Handle the loading state whilst appending many tracks better

1) Update the queue length periodically so that the user can see we're
   working
2) Clear any previous track and display "loading..." instead

3 files changed, 17 insertions, 1 deletions

diff --git a/src/tangara/audio/audio_events.hpp b/src/tangara/audio/audio_events.hpp
index 50fd4b00..a141832e 100644
--- a/src/tangara/audio/audio_events.hpp
+++ b/src/tangara/audio/audio_events.hpp
@@ -103,6 +103,7 @@ struct QueueUpdate : tinyfsm::Event {
     kRepeatingLastTrack,
     kTrackFinished,
     kDeserialised,
+    kBulkLoadingUpdate,
   };
   Reason reason;
 };
diff --git a/src/tangara/audio/audio_fsm.cpp b/src/tangara/audio/audio_fsm.cpp
index 54ea5b6c..163e56ec 100644
--- a/src/tangara/audio/audio_fsm.cpp
+++ b/src/tangara/audio/audio_fsm.cpp
@@ -112,10 +112,13 @@ void AudioState::react(const QueueUpdate& ev) {
         cmd.new_track = std::monostate{};
       }
       break;
+    case QueueUpdate::kBulkLoadingUpdate:
+      // Bulk loading updates are informational only; a separate QueueUpdate
+      // event will be sent when loading is done.
     case QueueUpdate::kDeserialised:
-    default:
       // The current track is deserialised separately in order to retain seek
       // position.
+    default:
       return;
   }
 
diff --git a/src/tangara/audio/track_queue.cpp b/src/tangara/audio/track_queue.cpp
index 761ea09a..4f90e2ea 100644
--- a/src/tangara/audio/track_queue.cpp
+++ b/src/tangara/audio/track_queue.cpp
@@ -26,6 +26,7 @@
 #include "database/track.hpp"
 #include "events/event_queue.hpp"
 #include "memory_resource.hpp"
+#include "random.hpp"
 #include "tasks.hpp"
 #include "track_queue.hpp"
 #include "ui/ui_fsm.hpp"
@@ -190,6 +191,8 @@ auto TrackQueue::append(Item i) -> void {
     // doesn't block.
     bg_worker_.Dispatch<void>([=, this]() {
       database::TrackIterator it = std::get<database::TrackIterator>(i);
+
+      size_t next_update_at = 10;
       while (true) {
         auto next = *it;
         if (!next) {
@@ -205,7 +208,16 @@ auto TrackQueue::append(Item i) -> void {
           }
         }
         it++;
+
+        // Appending very large iterators can take a while. Send out periodic
+        // queue updates during them so that the user has an idea what's going
+        // on.
+        if (!--next_update_at) {
+          next_update_at = util::sRandom->RangeInclusive(10, 20);
+          notifyChanged(false, Reason::kBulkLoadingUpdate);
+        }
       }
+
       {
         const std::unique_lock<std::shared_mutex> lock(mutex_);
         updateShuffler(was_queue_empty);