Refactor theTimelineItemIdentifier handling; stop relying on optional EventOrTransactionIds and be explicit when setting composer modes from the draft service.

ElementX/Sources/Services/Timeline/TimelineItemIdentifier.swift

@@ -0,0 +1,66 @@
+//
+// Copyright 2024 New Vector Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only
+// Please see LICENSE in the repository root for full details.
+//
+
+import Foundation
+import MatrixRustSDK
+
+/// A timeline item identifier
+/// - uniqueID: Stable id across state changes of the timeline item, it uniquely identifies an item in a timeline.
+/// Its value is consistent only per timeline instance, it should **not** be used to identify an item across timeline instances.
+/// - eventOrTransactionID: Contains the 2 possible identifiers of an event, either it has a remote event id or
+/// a local transaction id, never both or none.
+enum TimelineItemIdentifier: Hashable {
+    case event(uniqueID: String, eventOrTransactionID: EventOrTransactionId)
+    case virtual(uniqueID: String)
+    
+    var uniqueID: String {
+        switch self {
+        case .event(let uniqueID, _):
+            return uniqueID
+        case .virtual(let uniqueID):
+            return uniqueID
+        }
+    }
+    
+    var eventID: String? {
+        guard case let .event(_, eventOrTransactionID) = self else {
+            return nil
+        }
+        
+        switch eventOrTransactionID {
+        case .eventId(let eventID):
+            return eventID
+        default:
+            return nil
+        }
+    }
+    
+    var transactionID: String? {
+        guard case let .event(_, eventOrTransactionID) = self else {
+            return nil
+        }
+        
+        switch eventOrTransactionID {
+        case .transactionId(let transactionID):
+            return transactionID
+        default:
+            return nil
+        }
+    }
+}
+
+// MARK: - Mocks
+
+extension TimelineItemIdentifier {
+    static var randomEvent: Self {
+        .event(uniqueID: UUID().uuidString, eventOrTransactionID: .eventId(eventId: UUID().uuidString))
+    }
+    
+    static var randomVirtual: Self {
+        .virtual(uniqueID: UUID().uuidString)
+    }
+}