Introduce LocalNotification

This will be used for local notification data

damus/Util/LocalNotification.swift

@@ -0,0 +1,47 @@
+//
+//  LocalNotification.swift
+//  damus
+//
+//  Created by William Casarin on 2023-04-15.
+//
+
+import Foundation
+
+struct LossyLocalNotification {
+    let type: LocalNotificationType
+    let event_id: String
+    
+    func to_user_info() -> [AnyHashable: Any] {
+        return [
+            "type": self.type.rawValue,
+            "evid": self.event_id
+        ]
+    }
+    
+    static func from_user_info(user_info: [AnyHashable: Any]) -> LossyLocalNotification {
+        let target_id = user_info["evid"] as! String
+        let typestr = user_info["type"] as! String
+        let type = LocalNotificationType(rawValue: typestr)!
+        
+        return LossyLocalNotification(type: type, event_id: target_id)
+    }
+}
+
+struct LocalNotification {
+    let type: LocalNotificationType
+    let event: NostrEvent
+    let target: NostrEvent
+    let content: String
+    
+    func to_lossy() -> LossyLocalNotification {
+        return LossyLocalNotification(type: self.type, event_id: self.target.id)
+    }
+}
+
+enum LocalNotificationType: String {
+    case dm
+    case like
+    case mention
+    case repost
+    case zap
+}