random.h

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*/
 
#ifndef ROUTER_SRC_HELPER_STRING_RANDOM_H_
#define ROUTER_SRC_HELPER_STRING_RANDOM_H_
 
#include <algorithm>
#include <random>
 
namespace helper {
 
/**
 * Base class for generators.
 *
 * Generator must provide only following function:
 *
 *     static char generate()
 *
 *  and doesn't need to inherit from `GeneratorBase`.
 */
struct GeneratorBase {
  /**
   * Static method that generates random number.
   *
   * This method was introduced for easier changing the algorithm
   * in future. `range` argument decides about the generated numbers
   * range [0, range).
   */
  static int get_random_int(int range) {
    std::random_device rd;  // a seed source for the random number engine
    std::uniform_int_distribution<> distrib(0, range - 1);
    return distrib(rd);
  }
};
 
struct GeneratorSmallAlpha : public GeneratorBase {
 protected:
  const static char smallEnd = 'z';
  const static char smallBegin = 'a';
  const static char bigEnd = 'Z';
  const static char bigBegin = 'A';
 
  const static int smallRange = (smallEnd - smallBegin) + 1;
  const static int bigRange = (bigEnd - bigBegin) + 1;
 
 public:
  const static int kNumberOfCharacters = smallRange;
  static char generate() {
    std::random_device rd;  // a seed source for the random number engine
    std::uniform_int_distribution<> distrib(smallBegin, smallEnd);
    return distrib(rd);
  }
};
 
struct GeneratorAlpha : public GeneratorSmallAlpha {
 public:
  const static int kNumberOfCharacters = smallRange + bigRange;
 
  static char generate() {
    auto result = get_random_int(kNumberOfCharacters);
    if (result < smallRange) return smallBegin + result;
    result -= smallRange;
    return bigBegin + result;
  }
};
 
struct GeneratorAlphaNumeric : public GeneratorSmallAlpha {
 public:
  const static char numericEnd = '9';
  const static char numericBegin = '0';
 
  const static int numericRange = (numericEnd - numericBegin) + 1;
  const static int kNumberOfCharacters = smallRange + bigRange + numericRange;
 
  static char generate() {
    auto result = get_random_int(kNumberOfCharacters);
    if (result < smallRange) return smallBegin + result;
    result -= smallRange;
 
    if (result < bigRange) return bigBegin + result;
    result -= bigRange;
 
    return numericBegin + result;
  }
};
 
struct Generator8bitsValues : public GeneratorSmallAlpha {
 public:
  static char generate() {
    auto result = get_random_int(255);
 
    return static_cast<char>(result);
  }
};
 
template <typename Generator = GeneratorSmallAlpha>
inline std::string generate_string(uint32_t length) {
  std::string result(length, '0');
  std::generate(result.begin(), result.end(), &Generator::generate);
 
  return result;
}
 
template <uint32_t length, typename Generator = GeneratorSmallAlpha>
inline std::string generate_string() {
  return generate_string<Generator>(length);
}
 
}  // namespace helper
 
#endif  // ROUTER_SRC_HELPER_STRING_RANDOM_H_