Parse JSON from API with Swift

ParseJSONFromAPI.swift

import Foundation
import UIKit

// Data to JSON
typealias JSON = [String: AnyObject]

extension Data {
    func toJSON() -> JSON? {
        var json: JSON? = nil
        
        do {
            if let jsonObj = try JSONSerialization.jsonObject(with: self, options: .mutableContainers) as? JSON {
                json = jsonObj
            }
        } catch {
            print("JSON casting error")
        }
        
        return json
    }
}

// Create API Model
struct Song {
    var artistName: String
    var id: String
    var name: String
    var releaseDate: String
    var url: String
}

// Define Error
enum APIError: Error {
    case error(String)
    case errorURL
    
    var localizedDescription: String {
        switch self {
        case .error(let string):
            return string
        case .errorURL:
            return "URL String is error."
        }
    }
}

// Load API --> update call back
func loadAPI(completed: @escaping (Error?, [Song]?) -> Void) {
    // Create Request
    let urlString = "https://rss.applemarketingtools.com/api/v2/us/music/most-played/10/songs.json"
    guard let url = URL(string: urlString) else {
        // call back
        completed(APIError.errorURL, nil)
        return
    }
    
    var request = URLRequest(url: url)
    // add method
    request.httpMethod = "GET"
    
    // Connection
    // config
    let config = URLSessionConfiguration.ephemeral
    config.waitsForConnectivity = true
    
    // URLSession
    let session = URLSession(configuration: config)
    // task + call bacl
    let task = session.dataTask(with: request) { data, response, error in
        // main thread
        DispatchQueue.main.async {
            // check error
            if let error = error {
                // Request failed
                // call back
                completed(error, nil)
            } else {
                // Request success
                print("API OKAY!")
                // check data
                if let data = data,
                   let json = data.toJSON() {
                    // parse json
                    // Feed > Results > Item
                    let feed = json["feed"] as! JSON // dictionary
                    let results = feed["results"] as! [JSON] // array
                    
                    // array items
                    var songs: [Song] = []
                    
                    for item in results {
                        // get infor
                        let artistName = item["artistName"] as! String
                        let id = item["id"] as! String
                        let name = item["name"] as! String
                        let releaseDate = item["releaseDate"] as! String
                        let url = item["url"] as! String
                        // create object
                        let song = Song(artistName: artistName,
                                        id: id,
                                        name: name,
                                        releaseDate: releaseDate,
                                        url: url)
                        songs.append(song)
                    }
                    
                    // call back
                    completed(nil, songs)
                    
                } else {
                    // call back
                    completed(APIError.error("Data format is error."), nil)
                }
            }
        }
    }
    
    // resume
    task.resume()
}

// call api
loadAPI { error, songs in
    if let error = error {
        print("ERROR: \(error.localizedDescription)")
    } else {
        if let songs = songs {
            for song in songs {
                print("name: \(song.name) - \(song.artistName)")
            }
        } else {
            print("Data error!")
        }
    }
}