[AltStore] Refactors fetch apps logic to use Source model objects

AltStore/Operations/FetchSourceOperation.swift

@@ -0,0 +1,58 @@
+//
+//  FetchSourceOperation.swift
+//  AltStore
+//
+//  Created by Riley Testut on 7/30/19.
+//  Copyright © 2019 Riley Testut. All rights reserved.
+//
+
+import Foundation
+import Roxas
+
+@objc(FetchSourceOperation)
+class FetchSourceOperation: ResultOperation<Source>
+{
+    let sourceURL: URL
+    
+    private let session = URLSession(configuration: .default)
+    
+    private lazy var dateFormatter: DateFormatter = {
+        let dateFormatter = DateFormatter()
+        dateFormatter.dateFormat = "yyyy-MM-dd"
+        return dateFormatter
+    }()
+    
+    init(sourceURL: URL)
+    {
+        self.sourceURL = sourceURL
+    }
+    
+    override func main()
+    {
+        super.main()
+        
+        let dataTask = self.session.dataTask(with: self.sourceURL) { (data, response, error) in
+            DatabaseManager.shared.persistentContainer.performBackgroundTask { (context) in
+                do
+                {
+                    let (data, _) = try Result((data, response), error).get()
+                    
+                    let decoder = JSONDecoder()
+                    decoder.dateDecodingStrategy = .formatted(self.dateFormatter)
+                    decoder.managedObjectContext = context
+                    
+                    let source = try decoder.decode(Source.self, from: data)
+                    self.finish(.success(source))
+                }
+                catch
+                {
+                    self.finish(.failure(error))
+                }
+            }
+        }
+        
+        self.progress.addChild(dataTask.progress, withPendingUnitCount: 1)
+        
+        dataTask.resume()
+    }
+}