feat(backend): auto-download YouTube tracks saved to playlists

backend/Musify.Api/DataTransferObjects/PlayLists/AddYouTubeTrackRequest.cs

@@ -0,0 +1,8 @@
+namespace Musify.Api.DataTransferObjects.PlayLists;
+
+public record AddYouTubeTrackRequest(
+    string VideoId,
+    string Title,
+    string Artist,
+    int DurationSeconds,
+    string ThumbnailUrl);

backend/Musify.Api/Endpoints/PlayListEndpoints.cs

@@ -93,6 +93,17 @@ public static class PlayListEndpoints
             .Produces(StatusCodes.Status404NotFound)
             .Produces(StatusCodes.Status409Conflict);
 
+        group.MapPost("/{playlistId}/youtube-tracks", AddYouTubeTrackToPlayList)
+            .WithName("AddYouTubeTrackToPlayList")
+            .WithSummary("Add A YouTube Track To A PlayList, Downloading It In The Background If Needed.")
+            .AddEndpointFilter<ValidationFilter<AddYouTubeTrackRequest>>()
+            .RequireAuthorization()
+            .Produces<TrackApplicationResponse>(StatusCodes.Status201Created)
+            .ProducesValidationProblem()
+            .Produces(StatusCodes.Status401Unauthorized)
+            .Produces(StatusCodes.Status404NotFound)
+            .Produces(StatusCodes.Status409Conflict);
+
         group.MapDelete("/{playlistId}/tracks/{trackId}", RemoveTrackFromPlayList)
             .WithName("RemoveTrackFromPlayList")
             .WithSummary("Remove A Track From A PlayList.")
@@ -232,6 +243,27 @@ public static class PlayListEndpoints
         return result.ToHttpResult();
     }
 
+    private static async Task<IResult> AddYouTubeTrackToPlayList(
+        IMediator mediator,
+        CurrentUser currentUser,
+        Guid playlistId,
+        AddYouTubeTrackRequest request,
+        CancellationToken cancellationToken)
+    {
+        var result = await mediator.Send(
+            new AddYouTubeTrackToPlayListCommand(
+                currentUser.RequiredId,
+                playlistId,
+                request.VideoId,
+                request.Title,
+                request.Artist,
+                request.DurationSeconds,
+                request.ThumbnailUrl),
+            cancellationToken);
+
+        return result.ToCreatedResult(track => $"/tracks/{track.Id}");
+    }
+
     private static async Task<IResult> RemoveTrackFromPlayList(
         IMediator mediator,
         CurrentUser currentUser,

backend/Musify.Api/Validators/PlayLists/AddYouTubeTrackRequestValidator.cs

@@ -0,0 +1,29 @@
+using FluentValidation;
+using Musify.Api.DataTransferObjects.PlayLists;
+
+namespace Musify.Api.Validators.PlayLists;
+
+public sealed class AddYouTubeTrackRequestValidator : AbstractValidator<AddYouTubeTrackRequest>
+{
+    public AddYouTubeTrackRequestValidator()
+    {
+        RuleFor(x => x.VideoId)
+            .NotEmpty()
+            .Matches("^[A-Za-z0-9_-]{11}$");
+
+        RuleFor(x => x.Title)
+            .NotEmpty()
+            .MaximumLength(200);
+
+        RuleFor(x => x.Artist)
+            .MaximumLength(400);
+
+        RuleFor(x => x.DurationSeconds)
+            .GreaterThan(0);
+
+        RuleFor(x => x.ThumbnailUrl)
+            .NotEmpty()
+            .Must(url => Uri.TryCreate(url, UriKind.Absolute, out var uri) && uri.Scheme == Uri.UriSchemeHttps)
+            .WithMessage("ThumbnailUrl must be an absolute https URL.");
+    }
+}