Fix playback after restoring queue on boot

src/tangara/audio/audio_fsm.cpp

@@ -191,6 +191,11 @@ void AudioState::react(const internal::StreamStarted& ev) {
 
   if (!sIsPaused && !is_in_state<states::Playback>()) {
     transit<states::Playback>();
+  } else {
+    // Make sure everyone knows we've got a track ready to go, even if we're
+    // not playing it yet. This mostly matters when restoring the queue from
+    // disk after booting.
+    emitPlaybackUpdate(true);
   }
 }
 
@@ -485,12 +490,13 @@ void Playback::react(const system_fsm::SdStateChanged& ev) {
 
 void Playback::react(const internal::StreamHeartbeat& ev) {
   sStreamCues.update(sOutput->samplesUsed());
-  auto current = sStreamCues.current();
 
-  if (!current.first) {
-    transit<Standby>();
-  } else {
+  if (sStreamCues.hasStream()) {
     emitPlaybackUpdate(false);
+  } else {
+    // Finished the current stream, and there's nothing upcoming. We must be
+    // finished.
+    transit<Standby>();
   }
 }
 

src/tangara/audio/stream_cues.cpp

@@ -32,10 +32,14 @@ auto StreamCues::update(uint32_t sample) -> void {
 
 auto StreamCues::addCue(std::shared_ptr<TrackInfo> track, uint32_t sample)
     -> void {
-  upcoming_.push_back(Cue{
-      .track = track,
-      .start_at = sample,
-  });
+  if (sample == now_) {
+    current_ = {track, now_};
+  } else {
+    upcoming_.push_back(Cue{
+        .track = track,
+        .start_at = sample,
+    });
+  }
 }
 
 auto StreamCues::current() -> std::pair<std::shared_ptr<TrackInfo>, uint32_t> {
@@ -54,4 +58,8 @@ auto StreamCues::current() -> std::pair<std::shared_ptr<TrackInfo>, uint32_t> {
   return {current_->track, duration};
 }
 
+auto StreamCues::hasStream() -> bool {
+  return current_ || !upcoming_.empty();
+}
+
 }  // namespace audio

src/tangara/audio/stream_cues.hpp

@@ -26,9 +26,12 @@ class StreamCues {
 
   /* Updates the current track given the new most recently played sample. */
   auto update(uint32_t sample) -> void;
+
   /* Returns the current track, and how long it has been playing for. */
   auto current() -> std::pair<std::shared_ptr<TrackInfo>, uint32_t>;
 
+  auto hasStream() -> bool;
+
   auto addCue(std::shared_ptr<TrackInfo>, uint32_t start_at) -> void;
 
  private: