support for permalink and external url

Consolidate GetURL AppleEvent handling into AppDelegate+Scriptability
file
Add scripting access groups to sdef
Add exists command
Add ‘permalink’ and ‘external url’ properties to the article scripting
object
Add a unit test to verify the behavior of ‘current article’

Evergreen/Scriptability/AppDelegate+Scriptability.swift

@@ -19,10 +19,60 @@
 import Foundation
 import Data
 
+protocol AppDelegateAppleEvents {
+    func installAppleEventHandlers()
+    func getURL(_ event: NSAppleEventDescriptor, _ withReplyEvent: NSAppleEventDescriptor)
+}
+
 protocol ScriptingAppDelegate {
     var  scriptingCurrentArticle: Article?  {get}
     var  scriptingSelectedArticles: [Article]  {get}
     var  scriptingMainWindowController:ScriptingMainWindowController? {get}
 }
 
+extension AppDelegate : AppDelegateAppleEvents {
+    
+    // MARK: GetURL Apple Event
+
+    func installAppleEventHandlers() {
+        NSAppleEventManager.shared().setEventHandler(self, andSelector: #selector(AppDelegate.getURL(_:_:)), forEventClass: AEEventClass(kInternetEventClass), andEventID: AEEventID(kAEGetURL))
+    }
+    
+    @objc func getURL(_ event: NSAppleEventDescriptor, _ withReplyEvent: NSAppleEventDescriptor) {
+
+        guard let urlString = event.paramDescriptor(forKeyword: keyDirectObject)?.stringValue else {
+            return
+        }
+
+        let normalizedURLString = urlString.rs_normalizedURL()
+        if !normalizedURLString.rs_stringMayBeURL() {
+            return
+        }
+
+        DispatchQueue.main.async {
+
+            self.addFeed(normalizedURLString)
+        }
+    }
+}
+
+class EvergreenExistsCommand : NSExistsCommand {
+    
+    // cocoa default behavior doesn't work here, because of cases where we define an object's property
+    // to be another object type.  e.g., 'permalink of the current article' parses as
+    //    <property> of <property> of <top level object>
+    // cocoa would send the top level object (the app) a doesExist message for a nested property, and
+    // it errors out because it doesn't know how to handle that
+    // What we do instead is simply see if the defaultImplementation errors, and if it does, the object
+    // must not exist.  Otherwise, we return the result of the defaultImplementation
+    // The wrinkle is that it is possible that the direct object is a list, so we need to
+    // handle that case as well
+    
+    override func performDefaultImplementation() -> Any? {
+         guard let result = super.performDefaultImplementation() else { return NSNumber(booleanLiteral:false) }
+         return result
+        // return NSNumber(booleanLiteral:true)
+         //  scriptingContainer.handleDoObjectsExist(command:self)
+    }
+}