Analytics.swift

protocol TrackingEventType {
    var identifier: String { get }
    var properties: [String: Any] { get }
}

protocol TrackingProviderType {
    func track(event: TrackingEventType)
    func associate(with user: User)
    func disassociateUser()
    func setup()
}

protocol TrackingClientType: TrackingProviderType {
    var providers: [TrackingProviderType] { get }
    func add(provider: TrackingProviderType)
}

enum UserEvents {
    case created(user: User)
    case openApp
    case bought(product: Product)
    case sentMessage
}

extension UserEvents: TrackingEventType {
    var identifier: String {
        switch self {
        case .created:
            return "user.created"
        case .openApp:
            return "user.open-app"
        case .bought:
            return "user.bought"
        case .sentMessage:
            return "user.sent-message"
        }
    }

    var properties: [String: Any] {
        switch self {
        case let .created(user):
            return ["name": user.name, "age": user.age]
        case let .bought(product):
            return ["title": product.title, "price": product.price]
        default:
            return [:]
        }
    }
}

final class AmplitudeProvider: TrackingProviderType {
    private let amplitude = Amplitude()

    func setup() {
        amplitude.initializeApiKey("XXXX-XXXX")
        amplitude.eventUploadPeriodSeconds = 120
    }

    func track(event: TrackingEventType) {
        amplitude.logEvent(event.identifier, withEventProperties: event.properties)
    }

    func associate(with user: User) {
        amplitude.setUserId(user.id)

        let identify = AMPIdentify()
        identify.set("name", value: user.name)
        identify.set("price", value: user.price)
        amplitude.identify(identify)
    }

    func disassociateUser() {
        amplitude.setUserId(nil)
    }
}

class TrackingClient: TrackingClientType {
    var providers = [TrackingProviderType]()

    func add(provider: TrackingProviderType) {
        providers.append(provider)
    }

    func track(event: TrackingEventType) {
        for provider in providers {
            provider.track(event: event)
        }
    }
  
    func associate(with user: User) {
        for provider in providers {
            provider.associate(with: user)
        }
    }

    func disassociateUser() {
        for provider in providers {
            provider.disassociateUser()
        }
    }

    func setup() {
        for provider in providers {
            provider.setup()
        }
    }
}