AnalyticsService.swift

final class AnalyticsService: Sendable {
    static let shared = AnalyticsService()
    
    private let continuation: AsyncStream<AnalyticsEvent>.Continuation
    
    private init() {
        let (stream, continuation) = AsyncStream.makeStream(of: AnalyticsEvent.self)
        self.continuation = continuation
        
        // Background consumer
        Task.detached(priority: .utility) {
            var buffer: [AnalyticsEvent] = []
            
            for await event in stream {
                buffer.append(event)
                
                if buffer.count >= 50 {
                    await Self.send(buffer)
                    buffer.removeAll()
                }
            }
            
            // Flush remaining on termination
            if !buffer.isEmpty {
                await Self.send(buffer)
            }
        }
    }
    
    // Fire and forget — never blocks
    func track(_ event: AnalyticsEvent) {
        continuation.yield(event)
    }
    
    func shutdown() {
        continuation.finish()
    }
    
    private static func send(_ events: [AnalyticsEvent]) async {
        // Network call...
    }
}

struct AnalyticsEvent: Sendable {
    let name: String
    let timestamp: Date
    let properties: [String: String]
    
    static func screenView(_ name: String) -> AnalyticsEvent {
        AnalyticsEvent(name: "screen_view", timestamp: .now, properties: ["screen": name])
    }
}

// usage
AnalyticsService.shared.track(.screenView("Home"))