Rename Activity to UserIndicator

CommonKit/Source/UserIndicators/UserIndicator.swift

@@ -0,0 +1,102 @@
+// 
+// Copyright 2021 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 Foundation
+import UIKit
+
+/// A `UserIndicator` represents the state of a temporary visual indicator, such as loading spinner, success notification or an error message. It does not directly manage the UI, instead it delegates to a `presenter`
+/// whenever the UI should be shown or hidden.
+///
+/// More than one `UserIndicator` may be requested by the system at the same time (e.g. global syncing vs local refresh),
+/// and the `UserIndicatorQueue` will ensure that only one indicator is shown at a given time, putting the other in a pending queue.
+///
+/// A client that requests an indicator can specify a default timeout after which the indicator is dismissed, or it has to be manually
+/// responsible for dismissing it via `cancel` method, or by deallocating itself.
+public class UserIndicator {
+    public enum State {
+        case pending
+        case executing
+        case completed
+    }
+    
+    private let request: UserIndicatorRequest
+    private let completion: () -> Void
+
+    public private(set) var state: State
+    
+    public init(request: UserIndicatorRequest, completion: @escaping () -> Void) {
+        self.request = request
+        self.completion = completion
+        
+        state = .pending
+    }
+    
+    deinit {
+        complete()
+    }
+    
+    internal func start() {
+        guard state == .pending else {
+            return
+        }
+        
+        state = .executing
+        request.presenter.present()
+        
+        switch request.dismissal {
+        case .manual:
+            break
+        case .timeout(let interval):
+            Timer.scheduledTimer(withTimeInterval: interval, repeats: false) { [weak self] _ in
+                self?.complete()
+            }
+        }
+    }
+    
+    /// Cancel the indicator, triggering any dismissal action / animation
+    ///
+    /// Note: clients can call this method directly, if they have access to the `UserIndicator`.
+    /// Once cancelled, `UserIndicatorQueue` will automatically start the next `UserIndicator` in the queue.
+    public func cancel() {
+        complete()
+    }
+    
+    private func complete() {
+        guard state != .completed else {
+            return
+        }
+        if state == .executing {
+            request.presenter.dismiss()
+        }
+        
+        state = .completed
+        completion()
+    }
+}
+
+public extension UserIndicator {
+    func store<C>(in collection: inout C) where C: RangeReplaceableCollection, C.Element == UserIndicator {
+        collection.append(self)
+    }
+}
+
+public extension Collection where Element == UserIndicator {
+    func cancelAll() {
+        forEach {
+            $0.cancel()
+        }
+    }
+}