Update README.md

README.md

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-# blogspot_reader
+# Blogspot Reader
 
-A new Flutter project.
+Flutter app with heavy use of Firebase services to read blogs and get notified for new posts.
+**Note: Only [Blogger](https://blogger.com) sites.**
 
-## Getting Started
+## Tech stack
 
-This project is a starting point for a Flutter application.
 
-A few resources to get you started if this is your first Flutter project:
-
-- [Lab: Write your first Flutter app](https://flutter.dev/docs/get-started/codelab)
-- [Cookbook: Useful Flutter samples](https://flutter.dev/docs/cookbook)
-
-For help getting started with Flutter, view our
-[online documentation](https://flutter.dev/docs), which offers tutorials,
-samples, guidance on mobile development, and a full API reference.
+- [Flutter](https://flutter.dev): cross platform app development. This project only builds iOS and Android apps but Flutter has support for desktop and web apps too. Alternatives: React Native, Xamarin.
+  - [flutter_widget_from_html](https://pub.dev/packages/flutter_widget_from_html): render entry html
+  - [pull_to_refresh](https://pub.dev/packages/pull_to_refresh): pull-down-to-refresh and pull-up-to-load gestures
+  - [timeago](https://pub.dev/packages/timeago): relative time description (e.g. "5 minutes ago")
+  - [webfeed](https://pub.dev/packages/webfeed): Atom feed parser
+- [WebSub](https://www.w3.org/TR/websub/) (previously known as PubSubHubbub): subscription protocol for Blogspot feeds
+- [Firebase Messaging](https://firebase.google.com/docs/cloud-messaging/): cross platform push notification with support for image. Alternative: APNS for iOS. No alternative for Android.
+- [Firebase Functions](https://firebase.google.com/docs/functions/): FaaS / serverless platform. Alternatives: AWS Lambda, Azure Functions.
+  - `subscribe`: [subscribe to FCM topic](https://firebase.google.com/docs/cloud-messaging/manage-topics#suscribe_and_unsubscribe_using_the) and start [hub.mode=subscribe](https://www.w3.org/TR/websub/#subscriber-sends-subscription-request) flow
+  - `websub`: implement WebSub protocol [challenge](https://www.w3.org/TR/websub/#hub-verifies-intent) and [callback](https://www.w3.org/TR/websub/#content-distribution) flows
+  - `resubscribe`: cron, via [Cloud Scheduler](https://cloud.google.com/scheduler/), to refresh WebSub subscriptions
+- [Cloud Firestore](https://firebase.google.com/docs/firestore): realtime database service
+  - `subscriptions` collection: WebSub data
+  - `users` collection: user data (saved anonymously, via [Firebase Auth](https://firebase.google.com/docs/auth/))
+    - `users/{userId}/sites`: sites list