cache.h

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/*
  Copyright (c) 2022, 2025, Oracle and/or its affiliates.
 
  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License, version 2.0,
  as published by the Free Software Foundation.
 
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  but not limited to OpenSSL) that is licensed under separate terms,
  as designated in a particular file or component or in included license
  documentation.  The authors of MySQL hereby grant you an additional
  permission to link the program and your derivative works with the
  separately licensed software that they have either included with
  the program or referenced in the documentation.
 
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
 
  You should have received a copy of the GNU General Public License
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  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/
 
#ifndef ROUTER_SRC_REST_MRS_SRC_HELPER_CACHE_CACHE_H_
#define ROUTER_SRC_REST_MRS_SRC_HELPER_CACHE_CACHE_H_
 
#include <map>
 
#include "helper/cache/policy/lru.h"
 
namespace helper {
namespace cache {
 
template <typename Key, typename Value, uint32_t size,
          typename Policy = policy::Lru>
class Cache {
  using Algorithm = typename Policy::template Algorithm<Key, Value, size>;
  using Container = std::map<Key, Value>;
 
 public:
  void remove(const Key key) {
    auto it = container_.find(key);
 
    if (container_.end() != it) {
      key_cache_.remove(key);
      container_.erase(it);
    }
  }
 
  Value *get_cached_value(const Key key) {
    auto it = container_.find(key);
    if (container_.end() == it) {
      return nullptr;
    }
 
    key_cache_.access(key);
 
    return &it->second;
  }
 
  Value *set(const Key key, Value &&value) { return set_impl(key, value); }
  Value *set(const Key key, const Value &value) { return set_impl(key, value); }
  Container &get_container() { return container_; }
 
 private:
  template <typename V>
  Value *set_impl(const Key key, V &&value) {
    auto cached_value = get_cached_value(key);
    if (cached_value) {
      *cached_value = std::forward<V>(value);
      return cached_value;
    }
 
    Key *removed_key = nullptr;
    key_cache_.push(key, &removed_key);
 
    if (removed_key) {
      auto node = container_.extract(*removed_key);
      node.key() = key;
      node.mapped() = std::forward<V>(value);
      container_.insert(std::move(node));
      return &container_[key];
    }
 
    return &container_.emplace(std::make_pair(key, std::forward<V>(value)))
                .first->second;
  }
 
  // private:
  Algorithm key_cache_;
  Container container_;
};
 
}  // namespace cache
}  // namespace helper
 
#endif  // ROUTER_SRC_REST_MRS_SRC_HELPER_CACHE_CACHE_H_