/*
* Hash Function Base Class
* (C) 1999-2008 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#ifndef BOTAN_HASH_FUNCTION_BASE_CLASS_H_
#define BOTAN_HASH_FUNCTION_BASE_CLASS_H_

#include <botan/buf_comp.h>
#include <string>

namespace Botan {

/**
* This class represents hash function (message digest) objects
*/
class BOTAN_PUBLIC_API(2,0) HashFunction : public Buffered_Computation
   {
   public:
      /**
      * Create an instance based on a name, or return null if the
      * algo/provider combination cannot be found. If provider is
      * empty then best available is chosen.
      */
      static std::unique_ptr<HashFunction>
         create(const std::string& algo_spec,
                const std::string& provider = "");

      /**
      * Create an instance based on a name
      * If provider is empty then best available is chosen.
      * @param algo_spec algorithm name
      * @param provider provider implementation to use
      * Throws Lookup_Error if not not found.
      */
      static std::unique_ptr<HashFunction>
         create_or_throw(const std::string& algo_spec,
                         const std::string& provider = "");

      /**
      * @return list of available providers for this algorithm, empty if not available
      * @param algo_spec algorithm name
      */
      static std::vector<std::string> providers(const std::string& algo_spec);

      /**
      * @return new object representing the same algorithm as *this
      */
      virtual HashFunction* clone() const = 0;

      /**
      * @return provider information about this implementation. Default is "base",
      * might also return "sse2", "avx2", "openssl", or some other arbitrary string.
      */
      virtual std::string provider() const { return "base"; }

      virtual ~HashFunction() = default;

      /**
      * Reset the state.
      */
      virtual void clear() = 0;

      /**
      * @return the hash function name
      */
      virtual std::string name() const = 0;

      /**
      * @return hash block size as defined for this algorithm
      */
      virtual size_t hash_block_size() const { return 0; }

      /**
      * Return a new hash object with the same state as *this. This
      * allows computing the hash of several messages with a common
      * prefix more efficiently than would otherwise be possible.
      *
      * This function should be called `clone` but that was already
      * used for the case of returning an uninitialized object.
      * @return new hash object
      */
      virtual std::unique_ptr<HashFunction> copy_state() const = 0;
   };

}

#endif
