#include "aoc.h"

namespace aoc2017 {

uint64_t generator(uint64_t x, uint64_t factor) { return x * factor % 2147483647; }

bool lower16(uint64_t x) {
  uint8_t i[8] = {0};
  memcpy(i, &x, 8);
  return i[0] == 0 && i[1] == 0;
}

int forty_million(uint64_t a, uint64_t b) {
  int t{0};
  constexpr size_t mi = 40 * 1000000;
  for (size_t i = 0; i < mi; i++) {
    a = generator(a, 16807);
    b = generator(b, 48271);
    t += (int)lower16(a ^ b);
  }
  return t;
}

int five_million(uint64_t a, uint64_t b) {
  int t{0};
  constexpr size_t mi = 5 * 1000000;
  size_t p{0};
  uint64_t n2[2] = {0, 0};
  while (p < mi) {
    if (n2[0] == 0) {
      a = generator(a, 16807);
      if (a % 4 == 0) {
        n2[0] = a;
      }
    }
    if (n2[1] == 0) {
      b = generator(b, 48271);
      if (b % 8 == 0) {
        n2[1] = b;
      }
    }
    if (n2[0] > 0 && n2[1] > 0) {
      t += (int)lower16(n2[0] ^ n2[1]);
      n2[0] = 0;
      n2[1] = 0;
      p++;
    }
  }
  return t;
}

// Generator A starts with 873
// Generator B starts with 583
std::pair<int64_t, int64_t> day15(line_view) {
  // uint64_t a = 65;
  // uint64_t b = 8921;
  uint64_t a = 873;
  uint64_t b = 583;
  return {forty_million(a, b), five_million(a, b)};
}
} // namespace aoc2017