feat(app): ✨ following retrieval command

greataped/README.md

@@ -17,6 +17,7 @@
 10. [FollowActor](#follow-actor)
 11. [AuthorizeInteraction](#authorize-interaction)
 12. [GetFollowers](#get-followers)
+13. [GetFollowing](#get-following)
 
 ---
 
@@ -180,3 +181,18 @@ Result:
     string first
 ```
 [Back to List](#apis)
+
+## Get Following
+```
+Request:
+    string username
+
+Result:
+    string @context
+    string id
+    string type
+    int32 totalItems
+    repeated string orderedItems
+    string first
+```
+[Back to List](#apis)

greataped/app/commands/spi/get_following.go

@@ -0,0 +1,27 @@
+package spi
+
+import (
+	. "rail.town/infrastructure/components/constants"
+	. "rail.town/infrastructure/components/contracts"
+)
+
+func GetFollowing(x IDispatcher, username string) (IGetFollowingResult, error) {
+	identities := x.FilterIdentities(func(identity IIdentity) bool {
+		return identity.Username() == username
+	})
+
+	x.Assert(identities.HasExactlyOneItem()).Or(ERROR_USER_NOT_FOUND)
+	identity := identities.First()
+
+	actor := x.Format("%s/u/%s", x.PublicUrl(), identity.Username())
+
+	var orderedItems []string = []string{}
+	return x.NewGetFollowingResult(
+		ACTIVITY_STREAMS,                // context
+		x.Format("%s/following", actor), // id
+		ACTIVITY_PUB_ORDERED_COLLECTION, // type
+		int32(len(orderedItems)),        // totalItems
+		orderedItems,                    // orderedItems
+		"",                              // first
+	), nil
+}