Add screen engagement tracking of time spent and list items scrolled …

…on a screen (close #851)

Integrationtests/TestTrackEventsToMicro.swift

@@ -21,6 +21,7 @@ class TestTrackEventsToMicro: XCTestCase {
         super.setUp()
 
         let trackerConfig = TrackerConfiguration()
+            .screenEngagementAutotracking(false)
             .logLevel(.debug)
 
         tracker = Snowplow.createTracker(namespace: "testMicro-" + UUID().uuidString,

Sources/Core/Events/ScreenEnd.swift

@@ -0,0 +1,26 @@
+//  Copyright (c) 2013-2023 Snowplow Analytics Ltd. All rights reserved.
+//
+//  This program is licensed to you under the Apache License Version 2.0,
+//  and you may not use this file except in compliance with the Apache License
+//  Version 2.0. You may obtain a copy of the Apache License Version 2.0 at
+//  http://www.apache.org/licenses/LICENSE-2.0.
+//
+//  Unless required by applicable law or agreed to in writing,
+//  software distributed under the Apache License Version 2.0 is distributed on
+//  an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+//  express or implied. See the Apache License Version 2.0 for the specific
+//  language governing permissions and limitations there under.
+
+import Foundation
+
+class ScreenEnd: SelfDescribingAbstract {
+
+    override var schema: String {
+        return kSPScreenEndSchema
+    }
+
+    override var payload: [String : Any] {
+        return [:]
+    }
+
+}

Sources/Core/InternalQueue/TrackerControllerIQWrapper.swift

@@ -196,6 +196,11 @@ class TrackerControllerIQWrapper: TrackerController {
         get { return InternalQueue.sync { controller.screenViewAutotracking } }
         set { InternalQueue.sync { controller.screenViewAutotracking = newValue } }
     }
+
+    var screenEngagementAutotracking: Bool {
+        get { return InternalQueue.sync { controller.screenEngagementAutotracking } }
+        set { InternalQueue.sync { controller.screenEngagementAutotracking = newValue } }
+    }
 
     var trackerVersionSuffix: String? {
         get { return InternalQueue.sync { controller.trackerVersionSuffix } }

Sources/Core/ScreenViewTracking/ListItemViewModifier.swift

@@ -0,0 +1,54 @@
+// Copyright (c) 2013-2023 Snowplow Analytics Ltd. All rights reserved.
+//
+// This program is licensed to you under the Apache License Version 2.0,
+// and you may not use this file except in compliance with the Apache License
+// Version 2.0. You may obtain a copy of the Apache License Version 2.0 at
+// http://www.apache.org/licenses/LICENSE-2.0.
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the Apache License Version 2.0 is distributed on
+// an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+// express or implied. See the Apache License Version 2.0 for the specific
+// language governing permissions and limitations there under.
+
+#if canImport(SwiftUI)
+
+import SwiftUI
+import Foundation
+
+@available(iOS 13.0, macOS 10.15, macCatalyst 13.0, tvOS 13.0, *)
+@available(watchOS, unavailable)
+internal struct ListItemViewModifier: ViewModifier {
+    let index: Int
+    let itemsCount: Int?
+    let trackerNamespace: String?
+
+    /// Get tracker by namespace if configured, otherwise return the default tracker
+    private var tracker: TrackerController? {
+        if let namespace = trackerNamespace {
+            return Snowplow.tracker(namespace: namespace)
+        } else {
+            return Snowplow.defaultTracker()
+        }
+    }
+
+    /// Modifies the view to track the list item view when it appears
+    func body(content: Content) -> some View {
+        content.onAppear {
+            trackListItemView()
+        }
+    }
+
+    func trackListItemView() {
+        let event = ListItemView(index: index)
+        event.itemsCount = itemsCount
+
+        if let tracker = tracker {
+            _ = tracker.track(event)
+        } else {
+            logError(message: "List item view not tracked – tracker not initialized.")
+        }
+    }
+}
+
+#endif

Sources/Core/ScreenViewTracking/ScreenStateMachine.swift

@@ -17,6 +17,10 @@ class ScreenStateMachine: StateMachineProtocol {
     static var identifier: String { return "ScreenContext" }
     var identifier: String { return ScreenStateMachine.identifier }
 
+    var subscribedEventSchemasForEventsBefore: [String] {
+        return []
+    }
+
     var subscribedEventSchemasForTransitions: [String] {
         return [kSPScreenViewSchema]
     }
@@ -37,6 +41,10 @@ class ScreenStateMachine: StateMachineProtocol {
         return []
     }
 
