Improve Search handling

Legacy SearchEngine class really has three roles:
  1. Manage search plugins,
  2. Handle the search job, and
  3. Handle the download of the torrent file using the search plugin.
Now it is splitted into 3 classes: SearchManager, SearchHandler and
SearchDownloadHandler.
Search GUI is also improved.

src/base/search/searchhandler.h

@@ -0,0 +1,90 @@
+/*
+ * Bittorrent Client using Qt and libtorrent.
+ * Copyright (C) 2015, 2018  Vladimir Golovnev <glassez@yandex.ru>
+ * Copyright (C) 2006  Christophe Dumez <chris@qbittorrent.org>
+ *
+ * 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 <QByteArray>
+#include <QList>
+#include <QObject>
+
+class QProcess;
+class QTimer;
+
+struct SearchResult
+{
+    QString fileName;
+    QString fileUrl;
+    qlonglong fileSize;
+    qlonglong nbSeeders;
+    qlonglong nbLeechers;
+    QString siteUrl;
+    QString descrLink;
+};
+
+class SearchPluginManager;
+
+class SearchHandler : public QObject
+{
+    Q_OBJECT
+    Q_DISABLE_COPY(SearchHandler)
+
+    friend class SearchPluginManager;
+
+    SearchHandler(const QString &pattern, const QString &category
+                  , const QStringList &usedPlugins, SearchPluginManager *manager);
+
+public:
+    bool isActive() const;
+    QString pattern() const;
+    SearchPluginManager *manager() const;
+    QList<SearchResult> results() const;
+
+    void cancelSearch();
+
+signals:
+    void searchFinished(bool cancelled = false);
+    void searchFailed();
+    void newSearchResults(const QList<SearchResult> &results);
+
+private:
+    void readSearchOutput();
+    void processFailed();
+    void processFinished(int exitcode);
+    bool parseSearchResult(const QString &line, SearchResult &searchResult);
+
+    const QString m_pattern;
+    const QString m_category;
+    const QStringList m_usedPlugins;
+    SearchPluginManager *m_manager;
+    QProcess *m_searchProcess;
+    QTimer *m_searchTimeout;
+    QByteArray m_searchResultLineTruncated;
+    bool m_searchCancelled = false;
+    QList<SearchResult> m_results;
+};