Add support for saving embedded album covers

Fixes #286

src/covermanager/albumcoverimageresult.h

@@ -0,0 +1,53 @@
+/*
+ * Strawberry Music Player
+ * Copyright 2021, Jonas Kvinge <jonas@jkvinge.net>
+ *
+ * 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 ALBUMCOVERIMAGERESULT_H
+#define ALBUMCOVERIMAGERESULT_H
+
+#include "config.h"
+
+#include <QMetaType>
+#include <QByteArray>
+#include <QString>
+#include <QUrl>
+#include <QImage>
+
+struct AlbumCoverImageResult {
+  explicit AlbumCoverImageResult(const QUrl &_cover_url = QUrl(),
+                                 const QString &_mime_type = QString(),
+                                 const QByteArray &_image_data = QByteArray(),
+                                 const QImage &_image = QImage()) :
+                                 cover_url(_cover_url),
+                                 mime_type(_mime_type),
+                                 image_data(_image_data), image(_image) {}
+
+  explicit AlbumCoverImageResult(const QImage &_image) : image(_image) {}
+
+  QUrl cover_url;
+  QString mime_type;
+  QByteArray image_data;
+  QImage image;
+
+  bool is_valid() const { return !image_data.isNull() || !image.isNull(); }
+  bool is_jpeg() const { return mime_type == "image/jpeg" && !image_data.isEmpty(); }
+
+};
+Q_DECLARE_METATYPE(AlbumCoverImageResult)
+
+#endif  // ALBUMCOVERIMAGERESULT_H