Add Subsonic scrobble support (#545)

* add SubsonicScrobbler, add Scrobble method in SubsonicService

* new class SubsonicScrobbleRequest, use queue again, clean up

* add checkbox to enable server-side scrobbling to Subsonic settings page

* Check serversidescrobbling in SubsonicScrobbler::ReloadSettings instead of SubsonicService

TODO: SubsonicScrobbler::ReloadSettings needs to be called when
SubsonicSettings change.

src/scrobbler/subsonicscrobbler.h

@@ -0,0 +1,75 @@
+/*
+ * Strawberry Music Player
+ * Copyright 2018, Jonas Kvinge <jonas@jkvinge.net>
+ * Copyright 2020, Pascal Below <spezifisch@below.fr>
+ *
+ * Strawberry 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 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Strawberry 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 Strawberry.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef SUBSONICSCROBBLER_H
+#define SUBSONICSCROBBLER_H
+
+#include "config.h"
+
+#include <QtGlobal>
+#include <QObject>
+#include <QDateTime>
+#include <QVariant>
+#include <QString>
+
+#include "core/song.h"
+#include "scrobblerservice.h"
+
+class Application;
+class SubsonicService;
+
+class SubsonicScrobbler : public ScrobblerService {
+  Q_OBJECT
+
+ public:
+  explicit SubsonicScrobbler(Application *app, QObject *parent = nullptr);
+  ~SubsonicScrobbler() override;
+
+  static const char *kName;
+
+  void ReloadSettings() override;
+
+  bool IsEnabled() const override { return enabled_; }
+  bool IsAuthenticated() const override { return true; }
+
+  void UpdateNowPlaying(const Song &song) override;
+  void ClearPlaying() override;
+  void Scrobble(const Song &song) override;
+  void Error(const QString &error, const QVariant &debug = QVariant()) override;
+
+  void DoSubmit() override;
+  void Submitted() override { submitted_ = true; }
+  bool IsSubmitted() const override { return submitted_; }
+
+ public slots:
+  void WriteCache() override {}
+  void Submit() override;
+
+ private:
+  Application *app_;
+  SubsonicService *service_;
+  bool enabled_;
+  bool submitted_;
+  Song song_playing_;
+  QDateTime time_;
+
+};
+
+#endif  // SUBSONICSCROBBLER_H