Added frontend

frontend/src/App.css

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+.App {
+  text-align: center;
+}
+
+.App-logo {
+  animation: App-logo-spin infinite 20s linear;
+  height: 80px;
+}
+
+.App-header {
+  background-color: #222;
+  height: 150px;
+  padding: 20px;
+  color: white;
+}
+
+.App-title {
+  font-size: 1.5em;
+}
+
+.App-intro {
+  font-size: large;
+}
+
+@keyframes App-logo-spin {
+  from { transform: rotate(0deg); }
+  to { transform: rotate(360deg); }
+}

frontend/src/App.test.tsx

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+import * as React from 'react';
+import * as ReactDOM from 'react-dom';
+import App from './App';
+
+it('renders without crashing', () => {
+  const div = document.createElement('div');
+  ReactDOM.render(<App />, div);
+  ReactDOM.unmountComponentAtNode(div);
+});

frontend/src/App.tsx

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+import * as React from 'react';
+import './App.css';
+import { Id } from './shared';
+
+export interface NodeInfo {
+    name: string;
+}
+
+export interface BlockInfo {
+    height: number;
+    blockTime: number;
+}
+
+interface BestBlock {
+    action: 'best';
+    payload: number;
+}
+
+interface AddedNode {
+    action: 'added';
+    payload: [Id<Node>, NodeInfo, BlockInfo];
+}
+
+interface RemovedNode {
+    action: 'removed';
+    payload: Id<Node>;
+}
+
+interface Imported {
+    action: 'imported';
+    payload: [Id<Node>, BlockInfo];
+}
+
+type Message = BestBlock | AddedNode | RemovedNode | Imported;
+
+interface Node {
+    nodeInfo: NodeInfo,
+    blockInfo: BlockInfo,
+}
+
+interface State {
+    best: number,
+    nodes: Map<Id<Node>, Node>
+}
+
+export default class App extends React.Component<{}, State> {
+    public state: State = {
+        best: 0,
+        nodes: new Map()
+    };
+
+    constructor(props: {}) {
+        super(props);
+
+        const socket = new WebSocket(`ws://${window.location.hostname}:8080`);
+
+        socket.addEventListener('message', ({ data }) => {
+            this.onMessage(JSON.parse(data));
+        });
+    }
+
+    public render() {
+        return (
+            <div className="App">
+                <p>Best block: {this.state.best}</p>
+                <table>
+                    <thead>
+                        <tr>
+                            <th>Name</th><th>Block</th><th>Block time</th>
+                        </tr>
+                    </thead>
+                    <tbody>
+                    {
+                        this.nodes().map(([ id, node ]) => (
+                            <tr key={id}>
+                                <td>{node.nodeInfo.name}</td>
+                                <td>{node.blockInfo.height}</td>
+                                <td>{node.blockInfo.blockTime / 1000}s</td>
+                            </tr>
+                        ))
+                    }
+                    </tbody>
+                </table>
+            </div>
+        );
+    }
+
+    private nodes(): Array<[Id<Node>, Node]> {
+        return Array.from(this.state.nodes.entries());
+    }
+
+    private onMessage(message: Message) {
+        const { nodes } = this.state;
+
+        switch (message.action) {
+            case 'best': {
+                this.setState({ best: message.payload });
+            }
+            return;
+            case 'added': {
+                const [id, nodeInfo, blockInfo] = message.payload;
+                const node = { nodeInfo, blockInfo };
+
+                nodes.set(id, node);
+            }
+            break;
+            case 'removed': {
+                nodes.delete(message.payload);
+            }
+            break;
+            case 'imported': {
+                const [id, blockInfo] = message.payload;
+
+                const node = nodes.get(id);
+
+                if (!node) {
+                    return;
+                }
+
+                node.blockInfo = blockInfo;
+            }
+            break;
+            default:
+            return;
+        }
+
+        this.setState({ nodes });
+    }
+}

frontend/src/index.css

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+body {
+  margin: 0;
+  padding: 0;
+  font-family: sans-serif;
+}

frontend/src/index.tsx

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+import * as React from 'react';
+import * as ReactDOM from 'react-dom';
+import App from './App';
+import './index.css';
+import registerServiceWorker from './registerServiceWorker';
+
+ReactDOM.render(
+  <App />,
+  document.getElementById('root') as HTMLElement
+);
+registerServiceWorker();

