1 files changed, 103 insertions, 0 deletions
diff --git a/src/library/externaltrackcollection.h b/src/library/externaltrackcollection.h
new file mode 100644
index 0000000000..eeed8b5d42
--- /dev/null
+++ b/src/library/externaltrackcollection.h
@@ -0,0 +1,103 @@
+#pragma once
+
+#include <QDir>
+#include <QList>
+#include <QString>
+
+#include "track/trackref.h"
+
+
+class Track;
+
+class LibraryFeature;
+
+// This interface and base class enable to synchronize external
+// track collections with Mixxx. It provides methods that will
+// be invoked by Mixxx after tracks have been added, modified or
+// deleted in the internal track collection. It also notifies
+// external track collections if the metadata of a single track
+// has been saved. A track in the internal track collection always
+// refers to a single, local file.
+//
+// All functions must be implemented in a non-blocking fashion,
+// i.e. asynchronously. They will be invoked AFTER the corresponding
+// operation has been executed on the internal track collection.
+//
+// WARNING: External track collections MUST NOT modify the track
+// files while Mixxx is running to avoid file corruption caused by
+// concurrent write access!
+class ExternalTrackCollection : public QObject {
+Q_OBJECT
+
+  public:
+    virtual ~ExternalTrackCollection() = default;
+
+    virtual QString name() const = 0;
+
+    // Check if the connection to the extenal track collection
+    // has been established, i.e. if the synchronization is active.
+    virtual bool isActive() const = 0;
+
+    // Synchronously (blocking) stop the synchronization by
+    // finishing all pending requests.
+    virtual void shutdown() {}
+
+    // All tracks in the corresponding directory need to be
+    // relocated recursively by updating their location.
+    virtual /*async*/ void relocateDirectory(
+            const QString& oldRootDir,
+            const QString& newRootDir) = 0;
+
+    // A (potentially large) number of tracks has recently been
+    // modified by a batch update in the internal track collection.
+    // The metadata of those tracks might need to be loaded in order
+    // to send it to the external track collection.
+    virtual /*async*/ void updateTracks(
+            const QList<TrackRef>& updatedTracks) = 0;
+
+    // The tracks referenced by their (local) file path have been
+    // removed from the track collection and may also have disappeared
+    // from the file system.
+    virtual /*async*/ void purgeTracks(
+            const QList<QString>& trackLocations) = 0;
+
+    // All tracks in the corresponding directory have been removed
+    // recursively from the root directory and the directory may
+    // have disappeared from the file system.
+    virtual /*async*/ void purgeAllTracks(
+            const QDir& rootDir) = 0;
+
+    // Duplications have been resolved by removing the duplicate track
+    // and replacing any references with the corresponding replacement
+    // track.
+    // The default implementation first purges all duplicate tracks that
+    // have been removed and then updates all the replaced tracks.
+    struct DuplicateTrack {
+        TrackRef removed;
+        TrackRef replacedBy;
+    };
+    virtual /*async*/ void deduplicateTracks(
+            const QList<DuplicateTrack>& duplicateTracks);
+
+    // A new track has been added to the internal track collection or the
+    // modified metadata of an existing track has just been saved.
+    enum class ChangeHint {
+        Added,
+        Modified,
+    };
+    virtual /*async*/ void saveTrack(
+            const Track& track,
+            ChangeHint changeHint) = 0;
+
+    // Create the corresponding library feature (if desired) that will
+    // be hooked into the side pane in Mixxx.
+    virtual LibraryFeature* newLibraryFeature(
+            QObject* /*parent*/) {
+        return nullptr;
+    }
+
+  protected:
+    explicit ExternalTrackCollection(QObject* parent = nullptr)
+            : QObject(parent) {
+    }
+};