+    func eventsBefore(event: Event) -> [Event]? {
+        return nil
+    }
+
     func transition(from event: Event, state currentState: State?) -> State? {
         if let screenView = event as? ScreenView {
             let newState: ScreenState = screenState(from: screenView)

Sources/Core/ScreenViewTracking/ScreenSummaryState.swift

@@ -0,0 +1,64 @@
+//  Copyright (c) 2013-2023 Snowplow Analytics Ltd. All rights reserved.
+//
+//  This program is licensed to you under the Apache License Version 2.0,
+//  and you may not use this file except in compliance with the Apache License
+//  Version 2.0. You may obtain a copy of the Apache License Version 2.0 at
+//  http://www.apache.org/licenses/LICENSE-2.0.
+//
+//  Unless required by applicable law or agreed to in writing,
+//  software distributed under the Apache License Version 2.0 is distributed on
+//  an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+//  express or implied. See the Apache License Version 2.0 for the specific
+//  language governing permissions and limitations there under.
+
+import Foundation
+
+class ScreenSummaryState: State {
+
+    static var dateGenerator: () -> TimeInterval = { Date().timeIntervalSince1970 }
+
+    private var lastUpdateTimestamp: TimeInterval = ScreenSummaryState.dateGenerator()
+    var foregroundSeconds: TimeInterval = 0
+    var backgroundSeconds: TimeInterval = 0
+    var lastItemIndex: Int?
+    var itemsCount: Int?
+
+    var data: [String: Any] {
+        var data: [String: Any] = [
+            "foreground_sec": foregroundSeconds,
+            "background_sec": backgroundSeconds
+        ]
+        if let lastItemIndex = lastItemIndex { data["last_item_index"] = lastItemIndex }
+        if let itemsCount = itemsCount { data["items_count"] = itemsCount }
+        return data
+    }
+
+    func updateTransitionToForeground() {
+        let currentTimestamp = ScreenSummaryState.dateGenerator()
+
+        backgroundSeconds += currentTimestamp - lastUpdateTimestamp
+        lastUpdateTimestamp = currentTimestamp
+    }
+
+    func updateTransitionToBackground() {
+        let currentTimestamp = ScreenSummaryState.dateGenerator()
+
+        foregroundSeconds += currentTimestamp - lastUpdateTimestamp
+        lastUpdateTimestamp = currentTimestamp
+    }
+
+    func updateForScreenEnd() {
+        let currentTimestamp = ScreenSummaryState.dateGenerator()
+
+        foregroundSeconds += currentTimestamp - lastUpdateTimestamp
+        lastUpdateTimestamp = currentTimestamp
+    }
+
+    func updateWithListItemView(_ event: ListItemView) {
+        lastItemIndex = max(event.index, lastItemIndex ?? 0)
+        if let totalItems = event.itemsCount {
+            self.itemsCount = max(totalItems, self.itemsCount ?? 0)
+        }
+    }
+
+}

Sources/Core/ScreenViewTracking/ScreenSummaryStateMachine.swift

@@ -0,0 +1,91 @@
+//  Copyright (c) 2013-2023 Snowplow Analytics Ltd. All rights reserved.
+//
+//  This program is licensed to you under the Apache License Version 2.0,
+//  and you may not use this file except in compliance with the Apache License
+//  Version 2.0. You may obtain a copy of the Apache License Version 2.0 at
+//  http://www.apache.org/licenses/LICENSE-2.0.
+//
+//  Unless required by applicable law or agreed to in writing,
+//  software distributed under the Apache License Version 2.0 is distributed on
+//  an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+//  express or implied. See the Apache License Version 2.0 for the specific
+//  language governing permissions and limitations there under.
+
+import Foundation
+
+class ScreenSummaryStateMachine: StateMachineProtocol {
+    static var identifier: String { return "ScreenSummaryContext" }
+    var identifier: String { return ScreenSummaryStateMachine.identifier }
+
+    var subscribedEventSchemasForEventsBefore: [String] {
+        return [kSPScreenViewSchema]
+    }
+
+    var subscribedEventSchemasForTransitions: [String] {
+        return [kSPScreenViewSchema, kSPScreenEndSchema, kSPForegroundSchema, kSPBackgroundSchema, kSPListItemViewSchema]
+    }
+
+    var subscribedEventSchemasForEntitiesGeneration: [String] {
+        return [kSPScreenEndSchema, kSPForegroundSchema, kSPBackgroundSchema]
+    }
+
+    var subscribedEventSchemasForPayloadUpdating: [String] {
+        return []
+    }
+
+    var subscribedEventSchemasForAfterTrackCallback: [String] {
+        return []
+    }
+
+    var subscribedEventSchemasForFiltering: [String] {
+        return [kSPListItemViewSchema, kSPScreenEndSchema]
+    }
+
+    func eventsBefore(event: Event) -> [Event]? {
+        return [ScreenEnd()]
+    }
+
+    func transition(from event: Event, state currentState: State?) -> State? {
+        if event is ScreenView {
+            return ScreenSummaryState()
+        }
+        else if let state = currentState as? ScreenSummaryState {
+            switch event {
+            case is Foreground:
+                state.updateTransitionToForeground()
+            case is Background:
+                state.updateTransitionToBackground()
+            case is ScreenEnd:
+                state.updateForScreenEnd()
+            case let itemView as ListItemView:
+                state.updateWithListItemView(itemView)
+            default:
+                break
+            }
+        }
+        return currentState
+    }
+
+    func entities(from event: InspectableEvent, state: State?) -> [SelfDescribingJson]? {
+        guard let state = state as? ScreenSummaryState else { return nil }
+
+        return [
+            SelfDescribingJson(schema: kSPViewSummarySchema, andData: state.data)
+        ]
+    }
+
+    func payloadValues(from event: InspectableEvent, state: State?) -> [String : Any]? {
+        return nil
+    }
+
+    func filter(event: InspectableEvent, state: State?) -> Bool? {
+        if event.schema == kSPScreenEndSchema {
+            return state != nil
+        }
+        // do not track list item view events
+        return false
+    }
+
+    func afterTrack(event: InspectableEvent) {
+    }
+}

