[Docs] ES UI form library

.gitignore

@@ -63,3 +63,7 @@ report.asciidoc
 
 # TS incremental build cache
 *.tsbuildinfo
+
+# Docusaurus
+.docusaurus
+.cache-loader

package.json

@@ -40,6 +40,7 @@
     "preinstall": "node ./preinstall_check",
     "kbn": "node scripts/kbn",
     "es": "node scripts/es",
+    "docs": "docusaurus start ./src/plugins/es_ui_shared/docs",
     "test": "grunt test",
     "test:jest": "node scripts/jest",
     "test:jest_integration": "node scripts/jest_integration",
@@ -117,6 +118,8 @@
   "dependencies": {
     "@babel/core": "^7.11.1",
     "@babel/register": "^7.10.5",
+    "@docusaurus/core": "^2.0.0-alpha.62",
+    "@docusaurus/preset-classic": "^2.0.0-alpha.62",
     "@elastic/datemath": "5.0.3",
     "@elastic/elasticsearch": "7.9.1",
     "@elastic/eui": "29.0.0",
@@ -143,6 +146,7 @@
     "@kbn/monaco": "1.0.0",
     "@kbn/ui-shared-deps": "1.0.0",
     "@types/yauzl": "^2.9.1",
+    "@mdx-js/react": "^1.5.8",
     "JSONStream": "1.3.5",
     "abortcontroller-polyfill": "^1.4.0",
     "accept": "3.0.2",
@@ -154,6 +158,7 @@
     "chalk": "^2.4.2",
     "check-disk-space": "^2.1.0",
     "chokidar": "3.2.1",
+    "clsx": "^1.1.1",
     "color": "1.0.3",
     "commander": "3.0.2",
     "core-js": "^3.6.4",

src/plugins/es_ui_shared/docs/babel.config.js

@@ -0,0 +1,22 @@
+/*
+ * 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.
+ */
+
+module.exports = {
+  presets: [require.resolve('@docusaurus/core/lib/babel/preset')],
+};

src/plugins/es_ui_shared/docs/docs/form_lib/core/about.md

@@ -0,0 +1,77 @@
+---
+id: about
+title: Core
+sidebar_label: Getting started
+---
+
+The core exposes the main building blocks (hooks and components) needed to build your form.
+
+It is important to note that the core **is not** responsible of the rendering in the UI. Its resposibility is to return form and fields **state and handlers** that you will then have to connect to your React components. With that said, as in Kibana we work with [the EUI component library](https://elastic.github.io/eui), we have created special fields component that wrap the EUI components where the connection with the form lib is already done for you.  
+The takeaway is: the core of the form lib is agnostic of any UI rendering the form.
+
+## Getting started
+
+The three required component to build a form are
+
+- `useForm()` hook to declare a new form
+- `<Form />` component that will wrap your form and create a context for it
+- `<UseField />` component to declare a field
+
+Let's see them in action before going into details
+
+```js
+import { useForm, Form, UseField } from 'src/plugins/es_ui_shared/public';
+
+export const UserForm = () => {
+  const { form } = useForm(); // 1
+
+  return (
+    <Form form={form}> // 2
+      <UseField path="name" /> // 3 
+      <UseField path="lastName" />
+
+      <button onClick={form.submit}>Submit</button>
+    </Form>
+  );
+};
+```
+
+1. We use the `useForm` hook to declare a new form.
+2. We then wrap our form with the `<Form />` component, providing the `form` that we have just created.
+3. Finally, we declared two fields with the `<UseField />` component, providing a unique `path` for each one of them.
+
+If you were to run this code in the browser and click on the "Submit" button nothing would happen as we haven't defined yet any handler to execute when submitting the form. Let's do that now along with providing a `UserFormData` interface to the form, which we will get back in our `onSubmit` handler.
+
+```js
+import { useForm, Form, UseField, FormConfig } from 'src/plugins/es_ui_shared/public';
+
+interface UserFormData {
+  name: string;
+  lastName: string;
+}
+
+export const UserForm = () => {
+  const onFormSubmit: FormConfig<UserFormData>['onSubmit'] = async (data, isValid) => {
+    console.log("Is form valid:", isValid);
+    if (!isValid) {
+      // Maybe show a callout?
+      return;
+    }
+
+    console.log("Form data:", data);
+  };
+
+  const { form } = useForm({ onSubmit: onFormSubmit });
+
+  return (
+    <Form form={form}>
+      ...
+      <button onClick={form.submit}>Submit</button>
+    </Form>
+  );
+};
+```
+
+Great! We have our first working form. No state to worry about, just a simple declarative way to build our fields.
+
+Those of you who are attentive might have noticed that the above form _does_ render the fields in the UI although we said earlier that the core of the form lib is not responsile for any UI rendering. This is because the `<UseField />` has a fallback mechanism to render an `<input type="text" />` and hook to the field `value` and `onChange`. Unless you have styled your `input` elements and don't require other field types like `checkbox` or `select`, you will probably want to customize how the the `<UseField />` renders. We will see that in a future section.

