gui_file_thumbnails.h

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#pragma once
 
// Pictures of what's in files, as the OS shows them in its file views: a photo's, a frame of
// a video, a document's first page. Read off the UI thread.
 
#include <gui_core/gui_base_types.h>
#include <gui_core/style/gui_style_text.h>
 
#include <chrono>
#include <condition_variable>
#include <cstdint>
#include <filesystem>
#include <functional>
#include <list>
#include <mutex>
#include <string>
#include <thread>
#include <unordered_map>
#include <vector>
 
namespace tachyon
{
    class ITextSystem;


    class FileThumbnails
    {
    public:
        struct Picture
        {
            uint2                size {};
            std::vector<uint8_t> rgba;
        };

        using Reader = std::function<bool(const std::filesystem::path& file, uint32_t pixels, Picture& picture)>;
 
        explicit FileThumbnails(ITextSystem& textSystem, size_t capacity = 512, Reader reader = ShellReader(),
                                std::chrono::milliseconds inUse = std::chrono::milliseconds(500));
        ~FileThumbnails();
        FileThumbnails(const FileThumbnails&)            = delete;
        FileThumbnails& operator=(const FileThumbnails&) = delete;

        IconID Get(const std::filesystem::path& file, std::filesystem::file_time_type modified, uint32_t pixels);

        size_t Count() const { return m_entries.size(); }
        size_t Reading();

        static std::string Key(const std::filesystem::path& file, std::filesystem::file_time_type modified, uint32_t pixels);
        static Reader ShellReader();
 
    private:
        struct Entry
        {
            IconID                                icon    = IconID::Invalid;
            bool                                  pending = true;
            std::list<std::string>::iterator      used;   
            std::chrono::steady_clock::time_point asked;
        };
        struct Job
        {
            std::string           key;
            std::filesystem::path file;
            uint32_t              pixels = 0;
        };
        struct Done
        {
            std::string key;
            bool        ok = false;
            Picture     picture;
        };
 
        void Collect();
        void Forget(const std::string& key);
        void Work();
 
        ITextSystem&                           m_textSystem;
        size_t                                 m_capacity;
        Reader                                 m_reader;
        std::chrono::milliseconds              m_inUse;
        std::unordered_map<std::string, Entry> m_entries;
        std::list<std::string>                 m_used;   
 
        // Shared with the reading thread.
        std::mutex              m_mutex;
        std::condition_variable m_wake;
        std::vector<Job>        m_jobs;   
        std::vector<Done>       m_done;
        bool                    m_stop = false;
        std::thread             m_thread;   
    };
 
#ifdef _WIN32
    namespace detail
    {
        bool BitmapPixels(void* bitmap, uint32_t& width, uint32_t& height, std::vector<uint8_t>& rgba);
    }
#endif

}