From e8bb2fdc980298d0a732f1f18ee63aeacb97ab14 Mon Sep 17 00:00:00 2001
From: Stefan Dirix <sdirix@eclipsesource.com>
Date: Tue, 7 Nov 2023 13:36:49 +0100
Subject: [PATCH] wip: JSON Forms middleware support

Showcase of middleware support in JSON Forms React. Not tested at all.
---
 packages/react/src/JsonForms.tsx        |  5 ++
 packages/react/src/JsonFormsContext.tsx | 61 +++++++++++++++++++------
 2 files changed, 52 insertions(+), 14 deletions(-)

diff --git a/packages/react/src/JsonForms.tsx b/packages/react/src/JsonForms.tsx
index 7d06bcd8c..8b4856ada 100644
--- a/packages/react/src/JsonForms.tsx
+++ b/packages/react/src/JsonForms.tsx
@@ -28,6 +28,7 @@ import type Ajv from 'ajv';
 import type { ErrorObject } from 'ajv';
 import { UnknownRenderer } from './UnknownRenderer';
 import {
+  CoreActions,
   createId,
   Generate,
   isControl,
@@ -45,6 +46,7 @@ import {
 } from '@jsonforms/core';
 import {
   JsonFormsStateProvider,
+  Middleware,
   withJsonFormsRendererProps,
 } from './JsonFormsContext';
 
@@ -54,6 +56,7 @@ interface JsonFormsRendererState {
 
 export interface JsonFormsReactProps {
   onChange?(state: Pick<JsonFormsCore, 'data' | 'errors'>): void;
+  middleware?: Middleware;
 }
 
 export class JsonFormsDispatchRenderer extends React.Component<
@@ -203,6 +206,7 @@ export const JsonForms = (
     validationMode,
     i18n,
     additionalErrors,
+    middleware,
   } = props;
   const schemaToUse = useMemo(
     () => (schema !== undefined ? schema : Generate.jsonSchema(data)),
@@ -233,6 +237,7 @@ export const JsonForms = (
         i18n,
       }}
       onChange={onChange}
+      middleware={middleware}
     >
       <JsonFormsDispatch />
     </JsonFormsStateProvider>
diff --git a/packages/react/src/JsonFormsContext.tsx b/packages/react/src/JsonFormsContext.tsx
index b860f6a91..a25e39299 100644
--- a/packages/react/src/JsonFormsContext.tsx
+++ b/packages/react/src/JsonFormsContext.tsx
@@ -75,6 +75,7 @@ import {
   OwnPropsOfLabel,
   LabelProps,
   mapStateToLabelProps,
+  CoreActions,
 } from '@jsonforms/core';
 import debounce from 'lodash/debounce';
 import React, {
@@ -87,6 +88,7 @@ import React, {
   useMemo,
   useReducer,
   useRef,
+  useState,
 } from 'react';
 
 const initialCoreState: JsonFormsCore = {
@@ -126,33 +128,59 @@ const useEffectAfterFirstRender = (
   }, dependencies);
 };
 
+export interface Middleware {
+  (
+    state: JsonFormsCore,
+    action: CoreActions,
+    defaultDispatch: (
+      state: JsonFormsCore,
+      action: CoreActions
+    ) => JsonFormsCore
+  ): JsonFormsCore;
+}
+
+const defaultMiddleware: Middleware = (state, action, defaultDispatch) =>
+  defaultDispatch(state, action);
+
 export const JsonFormsStateProvider = ({
   children,
   initState,
   onChange,
+  middleware,
 }: any) => {
   const { data, schema, uischema, ajv, validationMode, additionalErrors } =
     initState.core;
 
-  const [core, coreDispatch] = useReducer(coreReducer, undefined, () =>
-    coreReducer(
+  const middlewareRef = useRef<Middleware>(middleware ?? defaultMiddleware);
+  middlewareRef.current = middleware ?? defaultMiddleware;
+
+  const [core, setCore] = useState<JsonFormsCore>(() =>
+    middlewareRef.current(
       initState.core,
       Actions.init(data, schema, uischema, {
         ajv,
         validationMode,
         additionalErrors,
-      })
+      }),
+      coreReducer
     )
   );
-  useEffect(() => {
-    coreDispatch(
-      Actions.updateCore(data, schema, uischema, {
-        ajv,
-        validationMode,
-        additionalErrors,
-      })
-    );
-  }, [data, schema, uischema, ajv, validationMode, additionalErrors]);
+
+  useEffect(
+    () =>
+      setCore((currentCore) =>
+        middlewareRef.current(
+          currentCore,
+          Actions.updateCore(data, schema, uischema, {
+            ajv,
+            validationMode,
+            additionalErrors,
+          }),
+          coreReducer
+        )
+      ),
+    [data, schema, uischema, ajv, validationMode, additionalErrors]
+  );
 
   const [config, configDispatch] = useReducer(configReducer, undefined, () =>
     configReducer(undefined, Actions.setConfig(initState.config))
@@ -185,6 +213,12 @@ export const JsonFormsStateProvider = ({
     initState.i18n?.translateError,
   ]);
 
+  const dispatch = useCallback((action: CoreActions) => {
+    setCore((currentCore) =>
+      middlewareRef.current(currentCore, action, coreReducer)
+    );
+  }, []);
+
   const contextValue = useMemo(
     () => ({
       core,
@@ -194,8 +228,7 @@ export const JsonFormsStateProvider = ({
       uischemas: initState.uischemas,
       readonly: initState.readonly,
       i18n: i18n,
-      // only core dispatch available
-      dispatch: coreDispatch,
+      dispatch: dispatch,
     }),
     [
       core,