Implement room status change upon attach or detach

Based on the simplified requirements described in #19.

The decision from 7d6acde to use actors as the mechanism for managing
mutable state means that I’ve had to make RoomStatus.{ current, error,
onChange(bufferingPolicy:) } async. As mentioned there, if later on we
decide this is too weird an API, then we can think of alternatives.

I really wanted to avoid making DefaultRoomStatus an actor; I tried to
find a way to isolate this state to the DefaultRoom actor (who logically
owns this state), by trying to make the DefaultRoomStatus access the
DefaultRoom-managed state, but I was not successful and didn’t want to
sink much time into it. It means that DefaultRoomStatus has suspension
points in order to access its current state, which I am not happy about.
But we can revisit later, perhaps armed with more knowledge of
concurrency and in less of a rush to get some initial functionality
implemented.

Resolves #19.

Sources/AblyChat/Room.swift

@@ -50,8 +50,9 @@ internal actor DefaultRoom: Room {
         fatalError("Not yet implemented")
     }
 
-    public nonisolated var status: any RoomStatus {
-        fatalError("Not yet implemented")
+    private let _status = DefaultRoomStatus()
+    internal nonisolated var status: any RoomStatus {
+        _status
     }
 
     /// Fetches the channels that contribute to this room.
@@ -69,11 +70,13 @@ internal actor DefaultRoom: Room {
         for channel in channels() {
             try await channel.attachAsync()
         }
+        await _status.transition(to: .attached)
     }
 
     public func detach() async throws {
         for channel in channels() {
             try await channel.detachAsync()
         }
+        await _status.transition(to: .detached)
     }
 }

Sources/AblyChat/RoomStatus.swift

@@ -1,10 +1,10 @@
 import Ably
 
 public protocol RoomStatus: AnyObject, Sendable {
-    var current: RoomLifecycle { get }
+    var current: RoomLifecycle { get async }
     // TODO: (https://github.com/ably-labs/ably-chat-swift/issues/12): consider how to avoid the need for an unwrap
-    var error: ARTErrorInfo? { get }
-    func onChange(bufferingPolicy: BufferingPolicy) -> Subscription<RoomStatusChange>
+    var error: ARTErrorInfo? { get async }
+    func onChange(bufferingPolicy: BufferingPolicy) async -> Subscription<RoomStatusChange>
 }
 
 public enum RoomLifecycle: Sendable {
@@ -31,3 +31,27 @@ public struct RoomStatusChange: Sendable {
         self.error = error
     }
 }
+
+internal actor DefaultRoomStatus: RoomStatus {
+    internal private(set) var current: RoomLifecycle = .initialized
+    // TODO: populate this (https://github.com/ably-labs/ably-chat-swift/issues/28)
+    internal private(set) var error: ARTErrorInfo?
+
+    // TODO: clean up old subscriptions (https://github.com/ably-labs/ably-chat-swift/issues/36)
+    private var subscriptions: [Subscription<RoomStatusChange>] = []
+
+    internal func onChange(bufferingPolicy: BufferingPolicy) -> Subscription<RoomStatusChange> {
+        let subscription: Subscription<RoomStatusChange> = .init(bufferingPolicy: bufferingPolicy)
+        subscriptions.append(subscription)
+        return subscription
+    }
+
+    /// Sets ``current`` to the given state, and emits a status change to all subscribers added via ``onChange(bufferingPolicy:)``.
+    internal func transition(to newState: RoomLifecycle) {
+        let statusChange = RoomStatusChange(current: newState, previous: current)
+        current = newState
+        for subscription in subscriptions {
+            subscription.emit(statusChange)
+        }
+    }
+}

