array-diff.m

@implementation NSArray (FDMapping)

// import, array diff
// https://github.com/glebd/google-toolbox-for-mac/blob/master/Foundation/GTMNSArray%2BMerge.m
// https://github.com/Wondermall/Doppelganger
// https://github.com/Basket/BKDeltaCalculator/blob/master/BKDeltaCalculator/BKDeltaCalculator.m

+ (void)ag_mapSourceArray:(NSArray *)source toDestArray:(NSArray *)dest sourceKey:(id (^)(id obj))sourceKeyBlock destKey:(id (^)(id obj))destKeyBlock compare:(NSComparisonResult (^)(id, id))compareBlock match:(void (^)(id, id))matchBlock {
    NSArray *sortedSource = [source sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        return compareBlock(sourceKeyBlock(obj1), sourceKeyBlock(obj2));
    }];
    NSArray *sortedDest = [dest sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        return compareBlock(destKeyBlock(obj1), destKeyBlock(obj2));
    }];
    
    // iterators
    NSEnumerator *destIterator = [sortedDest objectEnumerator];
    NSEnumerator *sourceIterator = [sortedSource objectEnumerator];
    id destObject = [destIterator nextObject];
    id sourceObject = [sourceIterator nextObject];
    
    while (destObject || sourceObject) {
        NSComparisonResult comparison;
        if (!destObject) { // if the import list has run out, the import identifier sorts last (i.e. remove remaining objects)
            comparison = NSOrderedDescending;
            
        } else if (!sourceObject) { // if managed object list has run out, the import identifier sorts first (i.e. add remaining objects)
            comparison = NSOrderedAscending;
            
        } else { // If neither list has run out, compare with the object
            comparison = compareBlock(destKeyBlock(destObject), sourceKeyBlock(sourceObject));
        }
        
        if (comparison == NSOrderedSame) {  // Identifiers match
            matchBlock(sourceObject, destObject);
            
            // Move ahead in both lists
            destObject = [destIterator nextObject];
            sourceObject = [sourceIterator nextObject];
            
        } else if (comparison == NSOrderedAscending) {  // Imported item sorts before stored item - add dest object
            destObject = [destIterator nextObject];
            
        } else {  // The stored item is not among those imported, and should be removed, then move ahead to the next stored item - remove source object
            sourceObject = [sourceIterator nextObject];
            
        }
    }
}