/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */

//

// Copyright (c) 2006 Georgia Tech Research Corporation

//

// This program is free software; you can redistribute it and/or modify

// it under the terms of the GNU General Public License version 2 as

// published by the Free Software Foundation;

//

// This program is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

//

// You should have received a copy of the GNU General Public License

// along with this program; if not, write to the Free Software

// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

//

// Author: Rajib Bhattacharjea<raj.b@gatech.edu>

//

#ifndef __random_variable_h__

#define __random_variable_h__

#include <vector>

#include <algorithm>

#define INFINITE_VALUE 1e307

namespace ns3{

class RngStream;

/**

 * \brief Pure virtual base class for RNG seeds

 */

class Seed {

  // Seed is used to seed the random number generator(s)

  // This is a base class for RandomSeed and ConstantSeed

public:

  virtual ~Seed();

  virtual bool IsRandom() const = 0;

};

/**

 * \brief random RNG seeds

 */

class RandomSeed : public Seed {

public:

  RandomSeed();

  ~RandomSeed();

  bool IsRandom() const;

};

/**

 * \brief constant RNG seeds

 */

class ConstantSeed : public Seed 

{

public:

  ConstantSeed(uint32_t); // Use six copies of the specified value

  ConstantSeed(uint32_t,uint32_t,uint32_t,uint32_t,uint32_t,uint32_t);  // Six seeds

  bool IsRandom() const;

  ~ConstantSeed();

public:

  uint32_t seeds[6];

};

/**

 * \brief The basic RNG for NS-3.

 *

 * Note: The underlying random number generation method used

 * by NS-3 is the RngStream code by Pierre L'Ecuyer at

 * the University of Montreal.

 * 

 * NS-3 has a rich set of  random number generators.

 * Class RandomVariable defines the base class functionalty

 * required for all random number generators.  By default, the underlying

 * generator is seeded with the time of day, and then deterministically

 * creates a sequence of seeds for each subsequent generator that is created.

 * The rest of the documentation outlines how to change this behavior.

 */

class RandomVariable { 

public:

  /**

   * \brief Constructor for a random number generator with a random seed.

   */

  RandomVariable();

  /**

   * \brief Copy constructor

   */  

  RandomVariable(const RandomVariable&);

  /**

   * \brief Destructor for a random number generator with a random seed.

   */

  virtual ~RandomVariable();

  /**

   * \brief Returns a random double from the underlying distribution

   * \return A floating point random value

   */

  virtual double  GetValue() = 0;     

  /**

   * \brief Returns a random integer integer from the underlying distribution

   * \return  Integer cast of ::GetValue()

   */

  virtual uint32_t GetIntValue();

  /**

   * \return A copy of this object

   */  

  virtual RandomVariable*   Copy() const = 0;

  /**

   */

  /**

   * \brief Set seeding behavior

   * 

   * Specify whether the POSIX device /dev/random is to

   * be used for seeding.  When this is used, the underlying

   * generator is seeded with data from /dev/random instead of

   * being seeded based upon the time of day.  For this to be effective,

   * it must be called before the creation of the first instance of a 

   * RandomVariable or subclass.  Example:

   * \code

   * RandomVariable::UseDevRandom();

   * UniformVariable x(2,3);  //these are seeded randomly

   * ExponentialVariable y(120); //etc

   * \endcode

   * \param udr True if /dev/random desired.

   */

  static  void UseDevRandom(bool udr = true);

   /**

   * \brief Use the global seed to force precisely reproducible results.

   *

   * It is often desirable to create a simulation that uses random

   * numbers, while at the same time is completely reproducible.

   * Specifying this set of six random seeds initializes the

   * random number generator with the specified seed.

   * Once this is set, all generators will produce fixed output

   * from run to run.  This is because each time a new generator is created,

   * the underlying RngStream deterministically creates a new seed based upon

   * the old one, hence a "stream" of RNGs.  Example:

   * \code

   * RandomVariable::UseGlobalSeed(...);

   * UniformVariable x(2,3);     //these will give the same output everytime

   * ExponentialVariable y(120); //as long as the seed stays the same

   * \endcode

   * \param s

   * \return True if seed is valid.

