solution

src/App.scss

@@ -21,3 +21,7 @@
 .message-body {
   white-space: pre-line;
 }
+
+iframe {
+  display: none;
+}

src/App.tsx

@@ -1,15 +1,30 @@
-import React from 'react';
-import 'bulma/bulma.sass';
+/* eslint-disable max-len */
 import '@fortawesome/fontawesome-free/css/all.css';
+import 'bulma/bulma.sass';
+import React from 'react';
 import './App.scss';
 
 import classNames from 'classnames';
-import { PostsList } from './components/PostsList';
+import { Loader } from './components/Loader';
 import { PostDetails } from './components/PostDetails';
+import { PostsList } from './components/PostsList';
 import { UserSelector } from './components/UserSelector';
-import { Loader } from './components/Loader';
+import { usePostsContext } from './hooks/usePostsContext';
+import { useUserContext } from './hooks/useUserContext';
 
 export const App: React.FC = () => {
+  const {
+    posts,
+    isPostsError,
+    isPostsPending,
+    selectedPost,
+  } = usePostsContext();
+  const { selectedUser } = useUserContext();
+
+  const hasError = !isPostsPending && isPostsError;
+  const withoutErrors = selectedUser && !isPostsError;
+  const fetchedWithoutErrors = withoutErrors && !isPostsPending;
+
   return (
     <main className="section">
       <div className="container">
@@ -21,24 +36,28 @@ export const App: React.FC = () => {
               </div>
 
               <div className="block" data-cy="MainContent">
-                <p data-cy="NoSelectedUser">
-                  No user selected
-                </p>
-
-                <Loader />
-
-                <div
-                  className="notification is-danger"
-                  data-cy="PostsLoadingError"
-                >
-                  Something went wrong!
-                </div>
-
-                <div className="notification is-warning" data-cy="NoPostsYet">
-                  No posts yet
-                </div>
-
-                <PostsList />
+                {!selectedUser && (
+                  <p data-cy="NoSelectedUser">
+                    No user selected
+                  </p>
+                )}
+                {withoutErrors && isPostsPending && (<Loader />)}
+                {fetchedWithoutErrors && (posts.length > 0
+                  ? <PostsList />
+                  : (
+                    <div className="notification is-warning" data-cy="NoPostsYet">
+                      No posts yet
+                    </div>
+                  )
+                )}
+                {hasError && (
+                  <div
+                    className="notification is-danger"
+                    data-cy="PostsLoadingError"
+                  >
+                    Something went wrong!
+                  </div>
+                )}
               </div>
             </div>
           </div>
@@ -50,11 +69,13 @@ export const App: React.FC = () => {
               'is-parent',
               'is-8-desktop',
               'Sidebar',
-              'Sidebar--open',
+              {
+                'Sidebar--open': selectedPost,
+              },
             )}
           >
             <div className="tile is-child box is-success ">
-              <PostDetails />
+              {selectedPost && <PostDetails />}
             </div>
           </div>
         </div>

src/Root.tsx

@@ -0,0 +1,16 @@
+import { App } from './App';
+import { CommentsContextProvider } from './context/CommentsContext';
+import { PostsContextProvider } from './context/PostsContext';
+import { UserContextProvider } from './context/UserContext';
+
+const Root: React.FC = () => (
+  <UserContextProvider>
+    <PostsContextProvider>
+      <CommentsContextProvider>
+        <App />
+      </CommentsContextProvider>
+    </PostsContextProvider>
+  </UserContextProvider>
+);
+
+export default Root;

src/components/NewCommentForm.tsx

@@ -1,8 +1,67 @@
-import React from 'react';
+import classNames from 'classnames';
+import React, { useState } from 'react';
+import { useCommentsContext } from '../hooks/useCommentsContext';
+
+const initialDetails = {
+  name: '',
+  email: '',
+  body: '',
+};
 