Sources/Core/StateMachine/DeepLinkStateMachine.swift

@@ -29,6 +29,10 @@ class DeepLinkStateMachine: StateMachineProtocol {
     static var identifier: String { return "DeepLinkContext" }
     var identifier: String { return DeepLinkStateMachine.identifier }
 
+    var subscribedEventSchemasForEventsBefore: [String] {
+        return []
+    }
+
     var subscribedEventSchemasForTransitions: [String] {
         return [DeepLinkReceived.schema, kSPScreenViewSchema]
     }
@@ -49,6 +53,10 @@ class DeepLinkStateMachine: StateMachineProtocol {
         return []
     }
 
+    func eventsBefore(event: Event) -> [Event]? {
+        return nil
+    }
+
     func transition(from event: Event, state: State?) -> State? {
         if let dlEvent = event as? DeepLinkReceived {
             return DeepLinkState(url: dlEvent.url, referrer: dlEvent.referrer)

Sources/Core/StateMachine/LifecycleStateMachine.swift

@@ -17,10 +17,16 @@ class LifecycleStateMachine: StateMachineProtocol {
     static var identifier: String { return "Lifecycle" }
     var identifier: String { return LifecycleStateMachine.identifier }
 
+    var subscribedEventSchemasForEventsBefore: [String] = []
+
+    func eventsBefore(event: Event) -> [Event]? {
+        return nil
+    }
+
     var subscribedEventSchemasForTransitions: [String] {
         return [kSPBackgroundSchema, kSPForegroundSchema]
     }
-
+    
     func transition(from event: Event, state currentState: State?) -> State? {
         if let e = event as? Foreground {
             return LifecycleState(asForegroundWithIndex: e.index)

Sources/Core/StateMachine/PluginStateMachine.swift

@@ -35,6 +35,14 @@ class PluginStateMachine: StateMachineProtocol {
         self.filterConfiguration = filterConfiguration
     }
 
+    var subscribedEventSchemasForEventsBefore: [String] {
+        return []
+    }
+
+    func eventsBefore(event: Event) -> [Event]? {
+        return nil
+    }
+
     var subscribedEventSchemasForTransitions: [String] {
         return []
     }

Sources/Core/StateMachine/StateMachineProtocol.swift

@@ -15,12 +15,16 @@ import Foundation
 
 protocol StateMachineProtocol {
     var identifier: String { get }
+    var subscribedEventSchemasForEventsBefore: [String] { get }
     var subscribedEventSchemasForTransitions: [String] { get }
     var subscribedEventSchemasForEntitiesGeneration: [String] { get }
     var subscribedEventSchemasForPayloadUpdating: [String] { get }
     var subscribedEventSchemasForAfterTrackCallback: [String] { get }
     var subscribedEventSchemasForFiltering: [String] { get }
 
+    /// Only available for self-describing events (inheriting from SelfDescribingAbstract)
+    func eventsBefore(event: Event) -> [Event]?
+
     /// Only available for self-describing events (inheriting from SelfDescribingAbstract)
     func transition(from event: Event, state: State?) -> State?