APICaller.swift

import Foundation

final class APICaller {
    private let baseUrl:String = "http://localhost:8080/"
    
    static let sharedInstance = APICaller()
    
    private init() {}
    
    func performCallToEndpoint<T : Transmittable>(_ endpoint:String, using method:String, body:Transmittable?, responseType: T.Type, completion: @escaping (_ error:Error?, _ serverError:ServerError?, _ response:T?) -> Void) {
        
        let request = createURLRequest(toEndpoint: endpoint, using:method, body: body)
        
        let task = URLSession.shared.dataTask(with: request) { data, response, error in
            guard error == nil else {
                print(error!)
                completion(error, nil, nil)
                return
            }
            
            if let httpResponse = response as? HTTPURLResponse {
                guard httpResponse.statusCode == 200 else {
                    let serverError = ServerError.decode(from: data);
                    completion(nil, serverError, nil)
                    return
                }
            }
            
            let serverResponse = T.decode(from: data)
            completion(nil, nil, serverResponse)
        }
        
        task.resume()
    }
    
    private func createURLRequest(toEndpoint endpoint:String, using method:String, body:Transmittable?) -> URLRequest {
        let url = URL(string: baseUrl + endpoint)!
        
        var request = URLRequest(url: url)
        request.httpMethod = method
        if let body = body {
             request.httpBody = body.encode()
        }
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        
        return request
    }
}