TF-2871 Add adr for push notification click logic on iOS

docs/adr/0048-push-notification-click-logic-on-ios.md

@@ -0,0 +1,71 @@
+# 38. Push notification click logic on iOS
+
+Date: 2024-06-07
+
+## Status
+
+Accepted
+
+## Context
+
+On iOS, we use `Notification Service Extension ( [NSE](https://developer.apple.com/documentation/usernotifications/modifying-content-in-newly-delivered-notifications))` to modify email content first when displaying push notifications to users.
+- In NSE we have implemented getting `new email list` based on `EmailDeliveryState` sent from FCM.
+- NSE only modifies and displays 1 notification, so we will display the notification for the last email in the list via NSE (is called `RemoteNotification`). 
+For the remaining emails we will use `[UNUserNotificationCenter](https://developer.apple.com/documentation/usernotifications/unusernotificationcenter)` to automatically display notifications (is called `LocalNotification`).
+
+## Decision
+
+Brief the logic flows when clicking notifications:
+
+1. Foreground/Background state
+
+- When clicking on notifications (both LocalNotification and RemoteNotification) the `didReceive` function of `UNUserNotificationCenter` in `AppDelegate` will be called.
+
+```swift
+ override func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {}
+```
+
+`response.notification.request.content.userInfo` is the contents of the push payload notification.
+We use `FlutterMethodChannel` to pass `UserInfo` from iOS native code to Flutter dart code
+
+```swift
+  self.notificationInteractionChannel?.invokeMethod(CoreUtils.USER_CLICK_NOTIFICATION_IN_FOREGROUND_METHOD_CALL_NAME, arguments: response.notification.request.content.userInfo)
+```
+
+2. Terminated state
+
+- With `RemoteNotification`, we will get the push notification payload through `launchOptions?[.remoteNotification]` in the `didFinishLaunchingWithOptions` function of `AppDelegate`
+
+```swift
+override func application(
+    _ application: UIApplication,
+    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
+) -> Bool {}
+```
+
+Save it in a `remoteNotificationPayload` variable in memory and use `FlutterMethodChannel` to retrieve it every time you open the app.
+
+```swift
+self.notificationInteractionChannel?.setMethodCallHandler { (call, result) in
+    switch call.method {
+        case CoreUtils.GET_REMOTE_NOTIFICATION_PAYLOAD_METHOD_CALL_NAME:
+            result(self.remoteNotificationPayload)
+            self.remoteNotificationPayload = nil
+        default:
+            break
+    }
+}
+```
+
+- As for `LocalNotification`, we will receive the push notification payload at the `didReceive` function of `UNUserNotificationCenter` (similar to `Foreground/Background state`)
+
+```swift
+ override func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {
+    self.remoteNotificationPayload = response.notification.request.content.userInfo
+ }
+```
+
+## Consequences
+
+- The application is correctly adjusted to the detailed screen email when clicking on the notification.
+- Any changes to the click push notification logic must be updated in this ADR.