[Form lib] Add useFormData() hook to listen to fields value changes

src/plugins/es_ui_shared/static/forms/hook_form_lib/components/form.tsx

@@ -21,6 +21,7 @@ import React, { ReactNode } from 'react';
 import { EuiForm } from '@elastic/eui';
 
 import { FormProvider } from '../form_context';
+import { FormDataContextProvider } from '../form_data_context';
 import { FormHook } from '../types';
 
 interface Props {
@@ -30,8 +31,14 @@ interface Props {
   [key: string]: any;
 }
 
-export const Form = ({ form, FormWrapper = EuiForm, ...rest }: Props) => (
-  <FormProvider form={form}>
-    <FormWrapper {...rest} />
-  </FormProvider>
-);
+export const Form = ({ form, FormWrapper = EuiForm, ...rest }: Props) => {
+  const { getFormData, __getFormData$ } = form;
+
+  return (
+    <FormDataContextProvider getFormData={getFormData} getFormData$={__getFormData$}>
+      <FormProvider form={form}>
+        <FormWrapper {...rest} />
+      </FormProvider>
+    </FormDataContextProvider>
+  );
+};

src/plugins/es_ui_shared/static/forms/hook_form_lib/components/form_data_provider.test.tsx

@@ -75,16 +75,7 @@ describe('<FormDataProvider />', () => {
       setInputValue('lastNameField', 'updated value');
     });
 
-    /**
-     * The children will be rendered three times:
-     * - Twice for each input value that has changed
-     * - once because after updating both fields, the **form** isValid state changes (from "undefined" to "true")
-     *   causing a new "form" object to be returned and thus a re-render.
-     *
-     * When the form object will be memoized (in a future PR), te bellow call count should only be 2 as listening
-     * to form data changes should not receive updates when the "isValid" state of the form changes.
-     */
-    expect(onFormData.mock.calls.length).toBe(3);
+    expect(onFormData).toBeCalledTimes(2);
 
     const [formDataUpdated] = onFormData.mock.calls[onFormData.mock.calls.length - 1] as Parameters<
       OnUpdateHandler
@@ -130,7 +121,7 @@ describe('<FormDataProvider />', () => {
       find,
     } = setup() as TestBed;
 
-    expect(onFormData.mock.calls.length).toBe(0); // Not present in the DOM yet
+    expect(onFormData).toBeCalledTimes(0); // Not present in the DOM yet
 
     // Make some changes to the form fields
     await act(async () => {
@@ -188,7 +179,7 @@ describe('<FormDataProvider />', () => {
       setInputValue('lastNameField', 'updated value');
     });
 
-    expect(onFormData.mock.calls.length).toBe(0);
+    expect(onFormData).toBeCalledTimes(0);
   });
 
   test('props.pathsToWatch (Array<string>): should not re-render the children when the field that changed is not in the watch list', async () => {
@@ -228,14 +219,14 @@ describe('<FormDataProvider />', () => {
     });
 
     // No re-render
-    expect(onFormData.mock.calls.length).toBe(0);
+    expect(onFormData).toBeCalledTimes(0);
 
     // Make some changes to fields in the watch list
     await act(async () => {
       setInputValue('nameField', 'updated value');
     });
 
-    expect(onFormData.mock.calls.length).toBe(1);
+    expect(onFormData).toBeCalledTimes(1);
 
     onFormData.mockReset();
 

src/plugins/es_ui_shared/static/forms/hook_form_lib/components/form_data_provider.ts

@@ -17,57 +17,20 @@
  * under the License.
  */
 
-import React, { useState, useEffect, useRef, useCallback } from 'react';
+import React from 'react';
 
 import { FormData } from '../types';
-import { useFormContext } from '../form_context';
+import { useFormData } from '../hooks';
 
 interface Props {
   children: (formData: FormData) => JSX.Element | null;
   pathsToWatch?: string | string[];
 }
 
 export const FormDataProvider = React.memo(({ children, pathsToWatch }: Props) => {
-  const form = useFormContext();
-  const { subscribe } = form;
-  const previousRawData = useRef<FormData>(form.__getFormData$().value);
-  const isMounted = useRef(false);
-  const [formData, setFormData] = useState<FormData>(previousRawData.current);
+  const { 0: formData, 2: isReady } = useFormData({ watch: pathsToWatch });
 
