feat: implement string to collection converter for handling did document context

src/StevanFreeborn.Atproto.IdentityResolver/Json/StringToCollectionConverter.cs

@@ -0,0 +1,32 @@
+using System.Collections.ObjectModel;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace StevanFreeborn.Atproto.IdentityResolver.Json;
+
+internal sealed class StringToCollectionConverter : JsonConverter<Collection<string>>
+{
+  public override Collection<string>? Read(
+    ref Utf8JsonReader reader,
+    Type typeToConvert,
+    JsonSerializerOptions options
+  )
+  {
+    return reader.TokenType switch
+    {
+      JsonTokenType.Null => [],
+      JsonTokenType.String => [reader.GetString()!],
+      JsonTokenType.StartArray => JsonSerializer.Deserialize<Collection<string>>(ref reader, options),
+      _ => throw new JsonException($"Unexpected token type '{reader.TokenType}' when deserializing {nameof(Collection<>)}.")
+    };
+  }
+
+  public override void Write(
+    Utf8JsonWriter writer,
+    Collection<string> value,
+    JsonSerializerOptions options
+  )
+  {
+    JsonSerializer.Serialize(writer, value, options);
+  }
+}

tests/StevanFreeborn.Atproto.IdentityResolver.Tests/Unit/StringToCollectionConverterTests.cs

@@ -0,0 +1,127 @@
+using System.Collections.ObjectModel;
+using System.Text;
+using System.Text.Json;
+
+using StevanFreeborn.Atproto.IdentityResolver.Json;
+
+namespace StevanFreeborn.Atproto.IdentityResolver.Tests.Unit;
+
+public sealed class StringToCollectionConverterTests
+{
+  private readonly StringToCollectionConverter _converter = new();
+  private readonly JsonSerializerOptions _options = new();
+
+  private Collection<string>? ReadJson(string json)
+  {
+    var reader = new Utf8JsonReader(Encoding.UTF8.GetBytes(json));
+    reader.Read();
+    return _converter.Read(ref reader, typeof(Collection<string>), _options);
+  }
+
+  private string WriteJson(Collection<string> value)
+  {
+    using var stream = new MemoryStream();
+    using var writer = new Utf8JsonWriter(stream);
+    
+    _converter.Write(writer, value, _options);
+    
+    return Encoding.UTF8.GetString(stream.ToArray());
+  }
+
+  [Fact]
+  public void Read_WhenJsonTokenIsNull_ItShouldReturnEmptyCollection()
+  {
+    var result = ReadJson("null");
+
+    result.Should().NotBeNull();
+    result.Should().BeEmpty();
+  }
+
+  [Fact]
+  public void Read_WhenJsonTokenIsString_ItShouldReturnCollectionWithSingleString()
+  {
+    var result = ReadJson("\"https://w3id.org/did/v1\"");
+
+    result.Should().NotBeNull();
+    result.Should().ContainSingle().Which.Should().Be("https://w3id.org/did/v1");
+  }
+
+  [Fact]
+  public void Read_WhenJsonTokenIsEmptyString_ItShouldReturnCollectionWithEmptyString()
+  {
+    var result = ReadJson("\"\"");
+
+    result.Should().NotBeNull();
+    result.Should().ContainSingle().Which.Should().Be(string.Empty);
+  }
+
+  [Fact]
+  public void Read_WhenJsonTokenIsArrayOfStrings_ItShouldReturnCollectionWithAllStrings()
+  {
+    var result = ReadJson("[\"https://w3id.org/did/v1\",\"https://w3id.org/security/suites/ed25519-2020/v1\"]");
+
+    result.Should().NotBeNull();
+    result.Should().HaveCount(2);
+    result.Should().ContainInOrder("https://w3id.org/did/v1", "https://w3id.org/security/suites/ed25519-2020/v1");
+  }
+
+  [Fact]
+  public void Read_WhenJsonTokenIsEmptyArray_ItShouldReturnEmptyCollection()
+  {
+    var result = ReadJson("[]");
+
+    result.Should().NotBeNull();
+    result.Should().BeEmpty();
+  }
+
+  [Theory]
+  [InlineData("123", "Number")]
+  [InlineData("true", "True")]
+  [InlineData("false", "False")]
+  [InlineData("{\"key\":\"value\"}", "StartObject")]
+  public void Read_WhenJsonTokenIsUnexpectedType_ItShouldThrowJsonException(string json, string expectedToken)
+  {
+    var act = () => ReadJson(json);
+
+    var e = act.Should().Throw<JsonException>();
+
+    e.WithMessage($"Unexpected token type '{expectedToken}' when deserializing Collection.");
+  }
+
+  [Fact]
+  public void Write_WhenCollectionContainsMultipleStrings_ItShouldSerializeAsJsonArray()
+  {
+    var collection = new Collection<string>
+    {
+      "https://w3id.org/did/v1",
+      "https://w3id.org/security/suites/ed25519-2020/v1"
+    };
+
+    var json = WriteJson(collection);
+
+    json.Should().Be("[\"https://w3id.org/did/v1\",\"https://w3id.org/security/suites/ed25519-2020/v1\"]");
+  }
+
+  [Fact]
+  public void Write_WhenCollectionContainsSingleString_ItShouldSerializeAsJsonArray()
+  {
+    var collection = new Collection<string>
+    {
+      "https://w3id.org/did/v1"
+    };
+
+    var json = WriteJson(collection);
+
+    json.Should().Be("[\"https://w3id.org/did/v1\"]");
+  }
+
+  [Fact]
+  public void Write_WhenCollectionIsEmpty_ItShouldSerializeAsEmptyJsonArray()
+  {
+    var collection = new Collection<string>();
+
+    var json = WriteJson(collection);
+
+    json.Should().Be("[]");
+  }
+}