import Foundation

// this is either a third party SDK interface or your own analytics client implementation
// that actually sends JSON across the wire to deliver tracked analytics events
protocol AnalyticsClient {
    func sendAnalyticsDataToTheBackend(_ eventJSON: [String: Any])
}

final class ConcreteAnalyticsClient: AnalyticsClient {
    func sendAnalyticsDataToTheBackend(_ eventJSON: [String: Any]) {
        print("sending event json: \(eventJSON)")
    }
}

// This is the analytics interface that the rest of your app relies on
protocol AnalyticsInterface {
    init(_ analyticsClient: AnalyticsClient)

    func track(_ event: AnalyticsEvent)
}

// this is a concrete implementation of analytics that is used by your app
final class Analytics: AnalyticsInterface {

    private let analyticsClient: AnalyticsClient

    required init(_ analyticsClient: AnalyticsClient) {
        self.analyticsClient = analyticsClient
    }

    func track(_ event: AnalyticsEvent) {
        print("tracking event \(event.asDictionary())")
        // here it suppose to use the injected analyitcs client actually issue a request to send over the JSON of the tracked event
        analyticsClient.sendAnalyticsDataToTheBackend(event.asDictionary())
    }
}

// this is a generic event that can be used for various kind of event tracking across your app
class AnalyticsEvent {
    let eventName: String
    var uiElement: String?
    var screen: String?

    init(_ eventName: String, uiElement: String? = nil, screen: String? = nil) {
        self.eventName = eventName
        self.uiElement = uiElement
        self.screen = screen
    }

    func asDictionary() -> [String: String] {
        return [
            "event_name": eventName,
            "screen": screen != nil ? screen! : "",
            "element": uiElement != nil ? uiElement! : ""
        ]
    }
}

// this is a case specific event that is crafted only for tracking login
class LoginAnalyticsEvent: AnalyticsEvent {
    let loggedInUserId: Int

    init(loggedInUserId: Int) {
        self.loggedInUserId = loggedInUserId
        super.init("User Logged In", uiElement: nil, screen: nil)
    }

    override func asDictionary() -> [String : String] {
        let eventDictionary = super.asDictionary()

        var fullDictionary = [
            "user_id": String(loggedInUserId)
        ]
        fullDictionary.merge(eventDictionary) { (newDictionaryValue, _) -> String in return newDictionaryValue }

        return fullDictionary
    }
}


// This is how you'd use analytics and events across your codebase

let analyticsClient = ConcreteAnalyticsClient()
let analytics = Analytics(analyticsClient)

var buttonTappedEvent = AnalyticsEvent("Tapped")
buttonTappedEvent.screen = "My Awesome Screen"
analytics.track(buttonTappedEvent)

let loginEvent = LoginAnalyticsEvent(loggedInUserId: 3)
analytics.track(loginEvent)