From 3687b0cc0e5435b77559a57fb6680f9ffb5c0d30 Mon Sep 17 00:00:00 2001
From: Timothy Baldridge <tbaldridge@gmail.com>
Date: Wed, 13 Dec 2023 11:56:44 -0700
Subject: [PATCH] Can retract attributes

---
 .../ACollectionAttribute.cs                   | 22 +++++++-
 .../AScalarAttribute.cs                       |  5 ++
 .../AttributeDefinition.cs                    |  2 +-
 .../EntityAttributeDefinition.cs              |  7 ++-
 .../IAccumulator.cs                           |  6 +++
 .../IEntityContext.cs                         |  5 +-
 .../IEventContext.cs                          | 25 +++++++++
 .../IEventStore.cs                            |  3 +-
 .../MultiEntityAttributeDefinition.cs         | 10 +++-
 src/NexusMods.EventSourcing/EntityContext.cs  |  2 +-
 .../Events/AddMod.cs                          |  3 +-
 .../Events/DeleteMod.cs                       | 17 ++++++
 .../Services.cs                               |  1 +
 .../BasicFunctionalityTests.cs                | 39 ++++++++++++++
 .../Contexts/InMemoryEventStore.cs            | 17 ++++--
 .../Contexts/TestContext.cs                   | 52 ++++++++++++++-----
 16 files changed, 189 insertions(+), 27 deletions(-)
 create mode 100644 tests/NexusMods.EventSourcing.TestModel/Events/DeleteMod.cs

diff --git a/src/NexusMods.EventSourcing.Abstractions/ACollectionAttribute.cs b/src/NexusMods.EventSourcing.Abstractions/ACollectionAttribute.cs
index 738aafee..ad9fe113 100644
--- a/src/NexusMods.EventSourcing.Abstractions/ACollectionAttribute.cs
+++ b/src/NexusMods.EventSourcing.Abstractions/ACollectionAttribute.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 
 namespace NexusMods.EventSourcing.Abstractions;
 
@@ -10,7 +11,26 @@ public class ACollectionAttribute<TOwner, TType>(string name) : IAttribute
     public string Name => name;
     public IAccumulator CreateAccumulator()
     {
-        throw new NotImplementedException();
+        return new Accumulator();
+    }
+
+    protected class Accumulator : IAccumulator
+    {
+        private HashSet<TType> _values = new();
+        public void Add(object value)
+        {
+            _values.Add((TType) value);
+        }
+
+        public void Retract(object value)
+        {
+            _values.Remove((TType) value);
+        }
+
+        public object Get()
+        {
+            return _values;
+        }
     }
 
     public Type Type => typeof(TType);
diff --git a/src/NexusMods.EventSourcing.Abstractions/AScalarAttribute.cs b/src/NexusMods.EventSourcing.Abstractions/AScalarAttribute.cs
index 9c995466..4fa29511 100644
--- a/src/NexusMods.EventSourcing.Abstractions/AScalarAttribute.cs
+++ b/src/NexusMods.EventSourcing.Abstractions/AScalarAttribute.cs
@@ -30,6 +30,11 @@ public void Add(object value)
             _value = (TVal) value;
         }
 
+        public void Retract(object value)
+        {
+            _value = default!;
+        }
+
         public object Get()
         {
             return _value!;
diff --git a/src/NexusMods.EventSourcing.Abstractions/AttributeDefinition.cs b/src/NexusMods.EventSourcing.Abstractions/AttributeDefinition.cs
index acb6b1f1..84b5690f 100644
--- a/src/NexusMods.EventSourcing.Abstractions/AttributeDefinition.cs
+++ b/src/NexusMods.EventSourcing.Abstractions/AttributeDefinition.cs
@@ -17,5 +17,5 @@ public class AttributeDefinition<TOwner, TType>(string attrName) : AScalarAttrib
     /// <param name="owner"></param>
     /// <returns></returns>
     /// <exception cref="NotImplementedException"></exception>
-    public TType Get(TOwner owner) => (TType)owner.Context.GetAccumulator(owner.Id, this).Get();
+    public TType Get(TOwner owner) => (TType)owner.Context.GetAccumulator<TOwner, AttributeDefinition<TOwner, TType>>(owner.Id, this).Get();
 }
diff --git a/src/NexusMods.EventSourcing.Abstractions/EntityAttributeDefinition.cs b/src/NexusMods.EventSourcing.Abstractions/EntityAttributeDefinition.cs
index f6c58a6c..59cfdd6f 100644
--- a/src/NexusMods.EventSourcing.Abstractions/EntityAttributeDefinition.cs
+++ b/src/NexusMods.EventSourcing.Abstractions/EntityAttributeDefinition.cs
@@ -6,5 +6,10 @@ public class EntityAttributeDefinition<TOwner, TType>(string attrName) : Attribu
     where TOwner : AEntity
     where TType : IEntity
 {
-    public TType GetEntity(TOwner owner) => throw new NotImplementedException();
+    public TType GetEntity(TOwner owner)
+    {
+        var accumulator = owner.Context.GetAccumulator<TOwner, EntityAttributeDefinition<TOwner, TType>>(owner.Id, this);
+        var entityId = (EntityId<TType>) accumulator.Get();
+        return owner.Context.Get(entityId);
+    }
 }
diff --git a/src/NexusMods.EventSourcing.Abstractions/IAccumulator.cs b/src/NexusMods.EventSourcing.Abstractions/IAccumulator.cs
index 6f94dfe9..fb612153 100644
--- a/src/NexusMods.EventSourcing.Abstractions/IAccumulator.cs
+++ b/src/NexusMods.EventSourcing.Abstractions/IAccumulator.cs
@@ -11,6 +11,12 @@ public interface IAccumulator
     /// <param name="value"></param>
     public void Add(object value);
 
