adding System.Text.Json serialiser with source generators

SpotifyAPI.Web.Tests/Clients/SpotifyClientConfigTest.cs

@@ -15,7 +15,7 @@ namespace SpotifyAPI.Web
 
       Assert.IsInstanceOf(typeof(SimplePaginator), defaultConfig.DefaultPaginator);
       Assert.IsInstanceOf(typeof(NetHttpClient), defaultConfig.HTTPClient);
-      Assert.IsInstanceOf(typeof(NewtonsoftJSONSerializer), defaultConfig.JSONSerializer);
+      Assert.IsInstanceOf(typeof(TextJsonSerializer), defaultConfig.JSONSerializer);
       Assert.AreEqual(SpotifyUrls.APIV1, defaultConfig.BaseAddress);
       Assert.AreEqual(null, defaultConfig.Authenticator);
       Assert.AreEqual(null, defaultConfig.HTTPLogger);
@@ -32,7 +32,7 @@ namespace SpotifyAPI.Web
 
       Assert.IsInstanceOf(typeof(SimplePaginator), defaultConfig.DefaultPaginator);
       Assert.IsInstanceOf(typeof(NetHttpClient), defaultConfig.HTTPClient);
-      Assert.IsInstanceOf(typeof(NewtonsoftJSONSerializer), defaultConfig.JSONSerializer);
+      Assert.IsInstanceOf(typeof(TextJsonSerializer), defaultConfig.JSONSerializer);
       Assert.AreEqual(SpotifyUrls.APIV1, defaultConfig.BaseAddress);
       Assert.AreEqual(null, defaultConfig.HTTPLogger);
       Assert.AreEqual(null, defaultConfig.RetryHandler);

SpotifyAPI.Web.Tests/Http/NewtonsoftJSONSerializerTest.cs

@@ -5,6 +5,8 @@ using Moq;
 using NUnit.Framework;
 using SpotifyAPI.Web.Http;
 using System.Net.Http;
+using System.Threading.Tasks;
+using System.Linq;
 
 namespace SpotifyAPI.Web.Tests
 {
@@ -82,9 +84,60 @@ namespace SpotifyAPI.Web.Tests
       Assert.AreEqual(apiResonse.Response, response.Object);
     }
 
-    public class TestResponseObject
+    [TestCase]
+    public async Task DeserializeResponse_TimeCurrentlyPlayingTestMessage()
     {
-      public bool HelloWorld { get; set; }
+      var serializer = new NewtonsoftJSONSerializer();
+      var response = new Mock<IResponse>();
+      response.SetupGet(r => r.Body).Returns(ExampleResponses.CurrentlyPlayingContext);
+      response.SetupGet(r => r.ContentType).Returns("application/json");
+
+      var times = new List<long>();
+      foreach (var iter in Enumerable.Range(0, 50))
+      {
+        var watch = System.Diagnostics.Stopwatch.StartNew();
+
+        IAPIResponse<CurrentlyPlayingContext> apiResonse = serializer.DeserializeResponse<CurrentlyPlayingContext>(response.Object);
+
+        watch.Stop();
+        times.Add(watch.ElapsedMilliseconds);
+
+        Assert.AreEqual(apiResonse.Response, response.Object);
+      }
+
+      var mean = times.Sum() / 50;
+
+      using StreamWriter file = new("newtonsoft.json_test.txt", append: true);
+      await file.WriteLineAsync($"CurrentlyPlayingContext: {mean}ms");
+
+    }
+
+    [TestCase]
+    public async Task DeserializeResponse_TimeUserTestMessage()
+    {
+      var serializer = new NewtonsoftJSONSerializer();
+      var response = new Mock<IResponse>();
+      response.SetupGet(r => r.Body).Returns(ExampleResponses.PublicUser);
+      response.SetupGet(r => r.ContentType).Returns("application/json");
+
+      var times = new List<long>();
+      foreach (var iter in Enumerable.Range(0, 50))
+      {
+        var watch = System.Diagnostics.Stopwatch.StartNew();
+
+        IAPIResponse<PublicUser> apiResonse = serializer.DeserializeResponse<PublicUser>(response.Object);
+
+        watch.Stop();
+        times.Add(watch.ElapsedMilliseconds);
+
+        Assert.AreEqual(apiResonse.Response, response.Object);
+      }
+
+      var mean = times.Sum() / 50;
+
+      using StreamWriter file = new("newtonsoft.json_test.txt", append: true);
+      await file.WriteLineAsync($"User: {mean}ms");
+
     }
   }
 }

