/* * keyvi - A key value store.
 *
 * Copyright 2015 Hendrik Muhs<hendrik.muhs@gmail.com>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * lru_generation_cache.h
 *
 *  Created on: May 2, 2014
 *      Author: hendrik
 */

#ifndef KEYVI_DICTIONARY_FSA_INTERNAL_LRU_GENERATION_CACHE_H_
#define KEYVI_DICTIONARY_FSA_INTERNAL_LRU_GENERATION_CACHE_H_

#include <vector>

#include "keyvi/dictionary/fsa/internal/minimization_hash.h"
#include "keyvi/dictionary/fsa/internal/packed_state.h"

namespace keyvi {
namespace dictionary {
namespace fsa {
namespace internal {

/**
 * A simple implementation of a lightweight least recently used cache using generations.
 */
template <class EntryT = PackedState<>>
class LeastRecentlyUsedGenerationsCache final {
 public:
  /**
   * Constructor of LeastRecentlyUsedGenerationsCache
   * @param memory_limit memory limit
   */
  explicit LeastRecentlyUsedGenerationsCache(size_t memory_limit) {
    current_generation_ = new MinimizationHash<EntryT>();

    auto memoryConfiguration = current_generation_->FindMemoryLimitConfigurationForLRUCache(memory_limit, 3, 6);

    size_per_generation_ = memoryConfiguration.best_fit_maximum_number_of_items_per_table;
    max_number_of_generations_ = memoryConfiguration.best_fit_generations;
  }

  /** Constructor of LeastRecentlyUsedGenerationsCache
   *
   *  @param sizePerGeneration The maximal size of one generation.
   *  @param maxNumberOfGenerations The maximum number of generations to keep.
   */
  LeastRecentlyUsedGenerationsCache(size_t size_per_generation, size_t max_number_of_generations)
      : size_per_generation_(size_per_generation), max_number_of_generations_(max_number_of_generations) {
    current_generation_ = new MinimizationHash<EntryT>();
  }

  ~LeastRecentlyUsedGenerationsCache() {
    delete current_generation_;
    for (MinimizationHash<EntryT> *generation : generations_) {
      delete generation;
    }
  }

  LeastRecentlyUsedGenerationsCache() = delete;
  LeastRecentlyUsedGenerationsCache &operator=(LeastRecentlyUsedGenerationsCache const &) = delete;
  LeastRecentlyUsedGenerationsCache(const LeastRecentlyUsedGenerationsCache &that) = delete;

  /** Add this object.
   * @param key The key to add
   */
  void Add(EntryT key) {
    if (current_generation_->Size() >= size_per_generation_) {
      MinimizationHash<EntryT> *newGeneration = nullptr;
      if (generations_.size() + 1 == max_number_of_generations_) {
        // remove(free) the first generation
        newGeneration = generations_[0];
        newGeneration->Reset();
        generations_.erase(generations_.begin());
      }

      generations_.push_back(current_generation_);

      if (newGeneration == nullptr) {
        newGeneration = new MinimizationHash<EntryT>();
      }

      current_generation_ = newGeneration;
    }

    current_generation_->Add(key);
  }

  template <typename EqualityType>
  const EntryT Get(EqualityType &key) {  // NOLINT
    EntryT state = current_generation_->Get(key);

    if (!state.IsEmpty()) {
      return state;
    }

    // try to find it in one of the generations
    for (size_t i = generations_.size(); i > 0; --i) {
      state = generations_[i - 1]->GetAndMove(key, current_generation_);

      if (!state.IsEmpty()) {
        return state;
      }
    }

    // return am empty state
    return EntryT();
  }

  /***
   * Clear the cache
   */
  void Clear() {
    current_generation_->Clear();
    for (MinimizationHash<EntryT> *generation : generations_) {
      delete generation;
    }
    generations_.clear();
  }

  /***
   * Get the memory usage of the cache and all underlying data.
   *
   * @return the memory usage
   */
  size_t GetMemoryUsage() const {
    size_t memory = current_generation_->GetMemoryUsage();
    for (auto generation : generations_) {
      memory += generation->GetMemoryUsage();
    }
    return memory;
  }

 private:
  size_t size_per_generation_;
  size_t max_number_of_generations_;
  MinimizationHash<EntryT> *current_generation_;
  std::vector<MinimizationHash<EntryT> *> generations_;
};

} /* namespace internal */
} /* namespace fsa */
} /* namespace dictionary */
} /* namespace keyvi */

#endif  // KEYVI_DICTIONARY_FSA_INTERNAL_LRU_GENERATION_CACHE_H_
