Add and remove tracks from playlists with position management and validation (project)
Implement adding and removing tracks from playlists with ownership validation, position management, and quota enforcement.
Playlist track management involves:
Location: src/NovaTuneApp/NovaTuneApp.ApiService/Models/Playlists/
namespace NovaTuneApp.ApiService.Models.Playlists;
/// <summary>
/// Request to add tracks to a playlist.
/// </summary>
/// <param name="TrackIds">Track IDs to add (1-100 per request)</param>
/// <param name="Position">Insert position (null = append to end)</param>
public record AddTracksRequest(
IReadOnlyList<string> TrackIds,
int? Position = null);
Location: src/NovaTuneApp/NovaTuneApp.ApiService/Validators/
using FluentValidation;
namespace NovaTuneApp.ApiService.Validators;
public class AddTracksRequestValidator : AbstractValidator<AddTracksRequest>
{
public AddTracksRequestValidator(IOptions<PlaylistOptions> options)
{
RuleFor(x => x.TrackIds)
.NotEmpty()
.WithMessage("At least one track ID is required")
.Must(ids => ids.Count <= options.Value.MaxTracksPerAddRequest)
.WithMessage($"Maximum {options.Value.MaxTracksPerAddRequest} tracks per request");
RuleForEach(x => x.TrackIds)
.Must(id => Ulid.TryParse(id, out _))
.WithMessage("Track ID must be a valid ULID");
RuleFor(x => x.Position)
.GreaterThanOrEqualTo(0)
.When(x => x.Position.HasValue)
.WithMessage("Position must be non-negative");
}
}
Location: src/NovaTuneApp/NovaTuneApp.ApiService/Services/PlaylistService.cs
public async Task<PlaylistDetails> AddTracksAsync(
string playlistId,
string userId,
AddTracksRequest request,
CancellationToken ct = default)
{
var playlist = await _session.LoadAsync<Playlist>($"Playlists/{playlistId}", ct);
if (playlist is null)
throw new PlaylistNotFoundException(playlistId);
if (playlist.UserId != userId)
throw new PlaylistAccessDeniedException(playlistId);
// Check track limit
if (playlist.TrackCount + request.TrackIds.Count > _options.Value.MaxTracksPerPlaylist)
{
throw new PlaylistTrackLimitExceededException(
playlistId,
playlist.TrackCount,
request.TrackIds.Count,
_options.Value.MaxTracksPerPlaylist);
}
// Load and validate all tracks
var trackDocIds = request.TrackIds.Select(id => $"Tracks/{id}").ToList();
var trackDocs = await _session.LoadAsync<Track>(trackDocIds, ct);
var validatedTracks = new List<Track>();
foreach (var trackId in request.TrackIds)
{
var docId = $"Tracks/{trackId}";
if (!trackDocs.TryGetValue(docId, out var track) || track is null)
throw new TrackNotFoundException(trackId);
if (track.UserId != userId)
throw new TrackAccessDeniedException(trackId);
if (track.Status == TrackStatus.Deleted)
throw new TrackDeletedException(trackId);
validatedTracks.Add(track);
}
var now = DateTimeOffset.UtcNow;
var insertPosition = request.Position ?? playlist.Tracks.Count;
// Validate insert position
if (insertPosition < 0 || insertPosition > playlist.Tracks.Count)
{
throw new InvalidPositionException(insertPosition, playlist.Tracks.Count + 1);
}
// Shift existing tracks at and after insert position
foreach (var entry in playlist.Tracks.Where(t => t.Position >= insertPosition))
{
entry.Position += request.TrackIds.Count;
}
// Create new track entries
var newEntries = request.TrackIds.Select((id, i) => new PlaylistTrackEntry
{
Position = insertPosition + i,
TrackId = id,
AddedAt = now
}).ToList();
playlist.Tracks.AddRange(newEntries);
// Sort by position to maintain order
playlist.Tracks = playlist.Tracks.OrderBy(t => t.Position).ToList();
// Update denormalized fields
playlist.TrackCount = playlist.Tracks.Count;
playlist.TotalDuration = CalculateTotalDuration(playlist.Tracks, trackDocs);
playlist.UpdatedAt = now;
await _session.SaveChangesAsync(ct);
_logger.LogInformation(
"Added {Count} tracks to playlist {PlaylistId} at position {Position} for user {UserId}",
request.TrackIds.Count, playlistId, insertPosition, userId);
return await MapToDetailsAsync(playlist, ct);
}
private TimeSpan CalculateTotalDuration(
List<PlaylistTrackEntry> entries,
IDictionary<string, Track?> trackDocs)
{
var total = TimeSpan.Zero;
foreach (var entry in entries)
{
if (trackDocs.TryGetValue($"Tracks/{entry.TrackId}", out var track) && track is not null)
{
total += track.Duration;
}
}
return total;
}
public async Task RemoveTrackAsync(
string playlistId,
string userId,
int position,
CancellationToken ct = default)
{