SpotifyAPI.Web.Tests/Http/SystemTextTests.cs

@@ -0,0 +1,134 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Net.Http;
+using System.Text;
+using System.Threading.Tasks;
+using Moq;
+using NUnit.Framework;
+using SpotifyAPI.Web.Http;
+
+namespace SpotifyAPI.Web.Tests
+{ 
+  public class SystemTextTests
+  {
+    public static IEnumerable<object> DontSerializeTestSource
+    {
+      get
+      {
+        yield return new TestCaseData(null);
+        yield return new TestCaseData("string");
+        yield return new TestCaseData(new MemoryStream(Encoding.UTF8.GetBytes("string")));
+        yield return new TestCaseData(new StringContent("string"));
+      }
+    }
+
+    [TestCaseSource(nameof(DontSerializeTestSource))]
+    public void SerializeRequest_SkipsAlreadySerialized(object input)
+    {
+      var serializer = new TextJsonSerializer();
+      var request = new Mock<IRequest>();
+      request.SetupGet(r => r.Body).Returns(input);
+
+      serializer.SerializeRequest(request.Object);
+
+      Assert.AreEqual(input, request.Object.Body);
+    }
+
+    [TestCase]
+    public void DeserializeResponse_SkipsNonJson()
+    {
+      var serializer = new TextJsonSerializer();
+      var response = new Mock<IResponse>();
+      response.SetupGet(r => r.Body).Returns("hello");
+      response.SetupGet(r => r.ContentType).Returns("media/mp4");
+
+      IAPIResponse<object> apiResonse = serializer.DeserializeResponse<object>(response.Object);
+      Assert.AreEqual(apiResonse.Body, null);
+      Assert.AreEqual(apiResonse.Response, response.Object);
+    }
+
+    [TestCase]
+    public void DeserializeResponse_HandlesJson()
+    {
+      var serializer = new TextJsonSerializer();
+      var response = new Mock<IResponse>();
+      response.SetupGet(r => r.Body).Returns("{\"hello_world\": false}");
+      response.SetupGet(r => r.ContentType).Returns("application/json");
+
+      IAPIResponse<TestResponseObject> apiResonse = serializer.DeserializeResponse<TestResponseObject>(response.Object);
+      Assert.AreEqual(apiResonse.Body?.HelloWorld, false);
+      Assert.AreEqual(apiResonse.Response, response.Object);
+    }
+
+    [TestCase]
+    public void DeserializeResponse_TestMessage()
+    {
+      var serializer = new TextJsonSerializer();
+      var response = new Mock<IResponse>();
+      response.SetupGet(r => r.Body).Returns(ExampleResponses.CurrentlyPlayingContext);
+      response.SetupGet(r => r.ContentType).Returns("application/json");
+
+      IAPIResponse<CurrentlyPlayingContext> apiResonse = serializer.DeserializeResponse<CurrentlyPlayingContext>(response.Object);
+
+      Assert.AreEqual(apiResonse.Response, response.Object);
+    }
+
+    [TestCase]
+    public async Task DeserializeResponse_TimeCurrentlyPlayingTestMessage()
+    {
+      var serializer = new TextJsonSerializer();
+      var response = new Mock<IResponse>();
+      response.SetupGet(r => r.Body).Returns(ExampleResponses.CurrentlyPlayingContext);
+      response.SetupGet(r => r.ContentType).Returns("application/json");
+
+      var times = new List<long>();
+      foreach(var iter in Enumerable.Range(0, 50))
+      {
+        var watch = System.Diagnostics.Stopwatch.StartNew();
+        
+        IAPIResponse<CurrentlyPlayingContext> apiResonse = serializer.DeserializeResponse<CurrentlyPlayingContext>(response.Object);
+
+        watch.Stop();
+        times.Add(watch.ElapsedMilliseconds);
+
+        Assert.AreEqual(apiResonse.Response, response.Object);
+      }
+
+      var mean = times.Sum() / 50;
+
+      using StreamWriter file = new("system.text.json_test.txt", append: true);
+      await file.WriteLineAsync($"CurrentlyPlayingContext: {mean}ms");
+      
+    }
+
+    [TestCase]
+    public async Task DeserializeResponse_TimeUserTestMessage()
+    {
+      var serializer = new TextJsonSerializer();
+      var response = new Mock<IResponse>();
+      response.SetupGet(r => r.Body).Returns(ExampleResponses.PublicUser);
+      response.SetupGet(r => r.ContentType).Returns("application/json");
+
+      var times = new List<long>();
+      foreach (var iter in Enumerable.Range(0, 50))
+      {
+        var watch = System.Diagnostics.Stopwatch.StartNew();
+
+        IAPIResponse<PublicUser> apiResonse = serializer.DeserializeResponse<PublicUser>(response.Object);
+
+        watch.Stop();
+        times.Add(watch.ElapsedMilliseconds);
+
+        Assert.AreEqual(apiResonse.Response, response.Object);
+      }
+
+      var mean = times.Sum() / 50;
+
+      using StreamWriter file = new("system.text.json_test.txt", append: true);
+      await file.WriteLineAsync($"User: {mean}ms");
+
+    }
+  }
+}