src/plugins/es_ui_shared/docs/docs/form_lib/core/default_value.md

@@ -0,0 +1,94 @@
+---
+id: default_value
+title: defaultValue
+sidebar_label: defaultValue
+---
+
+There are multiple places where you can define the default value of a field. Note that by "default value" we are saying "the initial value" of a field. Once the field is initiated it has its own internal state and can't be controlled.
+
+## Order of precedence
+
+1. As a prop on the `<UseField path="name" defaultValue="John" />` component
+2. In the **form** `defaultValue` config passed to `useForm({ defaultValue: { ... } })`
+3. In the **field** `defaultValue` config parameter (either passed as prop to `<UseFielld />` prop or declared inside a form Schema)
+4. If no default value is found above, it defaults to `""` (empty string)
+
+### As a prop on `<UseField />`
+
+This takes over any other `defaultValue` defined elsewhere. What you provide as prop is what you will have as default value for the field. Remember that the `<UseField />` **is not** a controlled component, so changing the `defaultValue` prop to another value does not have any effect.
+
+```js
+// Here we manually set the default value 
+<UseField path="user.firstName" defaultValue="John" />
+```
+
+### In the form `defaultValue` config passed to `useForm()`
+
+The above solution works well for very small forms, but with larger form it is not very convenient to manually add the default value of each field.
+
+```js
+// Let's imagine some data coming from the server
+const fetchedData = {
+  user: {
+    firstName: 'John',
+    lastName: 'Snow',
+  }
+}
+
+// We need to manually write each connection, which is not convenient
+<UseField path="user.firstName" defaultValue={fetchedData.user.firstName} />
+<UseField path="user.lastName" defaultValue={fetchedData.user.lastName} />
+```
+
+It is much easier to provide the `defaultValue` object (probably some data that we have fetched from the server) at the form level
+
+```js
+const { form } = useForm({ defaultValue: fetchedData });
+
+// And the defaultValue for each field will be automatically mapped to its paths
+<UseField path="user.firstName" />
+<UseField path="user.lastName" />
+```
+
+### In the field `defaultValue` config parameter of the field config
+
+When you are creating a new resource, the form is empty and there is no data coming from the server to map. You still migth want to define a default value for your fields.
+
+```js
+interface Props {
+  fetchedData?: { index: boolean }
+}
+
+export const MyForm = ({ fetchedData }: Props) => {
+  // fetchedData can be "undefined" or an object.
+  // If it is undefined, then the config.defaultValue will be used
+  const { form } = useForm({ defaultValue: fetchedData });
+
+  return (
+    <UseField path="index" config={{ defaultValue: true } />
+  );
+}
+```
+
+Or the same but using a form schema
+
+```js
+const schema = {
+  // Field config for the path "index" declared below
+  index: {
+    defaultValue: true,
+  },
+};
+
+export const MyComponent = ({ fetchedData }: Props) => {
+  // 1. If defaultValue is not undefined **and** there is a value at the "index" path, use it
+  // 2. otherwise if there is a schema with a config at the "index" path read its "defaultValue"
+  // 3. if it's still undefined, use an "" (empty string) - which will throw an error for a checkbox field-.
+  const { form } = useForm({ schema, defaultValue: fetchedData });
+
+  return (
+    <UseField path="index" />
+  );
+}
+```
+