var playlist = await _session.LoadAsync<Playlist>($"Playlists/{playlistId}", ct);
if (playlist is null)
throw new PlaylistNotFoundException(playlistId);
if (playlist.UserId != userId)
throw new PlaylistAccessDeniedException(playlistId);
// Find track at position
var trackToRemove = playlist.Tracks.FirstOrDefault(t => t.Position == position);
if (trackToRemove is null)
throw new PlaylistTrackNotFoundException(playlistId, position);
// Remove the track
playlist.Tracks.Remove(trackToRemove);
// Reindex positions for tracks after the removed one
foreach (var entry in playlist.Tracks.Where(t => t.Position > position))
{
entry.Position--;
}
// Update denormalized fields
playlist.TrackCount = playlist.Tracks.Count;
playlist.UpdatedAt = DateTimeOffset.UtcNow;
// Recalculate total duration
await RecalculateTotalDurationAsync(playlist, ct);
await _session.SaveChangesAsync(ct);
_logger.LogInformation(
"Removed track at position {Position} from playlist {PlaylistId} for user {UserId}",
position, playlistId, userId);
}
private async Task RecalculateTotalDurationAsync(Playlist playlist, CancellationToken ct)
{
if (playlist.Tracks.Count == 0)
{
playlist.TotalDuration = TimeSpan.Zero;
return;
}
var trackIds = playlist.Tracks.Select(t => $"Tracks/{t.TrackId}").ToList();
var tracks = await _session.LoadAsync<Track>(trackIds, ct);
playlist.TotalDuration = CalculateTotalDuration(playlist.Tracks, tracks);
}
Location: src/NovaTuneApp/NovaTuneApp.ApiService/Infrastructure/Exceptions/
namespace NovaTuneApp.ApiService.Infrastructure.Exceptions;
/// <summary>
/// Thrown when adding tracks would exceed the playlist track limit.
/// </summary>
public class PlaylistTrackLimitExceededException : Exception
{
public string PlaylistId { get; }
public int CurrentCount { get; }
public int AddCount { get; }
public int MaxCount { get; }
public PlaylistTrackLimitExceededException(
string playlistId,
int currentCount,
int addCount,
int maxCount)
: base($"Cannot add {addCount} tracks. Playlist has {currentCount} tracks, limit is {maxCount}.")
{
PlaylistId = playlistId;
CurrentCount = currentCount;
AddCount = addCount;
MaxCount = maxCount;
}
}
/// <summary>
/// Thrown when a track is not found at the specified position in a playlist.
/// </summary>
public class PlaylistTrackNotFoundException : Exception
{
public string PlaylistId { get; }
public int Position { get; }
public PlaylistTrackNotFoundException(string playlistId, int position)
: base($"No track found at position {position} in playlist {playlistId}")
{
PlaylistId = playlistId;
Position = position;
}
}
Location: src/NovaTuneApp/NovaTuneApp.ApiService/Endpoints/PlaylistEndpoints.cs
group.MapPost("/{playlistId}/tracks", HandleAddTracks)
.WithName("AddTracksToPlaylist")
.WithSummary("Add tracks to a playlist")
.Produces<PlaylistDetails>(StatusCodes.Status200OK)
.ProducesProblem(StatusCodes.Status400BadRequest)
.ProducesProblem(StatusCodes.Status403Forbidden)
.ProducesProblem(StatusCodes.Status404NotFound)
.RequireRateLimiting("playlist-tracks-add");
group.MapDelete("/{playlistId}/tracks/{position:int}", HandleRemoveTrack)
.WithName("RemoveTrackFromPlaylist")
.WithSummary("Remove a track from a playlist by position")
.Produces(StatusCodes.Status204NoContent)
.ProducesProblem(StatusCodes.Status404NotFound)
.RequireRateLimiting("playlist-tracks-remove");
private static async Task<IResult> HandleAddTracks(
[FromRoute] string playlistId,
[FromBody] AddTracksRequest request,
[FromServices] IPlaylistService playlistService,
[FromServices] IValidator<AddTracksRequest> validator,
ClaimsPrincipal user,
CancellationToken ct)
{
if (!Ulid.TryParse(playlistId, out _))
{
return Results.Problem(
title: "Invalid playlist ID",
detail: "Playlist ID must be a valid ULID.",
statusCode: StatusCodes.Status400BadRequest,
type: "https://novatune.dev/errors/invalid-playlist-id");
}
var validationResult = await validator.ValidateAsync(request, ct);
if (!validationResult.IsValid)
{
return Results.ValidationProblem(validationResult.ToDictionary());
}
var userId = user.FindFirstValue(ClaimTypes.NameIdentifier)!;
try
{
var playlist = await playlistService.AddTracksAsync(
playlistId, userId, request, ct);
return Results.Ok(playlist);
}
catch (PlaylistNotFoundException)
{
return Results.Problem(
title: "Playlist not found",
statusCode: StatusCodes.Status404NotFound,
type: "https://novatune.dev/errors/playlist-not-found");
}
