Separate responsibilities: start-listening command, API-side JSON converters, bulk track endpoints, mix kinds

backend/Core/Musify.Application/PlayLists/AddTrackToPlayList.cs

@@ -1,61 +0,0 @@
-using ErrorOr;
-using Mediator;
-using Microsoft.EntityFrameworkCore;
-using Microsoft.Extensions.Logging;
-using Musify.Application.Contracts;
-using Musify.Application.Shared;
-using Musify.Domain.Entities;
-using Musify.Domain.ValueObjects;
-
-namespace Musify.Application.PlayLists;
-
-public record AddTrackToPlayListCommand(long UserId, Guid PlayListId, Guid TrackId)
-    : ICommand<ErrorOr<Success>>;
-
-public class AddTrackToPlayListCommandHandler(
-    IDatabase database,
-    ILogger<AddTrackToPlayListCommandHandler> logger)
-    : ICommandHandler<AddTrackToPlayListCommand, ErrorOr<Success>>
-{
-    public async ValueTask<ErrorOr<Success>> Handle(AddTrackToPlayListCommand request, CancellationToken cancellationToken)
-    {
-        var playList = await database.PlayLists.FindOwnedAsync(request.PlayListId, request.UserId, cancellationToken);
-        if (playList.IsError)
-            return playList.Errors;
-
-        var trackExists = await database.Tracks
-            .AsNoTracking()
-            .AnyAsync(t => t.Id == request.TrackId && t.LifeCycleStatus == LifeCycleStatus.Active, cancellationToken);
-        if (!trackExists)
-            return AppErrors.NotFound("Track", request.TrackId);
-
-        var alreadyAdded = await database.PlayListHasTracks
-            .AsNoTracking()
-            .AnyAsync(plt => plt.PlayListId == request.PlayListId && plt.TrackId == request.TrackId, cancellationToken);
-        if (alreadyAdded)
-            return AlreadyInPlayList;
-
-        // Playlist positions are internal indexes, so they start at 0.
-        var nextPosition = (await database.PlayListHasTracks
-            .Where(plt => plt.PlayListId == request.PlayListId)
-            .MaxAsync(plt => (int?)plt.Position, cancellationToken) ?? -1) + 1;
-
-        await database.PlayListHasTracks.AddAsync(new PlayListHasTrack
-        {
-            PlayListId = request.PlayListId,
-            TrackId = request.TrackId,
-            Position = nextPosition
-        }, cancellationToken);
-
-        var saved = await database.TrySaveChangesAsync(AlreadyInPlayList, cancellationToken);
-        if (saved.IsError)
-            return saved;
-
-        logger.LogInformation("Added track {TrackId} to playlist {PlayListId} at position {Position}",
-            request.TrackId, request.PlayListId, nextPosition);
-
-        return Result.Success;
-    }
-
-    private static Error AlreadyInPlayList => AppErrors.Conflict("PlayList.TrackAlreadyAdded", "Track is already in the playlist.");
-}

backend/Core/Musify.Application/PlayLists/AddTracksToPlayList.cs

@@ -0,0 +1,73 @@
+using ErrorOr;
+using Mediator;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using Musify.Application.Contracts;
+using Musify.Application.Shared;
+using Musify.Domain.Entities;
+using Musify.Domain.ValueObjects;
+
+namespace Musify.Application.PlayLists;
+
+/// <summary>Appends tracks to a playlist in the given order, skipping the ones it already has.</summary>
+public record AddTracksToPlayListCommand(long UserId, Guid PlayListId, IReadOnlyList<Guid> TrackIds)
+    : ICommand<ErrorOr<Success>>;
+
+public class AddTracksToPlayListCommandHandler(
+    IDatabase database,
+    ILogger<AddTracksToPlayListCommandHandler> logger)
+    : ICommandHandler<AddTracksToPlayListCommand, ErrorOr<Success>>
+{
+    public async ValueTask<ErrorOr<Success>> Handle(AddTracksToPlayListCommand request, CancellationToken cancellationToken)
+    {
+        var playList = await database.PlayLists.FindOwnedAsync(request.PlayListId, request.UserId, cancellationToken);
+        if (playList.IsError)
+            return playList.Errors;
+
+        var requestedIds = request.TrackIds.Distinct().ToList();
+
+        var existingIds = await database.Tracks
+            .AsNoTracking()
+            .Where(track => requestedIds.Contains(track.Id) && track.LifeCycleStatus == LifeCycleStatus.Active)
+            .Select(track => track.Id)
+            .ToListAsync(cancellationToken);
+
+        var missing = requestedIds.FirstOrDefault(id => !existingIds.Contains(id));
+        if (missing != Guid.Empty)
+            return AppErrors.NotFound("Track", missing);
+
+        var alreadyInPlayList = await database.PlayListHasTracks
+            .AsNoTracking()
+            .Where(link => link.PlayListId == request.PlayListId && requestedIds.Contains(link.TrackId))
+            .Select(link => link.TrackId)
+            .ToListAsync(cancellationToken);
+
+        var toAdd = requestedIds.Where(id => !alreadyInPlayList.Contains(id)).ToList();
+        if (toAdd.Count == 0)
+            return Result.Success;
+
+        // Playlist positions are internal indexes, so they start at 0.
+        var nextPosition = (await database.PlayListHasTracks
+            .Where(link => link.PlayListId == request.PlayListId)
+            .MaxAsync(link => (int?)link.Position, cancellationToken) ?? -1) + 1;
+
+        foreach (var trackId in toAdd)
+        {
+            await database.PlayListHasTracks.AddAsync(new PlayListHasTrack
+            {
+                PlayListId = request.PlayListId,
+                TrackId = trackId,
+                Position = nextPosition++
+            }, cancellationToken);
+        }
+
+        var saved = await database.TrySaveChangesAsync(
+            AppErrors.Conflict("PlayList.ConcurrentChange", "The playlist changed while adding tracks. Try again."), cancellationToken);
+        if (saved.IsError)
+            return saved;
+
+        logger.LogInformation("Added {Count} tracks to playlist {PlayListId}", toAdd.Count, request.PlayListId);
+
+        return Result.Success;
+    }
+}

backend/Core/Musify.Application/PlayLists/Responses/PlayListApplicationResponse.cs

@@ -1,8 +1,6 @@
 using Musify.Domain.Entities;
 using Musify.Domain.ValueObjects;
 
-using System.Text.Json.Serialization;
-using Musify.Application.Serialization;
 
 namespace Musify.Application.PlayLists.Responses;
 
@@ -17,7 +15,7 @@ public record PlayListApplicationResponse(
     DateTime CreatedAt,
     DateTime UpdatedAt,
     IReadOnlyList<Guid> CoverTrackIds,
-    [property: JsonConverter(typeof(LongAsStringConverter))] long OwnerUserId,
+    long OwnerUserId,
     int TrackCount,
     double DurationSeconds)
 {