electron-bridge: Implement electron bridge.

This PR adds a bridge to communicate with the webapp in real time. As of now, the bridge listens for following events -

* When realm name changes
* When realm icon changes
* When the unread count changes

Partially fixes #425.

app/main/index.js

@@ -279,6 +279,10 @@ app.on('ready', () => {
 			});
 		});
 	});
+
+	ipcMain.on('realm-icon-changed', (event, serverURL, iconURL) => {
+		page.send('update-realm-icon', serverURL, iconURL);
+	});
 });
 
 app.on('before-quit', () => {

app/renderer/js/electron-bridge.js

@@ -0,0 +1,39 @@
+const events = require('events');
+const { ipcRenderer } = require('electron');
+
+// we have and will have some non camelcase stuff
+// while working with zulip so just turning the rule off
+// for the whole file.
+/* eslint-disable camelcase */
+class ElectronBridge extends events {
+	send_event(...args) {
+		this.emit(...args);
+	}
+
+	on_event(...args) {
+		this.on(...args);
+	}
+}
+
+const electron_bridge = new ElectronBridge();
+
+electron_bridge.on('total_unread_count', (...args) => {
+	ipcRenderer.send('unread-count', ...args);
+});
+
+electron_bridge.on('realm_name', (...args) => {
+	ipcRenderer.send('realm-name-changed', ...args);
+});
+
+electron_bridge.on('realm_icon_url', iconURL => {
+	const serverURL = location.origin;
+	iconURL = iconURL.includes('http') ? iconURL : `${serverURL}${iconURL}`;
+	ipcRenderer.send('realm-icon-changed', serverURL, iconURL);
+});
+
+// this follows node's idiomatic implementation of event
+// emitters to make event handling more simpler instead of using
+// functions zulip side will emit event using ElectronBrigde.send_event
+// which is alias of .emit and on this side we can handle the data by adding
+// a listener for the event.
+module.exports = electron_bridge;

app/renderer/js/main.js

@@ -397,6 +397,22 @@ class ServerManagerView {
 			const webContents = webview.getWebContents();
 			webContents.send('toggle-dnd', state, newSettings);
 		});
+
+		ipcRenderer.on('update-realm-icon', (event, serverURL, iconURL) => {
+			DomainUtil.getDomains().forEach((domain, index) => {
+				if (domain.url.includes(serverURL)) {
+					DomainUtil.saveServerIcon(iconURL).then(localIconUrl => {
+						const serverImgsSelector = `.tab .server-icons`;
+						const serverImgs = document.querySelectorAll(serverImgsSelector);
+						serverImgs[index].src = localIconUrl;
+
+						domain.icon = localIconUrl;
+						DomainUtil.db.push(`/domains[${index}]`, domain, true);
+						DomainUtil.reloadDB();
+					});
+				}
+			});
+		});
 	}
 
 	destroyTab(name, index) {

app/renderer/js/preload.js

@@ -12,6 +12,9 @@ require('./notification');
 // Prevent drag and drop event in main process which prevents remote code executaion
 require(__dirname + '/shared/preventdrag.js');
 
+// eslint-disable-next-line camelcase
+window.electron_bridge = require('./electron-bridge');
+
 const logout = () => {
 	// Create the menu for the below
 	document.querySelector('.dropdown-toggle').click();