ALAssetsLibrary+CustomPhotoAlbum.m

//
//  ALAssetsLibrary category to handle a custom photo album
//
//  Created by Marin Todorov on 10/26/11.
//  Copyright (c) 2011 Marin Todorov. All rights reserved.
//

#import "ALAssetsLibrary+CustomPhotoAlbum.h"

@interface ALAssetsLibrary (Private)

-(void)_addAssetURL:(NSURL *)assetURL
            toAlbum:(NSString *)albumName
       failureBlock:(ALAssetsLibraryAccessFailureBlock)failureBlock;

@end


@implementation ALAssetsLibrary (CustomPhotoAlbum)

#pragma mark - Public Method

- (void)saveImage:(UIImage *)image
          toAlbum:(NSString *)albumName
  completionBlock:(ALAssetsLibraryWriteImageCompletionBlock)completionBlock
     failureBlock:(ALAssetsLibraryAccessFailureBlock)failureBlock {
  // write the image data to the assets library (camera roll)
  [self writeImageToSavedPhotosAlbum:image.CGImage
                         orientation:(ALAssetOrientation)image.imageOrientation 
                     completionBlock:^(NSURL *assetURL, NSError *error) {
                       // run the completion block for writing image to saved
                       //   photos album
                       completionBlock(assetURL, error);
                       
                       // if an error occured, do not try to add the asset to
                       //   the custom photo album
                       if (error != nil)
                         return;
                       
                       // add the asset to the custom photo album
                       [self _addAssetURL:assetURL
                                  toAlbum:albumName
                             failureBlock:failureBlock];
                     }];
}

- (void)saveVideo:(NSURL *)videoUrl
          toAlbum:(NSString *)albumName
  completionBlock:(ALAssetsLibraryWriteImageCompletionBlock)completionBlock
     failureBlock:(ALAssetsLibraryAccessFailureBlock)failureBlock {
    // write the video to the assets library (camera roll)
    [self writeVideoAtPathToSavedPhotosAlbum: videoUrl
                             completionBlock:^(NSURL *assetURL, NSError *error) {
                           // run the completion block for writing image to saved
                           //   photos album
                           completionBlock(assetURL, error);
                           
                           // if an error occured, do not try to add the asset to
                           //   the custom photo album
                           if (error != nil)
                               return;
                           
                           // add the asset to the custom photo album
                           [self _addAssetURL:assetURL
                                      toAlbum:albumName
                                 failureBlock:failureBlock];
                       }];
}

#pragma mark - Private Method

-(void)_addAssetURL:(NSURL *)assetURL
            toAlbum:(NSString *)albumName
       failureBlock:(ALAssetsLibraryAccessFailureBlock)failureBlock {
  __block BOOL albumWasFound = NO;
  
  ALAssetsLibraryGroupsEnumerationResultsBlock enumerationBlock;
  enumerationBlock = ^(ALAssetsGroup *group, BOOL *stop) {
    // compare the names of the albums
    if ([albumName compare:[group valueForProperty:ALAssetsGroupPropertyName]] == NSOrderedSame) {
      // target album is found
      albumWasFound = YES;
      
      // get a hold of the photo's asset instance
      [self assetForURL:assetURL 
            resultBlock:^(ALAsset *asset) {
              // add photo to the target album
              [group addAsset:asset];
            }
           failureBlock:failureBlock];
      
      // album was found, bail out of the method
      return;
    }
    
    if (group == nil && albumWasFound == NO) {
      // photo albums are over, target album does not exist, thus create it
      
      // Since you use the assets library inside the block,
      //   ARC will complain on compile time that there’s a retain cycle.
      //   When you have this – you just make a weak copy of your object.
      //
      //   __weak ALAssetsLibrary * weakSelf = self;
      //
      // by @Marin.
      //
      // I don't use ARC right now, and it leads a warning.
      // by @Kjuly
      ALAssetsLibrary * weakSelf = self;
      
      // create new assets album
      [self addAssetsGroupAlbumWithName:albumName 
                            resultBlock:^(ALAssetsGroup *group) {
                              // get the photo's instance
                              [weakSelf assetForURL:assetURL 
                                        resultBlock:^(ALAsset *asset) {
                                          // add photo to the newly created album
                                          [group addAsset:asset];
                                        }
                                       failureBlock:failureBlock];
                            }
                           failureBlock:failureBlock];
      
      // should be the last iteration anyway, but just in case
      return;
    }
  };
  
  // search all photo albums in the library
  [self enumerateGroupsWithTypes:ALAssetsGroupAlbum 
                      usingBlock:enumerationBlock
                    failureBlock:failureBlock];
}

@end