chore: update migration steps

Author: tbozhikov

MIGRATE-TO-FIREBASE.md

@@ -1,13 +1,29 @@
-This is a migration guide which can help you switch your app from using push-plugin to using nativescript-plugin-firebase
-1. Go to your app's root folder and execute
+# Migration guide push-plugin -> Firebase plugin
+If you have an app that uses push-plugin for push notifications and need to switch to nativescript-plugin-firebase, this guide can help you. If you are just starting with push notifications, however, it would be best to use [Firebase plugin]("https://github.com/EddyVerbruggen/nativescript-plugin-firebase") and refer [its documentation on messaging]("https://github.com/EddyVerbruggen/nativescript-plugin-firebase/blob/master/docs/MESSAGING.md"). 
+#### 1. Add the plugin to your app
+Go to your app's root folder in terminal app and execute
 ```bash
 tns plugin add nativescript-plugin-firebase
 ```
 > Upon plugin installation, you'll be prompted to choose which features to use. Choose "yes" for Firebase Messaging (of course :)). By default, the plugin saves the configuration as a file (firebase.nativescript.json) to use it when reinstalling the plugin.
 
-2. Add `GoogleService-Info.plist` (for iOS) or `google-services.json` (for Android) in App_Resources/iOS (and App_Resources/Android, respectively). These are the configuration files that come from your Firebase apps. If you don't have such yet, go to https://console.firebase.google.com and create one. See [firebase plugin's docs]("https://github.com/EddyVerbruggen/nativescript-plugin-firebase/blob/master/docs/MESSAGING.md") for more info on initial setup.
+#### 2. Setup
+Add `GoogleService-Info.plist` (for iOS) or `google-services.json` (for Android) in App_Resources/iOS (and App_Resources/Android, respectively). These are the configuration files that come from your Firebase apps. If you don't have such yet, go to https://console.firebase.google.com and create one. See [Firebase plugin's docs]("https://github.com/EddyVerbruggen/nativescript-plugin-firebase/blob/master/docs/MESSAGING.md") for more info on initial setup.
 
-3. Add some code [to handle a notification]("https://github.com/EddyVerbruggen/nativescript-plugin-firebase/blob/master/docs/MESSAGING.md#handling-a-notification") 
+#### 3. Initialization prerequisite
+Make sure you [`require` the plugin in `app.ts` / `main.ts` / `main.aot.ts`](https://github.com/EddyVerbruggen/nativescript-plugin-firebase/blob/55cfb4f69cf8939f9101712fed22383196b08d36/demo/app/app.ts#L5)
+*before* `application.start()`, and do `init()` *after* the app has started (not in `app.ts` - not even in a timeout; move it out of `app.ts` entirely!). This ensures the notifications will be receivable in the background.
+
+EXAMPLE:
+```js
+// in app.ts
+// ...
+const firebase = require("nativescript-plugin-firebase");
+// ...
+app.start({ moduleName: 'main-page' });
+```
+
+#### 4. Add some code [to handle a notification]("https://github.com/EddyVerbruggen/nativescript-plugin-firebase/blob/master/docs/MESSAGING.md#handling-a-notification") 
 
 EXAMPLE: The following code using push-plugin:
 ```js
@@ -29,8 +45,10 @@ pushPlugin.register(this.pushSettings, (token: String) => {
     console.log((JSON.stringify(errorMessage));
 });
 ```
-... could be rewriten using firebase like:
+... could be rewriten using Firebase plugin like:
 ```js
+import * as firebase from "nativescript-plugin-firebase";
+
 firebase.init({
     onMessageReceivedCallback: (message: firebase.Message) => {
         console.log(`Message: ${message}`);
@@ -40,18 +58,37 @@ firebase.init({
     }
 });
 ```
-To test with sending messages, you can use the UI in Firebase Console, or use the  `https://fcm.googleapis.com/fcm/send` API. See the [testing docs section in firebase plugin]("https://github.com/EddyVerbruggen/nativescript-plugin-firebase/blob/master/docs/MESSAGING.md#testing").
+#### 5. Testing with messages 
+To test with real messages, you can use the UI in Firebase Console, or use the  `https://fcm.googleapis.com/fcm/send` API. See the [testing docs section in Firebase plugin]("https://github.com/EddyVerbruggen/nativescript-plugin-firebase/blob/master/docs/MESSAGING.md#testing").
+
+#### 6. Interactive Push Notifications - in push plugin they are set in the options argument passed to pushPlugin.register(options, callback) method. In Firebase plugin, it is done in a very similar way: 
+
+```js
+import * as firebase from "nativescript-plugin-firebase";
+import { messaging } from "nativescript-plugin-firebase/messaging";
+...
+const model = new messaging.PushNotificationModel();
+model.iosSettings = new messaging.IosPushSettings();
+model.iosSettings.interactiveSettings = new messaging.IosInteractivePushSettings();
+model.iosSettings.interactiveSettings.actions = [<<array of IosInteractiveNotificationAction>>]
+
+model.iosSettings.interactiveSettings.categories = [{ identifier: "SOME CATEGORY" }];
+
+model.onNotificationActionTakenCallback = () => {
+    // callback to hook to if you want to handle what action have been taken by the user
+};
+
+firebase.registerForInteractivePush(model: messaging.PushNotificationModel);
+```
+
+Some lines in the above example have been omitted. See [Firebase plugin's interactive notifications docs]("https://github.com/EddyVerbruggen/nativescript-plugin-firebase/blob/master/docs/MESSAGING.md#interactive-notifications-ios-only-for-now") for more details.
 
-4. 
+#### 7. areNotificationsEnabled() API
+In Firebase plugin it is pretty similar to the one in push-plugin, and even simpler to use:
 
------------
+```js
+import * as firebase from "nativescript-plugin-firebase";
 
-2.  You can go to demos and see there but below are how some usages of push-plugin translate to firebase:
- 
-pushPlugin.areNotificationsEnabled(<some-callback-func>) -> firebase.areNotificationsEnabled(): boolean
-| push-plugin | nativescript-plugin-firebase |
-| :-------------: | :-------------: | 
-| pushPlugin.areNotificationsEnabled(<some-callback-func>)      | firebase.areNotificationsEnabled(): boolean |
-| 
-pushPlugin.register(this.pushSettings)
-pushPlugin.registerUserNotificationSettings()      | firebase.registerForInteractivePush(model) |
+const areTheyEnabled = firebase.areNotificationsEnabled(); // synchronous, retruns boolean;
+```
+This API is also supported in Android, SDK version 24 and above