SpotifyAPI.Web.Tests/SpotifyAPI.Web.Tests.csproj

@@ -12,6 +12,7 @@
     <PackageReference Include="NUnit" Version="3.13.2" />
     <PackageReference Include="NUnit3TestAdapter" Version="4.1.0" />
     <PackageReference Include="NUnit.Console" Version="3.13.0" />
+    <PackageReference Include="System.IO" Version="4.3.0" />
   </ItemGroup>
 
   <ItemGroup>

SpotifyAPI.Web/Clients/Interfaces/IPlaylistsClient.cs

@@ -38,7 +38,7 @@ namespace SpotifyAPI.Web
     /// https://developer.spotify.com/documentation/web-api/reference-beta/#endpoint-get-playlists-tracks
     /// </remarks>
     /// <returns></returns>
-    Task<Paging<PlaylistTrack<IPlayableItem>>> GetItems(string playlistId);
+    Task<Paging<PlaylistTrack<BasePlayableItem>>> GetItems(string playlistId);
 
     /// <summary>
     /// Get full details of the items of a playlist owned by a Spotify user.
@@ -49,7 +49,7 @@ namespace SpotifyAPI.Web
     /// https://developer.spotify.com/documentation/web-api/reference-beta/#endpoint-get-playlists-tracks
     /// </remarks>
     /// <returns></returns>
-    Task<Paging<PlaylistTrack<IPlayableItem>>> GetItems(string playlistId, PlaylistGetItemsRequest request);
+    Task<Paging<PlaylistTrack<BasePlayableItem>>> GetItems(string playlistId, PlaylistGetItemsRequest request);
 
     /// <summary>
     /// Create a playlist for a Spotify user. (The playlist will be empty until you add tracks.)

SpotifyAPI.Web/Clients/PlaylistsClient.cs

@@ -26,19 +26,19 @@ namespace SpotifyAPI.Web
       return API.Post<SnapshotResponse>(URLs.PlaylistTracks(playlistId), null, request.BuildBodyParams());
     }
 
-    public Task<Paging<PlaylistTrack<IPlayableItem>>> GetItems(string playlistId)
+    public Task<Paging<PlaylistTrack<BasePlayableItem>>> GetItems(string playlistId)
     {
       var request = new PlaylistGetItemsRequest();
 
       return GetItems(playlistId, request);
     }
 
-    public Task<Paging<PlaylistTrack<IPlayableItem>>> GetItems(string playlistId, PlaylistGetItemsRequest request)
+    public Task<Paging<PlaylistTrack<BasePlayableItem>>> GetItems(string playlistId, PlaylistGetItemsRequest request)
     {
       Ensure.ArgumentNotNullOrEmptyString(playlistId, nameof(playlistId));
       Ensure.ArgumentNotNull(request, nameof(request));
 
-      return API.Get<Paging<PlaylistTrack<IPlayableItem>>>(URLs.PlaylistTracks(playlistId), request.BuildQueryParams());
+      return API.Get<Paging<PlaylistTrack<BasePlayableItem>>>(URLs.PlaylistTracks(playlistId), request.BuildQueryParams());
     }
 
     public Task<FullPlaylist> Create(string userId, PlaylistCreateRequest request)

SpotifyAPI.Web/Clients/SpotifyClientConfig.cs

@@ -187,7 +187,7 @@ namespace SpotifyAPI.Web
       return new SpotifyClientConfig(
         SpotifyUrls.APIV1,
         null,
-        new NewtonsoftJSONSerializer(),
+        new TextJsonSerializer(),
         new NetHttpClient(),
         null,
         null,