+    /// <summary>
+    /// Retracts a value from the accumulator.
+    /// </summary>
+    /// <param name="value"></param>
+    public void Retract(object value);
+
     /// <summary>
     /// Gets the accumulated value.
     /// </summary>
diff --git a/src/NexusMods.EventSourcing.Abstractions/IEntityContext.cs b/src/NexusMods.EventSourcing.Abstractions/IEntityContext.cs
index 50e11ce4..a71ada08 100644
--- a/src/NexusMods.EventSourcing.Abstractions/IEntityContext.cs
+++ b/src/NexusMods.EventSourcing.Abstractions/IEntityContext.cs
@@ -33,7 +33,10 @@ public interface IEntityContext
     /// <param name="attributeDefinition"></param>
     /// <typeparam name="TType"></typeparam>
     /// <typeparam name="TOwner"></typeparam>
+    /// <typeparam name="TAttribute"></typeparam>
     /// <returns></returns>
-    IAccumulator GetAccumulator<TType, TOwner>(EntityId ownerId, AttributeDefinition<TOwner,TType> attributeDefinition) where TOwner : IEntity;
+    IAccumulator GetAccumulator<TOwner, TAttribute>(EntityId ownerId, TAttribute attributeDefinition)
+        where TOwner : IEntity
+        where TAttribute : IAttribute;
 
 }
diff --git a/src/NexusMods.EventSourcing.Abstractions/IEventContext.cs b/src/NexusMods.EventSourcing.Abstractions/IEventContext.cs
index d2abc281..5a88687a 100644
--- a/src/NexusMods.EventSourcing.Abstractions/IEventContext.cs
+++ b/src/NexusMods.EventSourcing.Abstractions/IEventContext.cs
@@ -32,6 +32,31 @@ public void Emit<TOwner, TVal>(EntityId<TOwner> entity, MultiEntityAttributeDefi
         where TOwner : IEntity
         where TVal : IEntity;
 
+
+    /// <summary>
+    /// Retracts a value for the given attribute on the given entity
+    /// </summary>
+    /// <param name="entity"></param>
+    /// <param name="attr"></param>
+    /// <param name="value"></param>
+    /// <typeparam name="TOwner"></typeparam>
+    /// <typeparam name="TVal"></typeparam>
+    public void Retract<TOwner, TVal>(EntityId<TOwner> entity, AttributeDefinition<TOwner, TVal> attr, TVal value)
+        where TOwner : IEntity;
+
+    /// <summary>
+    /// Retracts a member value for the given attribute on the given entity
+    /// </summary>
+    /// <param name="entity"></param>
+    /// <param name="attr"></param>
+    /// <param name="value"></param>
+    /// <typeparam name="TOwner"></typeparam>
+    /// <typeparam name="TVal"></typeparam>
+    public void Retract<TOwner, TVal>(EntityId<TOwner> entity, MultiEntityAttributeDefinition<TOwner, TVal> attr,
+        EntityId<TVal> value)
+        where TOwner : IEntity
+        where TVal : IEntity;
+
     /// <summary>
     /// Emits the type attribute for the given entity so that polymorphic queries can be performed
     /// </summary>
diff --git a/src/NexusMods.EventSourcing.Abstractions/IEventStore.cs b/src/NexusMods.EventSourcing.Abstractions/IEventStore.cs
index 1661e675..850428a6 100644
--- a/src/NexusMods.EventSourcing.Abstractions/IEventStore.cs
+++ b/src/NexusMods.EventSourcing.Abstractions/IEventStore.cs
@@ -7,7 +7,6 @@ public interface IEventStore
 {
     public ValueTask Add<T>(T eventEntity) where T : IEvent;
 
