Add option to automatically remove .torrent files upon adding

Some browsers do not download files, intended for immediate opening,
into a temporary directory, and thus a regular download directories
accumulate those unneeded files.

The option allows qBittorrent to clean after itself and delete those
files whether they were succesfully added or not (user-selectable
policy).

src/base/torrentfileguard.h

@@ -0,0 +1,95 @@
+/*
+ * Bittorrent Client using Qt and libtorrent.
+ * Copyright (C) 2016  Eugene Shalygin <eugene.shalygin@gmail.com>
+ *
+ * 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.
+ */
+
+#include <QString>
+#include <QMetaType>
+
+class QMetaEnum;
+/// Utility class to defer file deletion
+class FileGuard
+{
+public:
+    FileGuard(const QString &path = QString());
+    ~FileGuard();
+
+    /// Cancels or re-enables deferred file deletion
+    void setAutoRemove(bool remove) noexcept;
+
+private:
+    QString m_path;
+    bool m_remove;
+};
+
+/// Reads settings for .torrent files from preferences
+/// and sets the file guard up accordingly
+class TorrentFileGuard
+{
+    Q_GADGET
+
+public:
+    TorrentFileGuard(const QString &path = QString());
+    ~TorrentFileGuard();
+
+    /// marks the torrent file as loaded (added) into the BitTorrent::Session
+    void markAsAddedToSession();
+    void setAutoRemove(bool remove);
+
+    enum AutoDeleteMode     // do not change these names: they are stored in config file
+    {
+        Never,
+        IfAdded,
+        Always
+    };
+
+    // static interface to get/set preferences
+    static AutoDeleteMode autoDeleteMode();
+    static void setautoDeleteMode(AutoDeleteMode mode);
+
+private:
+    static QMetaEnum modeMetaEnum();
+#if QT_VERSION < QT_VERSION_CHECK(5, 5, 0)
+    Q_ENUMS(AutoDeleteMode)
+#else
+    Q_ENUM(AutoDeleteMode)
+#endif
+    AutoDeleteMode m_mode;
+    bool m_wasAdded;
+    // Qt 4 moc has troubles with Q_GADGET: if Q_GADGET is present in a class, moc unconditionally
+    // references in the generated code the statiMetaObject from the class ancestor.
+    // Moreover, if the ancestor class has Q_GADGET but does not have other
+    // Q_ declarations, moc does not generate staticMetaObject for it. These results
+    // in referencing the non existent staticMetaObject and such code fails to compile.
+    // This problem is NOT present in Qt 5.7.0 and maybe in some older Qt 5 versions too
+    // Qt 4.8.7 has it.
+    // Therefore, we can't inherit FileGuard :(
+    FileGuard m_guard;
+};
+
+#if QT_VERSION < QT_VERSION_CHECK(5, 5, 0)
+Q_DECLARE_METATYPE(TorrentFileGuard::AutoDeleteMode)
+#endif