SpotifyAPI.Web/Http/APIConnector.cs

@@ -18,7 +18,7 @@ namespace SpotifyAPI.Web.Http
     public event EventHandler<IResponse>? ResponseReceived;
 
     public APIConnector(Uri baseAddress, IAuthenticator authenticator) :
-      this(baseAddress, authenticator, new NewtonsoftJSONSerializer(), new NetHttpClient(), null, null)
+      this(baseAddress, authenticator, new TextJsonSerializer(), new NetHttpClient(), null, null)
     { }
     public APIConnector(
       Uri baseAddress,

SpotifyAPI.Web/Http/TextJsonSerializer.cs

@@ -0,0 +1,93 @@
+using System;
+using System.Reflection;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using System.Text.Json.Serialization.Metadata;
+using System.IO;
+using System.Net.Http;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text.RegularExpressions;
+
+namespace SpotifyAPI.Web.Http
+{
+  public class SnakeCase : JsonNamingPolicy
+  {
+    public override string ConvertName(string name)
+    {
+      if(string.IsNullOrWhiteSpace(name))
+      {
+        return name;
+      }else
+      {
+        return Regex.Replace(string.Concat(name[0].ToString().ToLowerInvariant(), name.Substring(1)), "[A-Z]", "_$0").ToLowerInvariant();
+      }
+    }
+  }
+
+  public class TextJsonSerializer : IJSONSerializer
+  {
+    private ModelJsonContext JsonContext;
+
+    public TextJsonSerializer()
+    {
+      JsonContext = ModelJsonContext.Get();
+    }
+
+    public IAPIResponse<T> DeserializeResponse<T>(IResponse response)
+    {
+      Ensure.ArgumentNotNull(response, nameof(response));
+
+      if (
+        (
+          response.ContentType?.Equals("application/json", StringComparison.Ordinal) is true || response.ContentType == null
+        ))
+      {
+        if(response.Body is string bodyString && !string.IsNullOrWhiteSpace(bodyString))
+        {
+          var body = (T?)JsonSerializer.Deserialize(response.Body as string ?? "", typeof(T), JsonContext);
+
+          // In order to work out whether track or episode has been returned, first deserialise as BasePlayableItem 
+          // which has enum of current playing type, then deserialise again with concrete playing type
+          if (body is CurrentlyPlaying currentlyPlaying)
+          {
+            if(currentlyPlaying.Item.Type is ItemType.Track)
+            {
+              body = (T?) JsonSerializer.Deserialize(response.Body as string ?? "", typeof(CurrentlyPlaying<FullTrack>), JsonContext);
+            }
+            else if (currentlyPlaying.Item.Type is ItemType.Episode)
+            {
+              body = (T?) JsonSerializer.Deserialize(response.Body as string ?? "", typeof(CurrentlyPlaying<FullEpisode>), JsonContext);
+            }
+          }
+          if (body is CurrentlyPlayingContext currentlyPlayingContext)
+          {
+            if (currentlyPlayingContext.Item.Type is ItemType.Track)
+            {
+              body = (T?)JsonSerializer.Deserialize(response.Body as string ?? "", typeof(CurrentlyPlayingContext<FullTrack>), JsonContext);
+            }
+            else if (currentlyPlayingContext.Item.Type is ItemType.Episode)
+            {
+              body = (T?)JsonSerializer.Deserialize(response.Body as string ?? "", typeof(CurrentlyPlayingContext<FullEpisode>), JsonContext);
+            }
+          }
+
+          return new APIResponse<T>(response, body!);
+        }
+      }
+      return new APIResponse<T>(response);
+    }
+
+    public void SerializeRequest(IRequest request)
+    {
+      Ensure.ArgumentNotNull(request, nameof(request));
+
+      if (request.Body is string || request.Body is Stream || request.Body is HttpContent || request.Body is null)
+      {
+        return;
+      }
+
+      request.Body = JsonSerializer.Serialize(request.Body, request.Body.GetType(), JsonContext);
+    }
+  }
+}

