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/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
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/// Copyright holder is ArangoDB GmbH, Cologne, Germany
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/// Portions of the code are:
///
/// Copyright (c) 2014, lamerman
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//////////////////////////////////////////////////////////////////////////////////

#ifndef ARANGODB_LRUCACHE_H
#define ARANGODB_LRUCACHE_H 1

#include <cstddef>
#include <list>
#include <stdexcept>
#include <unordered_map>

namespace arangodb {
namespace basics {

template <typename key_t, typename value_t>
class LruCache {
 public:
  typedef typename std::pair<key_t, value_t> key_value_pair_t;
  typedef typename std::list<key_value_pair_t>::iterator list_iterator_t;

  LruCache(size_t max_size) : _max_size(max_size) {}

  void put(const key_t& key, const value_t& value) {
    auto it = _cache_items_map.find(key);
    _cache_items_list.push_front(key_value_pair_t(key, value));
    if (it != _cache_items_map.end()) {
      _cache_items_list.erase(it->second);
      _cache_items_map.erase(it);
    }
    _cache_items_map[key] = _cache_items_list.begin();

    if (_cache_items_map.size() > _max_size) {
      auto last = _cache_items_list.end();
      last--;
      _cache_items_map.erase(last->first);
      _cache_items_list.pop_back();
    }
  }

  value_t const* get(const key_t& key) {
    auto it = _cache_items_map.find(key);
    if (it == _cache_items_map.end()) {
      return nullptr;
    } else {
      _cache_items_list.splice(_cache_items_list.begin(), _cache_items_list, it->second);
      return &it->second->second;
    }
  }

  bool remove(key_t const& key) {
    auto it = _cache_items_map.find(key);
    if (it == _cache_items_map.end()) {
      return false;
    } else {
      _cache_items_list.erase(it->second);
      _cache_items_map.erase(it);
      return true;
    }
  }

  void clear() {
    _cache_items_map.clear();
    _cache_items_list.clear();
  }

  bool exists(const key_t& key) const {
    return _cache_items_map.find(key) != _cache_items_map.end();
  }

  size_t size() const { return _cache_items_map.size(); }

 private:
  std::list<key_value_pair_t> _cache_items_list;
  std::unordered_map<key_t, list_iterator_t> _cache_items_map;
  size_t _max_size;
};

}  // namespace basics
}  // namespace arangodb

#endif