-  const onFormData = useCallback(
-    ({ data: { raw } }) => {
-      // To avoid re-rendering the children for updates on the form data
-      // that we are **not** interested in, we can specify one or multiple path(s)
-      // to watch.
-      if (pathsToWatch) {
-        const valuesToWatchArray = Array.isArray(pathsToWatch)
-          ? (pathsToWatch as string[])
-          : ([pathsToWatch] as string[]);
-
-        if (valuesToWatchArray.some((value) => previousRawData.current[value] !== raw[value])) {
-          previousRawData.current = raw;
-          setFormData(raw);
-        }
-      } else {
-        setFormData(raw);
-      }
-    },
-    [pathsToWatch]
-  );
-
-  useEffect(() => {
-    const subscription = subscribe(onFormData);
-    return subscription.unsubscribe;
-  }, [subscribe, onFormData]);
-
-  useEffect(() => {
-    isMounted.current = true;
-    return () => {
-      isMounted.current = false;
-    };
-  }, []);
-
-  if (!isMounted.current && Object.keys(formData).length === 0) {
+  if (!isReady) {
     // No field has mounted yet, don't render anything
     return null;
   }

src/plugins/es_ui_shared/static/forms/hook_form_lib/form_data_context.tsx

@@ -0,0 +1,50 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import React, { createContext, useContext, useMemo } from 'react';
+
+import { FormData, FormHook } from './types';
+import { Subject } from './lib';
+
+export interface Context<T extends FormData = FormData> {
+  getFormData$: () => Subject<FormData>;
+  getFormData: FormHook<T>['getFormData'];
+}
+
+const FormDataContext = createContext<Context<any> | undefined>(undefined);
+
+interface Props extends Context {
+  children: React.ReactNode;
+}
+
+export const FormDataContextProvider = ({ children, getFormData$, getFormData }: Props) => {
+  const value = useMemo<Context>(
+    () => ({
+      getFormData,
+      getFormData$,
+    }),
+    [getFormData, getFormData$]
+  );
+
+  return <FormDataContext.Provider value={value}>{children}</FormDataContext.Provider>;
+};
+
+export function useFormDataContext<T extends FormData = FormData>() {
+  return useContext<Context<T> | undefined>(FormDataContext);
+}

src/plugins/es_ui_shared/static/forms/hook_form_lib/hooks/index.ts

@@ -19,3 +19,4 @@
 
 export { useField } from './use_field';
 export { useForm } from './use_form';
+export { useFormData } from './use_form_data';

src/plugins/es_ui_shared/static/forms/hook_form_lib/hooks/use_form.test.tsx

@@ -39,7 +39,7 @@ const onFormHook = (_form: FormHook<any>) => {
   formHook = _form;
 };
 
-describe('use_form() hook', () => {
+describe('useForm() hook', () => {
   beforeEach(() => {
     formHook = null;
   });

src/plugins/es_ui_shared/static/forms/hook_form_lib/hooks/use_form.ts

@@ -240,6 +240,12 @@ export function useForm<T extends FormData = FormData>(
 
       if (!field.isValidated) {
         setIsValid(undefined);
+
+        // When we submit the form (and set "isSubmitted" to "true"), we validate **all fields**.
+        // If a field is added and it is not validated it means that we have swapped fields and added new ones:
+        // --> we have basically have a new form in front of us.
+        // For that reason we make sure that the "isSubmitted" state is false.
+        setIsSubmitted(false);
       }
     },
     [updateFormDataAt]
@@ -389,6 +395,7 @@ export function useForm<T extends FormData = FormData>(
       isValid,
       id,
       submit: submitForm,
+      validate: validateAllFields,
       subscribe,
       setFieldValue,
       setFieldErrors,
@@ -428,6 +435,7 @@ export function useForm<T extends FormData = FormData>(
     addField,
     removeField,
     validateFields,
+    validateAllFields,
   ]);
 
   useEffect(() => {