lazyrootmixin.h

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/**********************************************************************
 * LeechCraft - modular cross-platform feature rich internet client.
 * Copyright (C) 2006-2014  Georg Rudoy
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE or copy at https://www.boost.org/LICENSE_1_0.txt)
 **********************************************************************/
 
#pragma once
 
#include <concepts>
#include <functional>
#include <utility>
#include <QAbstractItemModel>
 
namespace LC::Util
{
    template<std::derived_from<QAbstractItemModel> Model>
    class LazyRootMixin : public Model
    {
        const std::function<void ()> Load_;
        bool Loaded_ = false;
    public:
        template<typename... Args>
        explicit LazyRootMixin (std::function<void ()> load, Args&&... args)
        : Model { std::forward<Args> (args)... }
        , Load_ { std::move (load) }
        {
        }

        bool IsLoaded () const
        {
            return Loaded_;
        }

        void EnsureLoaded ()
        {
            if (!Loaded_)
                Reload ();
        }

        void Reload ()
        {
            Loaded_ = true;
            this->removeRows (0, this->rowCount ());
            Load_ ();
        }
 
        bool hasChildren (const QModelIndex& parent) const override
        {
            return IsUnloadedRoot (parent) || Model::hasChildren (parent);
        }
 
        bool canFetchMore (const QModelIndex& parent) const override
        {
            return IsUnloadedRoot (parent) || Model::canFetchMore (parent);
        }
 
        void fetchMore (const QModelIndex& parent) override
        {
            if (IsUnloadedRoot (parent))
                Reload ();
            else
                Model::fetchMore (parent);
        }
    private:
        bool IsUnloadedRoot (const QModelIndex& parent) const
        {
            return !parent.isValid () && !Loaded_;
        }
    };
}