random.h

// Copyright 2025 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#ifndef ACTIONENGINE_UTIL_RANDOM_H_
#define ACTIONENGINE_UTIL_RANDOM_H_
 
#include <iomanip>
#include <sstream>
#include <string>
 
#include <absl/random/distributions.h>
#include <absl/random/random.h>
 
namespace act {
 
inline std::string GenerateUUID4() {
  // TODO(hpnkv): Check this for correctness
  absl::BitGen gen;  // Abseil random number generator
 
  // Generate 16 random bytes
  std::array<uint8_t, 16> bytes{};
  for (int i = 0; i < 16; ++i) {
    bytes[i] = absl::Uniform<int>(gen, 0, 256);  // Generate random byte (0-255)
  }
 
  // Set the version (UUID version 4) - The 7th nibble (most significant nibble of 13th byte) must be 4
  bytes[6] = (bytes[6] & 0x0f) | 0x40;
 
  // Set the variant (the 9th nibble must be 8, 9, A, or B)
  bytes[8] = (bytes[8] & 0x3f) | 0x80;
 
  // Convert to string (UUID format: 8-4-4-4-12)
  std::ostringstream oss;
  for (size_t i = 0; i < bytes.size(); ++i) {
    if (i == 4 || i == 6 || i == 8 || i == 10) {
      oss << "-";
    }
    oss << std::hex << std::setw(2) << std::setfill('0')
        << static_cast<int>(bytes[i]);
  }
 
  return oss.str();
}
 
}  // namespace act
 
#endif  // ACTIONENGINE_UTIL_RANDOM_H_