Combine - fetching and decoding JSON data

CombineWebservice.swift

import Foundation
import Combine

class Webservice {
    
    private let dataFetcher = DataFetcher()
    
    func fetch<T: Decodable>(url: URL) -> AnyPublisher<T, WebserviceError> {
        dataFetcher.fetchData(url: url)
            .receive(on: RunLoop.main)
            .decode(type: T.self, decoder: JSONDecoder())
            .mapError { error in
                if let error = error as? DecodingError {
                    var errorToReport = error.localizedDescription
                    switch error {
                    case .dataCorrupted(let context):
                        let details = context.underlyingError?.localizedDescription ?? context.codingPath.map { $0.stringValue }.joined(separator: ".")
                        errorToReport = "\(context.debugDescription) - (\(details))"
                    case .keyNotFound(let key, let context):
                        let details = context.underlyingError?.localizedDescription ?? context.codingPath.map { $0.stringValue }.joined(separator: ".")
                        errorToReport = "\(context.debugDescription) (key: \(key), \(details))"
                    case .typeMismatch(let type, let context), .valueNotFound(let type, let context):
                        let details = context.underlyingError?.localizedDescription ?? context.codingPath.map { $0.stringValue }.joined(separator: ".")
                        errorToReport = "\(context.debugDescription) (type: \(type), \(details))"
                    @unknown default:
                        break
                    }
                    return WebserviceError.parserError(reason: errorToReport)
                }  else {
                    return WebserviceError.apiError(reason: error.localizedDescription)
                }
            }
            .eraseToAnyPublisher()
    }
    
}

class DataFetcher {
    
    func fetchData(url: URL) -> AnyPublisher<Data, WebserviceError> {
        let request = URLRequest(url: url)
        
        return URLSession.DataTaskPublisher(request: request, session: .shared)
            .tryMap { data, response in
                guard let httpResponse = response as? HTTPURLResponse, 200..<300 ~= httpResponse.statusCode else {
                    throw WebserviceError.responseError(reason: "Couldn't connect to the server")
                }
                return data
            }
            .mapError { error in
                if let error = error as? WebserviceError {
                    return error
                } else {
                    return WebserviceError.apiError(reason: error.localizedDescription)
                }
            }
            .eraseToAnyPublisher()
    }
    
}

enum WebserviceError: Error, LocalizedError {
    
    case apiError(reason: String)
    case parserError(reason: String)
    case responseError(reason: String)
    
}