#pragma once
#include "common.h"
#include <algorithm>

namespace aoc2021 {

struct heightmap {
  // 0 .. 99
  static const int grid = 100;
  static int areas[grid * grid];
  struct hchar {
    char value = 0;
    char checked = 0;
  };

  hchar hs[grid * grid];

  void load(int r, line_view lv) {
    const char* p = lv.line;
    for(int i = 0; i < grid; i++) {
      hs[grid * r + i].value = *(p + i) - '0';
    }
  }

  void low_point(int x, int y, int* d) const noexcept {
    char l = x == 0 ? 10 : hs[grid * y + x - 1].value;
    char r = x == grid - 1 ? 10 : hs[grid * y + x + 1].value;
    char t = y == 0 ? 10 : hs[grid * (y - 1) + x].value;
    char b = y == grid - 1 ? 10 : hs[grid * (y + 1) + x].value;

    char n = hs[grid * y + x].value;
    if (n < l && n < r && n < t && n < b) {
      *d += n + 1;
    }
  }

  void basin(int x, int y, int* area) {
    if (hs[grid * y + x].value < 9 && hs[grid * y + x].checked == 0) {
      *area += 1;
      hs[grid * y + x].checked = 1;
      std::pair<char, char> ps[4] = {{x-1, y}, {x+1, y}, {x, y-1}, {x, y+1}};
      for (auto& p : ps) {
        if (p.first >= 0 && p.first < grid && p.second >= 0 && p.second < grid) {
          basin(p.first, p.second, area);
        }
      }
    }
  }
  
  int risks() const noexcept {
    int r{0};
    for (int y = 0; y < grid; y++) {
      for (int x = 0; x < grid; x++) {
        low_point(x, y, &r);
      }
    }
    return r;
  }

  int top3() {
    for (int y = 0; y < grid; y++) {
      for (int x = 0; x < grid; x++) {
        areas[y * grid + x] = 0;
        basin(x, y, &areas[y * grid + x]);
      }
    }
    std::sort(areas, areas + grid * grid, [](int x, int y){ return x > y;});
    return areas[0] * areas[1] * areas[2];
  }
};

std::pair<int, int> day9(line_view file);

}