Remove CurrentValueSubject as protocol requirement (#807)

* Add CurrentValuePublisher

* Refactor to use CurrentValuePublisher

* Add comment

ElementX/Sources/Other/CurrentValuePublisher.swift

@@ -0,0 +1,45 @@
+//
+// Copyright 2023 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Combine
+
+/// A wrapper of CurrentValueSubject.
+/// The purpose of this type is to remove the possibility to send new values on the underlying subject.
+struct CurrentValuePublisher<Output, Failure: Error>: Publisher {
+    private let subject: CurrentValueSubject<Output, Failure>
+    
+    init(_ subject: CurrentValueSubject<Output, Failure>) {
+        self.subject = subject
+    }
+    
+    init(_ value: Output) {
+        self.init(CurrentValueSubject(value))
+    }
+    
+    func receive<S>(subscriber: S) where S: Subscriber, Failure == S.Failure, Output == S.Input {
+        subject.receive(subscriber: subscriber)
+    }
+    
+    var value: Output {
+        subject.value
+    }
+}
+
+extension CurrentValueSubject {
+    func asCurrentValuePublisher() -> CurrentValuePublisher<Output, Failure> {
+        .init(self)
+    }
+}

ElementX/Sources/Services/Room/RoomSummary/MockRoomSummaryProvider.swift

@@ -23,9 +23,9 @@ enum MockRoomSummaryProviderState {
 }
 
 class MockRoomSummaryProvider: RoomSummaryProviderProtocol {
-    let roomListPublisher: CurrentValueSubject<[RoomSummary], Never>
-    let statePublisher: CurrentValueSubject<RoomSummaryProviderState, Never>
-    let countPublisher: CurrentValueSubject<UInt, Never>
+    let roomListPublisher: CurrentValuePublisher<[RoomSummary], Never>
+    let statePublisher: CurrentValuePublisher<RoomSummaryProviderState, Never>
+    let countPublisher: CurrentValuePublisher<UInt, Never>
     
     convenience init() {
         self.init(state: .loading)

ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProvider.swift

@@ -25,13 +25,25 @@ class RoomSummaryProvider: RoomSummaryProviderProtocol {
     
     private var cancellables = Set<AnyCancellable>()
     
-    let roomListPublisher = CurrentValueSubject<[RoomSummary], Never>([])
-    let statePublisher = CurrentValueSubject<RoomSummaryProviderState, Never>(.notLoaded)
-    let countPublisher = CurrentValueSubject<UInt, Never>(0)
+    private let roomListSubject = CurrentValueSubject<[RoomSummary], Never>([])
+    private let stateSubject = CurrentValueSubject<RoomSummaryProviderState, Never>(.notLoaded)
+    private let countSubject = CurrentValueSubject<UInt, Never>(0)
+    
+    var roomListPublisher: CurrentValuePublisher<[RoomSummary], Never> {
+        roomListSubject.asCurrentValuePublisher()
+    }
+
+    var statePublisher: CurrentValuePublisher<RoomSummaryProviderState, Never> {
+        stateSubject.asCurrentValuePublisher()
+    }
+
+    var countPublisher: CurrentValuePublisher<UInt, Never> {
+        countSubject.asCurrentValuePublisher()
+    }
     
     private var rooms: [RoomSummary] = [] {
         didSet {
-            roomListPublisher.send(rooms)
+            roomListSubject.send(rooms)
         }
     }
     
@@ -44,15 +56,15 @@ class RoomSummaryProvider: RoomSummaryProviderProtocol {
             buildSummaryForRoomListEntry(roomListEntry)
         }
         
-        roomListPublisher.send(rooms) // didSet not called from initialisers
+        roomListSubject.send(rooms) // didSet not called from initialisers
         
         slidingSyncViewProxy.statePublisher
             .map(RoomSummaryProviderState.init)
-            .subscribe(statePublisher)
+            .subscribe(stateSubject)
             .store(in: &cancellables)
         
         slidingSyncViewProxy.countPublisher
-            .subscribe(countPublisher)
+            .subscribe(countSubject)
             .store(in: &cancellables)
         
         slidingSyncViewProxy.diffPublisher

ElementX/Sources/Services/Room/RoomSummary/RoomSummaryProviderProtocol.swift

@@ -53,13 +53,13 @@ enum RoomSummary: CustomStringConvertible {
 
 protocol RoomSummaryProviderProtocol {
     /// Publishes the currently available room summaries
-    var roomListPublisher: CurrentValueSubject<[RoomSummary], Never> { get }
+    var roomListPublisher: CurrentValuePublisher<[RoomSummary], Never> { get }
     
     /// Publishes the current state the summary provider is finding itself in
-    var statePublisher: CurrentValueSubject<RoomSummaryProviderState, Never> { get }
+    var statePublisher: CurrentValuePublisher<RoomSummaryProviderState, Never> { get }
     
     /// Publishes the total number of rooms
-    var countPublisher: CurrentValueSubject<UInt, Never> { get }
+    var countPublisher: CurrentValuePublisher<UInt, Never> { get }
         
     func updateVisibleRange(_ range: Range<Int>, timelineLimit: UInt)
 }

ElementX/Sources/Services/Timeline/MockRoomTimelineProvider.swift

@@ -17,7 +17,7 @@
 import Combine
 
 struct MockRoomTimelineProvider: RoomTimelineProviderProtocol {
-    var itemsPublisher = CurrentValueSubject<[TimelineItemProxy], Never>([])
+    var itemsPublisher = CurrentValuePublisher<[TimelineItemProxy], Never>([])
     
     private var itemProxies = [TimelineItemProxy]()
 }

ElementX/Sources/Services/Timeline/RoomTimelineProvider.swift

@@ -31,11 +31,15 @@ class RoomTimelineProvider: RoomTimelineProviderProtocol {
     private var cancellables = Set<AnyCancellable>()
     private let serialDispatchQueue: DispatchQueue
     
-    let itemsPublisher = CurrentValueSubject<[TimelineItemProxy], Never>([])
+    private let itemsSubject = CurrentValueSubject<[TimelineItemProxy], Never>([])
+    
+    var itemsPublisher: CurrentValuePublisher<[TimelineItemProxy], Never> {
+        itemsSubject.asCurrentValuePublisher()
+    }
     
     private var itemProxies: [TimelineItemProxy] {
         didSet {
-            itemsPublisher.send(itemProxies)
+            itemsSubject.send(itemProxies)
         }
     }
     

ElementX/Sources/Services/Timeline/RoomTimelineProviderProtocol.swift

@@ -18,5 +18,5 @@ import Combine
 import Foundation
 
 protocol RoomTimelineProviderProtocol {
-    var itemsPublisher: CurrentValueSubject<[TimelineItemProxy], Never> { get }
+    var itemsPublisher: CurrentValuePublisher<[TimelineItemProxy], Never> { get }
 }