-    public void EventsForEntity<TEntity, TIngester>(EntityId<TEntity> entityId, TIngester ingester)
-        where TEntity : IEntity
+    public void EventsForEntity<TIngester>(EntityId entityId, TIngester ingester)
         where TIngester : IEventIngester;
 }
diff --git a/src/NexusMods.EventSourcing.Abstractions/MultiEntityAttributeDefinition.cs b/src/NexusMods.EventSourcing.Abstractions/MultiEntityAttributeDefinition.cs
index 42639197..da87f370 100644
--- a/src/NexusMods.EventSourcing.Abstractions/MultiEntityAttributeDefinition.cs
+++ b/src/NexusMods.EventSourcing.Abstractions/MultiEntityAttributeDefinition.cs
@@ -7,5 +7,13 @@ public class MultiEntityAttributeDefinition<TOwner, TType>(string name) :
     ACollectionAttribute<TOwner, EntityId<TType>>(name) where TOwner : IEntity
     where TType : IEntity
 {
-    public IEnumerable<TType> GetAll(TOwner owner) => throw new NotImplementedException();
+    public IEnumerable<TType> GetAll(TOwner owner)
+    {
+        var tmp = owner.Context.GetAccumulator<TOwner, MultiEntityAttributeDefinition<TOwner, TType>>(owner.Id, this);
+        var ids = (HashSet<EntityId<TType>>) tmp.Get();
+        foreach (var id in ids)
+        {
+            yield return owner.Context.Get(id);
+        }
+    }
 }
diff --git a/src/NexusMods.EventSourcing/EntityContext.cs b/src/NexusMods.EventSourcing/EntityContext.cs
index 048e815a..a2ee425f 100644
--- a/src/NexusMods.EventSourcing/EntityContext.cs
+++ b/src/NexusMods.EventSourcing/EntityContext.cs
@@ -16,7 +16,7 @@ public ValueTask Add<TEvent>(TEvent entity) where TEvent : IEvent
         throw new System.NotImplementedException();
     }
 
-    public IAccumulator GetAccumulator<TType, TOwner>(EntityId ownerId, AttributeDefinition<TOwner, TType> attributeDefinition) where TOwner : IEntity
+    public IAccumulator GetAccumulator<TOwner, TAttribute>(EntityId ownerId, TAttribute attributeDefinition) where TOwner : IEntity where TAttribute : IAttribute
     {
         throw new System.NotImplementedException();
     }
diff --git a/tests/NexusMods.EventSourcing.TestModel/Events/AddMod.cs b/tests/NexusMods.EventSourcing.TestModel/Events/AddMod.cs
index 4b3638a8..a43e6032 100644
--- a/tests/NexusMods.EventSourcing.TestModel/Events/AddMod.cs
+++ b/tests/NexusMods.EventSourcing.TestModel/Events/AddMod.cs
@@ -21,6 +21,7 @@ public async ValueTask Apply<T>(T context) where T : IEventContext
         context.Emit(Id, Mod._enabled, Enabled);
         context.Emit(Id, Mod._loadout, LoadoutId);
         context.Emit(LoadoutId, Loadout._mods, Id);
-
     }
+
+    public static AddMod Create(string name, EntityId<Loadout> loadoutId) => new() { Name = name, Enabled = true, Id = EntityId<Mod>.NewId(), LoadoutId = loadoutId };
 }
diff --git a/tests/NexusMods.EventSourcing.TestModel/Events/DeleteMod.cs b/tests/NexusMods.EventSourcing.TestModel/Events/DeleteMod.cs
new file mode 100644
index 00000000..63459da8
--- /dev/null
+++ b/tests/NexusMods.EventSourcing.TestModel/Events/DeleteMod.cs
@@ -0,0 +1,17 @@
+using MemoryPack;
+using NexusMods.EventSourcing.Abstractions;
+using NexusMods.EventSourcing.TestModel.Model;
+
+namespace NexusMods.EventSourcing.TestModel.Events;
+
+[EventId("5CD171BF-4FFE-40E5-819B-987C48A20DF6")]
+[MemoryPackable]
+public partial record DeleteMod(EntityId<Mod> ModId, EntityId<Loadout> LoadoutId) : IEvent
+{
+    public ValueTask Apply<T>(T context) where T : IEventContext
+    {
+        context.Retract(LoadoutId, Loadout._mods, ModId);
+        context.Retract(ModId, Mod._loadout, LoadoutId);
+        return ValueTask.CompletedTask;
+    }
+}
diff --git a/tests/NexusMods.EventSourcing.TestModel/Services.cs b/tests/NexusMods.EventSourcing.TestModel/Services.cs
index 0ba2f28f..326fe000 100644
--- a/tests/NexusMods.EventSourcing.TestModel/Services.cs
+++ b/tests/NexusMods.EventSourcing.TestModel/Services.cs
@@ -16,6 +16,7 @@ public static IServiceCollection AddEvents(this IServiceCollection coll)
         coll.AddEvent<Events.AddMod>();
         coll.AddEvent<Events.SwapModEnabled>();
         coll.AddEvent<Events.RenameLoadout>();
+        coll.AddEvent<Events.DeleteMod>();
         return coll;
     }
 
