Photo.m

#import "UIImage+Resizing.h"

@implementation Photo 

@dynamic imagePath;
@dynamic thumbnailPath;

static const CGFloat kThumbnailWidth  = 75.0f;
static const CGFloat kThumbnailHeight = 75.0f;
static const CGFloat kJPEGQuality     = 0.85f;

#pragma mark -
#pragma mark Path generators

/**
 * Generates a unique path in the photos folder for the image that is to be saved to disk.
 * @return a generated path
 */
- (NSString*) generatePath
{	
	NSTimeInterval timeIntervalSeconds = [NSDate timeIntervalSinceReferenceDate];
	unsigned long long nanoseconds = (unsigned long long) floor(timeIntervalSeconds * 1000000);
	
	return [NSString stringWithFormat:@"Photos/%qu.jpg", nanoseconds];
}

/**
 * Generates a full path to the image, since the imagePath property only stores the path relative to
 * the Documents folder. The location of the application folder (and in turn, the Documents folder)
 * changes on every app deployment. This function fetches the Documents folder location and appends
 * the imagePath string to it, which results in a full path to the image.
 *
 * @return a full path to the image
 */
- (NSString*) fullImagePath
{
	NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
	return [(NSString*)[paths objectAtIndex:0] stringByAppendingPathComponent:self.imagePath];
}

/**
 * Generates a full path to the thumbnail. See fullImagePath description for details.
 * @return a full path to the thumbnail
 */
- (NSString*) fullThumbnailPath
{
	NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
	return [(NSString*)[paths objectAtIndex:0] stringByAppendingPathComponent:self.thumbnailPath];
}


#pragma mark -
#pragma mark Virtual image setter

/**
 * This method creates a thumbnail from the given image, saves both the thumbnail and the image
 * to disk, and updates thumbnailPath and imagePath accordingly.
 *
 * @param image The image to be saved to disk
 */
- (void) setImage:(UIImage*)image
{
	UIImage* thumbnail = [image resizedImageWithSize:CGSizeMake(kThumbnailWidth, kThumbnailHeight)];
	
	// Get autoreleased NSData representations
	NSData* imageData = UIImageJPEGRepresentation(image, kJPEGQuality);
	NSData* thumbnailData = UIImageJPEGRepresentation(thumbnail, kJPEGQuality);
	
	// Generate image path and save the image
	self.imagePath = [self generatePath];
	if ([imageData writeToFile:[self fullImagePath] atomically:YES] == NO) {
		// Saving failed, clean up and bail
		self.imagePath = nil;
		return;
	}
	
	// Generate thumbnail path and save the thumbnail
	self.thumbnailPath = [self generatePath];
	if ([thumbnailData writeToFile:[self fullThumbnailPath] atomically:YES] == NO) {
		// Saving failed, clean up
		[[NSFileManager defaultManager] removeItemAtPath:self.imagePath error:nil];
		self.imagePath = nil;
		self.thumbnailPath = nil;
		
		// Bail
		return;
	}
}


#pragma mark -
#pragma mark Virtual getter methods

/**
 * Virtual image getter method - returns an autoreleased UIImage object loaded from imagePath.
 * @return an autoreleased image, or nil if there was an error
 */
- (UIImage*) image
{
	if (self.imagePath == nil) {
		return nil;
	}
	
	return [[[UIImage alloc] initWithContentsOfFile:[self fullImagePath]] autorelease];
}


/**
 * Virtual thumbnail getter method - returns an autoreleased UIImage object loaded from thumbnailPath.
 * @return an autoreleased thumbnail, or nil if there was an error
 */
- (UIImage*) thumbnail
{
	if (self.thumbnailPath == nil) {
		return nil;
	}
	
	return [[[UIImage alloc] initWithContentsOfFile:[self fullThumbnailPath]] autorelease];
}

@end