/***************************************************************************
 *   Copyright (C) 2017 by Nicolas Carion                                  *
 *   This file is part of Kdenlive. See www.kdenlive.org.                  *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) version 3 or any later version accepted by the       *
 *   membership of KDE e.V. (or its successor approved  by the membership  *
 *   of KDE e.V.), which shall act as a proxy defined in Section 14 of     *
 *   version 3 of the license.                                             *
 *                                                                         *
 *   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     *
 *   along with this program.  If not, see <http://www.gnu.org/licenses/>. *
 ***************************************************************************/

#pragma once

#include "definitions.h"
#include <QDir>
#include <QImage>
#include <QMutex>
#include <memory>
#include <mutex>
#include <unordered_map>
#include <vector>

/** @brief This class class is an interface to the caches that store thumbnails.
    In Kdenlive, we use two such caches, a persistent that is stored on disk to allow thumbnails to be reused when reopening.
    The other one is a volatile LRU cache that lives in memory.
    Note that for the volatile cache uses a custom implementation.
    QCache is not suitable since it operates on pointers and since the object is removed from the cache when accessed.
    KImageCache is not suitable since it lacks a way to remove objects from the cache.
 * Note that this class is a Singleton
 */

class ThumbnailCache
{

public:
    // Returns the instance of the Singleton
    static std::unique_ptr<ThumbnailCache> &get();

    /* @brief Check whether a given thumbnail is in the cache
       @param binId is the id of the queried clip
       @param pos is the position where we query
       @param volatileOnly if true, we only check the volatile cache (no disk access)
     */
    bool hasThumbnail(const QString &binId, int pos, bool volatileOnly = false) const;

    /* @brief Get a given thumbnail from the cache
       @param binId is the id of the queried clip
       @param pos is the position where we query
       @param volatileOnly if true, we only check the volatile cache (no disk access)
    */
    QImage getThumbnail(const QString &binId, int pos, bool volatileOnly = false) const;

    /* @brief Get a given thumbnail from the cache
       @param binId is the id of the queried clip
       @param pos is the position where we query
       @param persistent if true, we store the image in the persistent cache, which generates a disk access
    */
    void storeThumbnail(const QString &binId, int pos, const QImage &img, bool persistent = false);

    /* @brief Removes all the thumbnails for a given clip */
    void invalidateThumbsForClip(const QString &binId);

    /* @brief Save all cached thumbs to disk */
    void saveCachedThumbs(QStringList keys);

protected:
    // Constructor is protected because class is a Singleton
    ThumbnailCache();

    // Return the key associated to a thumbnail
    static QString getKey(const QString &binId, int pos, bool *ok);

    // Return the dir where the persistent cache lives
    static QDir getDir(bool *ok);

    static std::unique_ptr<ThumbnailCache> instance;
    static std::once_flag m_onceFlag; // flag to create the repository only once;

    class Cache_t;
    std::unique_ptr<Cache_t> m_volatileCache;
    mutable QMutex m_mutex;

    // the following maps keeps track of the positions that we store for each clip in volatile caches.
    // Note that we don't track deletions due to items dropped from the cache. So the maps can contain more items that are currently stored.
    std::unordered_map<QString, std::vector<int>> m_storedVolatile;
    mutable std::unordered_map<QString, std::vector<int>> m_storedOnDisk;
};