frontend/src/registerServiceWorker.ts

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+// tslint:disable:no-console
+// In production, we register a service worker to serve assets from local cache.
+
+// This lets the app load faster on subsequent visits in production, and gives
+// it offline capabilities. However, it also means that developers (and users)
+// will only see deployed updates on the 'N+1' visit to a page, since previously
+// cached resources are updated in the background.
+
+// To learn more about the benefits of this model, read https://goo.gl/KwvDNy.
+// This link also includes instructions on opting out of this behavior.
+
+const isLocalhost = Boolean(
+  window.location.hostname === 'localhost' ||
+    // [::1] is the IPv6 localhost address.
+    window.location.hostname === '[::1]' ||
+    // 127.0.0.1/8 is considered localhost for IPv4.
+    window.location.hostname.match(
+      /^127(?:\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)){3}$/
+    )
+);
+
+export default function register() {
+  if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
+    // The URL constructor is available in all browsers that support SW.
+    const publicUrl = new URL(
+      process.env.PUBLIC_URL!,
+      window.location.toString()
+    );
+    if (publicUrl.origin !== window.location.origin) {
+      // Our service worker won't work if PUBLIC_URL is on a different origin
+      // from what our page is served on. This might happen if a CDN is used to
+      // serve assets; see https://github.com/facebookincubator/create-react-app/issues/2374
+      return;
+    }
+
+    window.addEventListener('load', () => {
+      const swUrl = `${process.env.PUBLIC_URL}/service-worker.js`;
+
+      if (isLocalhost) {
+        // This is running on localhost. Lets check if a service worker still exists or not.
+        checkValidServiceWorker(swUrl);
+
+        // Add some additional logging to localhost, pointing developers to the
+        // service worker/PWA documentation.
+        navigator.serviceWorker.ready.then(() => {
+          console.log(
+            'This web app is being served cache-first by a service ' +
+              'worker. To learn more, visit https://goo.gl/SC7cgQ'
+          );
+        });
+      } else {
+        // Is not local host. Just register service worker
+        registerValidSW(swUrl);
+      }
+    });
+  }
+}
+
+function registerValidSW(swUrl: string) {
+  navigator.serviceWorker
+    .register(swUrl)
+    .then(registration => {
+      registration.onupdatefound = () => {
+        const installingWorker = registration.installing;
+        if (installingWorker) {
+          installingWorker.onstatechange = () => {
+            if (installingWorker.state === 'installed') {
+              if (navigator.serviceWorker.controller) {
+                // At this point, the old content will have been purged and
+                // the fresh content will have been added to the cache.
+                // It's the perfect time to display a 'New content is
+                // available; please refresh.' message in your web app.
+                console.log('New content is available; please refresh.');
+              } else {
+                // At this point, everything has been precached.
+                // It's the perfect time to display a
+                // 'Content is cached for offline use.' message.
+                console.log('Content is cached for offline use.');
+              }
+            }
+          };
+        }
+      };
+    })
+    .catch(error => {
+      console.error('Error during service worker registration:', error);
+    });
+}
+
+function checkValidServiceWorker(swUrl: string) {
+  // Check if the service worker can be found. If it can't reload the page.
+  fetch(swUrl)
+    .then(response => {
+      // Ensure service worker exists, and that we really are getting a JS file.
+      if (
+        response.status === 404 ||
+        response.headers.get('content-type')!.indexOf('javascript') === -1
+      ) {
+        // No service worker found. Probably a different app. Reload the page.
+        navigator.serviceWorker.ready.then(registration => {
+          registration.unregister().then(() => {
+            window.location.reload();
+          });
+        });
+      } else {
+        // Service worker found. Proceed as normal.
+        registerValidSW(swUrl);
+      }
+    })
+    .catch(() => {
+      console.log(
+        'No internet connection found. App is running in offline mode.'
+      );
+    });
+}
+
+export function unregister() {
+  if ('serviceWorker' in navigator) {
+    navigator.serviceWorker.ready.then(registration => {
+      registration.unregister();
+    });
+  }
+}

frontend/src/shared

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+../../shared