fix #419 and #412

The `Layout` is now a prototype, and `Layout.update` is no longer a
public API. This is combined with a much more significant refactor of
the underlying rendering logic.

The biggest issue that has been resolved relates to the relationship
between `LifeCycleHook` and `Layout`. Previously, the `LifeCycleHook`
accepted a layout instance in its constructor and called
`Layout.update`. Additionally, the `Layout` would manipulate the
`LifeCycleHook.component` attribute whenever the component instance
changed after a render. The former behavior leads to a non-linear
code path that's a touch to follow.  The latter behavior is the most
egregious design issue since there's absolutely no local indication
that the component instance can be swapped out (not even a comment).

The new refactor no longer binds component or layout instances to a
`LifeCycleHook`. Instead, the hook simply receives an unparametrized
callback that can be triggered to schedule a render. While some error
logs lose clarity (since we can't say what component caused them). This
change precludes a need for the layout to ever mutate the hook.

To accomodate this change, the internal representation of the layout's
state had to change. Previsouly, a class-based approach was take, where
methods of the state-holding classes were meant to handle all use
cases. Now we rely much more heavily on very simple (and mostly static)
data structures that have purpose built constructor functions that much
more narrowly address each use case.

Author: rmorshea

docs/source/core-abstractions.rst

@@ -95,7 +95,7 @@ which we can re-render and see what changed:
         patch_1 = await layout.render()
 
         fake_event = LayoutEvent(target=static_handler.target, data=[{}])
-        await layout.dispatch(fake_event)
+        await layout.deliver(fake_event)
         patch_2 = await layout.render()
 
         for change in patch_2.changes:

src/idom/core/component.py

@@ -5,22 +5,18 @@
 
 from __future__ import annotations
 
-import abc
 import inspect
 from functools import wraps
 from typing import Any, Callable, Dict, Optional, Tuple, Union
 from uuid import uuid4
 
-from typing_extensions import Protocol, runtime_checkable
-
+from .proto import ComponentType
 from .vdom import VdomDict
 
 
-ComponentConstructor = Callable[..., "ComponentType"]
-ComponentRenderFunction = Callable[..., Union["ComponentType", VdomDict]]
-
-
-def component(function: ComponentRenderFunction) -> Callable[..., "Component"]:
+def component(
+    function: Callable[..., Union[ComponentType, VdomDict]]
+) -> Callable[..., "Component"]:
     """A decorator for defining an :class:`Component`.
 
     Parameters:
@@ -34,26 +30,14 @@ def constructor(*args: Any, key: Optional[Any] = None, **kwargs: Any) -> Compone
     return constructor
 
 
-@runtime_checkable
-class ComponentType(Protocol):
-    """The expected interface for all component-like objects"""
-
-    id: str
-    key: Optional[Any]
-
-    @abc.abstractmethod
-    def render(self) -> VdomDict:
-        """Render the component's :class:`VdomDict`."""
-
-
 class Component:
     """An object for rending component models."""
 
     __slots__ = "__weakref__", "_func", "_args", "_kwargs", "id", "key"
 
     def __init__(
         self,
-        function: ComponentRenderFunction,
+        function: Callable[..., Union[ComponentType, VdomDict]],
         key: Optional[Any],
         args: Tuple[Any, ...],
         kwargs: Dict[str, Any],

src/idom/core/dispatcher.py

@@ -5,34 +5,43 @@
 
 from __future__ import annotations
 
-import sys
 from asyncio import Future, Queue
 from asyncio.tasks import FIRST_COMPLETED, ensure_future, gather, wait
+from contextlib import asynccontextmanager
 from logging import getLogger
-from typing import Any, AsyncIterator, Awaitable, Callable, List, Sequence, Tuple
+from typing import (
+    Any,
+    AsyncIterator,
+    Awaitable,
+    Callable,
+    Dict,
+    List,
+    NamedTuple,
+    Sequence,
+    Tuple,
+    cast,
+)
 from weakref import WeakSet
 
 from anyio import create_task_group
+from jsonpatch import apply_patch, make_patch
 
+from idom.core.vdom import VdomJson
 from idom.utils import Ref
 
-from .layout import Layout, LayoutEvent, LayoutUpdate
-
-
-if sys.version_info >= (3, 7):  # pragma: no cover
-    from contextlib import asynccontextmanager  # noqa
-else:  # pragma: no cover
-    from async_generator import asynccontextmanager
+from .layout import LayoutEvent, LayoutUpdate
+from .proto import LayoutType
 
 
 logger = getLogger(__name__)
 
-SendCoroutine = Callable[[Any], Awaitable[None]]
+
+SendCoroutine = Callable[["VdomJsonPatch"], Awaitable[None]]
 RecvCoroutine = Callable[[], Awaitable[LayoutEvent]]
 
 
 async def dispatch_single_view(
-    layout: Layout,
+    layout: LayoutType[LayoutUpdate, LayoutEvent],
     send: SendCoroutine,
     recv: RecvCoroutine,
 ) -> None:
@@ -49,14 +58,14 @@ async def dispatch_single_view(
 
 @asynccontextmanager
 async def create_shared_view_dispatcher(
-    layout: Layout, run_forever: bool = False
+    layout: LayoutType[LayoutUpdate, LayoutEvent],
 ) -> AsyncIterator[_SharedViewDispatcherFuture]:
     """Enter a dispatch context where all subsequent view instances share the same state"""
     with layout:
         (
             dispatch_shared_view,
             model_state,
-            all_update_queues,
+            all_patch_queues,
         ) = await _make_shared_view_dispatcher(layout)
 
         dispatch_tasks: List[Future[None]] = []
@@ -85,16 +94,16 @@ def dispatch_shared_view_soon(
                 update_future.cancel()
                 break
             else:
-                update: LayoutUpdate = update_future.result()
+                patch = VdomJsonPatch.create_from(update_future.result())
 