   */ 

  static void UseGlobalSeed(const Seed& s);

private:

  static void Initialize();    // Initialize  the RNG system

  static void GetRandomSeeds(uint32_t seeds[6]);

private:

  static bool useDevRandom;    // True if using /dev/random desired

  static bool globalSeedSet;   // True if global seed has been specified

  static int  devRandom;       // File handle for /dev/random

  static uint32_t globalSeed[6]; // The global seed to use

protected:

  static unsigned long heuristic_sequence;

  RngStream* m_generator;  //underlying generator being wrapped

};

/**

 * \brief The uniform distribution RNG for NS-3.

 */

class UniformVariable : public RandomVariable {

public:

  /**

   * Creates a uniform random number generator in the

   * range [0.0 .. 1.0)

   */

  UniformVariable();

  /**

   * Creates a uniform random number generator with the specified range

   * \param s Low end of the range

   * \param l High end of the range

   */

  UniformVariable(double s, double l);

  UniformVariable(const UniformVariable& c);

  /**

   * \return A value between low and high values specified by the constructor

   */

  virtual double GetValue();

  virtual RandomVariable*  Copy() const;

private:

  double m_min;

  double m_max;

};

/**

 * \brief A random variable that returns a constant

 *

 * Class ConstantVariable defines a random number generator that

 * returns the same value every sample.

 */

class ConstantVariable : public RandomVariable { 

public:

  /**

   * Construct a ConstantVariable RNG that returns zero every sample

   */

  ConstantVariable();

  /**

   * Construct a ConstantVariable RNG that returns the specified value

   * every sample.

   * \param c Unchanging value for this RNG.

   */

  ConstantVariable(double c);

  ConstantVariable(const ConstantVariable& c) ;

  /**

   * \brief Specify a new constant RNG for this generator.

   * \param c New constant value for this RNG.

   */

  void    NewConstant(double c);

  /**

   * \return The constant value specified

   */

  virtual double  GetValue();

  virtual uint32_t GetIntValue();

  virtual RandomVariable*   Copy() const;

private:

  double m_const;

};

/**

 * \brief Return a sequential list of values

 *

 * Class SequentialVariable defines a random number generator that

 * returns a sequential sequence.  The sequence monotonically

 * increases for a period, then wraps around to the low value 

 * and begins monotonicaly increasing again.

 */

class SequentialVariable : public RandomVariable {

public:

  /**

   * \brief Constructor for the SequentialVariable RNG.

   *

   * The four parameters define the sequence.  For example

   * SequentialVariable(0,5,1,2) creates a RNG that has the sequence

   * 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 0, 0 ...

   * \param f First value of the sequence.

   * \param l One more than the last value of the sequence.

   * \param i Increment between sequence values

   * \param c Number of times each member of the sequence is repeated

   */

  SequentialVariable(double f, double l, double i = 1, uint32_t c = 1);

  /**

   * \brief Constructor for the SequentialVariable RNG.

   *

   * Differs from the first only in that the increment parameter is a

   * random variable

   * \param f First value of the sequence.

   * \param l One more than the last value of the sequence.

   * \param i Reference to a RandomVariable for the sequence increment

   * \param c Number of times each member of the sequence is repeated

   */

  SequentialVariable(double f, double l, const RandomVariable& i, uint32_t c = 1);

  SequentialVariable(const SequentialVariable& c);

  ~SequentialVariable();

  /**

   * \return The next value in the Sequence

   */

  virtual double GetValue();

  virtual RandomVariable*  Copy() const;

private:

  double m_min;

  double m_max;

  RandomVariable*  m_increment;

  uint32_t  m_consecutive;

  double m_current;

  uint32_t  m_currentConsecutive;

};

/**

 * \brief Exponentially Distributed random var

 *

 * ExponentialVariable defines a random variable with an exponential distribution

 */

class ExponentialVariable : public RandomVariable { 

public:

  /**

   * Constructs an exponential random variable  with a mean

   * value of 1.0.

   */

  ExponentialVariable();

  /**

   * \brief Constructs an exponential random variable with a specified mean

   * \param m Mean value for the random variable

   */

  explicit ExponentialVariable(double m);

  /**

   * \brief Constructs an exponential random variable with spefified

   * \brief mean and upper limit.

   *

   * Since exponential distributions can theoretically return unbounded values,

   * it is sometimes useful to specify a fixed upper limit.  Note however when

   * the upper limit is specified, the true mean of the distribution is 

   * slightly smaller than the mean value specified.

