue

    done.add(pos)

    start = visited[k-1][0]
    dir = visited[k-1][1]
    sv = set(visited[:k])
    if loop(start, dir, sv, obstacles | {pos}):
        res2 += 1