-            model_state.current = update.apply_to(model_state.current)
+            model_state.current = patch.apply_to(model_state.current)
             # push updates to all dispatcher callbacks
-            for queue in all_update_queues:
-                queue.put_nowait(update)
+            for queue in all_patch_queues:
+                queue.put_nowait(patch)
 
 
 def ensure_shared_view_dispatcher_future(
-    layout: Layout,
+    layout: LayoutType[LayoutUpdate, LayoutEvent],
 ) -> Tuple[Future[None], SharedViewDispatcher]:
     """Ensure the future of a dispatcher created by :func:`create_shared_view_dispatcher`"""
     dispatcher_future: Future[SharedViewDispatcher] = Future()
@@ -104,59 +113,93 @@ async def dispatch_shared_view_forever() -> None:
             (
                 dispatch_shared_view,
                 model_state,
-                all_update_queues,
+                all_patch_queues,
             ) = await _make_shared_view_dispatcher(layout)
 
             dispatcher_future.set_result(dispatch_shared_view)
 
             while True:
-                update = await layout.render()
-                model_state.current = update.apply_to(model_state.current)
+                patch = await render_json_patch(layout)
+                model_state.current = patch.apply_to(model_state.current)
                 # push updates to all dispatcher callbacks
-                for queue in all_update_queues:
-                    queue.put_nowait(update)
+                for queue in all_patch_queues:
+                    queue.put_nowait(patch)
 
     async def dispatch(send: SendCoroutine, recv: RecvCoroutine) -> None:
         await (await dispatcher_future)(send, recv)
 
     return ensure_future(dispatch_shared_view_forever()), dispatch
 
 
+async def render_json_patch(layout: LayoutType[LayoutUpdate, Any]) -> VdomJsonPatch:
+    """Render a class:`VdomJsonPatch` from a layout"""
+    return VdomJsonPatch.create_from(await layout.render())
+
+
+class VdomJsonPatch(NamedTuple):
+    """An object describing an update to a :class:`Layout` in the form of a JSON patch"""
+
+    path: str
+    """The path where changes should be applied"""
+
+    changes: List[Dict[str, Any]]
+    """A list of JSON patches to apply at the given path"""
+
+    def apply_to(self, model: VdomJson) -> VdomJson:
+        """Return the model resulting from the changes in this update"""
+        return cast(
+            VdomJson,
+            apply_patch(
+                model, [{**c, "path": self.path + c["path"]} for c in self.changes]
+            ),
+        )
+
+    @classmethod
+    def create_from(cls, update: LayoutUpdate) -> VdomJsonPatch:
+        """Return a patch given an layout update"""
+        return cls(update.path, make_patch(update.old or {}, update.new).patch)
+
+
 async def _make_shared_view_dispatcher(
-    layout: Layout,
-) -> Tuple[SharedViewDispatcher, Ref[Any], WeakSet[Queue[LayoutUpdate]]]:
-    initial_update = await layout.render()
-    model_state = Ref(initial_update.apply_to({}))
+    layout: LayoutType[LayoutUpdate, LayoutEvent],
+) -> Tuple[SharedViewDispatcher, Ref[Any], WeakSet[Queue[VdomJsonPatch]]]:
+    update = await layout.render()
+    model_state = Ref(update.new)
 
     # We push updates to queues instead of pushing directly to send() callbacks in
     # order to isolate the render loop from any errors dispatch callbacks might
     # raise.
-    all_update_queues: WeakSet[Queue[LayoutUpdate]] = WeakSet()
+    all_patch_queues: WeakSet[Queue[VdomJsonPatch]] = WeakSet()
 
     async def dispatch_shared_view(send: SendCoroutine, recv: RecvCoroutine) -> None:
-        update_queue: Queue[LayoutUpdate] = Queue()
+        patch_queue: Queue[VdomJsonPatch] = Queue()
         async with create_task_group() as inner_task_group:
-            all_update_queues.add(update_queue)
-            await send(LayoutUpdate.create_from({}, model_state.current))
+            all_patch_queues.add(patch_queue)
+            effective_update = LayoutUpdate("", None, model_state.current)
+            await send(VdomJsonPatch.create_from(effective_update))
             inner_task_group.start_soon(_single_incoming_loop, layout, recv)
-            inner_task_group.start_soon(_shared_outgoing_loop, send, update_queue)
+            inner_task_group.start_soon(_shared_outgoing_loop, send, patch_queue)
         return None
 
-    return dispatch_shared_view, model_state, all_update_queues
+    return dispatch_shared_view, model_state, all_patch_queues
 
 
-async def _single_outgoing_loop(layout: Layout, send: SendCoroutine) -> None:
+async def _single_outgoing_loop(
+    layout: LayoutType[LayoutUpdate, LayoutEvent], send: SendCoroutine
+) -> None:
     while True:
-        await send(await layout.render())
+        await send(await render_json_patch(layout))
 
 
-async def _single_incoming_loop(layout: Layout, recv: RecvCoroutine) -> None:
+async def _single_incoming_loop(
+    layout: LayoutType[LayoutUpdate, LayoutEvent], recv: RecvCoroutine
+) -> None:
     while True:
-        await layout.dispatch(await recv())
+        await layout.deliver(await recv())
 
 
 async def _shared_outgoing_loop(
-    send: SendCoroutine, queue: Queue[LayoutUpdate]
+    send: SendCoroutine, queue: Queue[VdomJsonPatch]
 ) -> None:
     while True:
         await send(await queue.get())