   * \param m Mean value of the random variable

   * \param b Upper bound on returned values

   */

  ExponentialVariable(double m, double b);

  ExponentialVariable(const ExponentialVariable& c);

  /**

   * \return A random value from this exponential distribution

   */

  virtual double GetValue();

  virtual RandomVariable* Copy() const;

private:

  double m_mean;  // Mean value of RV

  double m_bound; // Upper bound on value (if non-zero)

};

/**

 * \brief ParetoVariable distributed random var

 */

class ParetoVariable : public RandomVariable { // 

public:

  /**

   * Constructs a pareto random variable with a mean of 1 and a shape

   * parameter of 1.5

   */

  ParetoVariable();

  /**

   * Constructs a pareto random variable with specified mean and shape

   * parameter of 1.5

   * \param m Mean value of the distribution

   */

  explicit ParetoVariable(double m);

  /**

   * Constructs a pareto random variable with the specified mean value and

   * shape parameter.

   * \param m Mean value of the distribution

   * \param s Shape parameter for the distribution

   */

  ParetoVariable(double m, double s);

  /**

   * \brief Constructs a pareto random variable with the specified mean

   * \brief value, shape (alpha), and upper bound.

   * Since pareto distributions can theoretically return unbounded values,

   * it is sometimes useful to specify a fixed upper limit.  Note however

   * when the upper limit is specified, the true mean of the distribution

   * is slightly smaller than the mean value specified.

   * \param m Mean value

   * \param s Shape parameter

   * \param b Upper limit on returned values

   */

  ParetoVariable(double m, double s, double b);

  ParetoVariable(const ParetoVariable& c);

  /**

   * \return A random value from this Pareto distribution

   */

  virtual double GetValue();

  virtual RandomVariable* Copy() const;

private:

  double m_mean;  // Mean value of RV

  double m_shape; // Shape parameter

  double m_bound; // Upper bound on value (if non-zero)

};

/**

 * \brief WeibullVariable distributed random var

 */

class WeibullVariable : public RandomVariable {

public:

  /**

   * Constructs a weibull random variable  with a mean

   * value of 1.0 and a shape (alpha) parameter of 1

   */

  WeibullVariable();

  /**

   * Constructs a weibull random variable with the specified mean

   * value and a shape (alpha) parameter of 1.5.

   * \param m mean value of the distribution

   */

   WeibullVariable(double m) ;

  /**

   * Constructs a weibull random variable with the specified mean

   * value and a shape (alpha).

   * \param m Mean value for the distribution.

   * \param s Shape (alpha) parameter for the distribution.

   */

  WeibullVariable(double m, double s);

   /**

   * \brief Constructs a weibull random variable with the specified mean

   * \brief value, shape (alpha), and upper bound.

   * Since WeibullVariable distributions can theoretically return unbounded values,

   * it is sometimes usefull to specify a fixed upper limit.  Note however

   * that when the upper limit is specified, the true mean of the distribution

   * is slightly smaller than the mean value specified.

   * \param m Mean value for the distribution.

   * \param s Shape (alpha) parameter for the distribution.

   * \param b Upper limit on returned values

   */

  WeibullVariable(double m, double s, double b);

  WeibullVariable(const WeibullVariable& c);

  /**

   * \return A random value from this Weibull distribution

   */

  virtual double GetValue();

  virtual RandomVariable* Copy() const;

private:

  double m_mean;  // Mean value of RV

  double m_alpha; // Shape parameter

  double m_bound; // Upper bound on value (if non-zero)

};

/**

 * Class NormalVariable defines a random variable with a

 * normal (Gaussian) distribution.

 */

class NormalVariable : public RandomVariable { // Normally Distributed random var

public:

  /**

   * Constructs an normal random variable  with a mean

   * value of 0 and variance of 1.

   */ 

  NormalVariable();

  /**

   * \brief Construct a normal random variable with specified mean and variance

   * \param m Mean value

   * \param v Variance

   * \param b Bound.  The NormalVariable is bounded within +-bound.

   */ 

  NormalVariable(double m, double v, double b = INFINITE_VALUE);

  NormalVariable(const NormalVariable& c);

  /**

   * \return A value from this normal distribution

   */

  virtual double GetValue();

  virtual RandomVariable* Copy() const;

private:

  double m_mean;      // Mean value of RV

  double m_variance;  // Mean value of RV

  double m_bound;     // Bound on value (absolute value)

  bool     m_nextValid; // True if next valid

  double m_next;      // The algorithm produces two values at a time

};