diff --git a/tests/NexusMods.EventSourcing.Tests/BasicFunctionalityTests.cs b/tests/NexusMods.EventSourcing.Tests/BasicFunctionalityTests.cs
index a506d233..6667b0f4 100644
--- a/tests/NexusMods.EventSourcing.Tests/BasicFunctionalityTests.cs
+++ b/tests/NexusMods.EventSourcing.Tests/BasicFunctionalityTests.cs
@@ -34,4 +34,43 @@ public async void ChangingPropertyChangesTheValue()
         await _ctx.Add(RenameLoadout.Create(createEvent.Id, "New Name"));
         loadout.Name.Should().Be("New Name");
     }
+
+    [Fact]
+    public async void CanLinkEntities()
+    {
+        var loadoutEvent = CreateLoadout.Create("Test");
+        await _ctx.Add(loadoutEvent);
+        var loadout = _ctx.Get(loadoutEvent.Id);
+        loadout.Name.Should().Be("Test");
+
+        var modEvent = AddMod.Create("First Mod", loadoutEvent.Id);
+        await _ctx.Add(modEvent);
+
+        loadout.Mods.First().Name.Should().Be("First Mod");
+        loadout.Mods.First().Loadout.Should().BeSameAs(loadout);
+    }
+
+
+    [Fact]
+    public async void CanDeleteEntities()
+    {
+        var loadoutEvent = CreateLoadout.Create("Test");
+        await _ctx.Add(loadoutEvent);
+        var loadout = _ctx.Get(loadoutEvent.Id);
+        loadout.Name.Should().Be("Test");
+
+        var modEvent1 = AddMod.Create("First Mod", loadoutEvent.Id);
+        await _ctx.Add(modEvent1);
+
+        var modEvent2 = AddMod.Create("Second Mod", loadoutEvent.Id);
+        await _ctx.Add(modEvent2);
+
+        loadout.Mods.Count().Should().Be(2);
+
+        await _ctx.Add(new DeleteMod(modEvent1.Id, loadoutEvent.Id));
+
+        loadout.Mods.Count().Should().Be(1);
+
+        loadout.Mods.First().Name.Should().Be("Second Mod");
+    }
 }
diff --git a/tests/NexusMods.EventSourcing.Tests/Contexts/InMemoryEventStore.cs b/tests/NexusMods.EventSourcing.Tests/Contexts/InMemoryEventStore.cs
index f8e001ed..379d6863 100644
--- a/tests/NexusMods.EventSourcing.Tests/Contexts/InMemoryEventStore.cs
+++ b/tests/NexusMods.EventSourcing.Tests/Contexts/InMemoryEventStore.cs
@@ -44,17 +44,26 @@ public void Emit<TOwner, TVal>(EntityId<TOwner> entity, MultiEntityAttributeDefi
             Entities.Add(entity.Value);
         }
 
+        public void Retract<TOwner, TVal>(EntityId<TOwner> entity, AttributeDefinition<TOwner, TVal> attr, TVal value) where TOwner : IEntity
+        {
+            Entities.Add(entity.Value);
+        }
+
+        public void Retract<TOwner, TVal>(EntityId<TOwner> entity, MultiEntityAttributeDefinition<TOwner, TVal> attr, EntityId<TVal> value) where TOwner : IEntity where TVal : IEntity
+        {
+            Entities.Add(entity.Value);
+        }
+
         public void New<TType>(EntityId<TType> id) where TType : IEntity
         {
             Entities.Add(id.Value);
         }
     }
 
