/*

* EntropySource

* (C) 2008,2009,2014,2015,2016 Jack Lloyd

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#ifndef BOTAN_ENTROPY_H_

#define BOTAN_ENTROPY_H_

#include <botan/api.h>

#include <chrono>

#include <memory>

#include <string>

#include <string_view>

#include <vector>

namespace Botan {

class RandomNumberGenerator;

/**

* Abstract interface to a source of entropy

*/

class BOTAN_PUBLIC_API(2, 0) Entropy_Source {

   public:

      /**

      * Return a new entropy source of a particular type, or null

      * Each entropy source may require substantial resources (eg, a file handle

      * or socket instance), so try to share them among multiple RNGs, or just

      * use the preconfigured global list accessed by Entropy_Sources::global_sources()

      */

      static std::unique_ptr<Entropy_Source> create(std::string_view type);

      /**

      * @return name identifying this entropy source

      */

      virtual std::string name() const = 0;

      /**

      * Perform an entropy gathering poll

      * @param rng will be provided with entropy via calls to add_entropy

      * @return conservative estimate of actual entropy added to rng during poll

      */

      virtual size_t poll(RandomNumberGenerator& rng) = 0;

      Entropy_Source() = default;

      Entropy_Source(const Entropy_Source& other) = delete;

      Entropy_Source(Entropy_Source&& other) = delete;

      Entropy_Source& operator=(const Entropy_Source& other) = delete;

      virtual ~Entropy_Source() = default;

};

class BOTAN_PUBLIC_API(2, 0) Entropy_Sources final {

   public:

      static Entropy_Sources& global_sources();

      void add_source(std::unique_ptr<Entropy_Source> src);

      std::vector<std::string> enabled_sources() const;

      /**

      * Poll all sources to collect @p bits of entropy with a @p timeout.

      * Entropy collection is aborted as soon as either the requested number of

      * bits are obtained or the timeout runs out. If the target system does not

      * provide a clock, the timeout is ignored.

      *

      * Note that the timeout is cooperative. If the poll() method of an entropy

      * source blocks forever, this invocation will potentially also block.

      *

      * @returns the number of bits collected from the entropy sources

      */

      size_t poll(RandomNumberGenerator& rng, size_t bits, std::chrono::milliseconds timeout);

      /**

      * Poll just a single named source. Ordinally only used for testing

      */

      size_t poll_just(RandomNumberGenerator& rng, std::string_view src);

      Entropy_Sources() = default;

      explicit Entropy_Sources(const std::vector<std::string>& sources);

      Entropy_Sources(const Entropy_Sources& other) = delete;

      Entropy_Sources(Entropy_Sources&& other) = delete;

      Entropy_Sources& operator=(const Entropy_Sources& other) = delete;

   private:

      std::vector<std::unique_ptr<Entropy_Source>> m_srcs;

};

}  // namespace Botan

#endif