ExpiringDataCache.h

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/*
 * Copyright (c) 2020 pongasoft
 *
 * Licensed under the Apache License, Version 2.0 or the MIT license,
 * at your option. You may not use this file except in compliance with
 * one of these licenses. You may obtain copies of the licenses at:
 *
 * https://www.apache.org/licenses/LICENSE-2.0
 * https://opensource.org/licenses/MIT
 *
 * 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.
 *
 * @author Yan Pujante
 */
 
#ifndef JAMBA_EXPIRINGDATACACHE_H
#define JAMBA_EXPIRINGDATACACHE_H
 
#include <pongasoft/VST/Timer.h>
#include <functional>
 
#include <pongasoft/logging/logging.h>
 
namespace pongasoft::VST::VstUtils {
 
using namespace Steinberg;

template<typename T, typename Ptr = std::shared_ptr<T>, typename Loader = std::function<Ptr()>>
class ExpiringDataCache : ITimerCallback
{
public:
  using value_type = T;
  using pointer = Ptr;
  using loader = Loader;
 
public:
  ExpiringDataCache() = default;

  ExpiringDataCache(Loader iDataLoader, uint32 iTimeToLiveMilliseconds) :
    fDataLoader{std::move(iDataLoader)}, fTimeToLiveMilliseconds{iTimeToLiveMilliseconds} {}

  ExpiringDataCache(ExpiringDataCache const &iOther) :
    fDataLoader{iOther.fDataLoader}, fTimeToLiveMilliseconds{iOther.fTimeToLiveMilliseconds} {}

  ExpiringDataCache(ExpiringDataCache &&iOther) noexcept :
    fDataLoader{std::move(iOther.fDataLoader)}, fTimeToLiveMilliseconds{iOther.fTimeToLiveMilliseconds} {}

  ExpiringDataCache &operator=(ExpiringDataCache const &iOther) noexcept
  {
    fDataLoader = iOther.fDataLoader;
    fTimeToLiveMilliseconds = iOther.fTimeToLiveMilliseconds;
    fCachedData = nullptr;
    fTimer = nullptr;
 
    return *this;
  }

  ExpiringDataCache &operator=(ExpiringDataCache &&iOther) noexcept
  {
    fDataLoader = std::move(iOther.fDataLoader);
    fTimeToLiveMilliseconds = iOther.fTimeToLiveMilliseconds;
    fCachedData = nullptr;
    fTimer = nullptr;
 
    return *this;
  }

  explicit operator bool() const noexcept { return fDataLoader ? true : false; }

  Ptr getData()
  {
    if(fCachedData)
    {
      // resets the timer
      fTimer = AutoReleaseTimer::create(this, fTimeToLiveMilliseconds);
      return fCachedData;
    }
 
    fCachedData = fDataLoader ? fDataLoader() : nullptr;
 
    if(fCachedData)
      fTimer = AutoReleaseTimer::create(this, fTimeToLiveMilliseconds);
 
    return fCachedData;
  }
 
private:
  // Callback when the timer expires => remove cached data
  void onTimer(Timer *timer) override
  {
    fCachedData = nullptr;
    fTimer = nullptr;
  }
 
private:
  Loader fDataLoader{};
  uint32 fTimeToLiveMilliseconds{};
 
  Ptr fCachedData{};
  std::unique_ptr<AutoReleaseTimer> fTimer{};
};
 
}
 
#endif //JAMBA_EXPIRINGDATACACHE_H