catch (PlaylistAccessDeniedException)
{
return Results.Problem(
title: "Access denied",
statusCode: StatusCodes.Status403Forbidden,
type: "https://novatune.dev/errors/forbidden");
}
catch (TrackNotFoundException ex)
{
return Results.Problem(
title: "Track not found",
detail: $"Track {ex.Message} was not found.",
statusCode: StatusCodes.Status404NotFound,
type: "https://novatune.dev/errors/track-not-found");
}
catch (TrackAccessDeniedException ex)
{
return Results.Problem(
title: "Track access denied",
detail: $"You do not have access to track {ex.Message}.",
statusCode: StatusCodes.Status403Forbidden,
type: "https://novatune.dev/errors/track-forbidden");
}
catch (TrackDeletedException ex)
{
return Results.Problem(
title: "Track is deleted",
detail: $"Track {ex.Message} has been deleted and cannot be added to playlists.",
statusCode: StatusCodes.Status409Conflict,
type: "https://novatune.dev/errors/track-deleted");
}
catch (PlaylistTrackLimitExceededException ex)
{
return Results.Problem(
title: "Track limit exceeded",
detail: ex.Message,
statusCode: StatusCodes.Status403Forbidden,
type: "https://novatune.dev/errors/playlist-track-limit-exceeded",
extensions: new Dictionary<string, object?>
{
["currentCount"] = ex.CurrentCount,
["addCount"] = ex.AddCount,
["maxCount"] = ex.MaxCount
});
}
catch (InvalidPositionException ex)
{
return Results.Problem(
title: "Invalid position",
detail: ex.Message,
statusCode: StatusCodes.Status400BadRequest,
type: "https://novatune.dev/errors/invalid-position");
}
}
private static async Task<IResult> HandleRemoveTrack(
[FromRoute] string playlistId,
[FromRoute] int position,
[FromServices] IPlaylistService playlistService,
ClaimsPrincipal user,
CancellationToken ct)
{
if (!Ulid.TryParse(playlistId, out _))
{
return Results.Problem(
title: "Invalid playlist ID",
detail: "Playlist ID must be a valid ULID.",
statusCode: StatusCodes.Status400BadRequest,
type: "https://novatune.dev/errors/invalid-playlist-id");
}
if (position < 0)
{
return Results.Problem(
title: "Invalid position",
detail: "Position must be non-negative.",
statusCode: StatusCodes.Status400BadRequest,
type: "https://novatune.dev/errors/invalid-position");
}
var userId = user.FindFirstValue(ClaimTypes.NameIdentifier)!;
try
{
await playlistService.RemoveTrackAsync(playlistId, userId, position, ct);
return Results.NoContent();
}
catch (PlaylistNotFoundException)
{
return Results.Problem(
title: "Playlist not found",
statusCode: StatusCodes.Status404NotFound,
type: "https://novatune.dev/errors/playlist-not-found");
}
catch (PlaylistAccessDeniedException)
{
return Results.Problem(
title: "Access denied",
statusCode: StatusCodes.Status403Forbidden,
type: "https://novatune.dev/errors/forbidden");
}
catch (PlaylistTrackNotFoundException ex)
{
return Results.Problem(
title: "Track not found in playlist",
detail: $"No track at position {ex.Position}.",
statusCode: StatusCodes.Status404NotFound,
type: "https://novatune.dev/errors/track-not-in-playlist");
}
}
POST /playlists/01HXK.../tracks
{
"trackIds": ["01HXL...", "01HXM...", "01HXN..."],
"position": 5
}
{
"playlistId": "01HXK...",
"name": "My Playlist",
"trackCount": 25,
"totalDuration": "PT1H30M",
"updatedAt": "2025-01-08T12:00:00Z"
}
DELETE /playlists/01HXK.../tracks/5
204 No Content
| Rule | Error |
|---|---|
| TrackIds not empty | 400 Bad Request |
| Max 100 tracks per request | 400 Bad Request |
| All track IDs valid ULIDs | 400 Bad Request |
| All tracks exist | 404 Not Found |
| All tracks owned by user | 403 Forbidden |
| No tracks with Deleted status | 409 Conflict |
| Position in valid range | 400 Bad Request |
| Won't exceed 10,000 track limit | 403 Forbidden |
| Rule | Error |
|---|---|
| Position >= 0 | 400 Bad Request |
| Track exists at position | 404 Not Found |
| Playlist exists | 404 Not Found |
| User owns playlist | 403 Forbidden |
Per requirements (Req 7 clarifications), duplicates are allowed. The same track can appear multiple times in a playlist at different positions.
Positions are 0-based and contiguous:
[0, 1, 2, 3, 4] - Valid[0, 1, 3, 4] - Invalid (gap at position 2)After any add/remove operation, positions are automatically reindexed to maintain contiguity.
doc/implementation/stage-6/07-api-add-tracks.mddoc/implementation/stage-6/08-api-remove-track.mddoc/implementation/stage-6/10-service-interface.mddoc/implementation/stage-6/18-test-strategy.md