"""
Abstract: Custom that handles Drag and Drop for table views by acting as a datasource. 
"""
from Cocoa import *
import objc

class DragSupportDataSource (NSObject):
    # all the table views for which self is the datasource
    registeredTableViews = objc.ivar()

    def init(self):
        self = super(DragSupportDataSource, self).init()
        if self is None:
            return None

        self.registeredTableViews = NSMutableSet.alloc().init()
        return self;    

    # ******** table view data source necessities *********

    # We use this method as a way of registering for drag types for all 
    # the table views that will depend on us to implement D&D. Instead of 
    # setting up innumerable outlets, simply depend on the fact that every 
    # table view will ask its datasource for number of rows.
    def numberOfRowsInTableView_(self, aTableView):
        # this is potentially slow if there are lots of table views
        if not self.registeredTableViews.containsObject_(aTableView):
            aTableView.registerForDraggedTypes_([NSStringPboardType])
            #Cache the table views that have "registered" with us.
            self.registeredTableViews.addObject_(aTableView) 
        
        # return 0 so the table view will fall back to getting data from 
        # its binding
        return 0 

    def tableView_objectValueForTableColumn_row_(self, aView, aColumn, rowIdx):
        # return None so the table view will fall back to getting data from 
        # its binding 
        return None

    # put the managedobject's ID on the pasteboard as an URL
    def tableView_writeRowsWithIndexes_toPasteboard_(self, tv, rowIndexes, pboard):
        success = False
        
        infoForBinding = tv.infoForBinding_(NSContentBinding)
        if infoForBinding is not None:
            arrayController = infoForBinding.objectForKey_(NSObservedObjectKey)
            objects = arrayController.arrangedObjects().objectsAtIndexes_(
                    rowIndexes)

            objectIDs = NSMutableArray.array()
            for i in xrange(objects.count()):
                item = objects[i]
                objectID = item.objectID()
                representedURL = objectID.URIRepresentation()
                objectIDs.append(representedURL)

            pboard.declareTypes_owner_([NSStringPboardType], None)
            pboard.addTypes_owner_([NSStringPboardType], None)
            success = pboard.setString_forType_(
                    objectIDs.componentsJoinedByString_(', '), NSStringPboardType)
            
        return success

    # *************** actual drag and drop work *****************
    def tableView_validateDrop_proposedRow_proposedDropOperation_(
            self, tableView, info, row, operation):

        # Avoid drag&drop on self. This might be interersting to enable in 
        # light of ordered relationships
        if info.draggingSource() is not tableView:
            return NSDragOperationCopy
        else:
            return NSDragOperationNone

    def tableView_acceptDrop_row_dropOperation_(
            self, tableView, info, row, operation):

            success = False
            urlStrings = info.draggingPasteboard().stringForType_(NSStringPboardType)
        
            # get to the arraycontroller feeding the destination table view
            destinationContentBindingInfo = tableView.infoForBinding_(NSContentBinding)
            if destinationContentBindingInfo is not None:
            
                destinationArrayController = destinationContentBindingInfo.objectForKey_(NSObservedObjectKey)
                sourceArrayController = None
            
                # check for the arraycontroller feeding the source table view
                contentSetBindingInfo = destinationArrayController.infoForBinding_(NSContentSetBinding)
                if contentSetBindingInfo is not None:
                    sourceArrayController = contentSetBindingInfo.objectForKey_(NSObservedObjectKey)

                # there should be exactly one item selected in the source controller, otherwise the destination controller won't be able to manipulate the relationship when we do addObject:
                if (sourceArrayController is not None) and (sourceArrayController.selectedObjects().count() == 1):
                    context = destinationArrayController.managedObjectContext()
                    destinationControllerEntity = NSEntityDescription.entityForName_inManagedObjectContext_(destinationArrayController.entityName(), context)
                                
                    items = urlStrings.split(', ')
                    itemsToAdd = []
                
                    for i in xrange(len(items)):
                        urlString = items[i]
                        
                        # take the URL and get the managed object - assume 
                        # all controllers using the same context
                        url = NSURL.URLWithString_(urlString)
                        objectID = context.persistentStoreCoordinator().managedObjectIDForURIRepresentation_(url)
                        if objectID is not None:
                            object = context.objectRegisteredForID_(objectID)
                                                
                            # make sure objects match the entity expected by 
                            # the destination controller, and not already there
                            if object is not None and (object.entity() is destinationControllerEntity) and not (destinationArrayController.arrangedObjects().containsObject_(object)):
                                itemsToAdd.append(object)
                    
                    if len(itemsToAdd) > 0:
                        destinationArrayController.addObjects_(itemsToAdd)
                        success = True

            return success