added NSProgress support for migrations

CoreStore/Convenience Helpers/NSProgress+Convenience.swift

@@ -0,0 +1,112 @@
+//
+//  NSProgress+Convenience.swift
+//  CoreStore
+//
+//  Copyright (c) 2015 John Rommel Estropia
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+import Foundation
+import GCDKit
+
+
+// MARK: - NSProgress
+
+public extension NSProgress {
+    
+    // MARK: Public
+    
+    public func setProgressHandler(closure: ((progress: NSProgress) -> Void)?) {
+        
+        self.progressObserver.progressHandler = closure
+    }
+    
+    
+    // MARK: Private
+    
+    private struct PropertyKeys {
+        
+        static var progressObserver: Void?
+    }
+    
+    private var progressObserver: ProgressObserver {
+        
+        get {
+            
+            let object: AnyObject? = getAssociatedObjectForKey(&PropertyKeys.progressObserver, inObject: self)
+                
+            if let observer = object as? ProgressObserver {
+                
+                return observer
+            }
+            
+            let observer = ProgressObserver(self)
+            setAssociatedRetainedObject(
+                observer,
+                forKey: &PropertyKeys.progressObserver,
+                inObject: self
+            )
+            
+            return observer
+        }
+    }
+}
+
+
+@objc private final class ProgressObserver: NSObject {
+    
+    private weak var progress: NSProgress?
+    private var progressHandler: ((progress: NSProgress) -> Void)?
+    
+    private init(_ progress: NSProgress) {
+        
+        self.progress = progress
+        super.init()
+        
+        progress.addObserver(
+            self,
+            forKeyPath: "fractionCompleted",
+            options: .New,
+            context: nil
+        )
+    }
+    
+    deinit {
+        
+        progress?.removeObserver(self, forKeyPath: "fractionCompleted")
+    }
+    
+    override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
+        
+        guard let progress = self.progress where object as? NSProgress == progress && keyPath == "fractionCompleted" else {
+            
+            super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
+            return
+        }
+        
+        GCDQueue.Main.async { [weak self] () -> Void in
+            
+            if let strongSelf = self, let progress = strongSelf.progress {
+                
+                strongSelf.progressHandler?(progress: progress)
+            }
+        }
+    }
+}