import 'dart:math';
import 'dart:math';
import 'package:more/more.dart';

var d4 = [Point(0, -1), Point(1, 0), Point(0, 1), Point(-1, 0)];

String safeGet(Point<int> p, List<List<String>> grid) =>
    (p.y.between(0, grid.length - 1) && p.x.between(0, grid.first.length - 1))
        ? grid[p.y][p.x]
        : '!';

Point<int> findGuard(List<List<String>> grid) {
  for (var row in grid.indices()) {
    for (var col in grid.first.indices()) {
      if (grid[row][col] == '^') return Point(col, row);
    }
  }
  return Point(-1, -1); //!
}

Set<Point<int>> getTrack(Point<int> guard, List<List<String>> grid) =>
    checkPath(guard, grid).first.map((e) => e.first).toSet();

// Check the path, returning ({(point, dir)}, did it end in a loop).
(Set<(Point<int>, int)>, bool) checkPath(
    Point<int> guard0, List<List<String>> grid,
    {Point<int>? block}) {
  if (block != null) grid[block.y][block.x] = '#';
  var dir = 0;
  var guard = guard0;
  var track = <(Point<int>, int)>{};
  var isLoop = false;
  while (safeGet(guard, grid) != '!') {
    if (track.contains((guard, dir))) {
      isLoop = true;
      break;
    }
    track.add((guard, dir));
    var check = guard + d4[dir];
    if (safeGet(check, grid) == '#') {
      dir = (dir + 1) % 4;
    } else {
      guard += d4[dir];
    }
  }
  if (block != null) grid[block.y][block.x] = '.';
  return (track, isLoop);
}

part1(List<String> lines) {
  var grid = lines.map((e) => e.split('')).toList();
  return getTrack(findGuard(grid), grid).length;
}

part2(List<String> lines) {
  var grid = lines.map((e) => e.split('')).toList();
  var guard = findGuard(grid);
  return getTrack(guard, grid)
      .count((e) => checkPath(guard, grid, block: e).last);
}