WIP - linq deserializers

Fauna/Serialization/LinqElementDeserializer.cs

@@ -0,0 +1,55 @@
+namespace Fauna.Serialization;
+
+public class LinqProjectionDeserializer<T> : BaseDeserializer<T>
+{
+    private IDeserializer[] _fieldDeserializers;
+    private Delegate _mapper;
+
+    public LinqProjectionDeserializer(IDeserializer[] fields, Delegate mapper)
+    {
+        _fieldDeserializers = fields;
+        _mapper = mapper;
+    }
+
+    public override T Deserialize(SerializationContext context, ref Utf8FaunaReader reader)
+    {
+        if (reader.CurrentTokenType != TokenType.StartArray)
+            throw UnexpectedToken(reader.CurrentTokenType);
+
+        var fields = new object?[_fieldDeserializers.Length];
+
+        for (var i = 0; i < _fieldDeserializers.Length; i++)
+        {
+            if (!reader.Read()) throw new SerializationException("Unexpected end of stream");
+            if (reader.CurrentTokenType == TokenType.EndArray) throw UnexpectedToken(reader.CurrentTokenType);
+
+            fields[i] = _fieldDeserializers[i].Deserialize(context, ref reader);
+        }
+
+        if (!reader.Read()) throw new SerializationException("Unexpected end of stream");
+        if (reader.CurrentTokenType != TokenType.EndArray) throw UnexpectedToken(reader.CurrentTokenType);
+
+        return (T)_mapper.DynamicInvoke(fields)!;
+    }
+
+    private SerializationException UnexpectedToken(TokenType tokenType) =>
+        new SerializationException($"Unexpected token while deserializing LINQ element: {tokenType}");
+}
+
+public class LinqDocumentDeserializer<T> : BaseDeserializer<T>
+{
+    private IDeserializer _docDeserializer;
+    private Delegate _mapper;
+
+    public LinqDocumentDeserializer(IDeserializer doc, Delegate mapper)
+    {
+        _docDeserializer = doc;
+        _mapper = mapper;
+    }
+
+    public override T Deserialize(SerializationContext context, ref Utf8FaunaReader reader)
+    {
+        var doc = _docDeserializer.Deserialize(context, ref reader);
+        return (T)_mapper.DynamicInvoke(new[] { doc })!;
+    }
+}