#include <charconv>
#include <cstdint>
#include <iostream>
#include <algorithm>
#include "fast_float/fast_float.h"

char *uint8_to_chars_manual(char *ptr, uint8_t value) {
  if (value == 0) {
    *ptr++ = '0';
    return ptr;
  }
  char *start = ptr;
  while (value > 0) {
    *ptr++ = '0' + (value % 10);
    value /= 10;
  }
  // Reverse the digits written so far
  std::reverse(start, ptr);
  return ptr;
}

void uint32_to_ipv4_string(uint32_t ip, char *buffer) {
  uint8_t octets[4] = {static_cast<uint8_t>(ip >> 24),
                       static_cast<uint8_t>(ip >> 16),
                       static_cast<uint8_t>(ip >> 8), static_cast<uint8_t>(ip)};

  char *ptr = buffer;

  for (int i = 0; i < 4; ++i) {
    ptr = uint8_to_chars_manual(ptr, octets[i]);

    if (i < 3) {
      *ptr++ = '.';
    }
  }
  *ptr = '\0';
}

fastfloat_really_inline uint32_t ipv4_string_to_uint32(const char *str,
                                                       const char *end) {
  uint32_t ip = 0;
  const char *current = str;

  for (int i = 0; i < 4; ++i) {
    uint8_t value;
    auto r = fast_float::from_chars(current, end, value);
    if (r.ec != std::errc()) {
      throw std::invalid_argument("Invalid IP address format");
    }
    current = r.ptr;
    ip = (ip << 8) | value;

    if (i < 3) {
      if (current == end || *current++ != '.') {
        throw std::invalid_argument("Invalid IP address format");
      }
    }
  }
  return ip;
}

bool test_all_ipv4_conversions() {
  std::cout << "Testing all IPv4 conversions... 0, 1000, 2000, 3000, 4000, "
               "5000, 6000, 7000, 8000, 9000, ..."
            << std::endl;
  char buffer[16];
  for (uint64_t ip = 0; ip <= 0xFFFFFFFF; ip += 1000) {
    if (ip % 10000000 == 0) {
      std::cout << "." << std::flush;
    }
    uint32_to_ipv4_string(static_cast<uint32_t>(ip), buffer);
    const char *end = buffer + strlen(buffer);
    uint32_t parsed_ip = ipv4_string_to_uint32(buffer, end);
    if (parsed_ip != ip) {
      std::cerr << "Mismatch: original " << ip << ", parsed " << parsed_ip
                << std::endl;
      return false;
    }
  }
  std::cout << std::endl;
  return true;
}

int main() {
  if (test_all_ipv4_conversions()) {
    std::cout << "All IPv4 conversions passed!" << std::endl;
    return EXIT_SUCCESS;
  } else {
    std::cerr << "IPv4 conversion test failed!" << std::endl;
    return EXIT_FAILURE;
  }
}