Migrate app to TypeScript (#1637)

* Initial setup and migrated src/common

* WIP

* WIP

* WIP

* Main module basically finished

* Renderer process migrated

* Added CI step and some fixes

* Fixed remainder of issues and added proper ESLint config

* Fixed a couple issues

* Progress!

* Some more fixes

* Fixed a test

* Fix build step

* PR feedback

src/common/config/upgradePreferences.ts

@@ -0,0 +1,42 @@
+// Copyright (c) 2015-2016 Yuya Ochiai
+// Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+import {ConfigV2, ConfigV1, ConfigV0, AnyConfig} from 'types/config';
+
+import pastDefaultPreferences from './pastDefaultPreferences';
+
+function deepCopy<T>(object: T): T {
+    return JSON.parse(JSON.stringify(object));
+}
+
+function upgradeV0toV1(configV0: ConfigV0) {
+    const config = deepCopy(pastDefaultPreferences[1]);
+    config.teams.push({
+        name: 'Primary team',
+        url: configV0.url,
+    });
+    return config;
+}
+
+function upgradeV1toV2(configV1: ConfigV1) {
+    const config: ConfigV2 = Object.assign({}, deepCopy<ConfigV2>(pastDefaultPreferences[2]), configV1);
+    config.version = 2;
+    config.teams = configV1.teams.map((value, index) => {
+        return {
+            ...value,
+            order: index,
+        };
+    });
+    return config;
+}
+
+export default function upgradeToLatest(config: AnyConfig): ConfigV2 {
+    switch (config.version) {
+    case 2:
+        return config as ConfigV2;
+    case 1:
+        return upgradeToLatest(upgradeV1toV2(config as ConfigV1));
+    default:
+        return upgradeToLatest(upgradeV0toV1(config as ConfigV0));
+    }
+}