Implement BencodeResumeDataStorage class

Implement ResumeDataStorage class as base for all "resume data" storages.
Implement BencodeResumeDataStorage class and put all existing logic of
"resume data" loading/saving there.

src/base/bittorrent/resumedatastorage.h

@@ -0,0 +1,81 @@
+/*
+ * Bittorrent Client using Qt and libtorrent.
+ * Copyright (C) 2015, 2018  Vladimir Golovnev <glassez@yandex.ru>
+ *
+ * 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) any later version.
+ *
+ * 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, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * In addition, as a special exception, the copyright holders give permission to
+ * link this program with the OpenSSL project's "OpenSSL" library (or with
+ * modified versions of it that use the same license as the "OpenSSL" library),
+ * and distribute the linked executables. You must obey the GNU General Public
+ * License in all respects for all of the code used other than "OpenSSL".  If you
+ * modify file(s), you may extend this exception to your version of the file(s),
+ * but you are not obligated to do so. If you do not wish to do so, delete this
+ * exception statement from your version.
+ */
+
+#pragma once
+
+#include <optional>
+
+#include <libtorrent/fwd.hpp>
+
+#include <QDir>
+#include <QObject>
+#include <QVector>
+
+#include "infohash.h"
+#include "loadtorrentparams.h"
+
+class QByteArray;
+
+namespace BitTorrent
+{
+    class ResumeDataStorage : public QObject
+    {
+        Q_OBJECT
+        Q_DISABLE_COPY(ResumeDataStorage)
+
+    public:
+        using QObject::QObject;
+
+        virtual QVector<TorrentID> registeredTorrents() const = 0;
+        virtual std::optional<LoadTorrentParams> load(const TorrentID &id) const = 0;
+        virtual void store(const TorrentID &id, const LoadTorrentParams &resumeData) const = 0;
+        virtual void remove(const TorrentID &id) const = 0;
+        virtual void storeQueue(const QVector<TorrentID> &queue) const = 0;
+    };
+
+    class BencodeResumeDataStorage final : public ResumeDataStorage
+    {
+        Q_OBJECT
+        Q_DISABLE_COPY(BencodeResumeDataStorage)
+
+    public:
+        explicit BencodeResumeDataStorage(const QString &resumeFolderPath);
+
+        QVector<TorrentID> registeredTorrents() const override;
+        std::optional<LoadTorrentParams> load(const TorrentID &id) const override;
+        void store(const TorrentID &id, const LoadTorrentParams &resumeData) const override;
+        void remove(const TorrentID &id) const override;
+        void storeQueue(const QVector<TorrentID> &queue) const override;
+
+    private:
+        std::optional<LoadTorrentParams> loadTorrentResumeData(const QByteArray &data, const TorrentInfo &metadata) const;
+
+        const QDir m_resumeDataDir;
+        QVector<TorrentID> m_registeredTorrents;
+    };
+}