Update sampling to calculate per-run-of-app instead of per-session (#10769)

Author: samedson

FirebaseSessions/Sources/FirebaseSessions.swift

@@ -69,7 +69,8 @@ private enum GoogleDataTransportConfig {
       installations: installations
     )
 
-    let sessionGenerator = SessionGenerator(settings: settings)
+    let sessionGenerator = SessionGenerator(collectEvents: Sessions
+      .shouldCollectEvents(settings: settings))
     let coordinator = SessionCoordinator(
       installations: installations,
       fireLogger: fireLogger
@@ -195,6 +196,15 @@ private enum GoogleDataTransportConfig {
     }
   }
 
+  // MARK: - Sampling
+
+  static func shouldCollectEvents(settings: SettingsProtocol) -> Bool {
+    // Calculate whether we should sample events using settings data
+    // Sampling rate of 1 means we do not sample.
+    let randomValue = Double.random(in: 0 ... 1)
+    return randomValue <= settings.samplingRate
+  }
+
   // MARK: - Data Collection
 
   var isAnyDataCollectionEnabled: Bool {

FirebaseSessions/Sources/SessionGenerator.swift

@@ -39,15 +39,16 @@ struct SessionInfo {
 ///
 class SessionGenerator {
   private var thisSession: SessionInfo?
-  private var settings: SettingsProtocol
 
   private var firstSessionId = ""
   private var sessionIndex: Int32
+  private var collectEvents: Bool
 
-  init(settings: SettingsProtocol) {
-    self.settings = settings
+  init(collectEvents: Bool) {
     // This will be incremented to 0 on the first generation
     sessionIndex = -1
+
+    self.collectEvents = collectEvents
   }
 
   // Generates a new Session ID. If there was already a generated Session ID
@@ -61,12 +62,6 @@ class SessionGenerator {
 
     sessionIndex += 1
 
-    var collectEvents = true
-    let randomValue = Double.random(in: 0 ... 1)
-    if randomValue > settings.samplingRate {
-      collectEvents = false
-    }
-
     let newSession = SessionInfo(sessionId: newSessionId,
                                  firstSessionId: firstSessionId,
                                  dispatchEvents: collectEvents,

FirebaseSessions/Tests/Unit/Library/FirebaseSessionsTestsBase.swift

@@ -96,7 +96,8 @@ class FirebaseSessionsTestsBase: XCTestCase {
     // initialization of other classes
     preSessionsInit(mockSettings)
 
-    generator = SessionGenerator(settings: mockSettings)
+    generator = SessionGenerator(collectEvents: Sessions
+      .shouldCollectEvents(settings: mockSettings))
     initiator = SessionInitiator(settings: mockSettings, currentTimeProvider: {
       self.pausedClock
     })

FirebaseSessions/Tests/Unit/SessionGeneratorTests.swift

@@ -53,7 +53,8 @@ class SessionGeneratorTests: XCTestCase {
       localOverrides: localOverrideSettings,
       remoteSettings: remoteSettings
     )
-    generator = SessionGenerator(settings: sessionSettings)
+    generator = SessionGenerator(collectEvents: Sessions
+      .shouldCollectEvents(settings: sessionSettings))
   }
 
   func isValidSessionID(_ sessionID: String) -> Bool {
@@ -138,6 +139,10 @@ class SessionGeneratorTests: XCTestCase {
       remoteSettings: remoteSettings
     )
 
+    // Rebuild the SessionGenerator with the new settings
+    generator = SessionGenerator(collectEvents: Sessions
+      .shouldCollectEvents(settings: sessionSettings))
+
     let sessionInfo = generator.generateNewSession()
     XCTAssertTrue(sessionInfo.shouldDispatchEvents)
   }
@@ -150,7 +155,6 @@ class SessionGeneratorTests: XCTestCase {
         "session_timeout_seconds": 50,
       ],
     ]
-
     cache.removeCache()
     downloader = MockSettingsDownloader(successResponse: someSettings)
     remoteSettings = RemoteSettings(appInfo: appInfo, downloader: downloader, cache: cache)
@@ -164,7 +168,36 @@ class SessionGeneratorTests: XCTestCase {
       remoteSettings: remoteSettings
     )
 
+    // Rebuild the SessionGenerator with the new settings
+    generator = SessionGenerator(collectEvents: Sessions
+      .shouldCollectEvents(settings: sessionSettings))
+
+    let sessionInfo = generator.generateNewSession()
+    XCTAssertFalse(sessionInfo.shouldDispatchEvents)
+  }
+
+  func test_sessionsSampling_persistsPerRun() throws {
+    let mockSettings = MockSettingsProtocol()
+    mockSettings.samplingRate = 0
+
+    // Rebuild the SessionGenerator with the new settings
+    generator = SessionGenerator(collectEvents: Sessions
+      .shouldCollectEvents(settings: mockSettings))
+
     let sessionInfo = generator.generateNewSession()
     XCTAssertFalse(sessionInfo.shouldDispatchEvents)
+
+    // Try again
+    let sessionInfo2 = generator.generateNewSession()
+    XCTAssertFalse(sessionInfo2.shouldDispatchEvents)
+
+    // Start returning true from the calculator
+    mockSettings.samplingRate = 1
+
+    // Try again after the calculator starts returning true.
+    // It should still be false in the sessionInfo because the
+    // sampling rate is calculated per-run
+    let sessionInfo3 = generator.generateNewSession()
+    XCTAssertFalse(sessionInfo3.shouldDispatchEvents)
   }
 }