notify: add typesafe notify class

damus/Notify/Notify.swift

@@ -0,0 +1,44 @@
+//
+//  Notify.swift
+//  damus
+//
+//  Created by William Casarin on 2023-07-30.
+//
+
+import Foundation
+import Combine
+
+protocol Notify {
+    associatedtype Payload
+    static var name: Notification.Name { get }
+    var payload: Payload { get }
+}
+
+extension Notify {
+    static var name: Notification.Name {
+        Notification.Name("\(Self.self)")
+    }
+}
+
+// needed because static dispatch off protocol extensions doesn't work so well
+struct Notifications<T: Notify> {
+    let notify: T
+
+    init(_ notify: T) {
+        self.notify = notify
+    }
+}
+
+struct NotifyHandler<T> { }
+
+func notify_safe<T: Notify>(_ notify: Notifications<T>) {
+    let notify = notify.notify
+    NotificationCenter.default.post(name: T.name, object: notify.payload)
+}
+
+func handle_notify_safe<T: Notify>(_ handler: NotifyHandler<T>) -> AnyPublisher<T.Payload, Never> {
+    return NotificationCenter.default.publisher(for: T.name)
+        //.compactMap { notification in notification.object as? T.Payload }
+        .map { notification in notification.object as! T.Payload }
+        .eraseToAnyPublisher()
+}