AddQueryItemsBehavior.swift

enum SharedNetworkClient {
    static let googleMaps: NetworkClient = {
        let keyBehavior = AddQueryItemsBehavior(name: "key", value: "$YR_KEY")
        let configuration = RequestConfiguration(baseURLString: "https://maps.googleapis.com/", defaultRequestBehavior: keyBehavior)
        let client = NetworkClient(configuration: configuration)
        return client
    }()
}

struct AddQueryItemsBehavior: RequestBehavior {
    let queryItems: [URLQueryItem]

    init(queryItems: [URLQueryItem]) {
        self.queryItems = queryItems
    }
    init(name: String, value: String?) {
        self.init(queryItems: [URLQueryItem(name: name, value: value)])
    }

    func modify(request: URLRequest) -> URLRequest {
        var copy = request

        guard let url = copy.url else { fatalError() }

        guard var urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: false) else { fatalError() }

        urlComponents.queryItems = (urlComponents.queryItems ?? []) + queryItems

        guard let newURL = urlComponents.url else { fatalError() }

        copy.url = newURL

        return copy
    }
}