Dynamic category icons – Foursquare approach

gistfile1.m

- (AFHTTPRequestOperation *)imageFetchOperationForCategoryWithURL:(NSURL *)URL success:(void(^)(AFHTTPRequestOperation *operation, id response))success failure:(void(^)(AFHTTPRequestOperation *operation, NSError *error))failure
{
  static NSString *categoriesCacheDirectory;
	static NSCache *inMemoryCache;
	static dispatch_once_t onceToken;
	dispatch_once(&onceToken, ^{
		inMemoryCache = [[NSCache alloc] init];

		categoriesCacheDirectory =  [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
		categoriesCacheDirectory = [categoriesCacheDirectory stringByAppendingPathComponent:@"location_icons"];
	});
	
	NSString *urlHash = [[URL absoluteString] MD5Sum];
	__block UIImage *image = nil;

	// 1. We check in memory cache
	image = [inMemoryCache objectForKey:urlHash];
	if (image) {
		if (success) {
			success(nil, image);
		}
		return nil;
	}
	
	// 2. Trying to find image locally and pull it to cache
	NSString *filePath = [[categoriesCacheDirectory stringByAppendingPathComponent:urlHash] stringByAppendingPathExtension:@"png"];
	if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
		NSData *data = [NSData dataWithContentsOfFile:filePath];
		image = [UIImage imageWithData:data];
		
		// 2.1 Put it in the cache
		[inMemoryCache setObject:image
						  forKey:urlHash
							cost:0];
		if (success) {
			success(nil, image);
		}
		return nil;
	}
	
	// 3. Finally we have to pull the image from the network and compose custom icon
	NSURLRequest *request = [NSURLRequest requestWithURL:URL];
	AFHTTPRequestOperation *operation = [self HTTPRequestOperationWithRequest:request success:^(AFHTTPRequestOperation *operation, id responseObject) {
		
		// 3.0 Sanity
		if (![responseObject isKindOfClass:[NSData class]]) {
			if (failure) {
				failure(operation, [NSError errorWithDomain:NSCocoaErrorDomain
													   code:0
												   userInfo:@{ NSLocalizedDescriptionKey : [NSString stringWithFormat:@"Unexpected response type, expected NSData, got %@", [responseObject class]] }]);
			}
			return;
		}
		
		// 3.1 Make sure cache directory exist
		BOOL isDirectory = NO;
		BOOL isExist = [[NSFileManager defaultManager] fileExistsAtPath:categoriesCacheDirectory
															isDirectory:&isDirectory];
		if (!isExist || !isDirectory) {
			NSDictionary *attributes = nil;
			[[NSFileManager defaultManager] createDirectoryAtPath:categoriesCacheDirectory
									  withIntermediateDirectories:YES
													   attributes:attributes
															error:nil];
		}


		// 3.2 Compose custom image
		image = TPXCustomCategoryImageFromImageMaskData( responseObject );
		NSData *data = UIImagePNGRepresentation(image);

		// 3.3 Save to cache directory
		[data writeToFile:filePath
			   atomically:NO];
		
		// 3.4 Cache it!
		[inMemoryCache setObject:image
						  forKey:urlHash
							cost:0];
		
		if (success) {
			success(operation, image);
		}
	} failure:failure];
	
	[self enqueueHTTPRequestOperation:operation];
	
	return operation;
}

gistfile2.c

UIImage *TPXCustomCategoryImageFromImageMaskData(NSData *imageData)
{
	UIImage *iconImage = [UIImage imageWithData:imageData];
	
	CGSize imageSize = CGSizeMake(50, 50);
	CGRect imageFrame = (CGRect){CGPointZero, imageSize};
	CGFloat scale = [UIScreen mainScreen].scale;
	UIGraphicsBeginImageContextWithOptions(imageSize, NO, scale);
	CGContextRef context = UIGraphicsGetCurrentContext();
	CGRect outlineFrame = CGRectInset(imageFrame, 1, 1);
	UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:outlineFrame
													 byRoundingCorners:UIRectCornerAllCorners
														   cornerRadii:CGSizeMake(6, 6)];
	
	[[UIColor colorWithHue:0.056f
				saturation:0.030f
				brightness:0.773f
					 alpha:1.000f] setStroke];
	
	[[UIColor colorWithHue:0.083f
				saturation:0.041f
				brightness:0.961f
					 alpha:1.000f] setFill];
	
	bezierPath.lineWidth = 1;
	[bezierPath stroke];
	[bezierPath fill];
	
	[[UIColor clearColor] setStroke];
	
	// Create a mask
	CGImageRef originalImageRef = iconImage.CGImage;
	CGContextTranslateCTM(context, 0, CGRectGetHeight(imageFrame));
	CGContextScaleCTM(context, 1.0, -1.0);
	CGRect centredImageRect = (CGRect){CGPointZero, imageSize};
	centredImageRect = CGRectInset(centredImageRect, 5, 5);
	CGContextClipToMask(context, centredImageRect, originalImageRef);

	// Fill it
	[[UIColor colorWithWhite:0.545f
					   alpha:1.000f] setFill];
	CGContextFillRect(context, imageFrame);
	
	UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
	UIGraphicsEndImageContext();
	
	return image;
}