Support serialization of accumulators

src/NexusMods.EventSourcing.Abstractions/ACollectionAttribute.cs

@@ -1,5 +1,8 @@
 using System;
+using System.Buffers;
 using System.Collections.Generic;
+using System.Linq;
+using NexusMods.EventSourcing.Abstractions.Serialization;
 
 namespace NexusMods.EventSourcing.Abstractions;
 
@@ -31,6 +34,20 @@ public object Get()
         {
             return _values;
         }
+
+        /// <inheritdoc />
+        public void WriteTo(IBufferWriter<byte> writer, ISerializationRegistry registry)
+        {
+            registry.Serialize(writer, _values.ToArray());
+        }
+
+        /// <inheritdoc />
+        public int ReadFrom(ref ReadOnlySpan<byte> reader, ISerializationRegistry registry)
+        {
+            var read = registry.Deserialize(reader, out TType[] values);
+            _values = [..values];
+            return read;
+        }
     }
 
     public Type Type => typeof(TType);

src/NexusMods.EventSourcing.Abstractions/IAccumulator.cs

@@ -1,8 +1,27 @@
+using System;
+using System.Buffers;
+using NexusMods.EventSourcing.Abstractions.Serialization;
+
 namespace NexusMods.EventSourcing.Abstractions;
 
 /// <summary>
 /// An accumulator is used to accumulate values from events, it is opaque to everything but the attribute definition that created it.
 /// </summary>
 public interface IAccumulator
 {
+
+    /// <summary>
+    /// Writes the accumulator to the given buffer writer.
+    /// </summary>
+    /// <param name="writer"></param>
+    /// <param name="registry"></param>
+    public void WriteTo(IBufferWriter<byte> writer, ISerializationRegistry registry);
+
+    /// <summary>
+    /// Reads the accumulator from the given buffer reader, the span may be larger than the accumulator. Returns the
+    /// number of bytes read.
+    /// </summary>
+    /// <param name="reader"></param>
+    /// <param name="registry"></param>
+    public int ReadFrom(ref ReadOnlySpan<byte> reader, ISerializationRegistry registry);
 }

src/NexusMods.EventSourcing.Abstractions/MultiEntityAttributeDefinition.cs

@@ -1,7 +1,10 @@
 using System;
+using System.Buffers;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Linq;
 using NexusMods.EventSourcing.Abstractions.Collections;
+using NexusMods.EventSourcing.Abstractions.Serialization;
 
 namespace NexusMods.EventSourcing.Abstractions;
 
@@ -146,4 +149,20 @@ public void Remove(EntityId<TType> id)
     {
         Ids.Remove(id);
     }
+
+    /// <inheritdoc />
+    public void WriteTo(IBufferWriter<byte> writer, ISerializationRegistry registry)
+    {
+        registry.Serialize(writer, Ids.ToArray());
+    }
+
+    /// <inheritdoc />
+    public int ReadFrom(ref ReadOnlySpan<byte> reader, ISerializationRegistry registry)
+    {
+        var read = registry.Deserialize(reader, out EntityId<TType>[] ids);
+        Ids.Clear();
+        foreach (var id in ids)
+            Ids.Add(id);
+        return read;
+    }
 }

src/NexusMods.EventSourcing.Abstractions/ScalarAttribute.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Buffers;
+using NexusMods.EventSourcing.Abstractions.Serialization;
 
 namespace NexusMods.EventSourcing.Abstractions;
 
@@ -74,4 +76,16 @@ public class ScalarAccumulator<TVal> : IAccumulator
      /// The value of the accumulator
      /// </summary>
      public TVal Value = default! ;
+
+     /// <inheritdoc />
+     public void WriteTo(IBufferWriter<byte> writer, ISerializationRegistry registry)
+     {
+         registry.Serialize(writer, Value);
+     }
+
+     /// <inheritdoc />
+     public int ReadFrom(ref ReadOnlySpan<byte> span, ISerializationRegistry registry)
+     {
+         return registry.Deserialize(span, out Value);
+     }
  }

src/NexusMods.EventSourcing.Abstractions/Serialization/ISerializationRegistry.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Buffers;
 
 namespace NexusMods.EventSourcing.Abstractions.Serialization;
 
@@ -22,4 +23,20 @@ public interface ISerializationRegistry
     /// <param name="serializedType"></param>
     /// <param name="serializer"></param>
     public void RegisterSerializer(Type serializedType, ISerializer serializer);
+
+    /// <summary>
+    /// Serializes the given value into the given buffer writer.
+    /// </summary>
+    /// <param name="writer"></param>
+    /// <param name="value"></param>
+    /// <typeparam name="TVal"></typeparam>
+    public void Serialize<TVal>(IBufferWriter<byte> writer, TVal value);
+
+    /// <summary>
+    /// Deserializes the given bytes into the given type, returning the number of bytes read.
+    /// </summary>
+    /// <param name="bytes"></param>
+    /// <typeparam name="TVal"></typeparam>
+    /// <returns></returns>
+    public int Deserialize<TVal>(ReadOnlySpan<byte> bytes, out TVal value);
 }