Tests/AblyChatTests/DefaultRoomStatusTests.swift

@@ -0,0 +1,46 @@
+@testable import AblyChat
+import XCTest
+
+class DefaultRoomStatusTests: XCTestCase {
+    func test_current_startsAsInitialized() async {
+        let status = DefaultRoomStatus()
+        let current = await status.current
+        XCTAssertEqual(current, .initialized)
+    }
+
+    func test_error_startsAsNil() async {
+        let status = DefaultRoomStatus()
+        let error = await status.error
+        XCTAssertNil(error)
+    }
+
+    func test_transition() async {
+        // Given: A RoomStatus
+        let status = DefaultRoomStatus()
+        let originalState = await status.current
+        let newState = RoomLifecycle.attached // arbitrary
+
+        let subscription1 = await status.onChange(bufferingPolicy: .unbounded)
+        let subscription2 = await status.onChange(bufferingPolicy: .unbounded)
+
+        async let statusChange1 = subscription1.first { $0.current == newState }
+        async let statusChange2 = subscription2.first { $0.current == newState }
+
+        // When: transition(to:) is called
+        await status.transition(to: newState)
+
+        // Then: It emits a status change to all subscribers added via onChange(bufferingPolicy:), and updates its `current` property to the new state
+        guard let statusChange1 = await statusChange1, let statusChange2 = await statusChange2 else {
+            XCTFail("Expected status changes to be emitted")
+            return
+        }
+
+        for statusChange in [statusChange1, statusChange2] {
+            XCTAssertEqual(statusChange.previous, originalState)
+            XCTAssertEqual(statusChange.current, newState)
+        }
+
+        let current = await status.current
+        XCTAssertEqual(current, .attached)
+    }
+}

Tests/AblyChatTests/DefaultRoomTests.swift

@@ -18,13 +18,24 @@ class DefaultRoomTests: XCTestCase {
         let realtime = MockRealtime.create(channels: channels)
         let room = DefaultRoom(realtime: realtime, roomID: "basketball", options: .init())
 
+        let subscription = await room.status.onChange(bufferingPolicy: .unbounded)
+        async let attachedStatusChange = subscription.first { $0.current == .attached }
+
         // When: `attach` is called on the room
         try await room.attach()
 
-        // Then: `attach(_:)` is called on each of the channels, and the room `attach` call succeeds
+        // Then: `attach(_:)` is called on each of the channels, the room `attach` call succeeds, and the room transitions to ATTACHED
         for channel in channelsList {
             XCTAssertTrue(channel.attachCallCounter.isNonZero)
         }
+
+        guard let attachedStatusChange = await attachedStatusChange else {
+            XCTFail("Expected status change to ATTACHED but didn't get one")
+            return
+        }
+        let currentStatus = await room.status.current
+        XCTAssertEqual(currentStatus, .attached)
+        XCTAssertEqual(attachedStatusChange.current, .attached)
     }
 
     func test_attach_attachesAllChannels_andFailsIfOneFails() async throws {
@@ -73,13 +84,24 @@ class DefaultRoomTests: XCTestCase {
         let realtime = MockRealtime.create(channels: channels)
         let room = DefaultRoom(realtime: realtime, roomID: "basketball", options: .init())
 
+        let subscription = await room.status.onChange(bufferingPolicy: .unbounded)
+        async let detachedStatusChange = subscription.first { $0.current == .detached }
+
         // When: `detach` is called on the room
         try await room.detach()
 
-        // Then: `detach(_:)` is called on each of the channels, and the room `detach` call succeeds
+        // Then: `detach(_:)` is called on each of the channels, the room `detach` call succeeds, and the room transitions to DETACHED
         for channel in channelsList {
             XCTAssertTrue(channel.detachCallCounter.isNonZero)
         }
+
+        guard let detachedStatusChange = await detachedStatusChange else {
+            XCTFail("Expected status change to DETACHED but didn't get one")
+            return
+        }
+        let currentStatus = await room.status.current
+        XCTAssertEqual(currentStatus, .detached)
+        XCTAssertEqual(detachedStatusChange.current, .detached)
     }
 
     func test_detach_detachesAllChannels_andFailsIfOneFails() async throws {