-
-    public void EventsForEntity<TEntity, TIngester>(EntityId<TEntity> entityId, TIngester ingester)
-        where TEntity : IEntity where TIngester : IEventIngester
+    public void EventsForEntity<TIngester>(EntityId entityId, TIngester ingester)
+        where TIngester : IEventIngester
     {
-        foreach (var data in _events[entityId.Value])
+        foreach (var data in _events[entityId])
         {
             var @event = serializer.Deserialize(data)!;
             ingester.Ingest(@event);
diff --git a/tests/NexusMods.EventSourcing.Tests/Contexts/TestContext.cs b/tests/NexusMods.EventSourcing.Tests/Contexts/TestContext.cs
index 0dd9fe86..bec5c647 100644
--- a/tests/NexusMods.EventSourcing.Tests/Contexts/TestContext.cs
+++ b/tests/NexusMods.EventSourcing.Tests/Contexts/TestContext.cs
@@ -19,36 +19,38 @@ public TEntity Get<TEntity>(EntityId<TEntity> id) where TEntity : IEntity
             return (TEntity)entity;
         }
 
-        var ingester = new Ingester(id.Value);
-
-        _store.EventsForEntity(id, ingester);
-
-        var type = (Type)ingester.Values[IEntity.TypeAttribute].Get();
+        var values = LoadValues(id.Value);
 
+        var type = (Type)values[IEntity.TypeAttribute].Get();
         var createdEntity = (TEntity)Activator.CreateInstance(type, this, id.Value)!;
         _entities.Add(id.Value, createdEntity);
-        _values.Add(id.Value, ingester.Values);
 
         return createdEntity;
     }
 
+    private Dictionary<IAttribute, IAccumulator> LoadValues(EntityId id)
+    {
+        var ingester = new Ingester(id);
+        _store.EventsForEntity(id, ingester);
+        _values.Add(id, ingester.Values);
+        return ingester.Values;
+    }
+
     public async ValueTask Add<TEvent>(TEvent entity) where TEvent : IEvent
     {
-        _entities.Clear();
         _values.Clear();
         await _store.Add(entity);
     }
 
-    public IAccumulator GetAccumulator<TType, TOwner>(EntityId ownerId, AttributeDefinition<TOwner, TType> attributeDefinition)
-        where TOwner : IEntity
+    public IAccumulator GetAccumulator<TOwner, TAttribute>(EntityId ownerId, TAttribute attributeDefinition)
+        where TOwner: IEntity
+        where TAttribute : IAttribute
     {
         if (_values.TryGetValue(ownerId, out var values))
             return values[attributeDefinition];
 
-        Get(EntityId<TOwner>.From(ownerId.Value));
-        values = _values[ownerId];
-
-        return values[attributeDefinition];
+        var loadedValues = LoadValues(ownerId);
+        return loadedValues[attributeDefinition];
     }
 
     private readonly struct Ingester(EntityId id) : IEventIngester, IEventContext
@@ -94,7 +96,29 @@ public void Emit<TOwner, TVal>(EntityId entity, AttributeDefinition<TOwner, TVal
 
         public void Emit<TOwner, TVal>(EntityId<TOwner> entity, MultiEntityAttributeDefinition<TOwner, TVal> attr, EntityId<TVal> value) where TOwner : IEntity where TVal : IEntity
         {
-            throw new NotImplementedException();
+            if (entity.Value != id.Value)
+                return;
+
+            var accumulator = GetAccumulator(attr);
+            accumulator.Add(value);
+        }
+
+        public void Retract<TOwner, TVal>(EntityId<TOwner> entity, AttributeDefinition<TOwner, TVal> attr, TVal value) where TOwner : IEntity
+        {
+            if (entity.Value != id.Value)
+                return;
+
+            var accumulator = GetAccumulator(attr);
+            accumulator.Retract(value!);
+        }
+
+        public void Retract<TOwner, TVal>(EntityId<TOwner> entity, MultiEntityAttributeDefinition<TOwner, TVal> attr, EntityId<TVal> value) where TOwner : IEntity where TVal : IEntity
+        {
+            if (entity.Value != id.Value)
+                return;
+
+            var accumulator = GetAccumulator(attr);
+            accumulator.Retract(value);
         }
 
         public void New<TType>(EntityId<TType> newId) where TType : IEntity