SpotifyAPI.Web/Models/ModelJsonContext.cs

@@ -0,0 +1,88 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using SpotifyAPI.Web.Http;
+
+namespace SpotifyAPI.Web
+{
+  [JsonSerializable(typeof(Actions))]
+  [JsonSerializable(typeof(AlbumsResponse))]
+  [JsonSerializable(typeof(ArtistsRelatedArtistsResponse))]
+  [JsonSerializable(typeof(ArtistsResponse))]
+  [JsonSerializable(typeof(ArtistsTopTracksResponse))]
+  [JsonSerializable(typeof(AuthorizationCodeRefreshResponse))]
+  [JsonSerializable(typeof(AuthorizationCodeTokenResponse))]
+  [JsonSerializable(typeof(CategoriesResponse))]
+  [JsonSerializable(typeof(Category))]
+  [JsonSerializable(typeof(CategoryPlaylistsResponse))]
+  [JsonSerializable(typeof(ClientCredentialsTokenResponse))]
+  [JsonSerializable(typeof(Context))]
+  [JsonSerializable(typeof(Copyright))]
+  [JsonSerializable(typeof(CurrentlyPlaying))]
+  [JsonSerializable(typeof(CurrentlyPlaying<FullEpisode>))]
+  [JsonSerializable(typeof(CurrentlyPlaying<FullTrack>))]
+  [JsonSerializable(typeof(CurrentlyPlayingContext))]
+  [JsonSerializable(typeof(CurrentlyPlayingContext<FullEpisode>))]
+  [JsonSerializable(typeof(CurrentlyPlayingContext<FullTrack>))]
+  [JsonSerializable(typeof(Cursor))]
+  [JsonSerializable(typeof(Device))]
+  [JsonSerializable(typeof(DeviceResponse))]
+  [JsonSerializable(typeof(EpisodesResponse))]
+  [JsonSerializable(typeof(FeaturedPlaylistsResponse))]
+  [JsonSerializable(typeof(FollowedArtistsResponse))]
+  [JsonSerializable(typeof(Followers))]
+  [JsonSerializable(typeof(FullAlbum))]
+  [JsonSerializable(typeof(FullEpisode))]
+  [JsonSerializable(typeof(FullPlaylist))]
+  [JsonSerializable(typeof(FullShow))]
+  [JsonSerializable(typeof(FullTrack))]
+  [JsonSerializable(typeof(Image))]
+  [JsonSerializable(typeof(LinkedTrack))]
+  [JsonSerializable(typeof(NewReleasesResponse))]
+  [JsonSerializable(typeof(PKCETokenResponse))]
+  [JsonSerializable(typeof(PlayHistoryItem))]
+  [JsonSerializable(typeof(PlaylistTrack<FullTrack>))]
+  [JsonSerializable(typeof(PlaylistTrack<FullEpisode>))]
+  [JsonSerializable(typeof(PrivateUser))]
+  [JsonSerializable(typeof(PublicUser))]
+  [JsonSerializable(typeof(RecommendationGenresResponse))]
+  [JsonSerializable(typeof(RecommendationSeed))]
+  [JsonSerializable(typeof(RecommendationsResponse))]
+  [JsonSerializable(typeof(ResumePoint))]
+  [JsonSerializable(typeof(SavedAlbum))]
+  [JsonSerializable(typeof(SavedEpisodes))]
+  [JsonSerializable(typeof(SavedShow))]
+  [JsonSerializable(typeof(SavedTrack))]
+  [JsonSerializable(typeof(SearchResponse))]
+  [JsonSerializable(typeof(Section))]
+  [JsonSerializable(typeof(Segment))]
+  [JsonSerializable(typeof(ShowsResponse))]
+  [JsonSerializable(typeof(SimpleAlbum))]
+  [JsonSerializable(typeof(SimpleArtist))]
+  [JsonSerializable(typeof(SimpleEpisode))]
+  [JsonSerializable(typeof(SimplePlaylist))]
+  [JsonSerializable(typeof(SimpleShow))]
+  [JsonSerializable(typeof(SimpleTrack))]
+  [JsonSerializable(typeof(SnapshotResponse))]
+  [JsonSerializable(typeof(TestResponseObject))]
+  [JsonSerializable(typeof(TimeInterval))]
+  [JsonSerializable(typeof(TrackAudio))]
+  [JsonSerializable(typeof(TrackAudioAnalysis))]
+  [JsonSerializable(typeof(TrackMeta))]
+  [JsonSerializable(typeof(TracksAudioFeaturesResponse))]
+  [JsonSerializable(typeof(TracksResponse))]
+  public partial class ModelJsonContext : JsonSerializerContext
+  {
+    public static ModelJsonContext Get()
+    {
+      return new ModelJsonContext(new JsonSerializerOptions()
+      {
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+        PropertyNamingPolicy = new SnakeCase(),
+        Converters =
+        {
+          new JsonStringEnumConverter()
+        }
+      });
+    }
+  }
+}

SpotifyAPI.Web/Models/Response/BasePlayableItem.cs

@@ -9,10 +9,10 @@ namespace SpotifyAPI.Web
     Episode
   }
 
-  public interface IPlayableItem
+  public class BasePlayableItem
   {
     [JsonConverter(typeof(StringEnumConverter))]
-    ItemType Type { get; }
+    public ItemType Type { get; }
   }
 }
 

