fix: Add maxQueuedEventCount parameter to trim events in storage if o…

…ver a limit (#222)

Sources/Amplitude/Amplitude.swift

@@ -72,6 +72,10 @@ public class Amplitude {
         configuration.optOutChanged = { [weak self] optOut in
             self?.timeline.onOptOutChanged(optOut)
         }
+
+        trackingQueue.async { [self] in
+            self.trimQueuedEvents()
+        }
     }
 
     convenience init(apiKey: String, configuration: Configuration) {
@@ -450,4 +454,30 @@ public class Amplitude {
     internal func isSandboxEnabled() -> Bool {
         return SandboxHelper().isSandboxEnabled()
     }
+
+    func trimQueuedEvents() {
+        logger?.debug(message: "Trimming queued events..")
+        guard configuration.maxQueuedEventCount > 0,
+              let eventBlocks: [URL] = storage.read(key: .EVENTS),
+              !eventBlocks.isEmpty else {
+            return
+        }
+
+        var eventCount = 0
+        // Blocks are returned in sorted order, oldest -> newest. Reverse to count newest blocks first.
+        // Only whole blocks are deleted, meaning up to maxQueuedEventCount + flushQueueSize - 1
+        // events may be left on device.
+        for eventBlock in eventBlocks.reversed() {
+            if eventCount < configuration.maxQueuedEventCount {
+                if let eventString = storage.getEventsString(eventBlock: eventBlock),
+                   let eventArray =  BaseEvent.fromArrayString(jsonString: eventString) {
+                    eventCount += eventArray.count
+                }
+            } else {
+                logger?.debug(message: "Trimming \(eventBlock)")
+                storage.remove(eventBlock: eventBlock)
+            }
+        }
+        logger?.debug(message: "Completed trimming events, kept \(eventCount) most recent events")
+    }
 }

Sources/Amplitude/Configuration.swift

@@ -48,6 +48,7 @@ public class Configuration {
     public internal(set) var autocapture: AutocaptureOptions
     public var offline: Bool?
     internal let diagonostics: Diagnostics
+    public var maxQueuedEventCount = -1
     var optOutChanged: ((Bool) -> Void)?
 
     @available(*, deprecated, message: "Please use the `autocapture` parameter instead.")
@@ -135,6 +136,7 @@ public class Configuration {
         // `trackingSessionEvents` has been replaced by `defaultTracking.sessions`
         autocapture: AutocaptureOptions = .sessions,
         identifyBatchIntervalMillis: Int = Constants.Configuration.IDENTIFY_BATCH_INTERVAL_MILLIS,
+        maxQueuedEventCount: Int = -1,
         migrateLegacyData: Bool = true,
         offline: Bool? = false
     ) {
@@ -167,6 +169,7 @@ public class Configuration {
         self.minTimeBetweenSessionsMillis = minTimeBetweenSessionsMillis
         self.autocapture = autocapture
         self.identifyBatchIntervalMillis = identifyBatchIntervalMillis
+        self.maxQueuedEventCount = maxQueuedEventCount
         self.migrateLegacyData = migrateLegacyData
         // Logging is OFF by default
         self.loggerProvider.logLevel = logLevel.rawValue

Tests/AmplitudeTests/AmplitudeTests.swift

@@ -843,6 +843,77 @@ final class AmplitudeTests: XCTestCase {
         wait(for: [deallocExpectation], timeout: 10.0)
     }
 
+    func testTrimQueuedEvents() {
+        class TrimTestStorage: Storage {
+
+            private var events: [URL: Int] = [:]
+
+            func addEventFile(url: URL, eventCount: Int) {
+                events[url] = eventCount
+            }
+
+            func write(key: StorageKey, value: Any?) throws {}
+
+            func read<T>(key: StorageKey) -> T? {
+                switch key {
+                case .EVENTS:
+                    return events.keys.sorted(by: {$0.absoluteString < $1.absoluteString}) as? T
+                default:
+                    return nil
+                }
+            }
+
+            func getEventsString(eventBlock: URL) -> String? {
+                guard let eventCount = events[eventBlock] else {
+                    return nil
+                }
+
+                let events = (0..<eventCount).map { BaseEvent(eventType: "Event \($0)") }
+
+                guard let jsonData = try? JSONEncoder().encode(events) else {
+                    return nil
+                }
+
+                return String(data: jsonData, encoding: .utf8)
+            }
+
+            func remove(eventBlock: URL) {
+                events[eventBlock] = nil
+            }
+
+            func splitBlock(eventBlock: URL, events: [BaseEvent]) {}
+
+            func rollover() {}
+
+            func reset() {}
+
+            func getResponseHandler(configuration: Configuration,
+                                    eventPipeline: EventPipeline,
+                                    eventBlock: URL,
+                                    eventsString: String) -> ResponseHandler {
+                abort()
+            }
+        }
+
+        let storage = TrimTestStorage()
+        storage.addEventFile(url: URL(string: "file://test/0")!, eventCount: 10)
+        storage.addEventFile(url: URL(string: "file://test/1")!, eventCount: 10)
+        storage.addEventFile(url: URL(string: "file://test/2")!, eventCount: 10)
+        storage.addEventFile(url: URL(string: "file://test/3")!, eventCount: 10)
+
+        let amplitude = Amplitude(configuration: Configuration(apiKey: "test-api-key",
+                                                               storageProvider: storage,
+                                                               maxQueuedEventCount: 15))
+        amplitude.waitForTrackingQueue()
+
+        let allEventBlocks: [URL] = storage.read(key: .EVENTS) ?? []
+
+        XCTAssert(!allEventBlocks.contains(URL(string: "file://test/0")!))
+        XCTAssert(!allEventBlocks.contains(URL(string: "file://test/1")!))
+        XCTAssert(allEventBlocks.contains(URL(string: "file://test/2")!))
+        XCTAssert(allEventBlocks.contains(URL(string: "file://test/3")!))
+    }
+
     func getDictionary(_ props: [String: Any?]) -> NSDictionary {
         return NSDictionary(dictionary: props as [AnyHashable: Any])
     }

Tests/AmplitudeTests/Utilities/EventPipelineTests.swift

@@ -122,7 +122,7 @@ final class EventPipelineTests: XCTestCase {
         pipeline?.storage?.rollover()
 
         let testEvent2 = BaseEvent(userId: "unit-test", deviceId: "unit-test-machine", eventType: "testEvent2")
-        try? pipeline.storage?.write(key: StorageKey.EVENTS, value: testEvent)
+        try? pipeline.storage?.write(key: StorageKey.EVENTS, value: testEvent2)
         pipeline.storage?.rollover()
 
         let httpResponseExpectation1 = expectation(description: "httpresponse1")