module;

// Might as well since we're using OpenSSL
#include <openssl/err.h>
#include <openssl/rand.h>

module routemon:trace$impl;

import :trace;

namespace routemon::trace {

uuid7::uuid7()
{
  namespace chrono = std::chrono;
  auto const unix_time_ms_signed = static_cast<std::int64_t>(
      chrono::duration_cast<chrono::milliseconds>(
          chrono::system_clock::now().time_since_epoch())
          .count());
  if (unix_time_ms_signed < 0)
    throw std::runtime_error{"system time before UNIX epoch"};
  auto const unix_time_ms = static_cast<std::uint64_t>(unix_time_ms_signed);
  if (std::countl_zero(unix_time_ms) < 16)
    throw std::runtime_error{"system time too great"};

  auto rand = std::array<unsigned char, 10>{};
  int s = RAND_bytes(rand.data(), static_cast<int>(rand.size()));
  if (s != 1)
  {
    unsigned long e = ERR_get_error();
    throw std::runtime_error{std::format(
        "failed to generate UUID(v7): {} ({}, code {})",
        ERR_reason_error_string(e), ERR_lib_error_string(e), e)};
  }

  auto version = std::uint64_t{0b0111};
  auto variant = std::uint64_t{0b10};

  hi_ |= unix_time_ms << 16;
  hi_ |= version << 12;
  hi_ |= std::uint64_t{rand[0]} << 4;
  hi_ |= std::uint64_t{rand[1]};
  lo_ |= variant << 62;
  lo_ |= std::uint64_t{rand[2]} << 54;
  lo_ |= std::uint64_t{rand[3]} << 48;
  lo_ |= std::uint64_t{rand[4]} << 40;
  lo_ |= std::uint64_t{rand[5]} << 32;
  lo_ |= std::uint64_t{rand[6]} << 24;
  lo_ |= std::uint64_t{rand[7]} << 16;
  lo_ |= std::uint64_t{rand[8]} << 8;
  lo_ |= std::uint64_t{rand[9]};
}

auto uuid7::format(std::array<char, 37>& target) -> void
{
  auto p____hi_hi = (hi_ & 0xffff'ffff'0000'0000) >> 32;
  auto p_hi_lo_hi = (hi_ & 0x0000'0000'ffff'0000) >> 16;
  auto p_lo_lo_hi = (hi_ & 0x0000'0000'0000'ffff) >> 0;
  auto p____hi_lo = (lo_ & 0xffff'0000'0000'0000) >> 48;
  auto p____lo_lo = (lo_ & 0x0000'ffff'ffff'ffff) >> 0;

  std::format_to(
      target.begin(), "{:0>8x}-{:0>4x}-{:0>4x}-{:0>4x}-{:0>12x}", p____hi_hi,
      p_hi_lo_hi, p_lo_lo_hi, p____hi_lo, p____lo_lo);
  target.back() = '\0';
}

id::id() { uuid7{}.format(chars_); }

auto id::as_string() const -> util::zstring_view
{
  return util::zstring_view{chars_.data(), chars_.size() - 1};
}

} // namespace routemon::trace