text: // Copyright (c) 2012-2014 The Bitcoin developers
  // Copyright (c) 2020 The CRYPTCORE developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef BITCOIN_DBWRAPPER_H
  #define BITCOIN_DBWRAPPER_H
  
  #include "clientversion.h"
  #include "fs.h"
  #include "serialize.h"
  #include "streams.h"
  #include "util.h"
  #include "version.h"
  
  
  #include <leveldb/db.h>
  #include <leveldb/write_batch.h>
  
  
  static const size_t DBWRAPPER_PREALLOC_KEY_SIZE = 64;
  static const size_t DBWRAPPER_PREALLOC_VALUE_SIZE = 1024;
  
  
  class dbwrapper_error : public std::runtime_error
  {
  public:
      dbwrapper_error(const std::string& msg) : std::runtime_error(msg) {}
  };
  
  class CDBWrapper;
  
  /** These should be considered an implementation detail of the specific database.
   */
  namespace dbwrapper_private {
  
  /** Handle database error by throwing dbwrapper_error exception.
   */
  void HandleError(const leveldb::Status& status);
  
  };
  
  
  /** Batch of changes queued to be written to a CDBWrapper */
  class CDBBatch
  {
      friend class CDBWrapper;
  
  private:
      leveldb::WriteBatch batch;
  
  public:
  
      template <typename K, typename V>
      void Write(const K& key, const V& value)
      {
          CDataStream ssKey(SER_DISK, CLIENT_VERSION);
          ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
          ssKey << key;
          leveldb::Slice slKey(&ssKey[0], ssKey.size());
  
          CDataStream ssValue(SER_DISK, CLIENT_VERSION);
          ssValue.reserve(DBWRAPPER_PREALLOC_VALUE_SIZE);
          ssValue << value;
          leveldb::Slice slValue(&ssValue[0], ssValue.size());
  
          batch.Put(slKey, slValue);
      }
  
      template <typename K>
      void Erase(const K& key)
      {
          CDataStream ssKey(SER_DISK, CLIENT_VERSION);
          ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
          ssKey << key;
          leveldb::Slice slKey(&ssKey[0], ssKey.size());
  
          batch.Delete(slKey);
      }
  };
  
  class CDBIterator
  {
  private:
      leveldb::Iterator *piter;
  
  public:
      /**
       * @param[in] _piter            The original leveldb iterator.
       */
      CDBIterator(leveldb::Iterator *_piter) : piter(_piter) { };
      ~CDBIterator();
  
      bool Valid();
  
      void SeekToFirst();
  
      template<typename K> void Seek(const K& key) {
          CDataStream ssKey(SER_DISK, CLIENT_VERSION);
          ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
          ssKey << key;
          leveldb::Slice slKey(&ssKey[0], ssKey.size());
          piter->Seek(slKey);
      }
  
      void Next();
  
      template<typename K> bool GetKey(K& key) {
          leveldb::Slice slKey = piter->key();
          try {
              CDataStream ssKey(slKey.data(), slKey.data() + slKey.size(), SER_DISK, CLIENT_VERSION);
              ssKey >> key;
          } catch(std::exception &e) {
              return false;
          }
          return true;
      }
  
      unsigned int GetKeySize() {
          return piter->key().size();
      }
  
      template<typename V> bool GetValue(V& value) {
          leveldb::Slice slValue = piter->value();
          try {
              CDataStream ssValue(slValue.data(), slValue.data() + slValue.size(), SER_DISK, CLIENT_VERSION);
              ssValue >> value;
          } catch(std::exception &e) {
              return false;
          }
          return true;
      }
  
      unsigned int GetValueSize() {
          return piter->value().size();
      }
  
  };
  
  class CDBWrapper
  {
  private:
      //! custom environment this database is using (may be NULL in case of default environment)
      leveldb::Env* penv;
  
      //! database options used
      leveldb::Options options;
  
      //! options used when reading from the database
      leveldb::ReadOptions readoptions;
  
      //! options used when iterating over values of the database
      leveldb::ReadOptions iteroptions;
  
      //! options used when writing to the database
      leveldb::WriteOptions writeoptions;
  
      //! options used when sync writing to the database
      leveldb::WriteOptions syncoptions;
  
      //! the database itself
      leveldb::DB* pdb;
  
  public:
      /**
       * @param[in] path        Location in the filesystem where leveldb data will be stored.
       * @param[in] nCacheSize  Configures various leveldb cache settings.
       * @param[in] fMemory     If true, use leveldb's memory environment.
       * @param[in] fWipe       If true, remove all existing data.
       */
      CDBWrapper(const fs::path& path, size_t nCacheSize, bool fMemory = false, bool fWipe = false);
      ~CDBWrapper();
  
      template <typename K, typename V>
      bool Read(const K& key, V& value) const
      {
          CDataStream ssKey(SER_DISK, CLIENT_VERSION);
          ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
          ssKey << key;
          leveldb::Slice slKey(&ssKey[0], ssKey.size());
  
          std::string strValue;
          leveldb::Status status = pdb->Get(readoptions, slKey, &strValue);
          if (!status.ok()) {
              if (status.IsNotFound())
                  return false;
              LogPrintf("LevelDB read failure: %s\n", status.ToString());
              dbwrapper_private::HandleError(status);
          }
          try {
              CDataStream ssValue(strValue.data(), strValue.data() + strValue.size(), SER_DISK, CLIENT_VERSION);
              ssValue >> value;
          } catch (const std::exception&) {
              return false;
          }
          return true;
      }
  
      template <typename K, typename V>
      bool Write(const K& key, const V& value, bool fSync = false)
      {
          CDBBatch batch;
          batch.Write(key, value);
          return WriteBatch(batch, fSync);
      }
  
      template <typename K>
      bool Exists(const K& key) const
      {
          CDataStream ssKey(SER_DISK, CLIENT_VERSION);
          ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
          ssKey << key;
          leveldb::Slice slKey(&ssKey[0], ssKey.size());
  
          std::string strValue;
          leveldb::Status status = pdb->Get(readoptions, slKey, &strValue);
          if (!status.ok()) {
              if (status.IsNotFound())
                  return false;
              LogPrintf("LevelDB read failure: %s\n", status.ToString());
              dbwrapper_private::HandleError(status);
          }
          return true;
      }
  
      template <typename K>
      bool Erase(const K& key, bool fSync = false)
      {
          CDBBatch batch;
          batch.Erase(key);
          return WriteBatch(batch, fSync);
      }
  
      bool WriteBatch(CDBBatch& batch, bool fSync = false);
  
      // not available for LevelDB; provide for compatibility with BDB
      bool Flush()
      {
          return true;
      }
  
      bool Sync()
      {
          CDBBatch batch;
          return WriteBatch(batch, true);
      }
  
      // not exactly clean encapsulation, but it's easiest for now
      CDBIterator* NewIterator()
      {
          return new CDBIterator(pdb->NewIterator(iteroptions));
      }
  
     /**
      * Return true if the database managed by this class contains no entries.
      */
      bool IsEmpty();
  
  };
  
  #endif // BITCOIN_DBWRAPPER_H
  