feat: support multi-kind contexts in template interpolation (#48)

This PR allows for Mustache interpolation of multi-kind contexts. Developers can refer to single kinds by their name, e.g. ldctx.user or ldctx.device.

pkgs/sdk/server-ai/src/LdAiClient.cs

@@ -97,6 +97,25 @@ public ILdAiConfigTracker ModelConfig(string key, Context context, LdAiConfig de
 
     }
 
+
+    private static IDictionary<string, object> AddSingleKindContextAttributes(Context context)
+    {
+        var attributes = new Dictionary<string, object>
+        {
+            ["kind"] = context.Kind.ToString(),
+            ["key"] = context.Key,
+            ["anonymous"] = context.Anonymous
+        };
+
+        foreach (var key in context.OptionalAttributeNames)
+        {
+            attributes[key] = ValueToObject(context.GetValue(AttributeRef.FromLiteral(key)));
+        }
+
+        return attributes;
+    }
+
+
     /// <summary>
     /// Retrieves all attributes from the given context, including private attributes. The attributes
     /// are converted into C# primitives recursively.
@@ -105,17 +124,23 @@ public ILdAiConfigTracker ModelConfig(string key, Context context, LdAiConfig de
     /// <returns>the attributes</returns>
     private static IDictionary<string, object> GetAllAttributes(Context context)
     {
-        var attributes = new Dictionary<string, object>();
-        foreach (var key in context.OptionalAttributeNames)
+        if (!context.Multiple)
         {
-            attributes[key] = ValueToObject(context.GetValue(AttributeRef.FromLiteral(key)));
+            return AddSingleKindContextAttributes(context);
         }
 
-        attributes["kind"] = context.Kind.ToString();
-        attributes["key"] = context.Key;
-        attributes["anonymous"] = context.Anonymous;
+        var attrs = new Dictionary<string, object>
+        {
+            ["kind"] = context.Kind,
+            ["key"] = context.FullyQualifiedKey
+        };
 
-        return attributes;
+        foreach (var kind in context.MultiKindContexts)
+        {
+            attrs[kind.Kind.ToString()] = AddSingleKindContextAttributes(kind);
+        }
+
+        return attrs;
     }
 
     /// <summary>

pkgs/sdk/server-ai/test/InterpolationTests.cs

@@ -170,4 +170,70 @@ public void TestInterpolationWithNestedContextAttributes()
         var result = Eval("I can ingest over {{ ldctx.stats.power }} tokens per second!", context, null);
         Assert.Equal("I can ingest over 9000 tokens per second!", result);
     }
+
+    [Fact]
+    public void TestInterpolationWithMultiKindContext()
+    {
+        var user = Context.Builder(ContextKind.Default, "123")
+            .Set("cat_ownership", LdValue.ObjectFrom(new Dictionary<string, LdValue>
+            {
+                { "count", LdValue.Of(12) }
+            })).Build();
+
+        var cat = Context.Builder(ContextKind.Of("cat"), "456")
+            .Set("health", LdValue.ObjectFrom(new Dictionary<string, LdValue>
+            {
+                { "hunger", LdValue.Of("off the charts") }
+            })).Build();
+
+        var context = Context.MultiBuilder().Add(user).Add(cat).Build();
+
+        var nestedVars = Eval("As an owner of {{ ldctx.user.cat_ownership.count }} cats, I must report that my cat's hunger level is {{ ldctx.cat.health.hunger }}!", context, null);
+        Assert.Equal("As an owner of 12 cats, I must report that my cat's hunger level is off the charts!", nestedVars);
+
+        var canonicalKeys = Eval("multi={{ ldctx.key }} user={{ ldctx.user.key }} cat={{ ldctx.cat.key }}", context, null);
+        Assert.Equal("multi=cat:456:user:123 user=123 cat=456", canonicalKeys);
+    }
+
+    [Fact]
+    public void TestInterpolationMultiKindDoesNotHaveAnonymousAttribute()
+    {
+        var user = Context.Builder(ContextKind.Default, "123")
+            .Set("cat_ownership", LdValue.ObjectFrom(new Dictionary<string, LdValue>
+            {
+                { "count", LdValue.Of(12) }
+            })).Build();
+
+        var cat = Context.Builder(ContextKind.Of("cat"), "456")
+            .Set("health", LdValue.ObjectFrom(new Dictionary<string, LdValue>
+            {
+                { "hunger", LdValue.Of("off the charts") }
+            })).Build();
+
+        var context = Context.MultiBuilder().Add(user).Add(cat).Build();
+
+        var result = Eval("anonymous=<{{ ldctx.anonymous }}>", context, null);
+        Assert.Equal("anonymous=<>", result);
+    }
+
+    [Fact]
+    public void TestInterpolationMultiKindContextHasKindMulti()
+    {
+        var user = Context.Builder(ContextKind.Default, "123")
+            .Set("cat_ownership", LdValue.ObjectFrom(new Dictionary<string, LdValue>
+            {
+                { "count", LdValue.Of(12) }
+            })).Build();
+
+        var cat = Context.Builder(ContextKind.Of("cat"), "456")
+            .Set("health", LdValue.ObjectFrom(new Dictionary<string, LdValue>
+            {
+                { "hunger", LdValue.Of("off the charts") }
+            })).Build();
+
+        var context = Context.MultiBuilder().Add(user).Add(cat).Build();
+
+        var result = Eval("kind={{ ldctx.kind }}", context, null);
+        Assert.Equal("kind=multi", result);
+    }
 }