NetworkCall.swift

public typealias AccessTokenPublisher = AnyPublisher<String, Error>


func fetchAuthorizedURLRequest(_ urlRequest: URLRequest,
                               accessToken: AccessTokenPublisher) -> AnyPublisher<Data, Error> {
    accessToken
        .flatMap { (accessToken: String) -> AnyPublisher<(data: Data, response: URLResponse), Error> in

            URLSession.shared.dataTaskPublisher(
                for: urlRequest.requestWithToken(accessToken)
            )
            // The URLError should be mapped to Error
            .mapError { (urlError: URLError) -> Error in
                urlError
            }
            .eraseToAnyPublisher()
        }
        .tryMap { result in
            guard let urlResponse = result.response as? HTTPURLResponse, (200...299).contains(urlResponse.statusCode) else {
                let statusCode = (result.response as? HTTPURLResponse)?.statusCode ?? 500

                throw APIError(
                    statusCode: statusCode,
                    data: result.data)
            }
            return result.data
        }
        .eraseToAnyPublisher()
}

extension URLRequest {
    func requestWithToken(_ token: String?) -> URLRequest {
        var newRequest = self
        var value: String? = nil
        if let token = token {
            value = "Bearer \(token)"
        }
        newRequest.setValue(value, forHTTPHeaderField: "Authorization")
        return newRequest
    }
}

struct APIError: Decodable, Error, CustomDebugStringConvertible {
    let statusCode: Int
    let data: Data

    var debugDescription: String {
        let string = String(data: data, encoding: .utf8) ?? "<NONE>"
            return "\(statusCode): \(string)"
        }
}