#include <ctype.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "aocdailies.h"
#include "aocutils.h"

/* === aoc202406 =======================================================
   Hmmm, I've done something like this already this year... on day 4
   I need rcmap() moved to aocutils ... done; now it's called `linearize2d`
===================================================================== */

static bool validpos(unsigned s, int r, int c) {
    if (r < 0) return false;
    if (c < 0) return false;
    if ((unsigned)r >= s - 1) return false;
    if ((unsigned)c >= s - 1) return false;
    return true;
}

static void rightturn(int *drow, int *dcol) {
    if (*drow) { *dcol = -*drow; *drow = 0; }
    else       { *drow =  *dcol; *dcol = 0; }
}

void aoc202406(char *data, size_t len) {

    (void)len;
    // assume data is well-formatted and has the same number of rows and columns
    unsigned size = 1 + strchr(data, '\n') - data;
    unsigned linear_pos = strchr(data, '^') - data;
    int row_pos = (int)(linear_pos / size);
    int col_pos = (int)(linear_pos % size);
    int deltarow = -1, deltacol = 0;
    //printf("character at [%u, %u] is '%c'\n", row_pos, col_pos, data[linearize2d(size, row_pos, col_pos)]);
    unsigned visited = 1;
    data[linearize2d(size, (unsigned)row_pos, (unsigned)col_pos)] = 'X'; // initial place visited
    while (validpos(size, row_pos + deltarow, col_pos + deltacol)) {
        switch (data[linearize2d(size, (unsigned)(row_pos+deltarow), (unsigned)(col_pos+deltacol))]) {
            default: exit(EXIT_FAILURE); // does not happen
            case '#': rightturn(&deltarow, &deltacol); break;
            case '.': visited++;
                      data[linearize2d(size, (unsigned)(row_pos+deltarow), (unsigned)(col_pos+deltacol))] = 'X';
                      /*fallthrough*/
            case 'X': row_pos += deltarow;
                      col_pos += deltacol;
                      break;
        }
    }
    printf("The guard visits %u positions before leaving the area.\n", visited);
}

/* === aoc202405 =======================================================
===================================================================== */

static int ppcmp(unsigned a, unsigned b, unsigned (*r)[2], size_t nr) {
    for (size_t k = 0; k < nr; k++) {