/**
 * XMSS Index Registry
 * (C) 2016 Matthias Gierlings
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 **/

#ifndef BOTAN_XMSS_INDEX_REGISTRY_H__
#define BOTAN_XMSS_INDEX_REGISTRY_H__

#include <stdint.h>
#include <cstddef>
#include <limits>
#include <memory>
#include <string>
#include <botan/hash.h>
#include <botan/secmem.h>
#include <botan/types.h>
#include <botan/atomic.h>
#include <botan/mutex.h>

namespace Botan {

/**
 * A registry for XMSS private keys, keeps track of the leaf index for
 * independend copies of the same key.
 **/
class XMSS_Index_Registry
   {
   public:
      XMSS_Index_Registry(const XMSS_Index_Registry&) = delete;
      XMSS_Index_Registry& operator=(const XMSS_Index_Registry&) = delete;

      /**
       * Retrieves a handle to the process-wide unique XMSS index registry.
       *
       * @return Reference to unique XMSS index registry.
       **/
      static XMSS_Index_Registry& get_instance()
         {
         static XMSS_Index_Registry self;
         return self;
         }

      /**
       * Retrieves the last unused leaf index for the private key identified
       * by private_seed and prf. The leaf index will be updated properly
       * across independent copies of private_key.
       *
       * @param private_seed Part of the unique identifier for an
       *                     XMSS_PrivateKey.
       * @param prf Part of the unique identifier for an XMSS_PrivateKey.
       *
       * @return last unused leaf index for private_key.
       **/
      std::shared_ptr<Atomic<size_t>>
                                   get(const secure_vector<byte>& private_seed,
                                       const secure_vector<byte>& prf);

   private:
      XMSS_Index_Registry()
         : m_key_ids(), m_leaf_indices(), m_mutex() {}

      static const std::string m_index_hash_function;

      /**
       * Creates a unique 64-bit id for an XMSS_Private key, by interpreting
       * the first 64-bit of HASH(PRIVATE_SEED || PRF) as 64 bit integer
       * value.
       *
       * @return unique integral identifier for an XMSS private key.
       **/
      uint64_t make_key_id(const secure_vector<byte>& private_seed,
                           const secure_vector<byte>& prf) const;

      /**
       * Retrieves the index position of a key within the registry or
       * max(size_t) if key has not been found.
       *
       * @param unique id of the XMSS private key (see make_key_id()).
       *
       * @return index position of key or max(size_t) if key not found.
       **/
      size_t get(uint64_t id) const;

      /**
       * If XMSS_PrivateKey identified by id is already registered, the
       * position of the according registry entry is returned. If last_unused
       * is bigger than the last unused index stored for the key identified by
       * id the unused leaf index for this key is set to last_unused. If no key
       * matching id is registed yet, an entry of id is added, with the last
       * unused leaf index initialized to the value of last_unused.
       *
       * @last_unused Initial value for the last unused leaf index of the
       *              registered key.
       *
       * @return positon of leaf index registry entry for key identified
       *         by id.
       **/
      size_t add(uint64_t id, size_t last_unused = 0);

      std::vector<uint64_t> m_key_ids;
      std::vector<std::shared_ptr<Atomic<size_t>>> m_leaf_indices;
      mutex_type m_mutex;
   };

}

#endif