add util methods to LayoutUpdate

idom/core/dispatcher.py

@@ -4,7 +4,6 @@
 
 from anyio import create_task_group
 from anyio.abc import TaskGroup
-from jsonpatch import make_patch, apply_patch
 
 from .layout import (
     LayoutEvent,
@@ -122,14 +121,14 @@ async def run(
     async def _render_loop(self) -> None:
         while True:
             update = await super()._outgoing(self.layout, None)
-            self._model_state = _apply_layout_update(self._model_state, update)
+            self._model_state = update.apply_to(self._model_state)
             # append updates to all other contexts
             for queue in self._update_queues.values():
                 await queue.put(update)
 
     async def _outgoing_loop(self, send: SendCoroutine, context: Any) -> None:
         self._update_queues[context] = asyncio.Queue()
-        await send(LayoutUpdate("", make_patch({}, self._model_state).patch))
+        await send(LayoutUpdate.create_from({}, self._model_state))
         await super()._outgoing_loop(send, context)
 
     async def _outgoing(self, layout: Layout, context: str) -> LayoutUpdate:
@@ -142,9 +141,3 @@ async def _join_event(self) -> AsyncIterator[asyncio.Event]:
             yield event
         finally:
             event.set()
-
-
-def _apply_layout_update(doc: Dict[str, Any], update: LayoutUpdate) -> Any:
-    return apply_patch(
-        doc, [{**c, "path": update.path + c["path"]} for c in update.changes]
-    )

idom/core/layout.py

@@ -15,7 +15,7 @@
 )
 
 from loguru import logger
-from jsonpatch import make_patch
+from jsonpatch import make_patch, apply_patch
 
 from .element import AbstractElement
 from .events import EventHandler, EventTarget
@@ -29,6 +29,16 @@ class LayoutUpdate(NamedTuple):
     path: str
     changes: List[Dict[str, Any]]
 
+    def apply_to(self, model: Any) -> Any:
+        """Return the model resulting from the changes in this update"""
+        return apply_patch(
+            model, [{**c, "path": self.path + c["path"]} for c in self.changes]
+        )
+
+    @classmethod
+    def create_from(cls, source: Any, target: Any) -> "LayoutUpdate":
+        return cls("", make_patch(source, target).patch)
+
 
 class LayoutEvent(NamedTuple):
     target: str