/*
* RandomNumberGenerator
* (C) 1999-2009 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/

#ifndef BOTAN_RANDOM_NUMBER_GENERATOR_H__
#define BOTAN_RANDOM_NUMBER_GENERATOR_H__

#include <botan/entropy_src.h>
#include <botan/exceptn.h>
#include <string>

namespace Botan {

/**
* This class represents a random number (RNG) generator object.
*/
class BOTAN_DLL RandomNumberGenerator
   {
   public:
      /**
      * Create a seeded and active RNG object for general application use
      */
      static RandomNumberGenerator* make_rng();

      /**
      * Randomize a byte array.
      * @param output the byte array to hold the random output.
      * @param length the length of the byte array output.
      */
      virtual void randomize(byte output[], size_t length) = 0;

      /**
      * Return a random vector
      * @param bytes number of bytes in the result
      * @return randomized vector of length bytes
      */
      SecureVector<byte> random_vec(size_t bytes)
         {
         SecureVector<byte> output(bytes);
         randomize(&output[0], output.size());
         return output;
         }

      /**
      * Return a random byte
      * @return random byte
      */
      byte next_byte();

      /**
      * Check whether this RNG is seeded.
      * @return true if this RNG was already seeded, false otherwise.
      */
      virtual bool is_seeded() const { return true; }

      /**
      * Clear all internally held values of this RNG.
      */
      virtual void clear() = 0;

      /**
      * Return the name of this object
      */
      virtual std::string name() const = 0;

      /**
      * Seed this RNG using the entropy sources it contains.
      * @param bits_to_collect is the number of bits of entropy to
               attempt to gather from the entropy sources
      */
      virtual void reseed(size_t bits_to_collect) = 0;

      /**
      * Add this entropy source to the RNG object
      * @param source the entropy source which will be retained and used by RNG
      */
      virtual void add_entropy_source(EntropySource* source) = 0;

      /**
      * Add entropy to this RNG.
      * @param in a byte array containg the entropy to be added
      * @param length the length of the byte array in
      */
      virtual void add_entropy(const byte in[], size_t length) = 0;

      RandomNumberGenerator() {}
      virtual ~RandomNumberGenerator() {}
   private:
      RandomNumberGenerator(const RandomNumberGenerator&) {}
      RandomNumberGenerator& operator=(const RandomNumberGenerator&)
         { return (*this); }
   };

/**
* Null/stub RNG - fails if you try to use it for anything
*/
class BOTAN_DLL Null_RNG : public RandomNumberGenerator
   {
   public:
      void randomize(byte[], size_t) { throw PRNG_Unseeded("Null_RNG"); }
      void clear() {}
      std::string name() const { return "Null_RNG"; }

      void reseed(size_t) {}
      bool is_seeded() const { return false; }
      void add_entropy(const byte[], size_t) {}
      void add_entropy_source(EntropySource* es) { delete es; }
   };

}

#endif