half-way generalized KVO undoer

SPLangUndoer.h

#import <Cocoa/Cocoa.h>
#import "SPLangNode.h"

@interface SPLangUndoer : NSObject {
	NSUndoManager *mgr;
	SPLangNode *root;
}
-(id)initWatchingTree:(SPLangNode*)tree withUndo:(NSUndoManager*)undoManager;
@end

SPLangUndoer.m

#import "SPLangUndoer.h"

@interface SPLangUndoer ()
@property (retain) NSUndoManager *mgr;
@property (retain) SPLangNode *root;
-(void)watchNodeWithSubtree:(SPLangNode*)node;
-(void)unwatchNodeWithSubtree:(SPLangNode*)node;
-(void)watchTranslation:(SPTranslation*)translation;
-(void)unwatchTranslation:(SPTranslation*)translation;
@end

static NSString *UndoKVOContext = @"UndoKVOContext";


@implementation SPLangUndoer
@synthesize mgr, root;
-(id)initWatchingTree:(SPLangNode*)tree withUndo:(NSUndoManager*)undoManager;
{
	self.mgr = undoManager;
	self.root = tree;
	[self watchNodeWithSubtree:tree];
	return self;
}
-(void)dealloc;
{
	[self unwatchNodeWithSubtree:self.root];
	self.mgr = nil;
	self.root = nil;
	[super dealloc];
}

-(void)watchNodeWithSubtree:(SPLangNode*)node;
{
	for (NSString *prop in [[node class] undoableKeyPaths])
		[node addObserver:self forKeyPath:prop options:NSKeyValueObservingOptionOld|NSKeyValueObservingOptionNew context:UndoKVOContext];
	
	for (SPTranslation *translation in [node valueForKey:@"translations"])
		[self watchTranslation:translation];

	for (SPLangNode *child in [node valueForKey:@"children"])
		[self watchNodeWithSubtree:child];
}
-(void)unwatchNodeWithSubtree:(SPLangNode*)node;
{
	for (SPLangNode *child in [node valueForKey:@"children"])
		[self unwatchNodeWithSubtree:child];
		
	for (SPTranslation *translation in [node valueForKey:@"translations"])
		[self unwatchTranslation:translation];
	
	for (NSString *prop in [[node class] undoableKeyPaths])
		[node removeObserver:self forKeyPath:prop];
}
-(void)watchTranslation:(SPTranslation*)translation;
{
	for (NSString *prop in [[translation class] undoableKeyPaths])
		[translation addObserver:self forKeyPath:prop options:NSKeyValueObservingOptionOld|NSKeyValueObservingOptionNew context:UndoKVOContext];
}
-(void)unwatchTranslation:(SPTranslation*)translation;
{
	for (NSString *prop in [[translation class] undoableKeyPaths])
		[translation removeObserver:self forKeyPath:prop];
}
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
	NSKeyValueChange kind = [[change objectForKey:NSKeyValueChangeKindKey] intValue];
	NSIndexSet *changedIndices = [change objectForKey:NSKeyValueChangeIndexesKey];
	NSUInteger anIndex = [changedIndices firstIndex]; // wrong but good enough?
	id old = [change objectForKey:NSKeyValueChangeOldKey];
	id new = [change objectForKey:NSKeyValueChangeNewKey];

	if([keyPath isEqual:@"children"]) {
		if(kind == NSKeyValueChangeRemoval || kind == NSKeyValueChangeReplacement || kind == NSKeyValueChangeSetting)
			for (SPLangNode *node in old) {
				[self unwatchNodeWithSubtree:node];
				[[mgr prepareWithInvocationTarget:object] insertObject:node inChildrenAtIndex:anIndex];
			}
		if(kind == NSKeyValueChangeInsertion || kind == NSKeyValueChangeReplacement || kind == NSKeyValueChangeSetting)
			for (SPLangNode *node in new) {
				[self watchNodeWithSubtree:node];
				[[mgr prepareWithInvocationTarget:object] removeObjectFromChildrenAtIndex:[[object valueForKey:@"children"] indexOfObject:node]];
			}
	} else if([keyPath isEqual:@"translations"]) {
		if(kind == NSKeyValueChangeRemoval || kind == NSKeyValueChangeReplacement || kind == NSKeyValueChangeSetting)
			for (SPTranslation *trans in old) {
				[self unwatchTranslation:trans];
				[[mgr prepareWithInvocationTarget:object] insertObject:trans inTranslationsAtIndex:anIndex];
			}
		if(kind == NSKeyValueChangeInsertion || kind == NSKeyValueChangeReplacement || kind == NSKeyValueChangeSetting)
			for (SPTranslation *trans in new) {
				[self watchTranslation:trans];
				[[mgr prepareWithInvocationTarget:[object mutableArrayValueForKey:@"translations"]] removeObject:trans]; 
			}
	} else {
		[[mgr prepareWithInvocationTarget:object] setValue:old forKeyPath:keyPath];
	}
	
	
}
@end