SpotifyAPI.Web/Models/Response/CurrentlyPlaying.cs

@@ -13,9 +13,17 @@ namespace SpotifyAPI.Web
     /// </summary>
     /// <value></value>
     [JsonConverter(typeof(PlayableItemConverter))]
-    public IPlayableItem Item { get; set; } = default!;
+    public BasePlayableItem Item { get; set; } = default!;
     public int? ProgressMs { get; set; }
     public long Timestamp { get; set; }
   }
+
+  public class CurrentlyPlaying<T>: CurrentlyPlaying where T : BasePlayableItem
+  {
+    public new T Item { 
+      get => (T) base.Item; 
+      set => base.Item = value; 
+    }
+  }
 }
 

SpotifyAPI.Web/Models/Response/CurrentlyPlayingContext.cs

@@ -17,10 +17,19 @@ namespace SpotifyAPI.Web
     /// </summary>
     /// <value></value>
     [JsonConverter(typeof(PlayableItemConverter))]
-    public IPlayableItem Item { get; set; } = default!;
+    public BasePlayableItem Item { get; set; } = default!;
 
     public string CurrentlyPlayingType { get; set; } = default!;
     public Actions Actions { get; set; } = default!;
   }
+
+  public class CurrentlyPlayingContext<T> : CurrentlyPlayingContext where T : BasePlayableItem
+  {
+    public new T Item
+    {
+      get => (T)base.Item;
+      set => base.Item = value;
+    }
+  }
 }
 

SpotifyAPI.Web/Models/Response/FullEpisode.cs

@@ -4,7 +4,7 @@ using Newtonsoft.Json.Converters;
 
 namespace SpotifyAPI.Web
 {
-  public class FullEpisode : IPlayableItem
+  public class FullEpisode : BasePlayableItem
   {
     public string AudioPreviewUrl { get; set; } = default!;
     public string Description { get; set; } = default!;

SpotifyAPI.Web/Models/Response/FullPlaylist.cs

@@ -19,7 +19,7 @@ namespace SpotifyAPI.Web
     /// A list of PlaylistTracks, which items can be a FullTrack or FullEpisode
     /// </summary>
     /// <value></value>
-    public Paging<PlaylistTrack<IPlayableItem>>? Tracks { get; set; } = default!;
+    public Paging<PlaylistTrack<BasePlayableItem>>? Tracks { get; set; } = default!;
     public string? Type { get; set; } = default!;
     public string? Uri { get; set; } = default!;
   }

SpotifyAPI.Web/Models/Response/FullTrack.cs

@@ -4,7 +4,7 @@ using Newtonsoft.Json.Converters;
 
 namespace SpotifyAPI.Web
 {
-  public class FullTrack : IPlayableItem
+  public class FullTrack : BasePlayableItem
   {
     public SimpleAlbum Album { get; set; } = default!;
     public List<SimpleArtist> Artists { get; set; } = default!;

SpotifyAPI.Web/Models/Response/Image.cs

@@ -2,8 +2,8 @@ namespace SpotifyAPI.Web
 {
   public class Image
   {
-    public int Height { get; set; }
-    public int Width { get; set; }
+    public int? Height { get; set; }
+    public int? Width { get; set; }
     public string Url { get; set; } = default!;
   }
 }

SpotifyAPI.Web/Models/Response/SimplePlaylist.cs

@@ -21,7 +21,7 @@ namespace SpotifyAPI.Web
     /// A list of PlaylistTracks, which items can be a FullTrack or FullEpisode
     /// </summary>
     /// <value></value>
-    public Paging<PlaylistTrack<IPlayableItem>> Tracks { get; set; } = default!;
+    public Paging<PlaylistTrack<BasePlayableItem>> Tracks { get; set; } = default!;
     public string Type { get; set; } = default!;
     public string Uri { get; set; } = default!;
   }

SpotifyAPI.Web/Models/Response/TestResponseObject.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace SpotifyAPI.Web
+{
+  public class TestResponseObject
+  {
+    public bool HelloWorld { get; set; }
+  }
+}

SpotifyAPI.Web/SpotifyAPI.Web.csproj

@@ -31,10 +31,11 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All"/>
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.1">
       <PrivateAssets>None</PrivateAssets>
     </PackageReference>
+    <PackageReference Include="System.Text.Json" Version="6.0.1" />
   </ItemGroup>
 
   <PropertyGroup>