feat(tracks): add user listening history

Record a listening-history entry when a stream ticket is issued and expose GET /users/{id}/listening-history to read it back.

backend/Musify.Application/Tracks/GetListeningHistory.cs

@@ -0,0 +1,28 @@
+using Mediator;
+using Musify.Application.Contracts;
+using Musify.Application.Tracks.Responses;
+
+namespace Musify.Application.Tracks
+{
+    public record GetListeningHistoryQuery(long UserId) : IQuery<IEnumerable<TrackApplicationResponse>>;
+
+    public class GetListeningHistoryQueryHandler(
+        IDatabase database)
+        : IQueryHandler<GetListeningHistoryQuery, IEnumerable<TrackApplicationResponse>>
+    {
+        public ValueTask<IEnumerable<TrackApplicationResponse>> Handle(GetListeningHistoryQuery query, CancellationToken cancellationToken)
+        {
+            var listeningHistory = database.ListeningHistories
+                .Where(l => l.UserId == query.UserId)
+                .Select(l => l.TrackId)
+                .ToList();
+
+            var tracks = database.Tracks
+                .Where(t => listeningHistory.Contains(t.Id))
+                .Select(TrackApplicationResponse.FromEntity)
+                .AsEnumerable();
+
+            return ValueTask.FromResult(tracks);
+        }
+    }
+}

backend/Musify.Application/Tracks/GetTrackStream.cs

@@ -5,6 +5,7 @@ using Microsoft.Extensions.Logging;
 using Musify.Application.Configuration;
 using Musify.Application.Contracts;
 using Musify.Application.Tracks.Responses;
+using Musify.Domain.Entities;
 using Musify.Domain.ValueObjects;
 
 namespace Musify.Application.Tracks
@@ -27,7 +28,7 @@ namespace Musify.Application.Tracks
                 .Select(t => new { t.Id, t.AudioTranscodeProcessingStatus, t.AudioFolderName } )
                 .SingleOrDefaultAsync(cancellationToken);
 
-            if (track is null)
+            if (track == null)
                 return Error.NotFound();
 
             if (string.IsNullOrWhiteSpace(track.AudioFolderName)
@@ -50,6 +51,16 @@ namespace Musify.Application.Tracks
 
             logger.LogInformation("Issued stream ticket for track {TrackId} to user {UserId}", request.TrackId, request.UserId);
 
+            var newListeningHistory = new ListeningHistory
+            {
+                UserId = request.UserId,
+                TrackId = request.TrackId,
+            };
+            await database.ListeningHistories.AddAsync(newListeningHistory, cancellationToken);
+            await database.SaveChangesAsync(cancellationToken);
+
+            logger.LogDebug("Listening history added for track {TrackId} by user {UserId}", request.TrackId, request.UserId);
+
             return new TrackStreamResponse(manifestUrl, ticket.Token, ticket.ExpiresInSeconds);
         }
     }