Update DomainUtil and finish PreferenceView.

app/renderer/js/utils/domain-util.js

@@ -2,6 +2,7 @@
 
 const {app} = require('electron').remote;
 const JsonDB = require('node-json-db');
+const request = require('request');
 
 class DomainUtil {
     constructor() {
@@ -12,18 +13,37 @@ class DomainUtil {
         return this.db.getData('/domains');
     }
 
-    addDomain() {
-        const servers = {
-            url: 'https://chat.zulip.org',
-            alias: 'Zulip 2333',
-            icon: 'https://chat.zulip.org/static/images/logo/zulip-icon-128x128.271d0f6a0ca2.png'
-        }
+    addDomain(server) {
+        server.icon = server.icon || 'https://chat.zulip.org/static/images/logo/zulip-icon-128x128.271d0f6a0ca2.png';
         this.db.push("/domains[]", servers, true);
     }
 
     removeDomains() {
         this.db.delete("/domains");
     }
+
+    removeDomain(index) {
+        this.db.delete(`/domains[${index}]`);
+    }
+
+    checkDomain(domain) {
+        const hasPrefix = (domain.indexOf('http') == 0);
+        if (!hasPrefix) {
+            domain = (domain.indexOf('localhost:') >= 0)? `http://${domain}` : `https://${domain}`;
+        }
+
+		const checkDomain = domain + '/static/audio/zulip.ogg';
+
+        return new Promise((res, rej) => {
+            request(checkDomain, (error, response) => {
+                if (!error && response.statusCode !== 404) {
+                    res(domain);
+                } else {
+                    rej('Not a valid Zulip server');
+                }
+            });
+        })
+    }
 }
 
 module.exports = DomainUtil;