ActivityListener

Sources/Scout/Core/ActivityListener.swift

@@ -0,0 +1,118 @@
+//
+// Copyright 2024 Mikhail Kasianov
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import CoreData
+import UIKit
+
+/// An actor responsible for listening to application activity notifications and managing session monitoring.
+///
+/// The `ActivityListener` actor observes specific application lifecycle notifications to trigger and complete
+/// session monitoring actions. It ensures that the session monitor is properly notified when the application
+/// becomes active or resigns active.
+///
+/// - Note: This actor is implemented as a singleton using the `shared` static property.
+///
+/// - Throws: `ActivityListener.Error.alreadySetup` if the listener is already set up.
+///
+/// - Example:
+/// ```swift
+/// do {
+///     try await ActivityListener.shared.setup()
+/// } catch {
+///     print(error.localizedDescription)
+/// }
+/// ```
+///
+/// - SeeAlso: `SessionMonitor`
+///
+public actor ActivityListener {
+
+    enum Error: LocalizedError {
+        case alreadySetup
+
+        public var errorDescription: String? {
+            switch self {
+            case .alreadySetup:
+                return "ActivityListener is already setup"
+            }
+        }
+    }
+
+    /// A singleton instance of `ActivityListener`.
+    /// Use this shared instance to access the activity listener throughout the application.
+    ///
+    public static let shared = ActivityListener()
+
+    // MARK: - Setup
+
+    private var isSetup = false
+
+    /// Sets up the activity listener.
+    ///
+    /// This method initializes and configures the necessary components for the activity listener
+    /// to start monitoring and handling events.
+    ///
+    /// - Throws: An error if the listener is already set up.
+    ///
+    public func setup() throws {
+        guard !isSetup else {
+            throw Error.alreadySetup
+        }
+
+        isSetup = true
+
+        Task(operation: observeBecomeActive)
+        Task(operation: observeResignActive)
+    }
+}
+
+// MARK: - Notifications
+
+/// Extension for `ActivityListener` to handle notification observations.
+///
+/// This extension contains methods to observe specific application lifecycle notifications
+/// and perform corresponding actions. It uses asynchronous sequences to listen for notifications
+/// and execute the provided actions when the notifications are received.
+///
+/// - Note: This extension is used internally by the `ActivityListener` actor to manage
+/// session monitoring based on application activity.
+///
+/// - SeeAlso: `ActivityListener.setup()`
+///
+extension ActivityListener {
+
+    func observeBecomeActive() async {
+        await notifications(named: UIApplication.didBecomeActiveNotification) {
+            try await SessionMonitor.trigger()
+        }
+    }
+
+    func observeResignActive() async {
+        await notifications(named: UIApplication.willResignActiveNotification) {
+            try await SessionMonitor.complete()
+        }
+    }
+}
+
+// MARK: - Private
+
+extension ActivityListener {
+
+    private typealias NotificationAction = () async throws -> Void
+
+    private func notifications(named name: Notification.Name, action: NotificationAction) async {
+        let notifications = NotificationCenter.default.notifications(named: name).map { _ in () }
+
+        for await _ in notifications {
+            do {
+                try await action()
+            } catch {
+                print(error.localizedDescription)
+            }
+        }
+    }
+}