#include "aoc.h"

typedef enum Direction {
    Up, Right, Down, Left
} Direction;

static const int offsets[4][2] = {
    [Up]    = { 0, -1},
    [Right] = { 1,  0},
    [Down]  = { 0,  1},
    [Left]  = {-1,  0}
};

i32 traverse(Grid *grid, int x, int y, Direction facing, Arena arena) {
    u8 *visited = ARENA_ALLOC_ARRAY(&arena, u8, grid->width * grid->height);

    i32 result = 0;
    for (;;) {
        int index = y * grid->width + x;
        if (visited[index] & (1 << facing)) {
            // loop detected
            result = -1;
            break;
        }
        else if (visited[index] == 0) {
            result++;
        }
        visited[index] |= (1 << facing);

        int nx = x + offsets[facing][0];
        int ny = y + offsets[facing][1];
        if (nx >= 0 && ny >= 0 && nx < grid->width && ny < grid->height) {
            i32 next_index = ny * grid->width + nx;
            if (grid->grid[next_index] == '#') {
                facing = (facing + 1) % 4;
            }
            else {
                x = nx;
                y = ny;
            }
        }
        else {
            break;
        }
    }
    return result;
}

int main(int argc, char **argv) {
    Arena *arena = make_arena(Megabytes(1));

    str input = read_file(arena, argv[1]);
    Grid grid = parse_grid(input, arena);

    int start_x = -1, start_y = -1;
    for (int y = 0; y < grid.height; y++) {
        for (int x = 0; x < grid.width; x++) {
            if (grid_at(&grid, x, y) == '^') {
                start_x = x;
                start_y = y;
                grid.grid[y * grid.width + x] = ':';
            }
        }
    }

    i32 part_1 = traverse(&grid, start_x, start_y, Up, *arena);

    i32 part_2 = 0;
    for (int y = 0; y < grid.height; y++) {
        for (int x = 0; x < grid.width; x++) {
            if (x == start_x && y == start_y) {
                continue;
            }
            int index = y * grid.width + x;
            u8 saved;
            if ((saved = grid.grid[index]) != '#') {
                grid.grid[index] = '#';
                i32 visited = traverse(&grid, start_x, start_y, Up, *arena);
                part_2 += (visited == -1);
                grid.grid[index] = saved;
            }
        }
    }

    printf("%d\n", part_1);
    printf("%d\n", part_2);
}