JUCE/modules/juce_audio_utils/gui/juce_AudioThumbnailCache.h

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2017 - ROLI Ltd.

   JUCE is an open source library subject to commercial or open-source
   licensing.

   By using JUCE, you agree to the terms of both the JUCE 5 End-User License
   Agreement and JUCE 5 Privacy Policy (both updated and effective as of the
   27th April 2017).

   End User License Agreement: www.juce.com/juce-5-licence
   Privacy Policy: www.juce.com/juce-5-privacy-policy

   Or: You may also use this code under the terms of the GPL v3 (see
   www.gnu.org/licenses).

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{

//==============================================================================
/**
    An instance of this class is used to manage multiple AudioThumbnail objects.

    The cache runs a single background thread that is shared by all the thumbnails
    that need it, and it maintains a set of low-res previews in memory, to avoid
    having to re-scan audio files too often.

    @see AudioThumbnail

    @tags{Audio}
*/
class JUCE_API  AudioThumbnailCache
{
public:
    //==============================================================================
    /** Creates a cache object.

        The maxNumThumbsToStore parameter lets you specify how many previews should
        be kept in memory at once.
    */
    explicit AudioThumbnailCache (int maxNumThumbsToStore);

    /** Destructor. */
    virtual ~AudioThumbnailCache();

    //==============================================================================
    /** Clears out any stored thumbnails. */
    void clear();

    /** Reloads the specified thumb if this cache contains the appropriate stored
        data.

        This is called automatically by the AudioThumbnail class, so you shouldn't
        normally need to call it directly.
    */
    bool loadThumb (AudioThumbnailBase& thumb, int64 hashCode);

    /** Stores the cachable data from the specified thumb in this cache.

        This is called automatically by the AudioThumbnail class, so you shouldn't
        normally need to call it directly.
    */
    void storeThumb (const AudioThumbnailBase& thumb, int64 hashCode);

    /** Tells the cache to forget about the thumb with the given hashcode. */
    void removeThumb (int64 hashCode);

    //==============================================================================
    /** Attempts to re-load a saved cache of thumbnails from a stream.
        The cache data must have been written by the writeToStream() method.
        This will replace all currently-loaded thumbnails with the new data.
    */
    bool readFromStream (InputStream& source);

    /** Writes all currently-loaded cache data to a stream.
        The resulting data can be re-loaded with readFromStream().
    */
    void writeToStream (OutputStream& stream);

    /** Returns the thread that client thumbnails can use. */
    TimeSliceThread& getTimeSliceThread() noexcept      { return thread; }

protected:
    /** This can be overridden to provide a custom callback for saving thumbnails
        once they have finished being loaded.
    */
    virtual void saveNewlyFinishedThumbnail (const AudioThumbnailBase&, int64 hashCode);

    /** This can be overridden to provide a custom callback for loading thumbnails
        from pre-saved files to save the cache the trouble of having to create them.
    */
    virtual bool loadNewThumb (AudioThumbnailBase&, int64 hashCode);

private:
    //==============================================================================
    TimeSliceThread thread;

    class ThumbnailCacheEntry;
    OwnedArray<ThumbnailCacheEntry> thumbs;
    CriticalSection lock;
    int maxNumThumbsToStore;

    ThumbnailCacheEntry* findThumbFor (int64 hash) const;
    int findOldestThumb() const;

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (AudioThumbnailCache)
};

} // namespace juce