 export const NewCommentForm: React.FC = () => {
+  const { addingComment, handleAddComment } = useCommentsContext();
+  const [commentDetails, setCommentDetails] = useState(initialDetails);
+  const [nameError, setNameError] = useState(false);
+  const [emailError, setEmailError] = useState(false);
+  const [bodyError, setBodyError] = useState(false);
+
+  const handleResetForm = () => {
+    setNameError(false);
+    setEmailError(false);
+    setBodyError(false);
+    setCommentDetails(prev => ({
+      ...prev,
+      body: '',
+    }));
+  };
+
+  const handleSubmitForm = (event: React.FormEvent) => {
+    event.preventDefault();
+
+    if (!commentDetails.name) {
+      setNameError(true);
+    }
+
+    if (!commentDetails.email) {
+      setEmailError(true);
+    }
+
+    if (!commentDetails.body) {
+      setBodyError(true);
+    }
+
+    if (commentDetails.name
+      && commentDetails.email
+      && commentDetails.body
+    ) {
+      handleAddComment(commentDetails);
+      handleResetForm();
+    }
+  };
+
+  const handleDetailsChange = (fieldName: string, value: string) => {
+    setCommentDetails(prev => ({
+      ...prev,
+      [fieldName]: value,
+    }));
+  };
+
   return (
-    <form data-cy="NewCommentForm">
+    <form
+      data-cy="NewCommentForm"
+      onReset={handleResetForm}
+      onSubmit={handleSubmitForm}
+    >
       <div className="field" data-cy="NameField">
         <label className="label" htmlFor="comment-author-name">
           Author Name
@@ -14,24 +73,32 @@ export const NewCommentForm: React.FC = () => {
             name="name"
             id="comment-author-name"
             placeholder="Name Surname"
-            className="input is-danger"
+            className={classNames('input', {
+              'is-danger': nameError,
+            })}
+            value={commentDetails.name}
+            onChange={e => handleDetailsChange(e.target.name, e.target.value)}
           />
 
           <span className="icon is-small is-left">
             <i className="fas fa-user" />
           </span>
 
-          <span
-            className="icon is-small is-right has-text-danger"
-            data-cy="ErrorIcon"
-          >
-            <i className="fas fa-exclamation-triangle" />
-          </span>
+          {nameError && (
+            <span
+              className="icon is-small is-right has-text-danger"
+              data-cy="ErrorIcon"
+            >
+              <i className="fas fa-exclamation-triangle" />
+            </span>
+          )}
         </div>
 
-        <p className="help is-danger" data-cy="ErrorMessage">
-          Name is required
-        </p>
+        {nameError && (
+          <p className="help is-danger" data-cy="ErrorMessage">
+            Name is required
+          </p>
+        )}
       </div>
 
       <div className="field" data-cy="EmailField">
@@ -45,24 +112,32 @@ export const NewCommentForm: React.FC = () => {
             name="email"
             id="comment-author-email"
             placeholder="email@test.com"
-            className="input is-danger"
+            className={classNames('input', {
+              'is-danger': emailError,
+            })}
+            value={commentDetails.email}
+            onChange={e => handleDetailsChange(e.target.name, e.target.value)}
           />
 
           <span className="icon is-small is-left">
             <i className="fas fa-envelope" />
           </span>
 
-          <span
-            className="icon is-small is-right has-text-danger"
-            data-cy="ErrorIcon"
-          >
-            <i className="fas fa-exclamation-triangle" />
-          </span>
+          {emailError && (
+            <span
+              className="icon is-small is-right has-text-danger"
+              data-cy="ErrorIcon"
+            >
+              <i className="fas fa-exclamation-triangle" />
+            </span>
+          )}
         </div>
 
-        <p className="help is-danger" data-cy="ErrorMessage">
-          Email is required
-        </p>
+        {emailError && (
+          <p className="help is-danger" data-cy="ErrorMessage">
+            Email is required
+          </p>
+        )}
       </div>
 
       <div className="field" data-cy="BodyField">
@@ -75,25 +150,39 @@ export const NewCommentForm: React.FC = () => {
             id="comment-body"
             name="body"
             placeholder="Type comment here"
-            className="textarea is-danger"
+            className={classNames('textarea', {
+              'is-danger': bodyError,
+            })}
+            value={commentDetails.body}
+            onChange={e => handleDetailsChange(e.target.name, e.target.value)}
           />
         </div>
 
-        <p className="help is-danger" data-cy="ErrorMessage">
-          Enter some text
-        </p>
+        {bodyError && (
+          <p className="help is-danger" data-cy="ErrorMessage">
+            Enter some text
+          </p>
+        )}
       </div>
 
       <div className="field is-grouped">
         <div className="control">
-          <button type="submit" className="button is-link is-loading">
+          <button
+            type="submit"
+            className={classNames('button is-link', {
+              'is-loading': addingComment,
+            })}
+          >
             Add
           </button>
         </div>
 
         <div className="control">
           {/* eslint-disable-next-line react/button-has-type */}
-          <button type="reset" className="button is-link is-light">
+          <button
+            type="reset"
+            className="button is-link is-light"
+          >
             Clear
           </button>
         </div>