#!/usr/bin/env python
# 2024 - Advent Of Code 6 - part 2

# file = 'input_example.txt'
file = 'input.txt'

input_lines = []
with open(file, encoding="utf-8") as f:
    for l in f.readlines():
        input_lines.append(list(l.strip()))

MAX_X = len(input_lines[0])
MAX_Y = len(input_lines)

vector=(0, 0)
gx = 0
gy = 0
for y in range(0, MAX_Y):
    for x in range(0, MAX_X):
        g = input_lines[y][x]
        if g not in ('.', '#'):
            gx = x
            gy = y
            print(f'found guard at {x}, {y}')
            if g == '^':
                vector = (0, -1)
            if g == 'v':
                vector = (0, 1)
            if g == '>':
                vector = (1, 0)
            if g == '<':
                vector = (-1, 0)
            print(f'{vector=}')

moves = [(0,-1), (1, 0), (0, 1), (-1, 0)]
move = moves.index(vector)

def move_and_detect(grid, posx, posy, v, m):
    visited = [(posx, posy, v)]
    while 0 < posx < MAX_X and 0 < posy < MAX_Y:
        nx = posx + v[0]
        ny = posy + v[1]
        if nx < 0 or nx >= MAX_X or ny < 0 or ny >= MAX_Y:
            return False
        if grid[ny][nx] != '#':
            posx += v[0]
            posy += v[1]
            if (posx, posy, v) in visited:
                return True
            visited.append((posx, posy, v))
        else:
            m += 1
            v = moves[m % 4]

    return False

start_gx = gx
start_gy = gy
start_vector = vector
start_move = move
found_loop = set()
while 0 <= gx < MAX_X and 0 <= gy < MAX_Y:
    nextx = gx + vector[0]
    nexty = gy + vector[1]
    if nextx < 0 or nextx >= MAX_X or nexty < 0 or nexty >= MAX_Y:
        break
    if input_lines[nexty][nextx] != '#':
        # print(f'testing bloc at {nextx}, {nexty}')
        old_value = input_lines[nexty][nextx]
        input_lines[nexty][nextx] = '#'
        if (nextx, nexty) not in found_loop:
            if move_and_detect(input_lines, start_gx, start_gy, start_vector, start_move):
                print(f'found loop with bloc at {nextx}, {nexty}')
                found_loop.add((nextx, nexty))
        input_lines[nexty][nextx] = old_value
        gx = nextx
        gy = nexty
    else:
        move += 1
        vector = moves[move % 4]
        # print(f'new vector: {vector}')

print(f'{len(found_loop)=}')