#!/usr/bin/env python3

import sys

import numpy as np
import scipy as sp

dtype = np.int32

input_file = sys.argv[1]

with open(input_file) as fd:
    lines = [line.rstrip() for line in fd.readlines()]

height = len(lines)
width = len(lines[0])
start = height - 2, 1
stop = 1, width - 2

directions = [
    (-1, 0),  # ^ North
    (0, 1),  # > East
    (1, 0),  # v South
    (0, -1),  # < West
]
directions_keys = ("^", ">", "v", "<")

walls = np.zeros((height, width), dtype)
for i in range(height):
    for j in range(width):
        if lines[i][j] == "#":
            walls[i, j] = 1
invwalls = 1 - walls

# print("Walls")
# print(walls)

# TEST 4

scores = np.zeros((height, width, len(directions)), dtype)
scores[start[0], start[1], 1] = 1

for i in range(1000):
    print("Step", i)
    oldscores = scores.copy()
    for od, odir in enumerate(directions):
        for nd, ndir in enumerate(directions):
            score = scores[:, :, nd]
            moved = sp.ndimage.shift(oldscores[:, :, od], ndir)
            increment = 1 if nd == od else 1001
            moved = (moved + increment) * (moved > 0)
            moved = moved * invwalls
            mask = (moved > 0) & ((score == 0) | (score > moved))
            scores[:, :, nd] = (score * ~mask) + (moved * mask)

    # for d, dir in enumerate(directions):
    #     print("Direction", directions_keys[d])
    #     print(scores[:, :, d])

    if (scores == oldscores).all():
        break
else:
    print("Limit!")

end_score = min(filter(lambda d: d > 0, scores[stop])) - 1
print(f"{end_score=}")

# TEST 3

# scores = [np.zeros((height, width), dtype) for _ in directions]
# scores[1][start] = 1
#
# for i in range(100):
#     print("Step", i)
#     for od, odir in enumerate(directions):
#         oldscore = scores[od].copy()
#         for nd, ndir in enumerate(directions):
#             score = scores[nd]
#             moved = sp.ndimage.shift(oldscore, ndir)
#             increment = 1 if nd == od else 1001
#             moved = (moved + increment) * (moved > 0)
#             moved = moved * invwalls
#             mask = (moved > 0) & ((score == 0) | (score > moved))
#             scores[nd] = (score * ~mask) + (moved * mask)
#
#     final_score = None
#     for d, dir in enumerate(directions):
#         print("Direction", directions_keys[d])
#         print(scores[d])
#         end_score = scores[d][stop]
#         if end_score > 0:
#             if final_score is None or end_score < final_score:
#                 final_score = end_score
#
#     if final_score:
#         final_score -= 1
#         print(f"{final_score=}")
#         break
# else:
#     print("Limit!")


# TEST 2

# score = np.zeros((height, width), dtype)
# score[start] = 1
#
# for i in range(10):
#     print("Step", i)
#     oldscore = score.copy()
#     for nd, ndir in enumerate(directions):
#         moved = sp.ndimage.shift(oldscore, ndir)
#         moved = (moved + 1) * (moved > 0)
#         moved = moved * invwalls
#         mask = (moved > 0) & ((score == 0) | (score > moved))
#         score = (score * ~mask) + (moved * mask)
#     print(score)

# TEST 1

# directions = np.array([[0, 1, 0], [1, 1, 1], [0, 1, 0]], dtype)
#
# visited = np.zeros((height, width), dtype)
# visited[start] = 1
#
# for i in range(1000):
#     print("Step", i)
#     new = sp.signal.convolve2d(visited, directions, mode="same")
#     visited = (((new > 0) - walls) > 0)
#     print(visited * 1)
#     if visited[stop]:
#         break
# else:
#     print("Limit!")
# print(i)