text: /*
   * This file is part of the SDWebImage package.
   * (c) Olivier Poitrey <rs@dailymotion.com>
   *
   * For the full copyright and license information, please view the LICENSE
   * file that was distributed with this source code.
   */
  
  #import <Foundation/Foundation.h>
  #import "SDWebImageManager.h"
  
  @class SDWebImagePrefetcher;
  
  @interface SDWebImagePrefetchToken : NSObject <SDWebImageOperation>
  
  /**
   * Cancel the current prefetching.
   */
  - (void)cancel;
  
  /**
   list of URLs of current prefetching.
   */
  @property (nonatomic, copy, readonly, nullable) NSArray<NSURL *> *urls;
  
  @end
  
  @protocol SDWebImagePrefetcherDelegate <NSObject>
  
  @optional
  
  /**
   * Called when an image was prefetched. Which means it's called when one URL from any of prefetching finished.
   *
   * @param imagePrefetcher The current image prefetcher
   * @param imageURL        The image url that was prefetched
   * @param finishedCount   The total number of images that were prefetched (successful or not)
   * @param totalCount      The total number of images that were to be prefetched
   */
  - (void)imagePrefetcher:(nonnull SDWebImagePrefetcher *)imagePrefetcher didPrefetchURL:(nullable NSURL *)imageURL finishedCount:(NSUInteger)finishedCount totalCount:(NSUInteger)totalCount;
  
  /**
   * Called when all images are prefetched. Which means it's called when all URLs from all of prefetching finished.
   * @param imagePrefetcher The current image prefetcher
   * @param totalCount      The total number of images that were prefetched (whether successful or not)
   * @param skippedCount    The total number of images that were skipped
   */
  - (void)imagePrefetcher:(nonnull SDWebImagePrefetcher *)imagePrefetcher didFinishWithTotalCount:(NSUInteger)totalCount skippedCount:(NSUInteger)skippedCount;
  
  @end
  
  typedef void(^SDWebImagePrefetcherProgressBlock)(NSUInteger noOfFinishedUrls, NSUInteger noOfTotalUrls);
  typedef void(^SDWebImagePrefetcherCompletionBlock)(NSUInteger noOfFinishedUrls, NSUInteger noOfSkippedUrls);
  
  /**
   * Prefetch some URLs in the cache for future use. Images are downloaded in low priority.
   */
  @interface SDWebImagePrefetcher : NSObject
  
  /**
   * The web image manager used by prefetcher to prefetch images.
   * @note You can specify a standalone manager and downloader with custom configuration suitable for image prefetching. Such as `currentDownloadCount` or `downloadTimeout`.
   */
  @property (strong, nonatomic, readonly, nonnull) SDWebImageManager *manager;
  
  /**
   * Maximum number of URLs to prefetch at the same time. Defaults to 3.
   */
  @property (nonatomic, assign) NSUInteger maxConcurrentPrefetchCount;
  
  /**
   * The options for prefetcher. Defaults to SDWebImageLowPriority.
   */
  @property (nonatomic, assign) SDWebImageOptions options;
  
  /**
   * The context for prefetcher. Defaults to nil.
   */
  @property (nonatomic, copy, nullable) SDWebImageContext *context;
  
  /**
   * Queue options for prefetcher when call the progressBlock, completionBlock and delegate methods. Defaults to Main Queue.
   * @note The call is asynchronously to avoid blocking target queue.
   * @note The delegate queue should be set before any prefetching start and may not be changed during prefetching to avoid thread-safe problem.
   */
  @property (strong, nonatomic, nonnull) dispatch_queue_t delegateQueue;
  
  /**
   * The delegate for the prefetcher. Defatuls to nil.
   */
  @property (weak, nonatomic, nullable) id <SDWebImagePrefetcherDelegate> delegate;
  
  /**
   * Returns the global shared image prefetcher instance. It use a standalone manager which is different from shared manager.
   */
  @property (nonatomic, class, readonly, nonnull) SDWebImagePrefetcher *sharedImagePrefetcher;
  
  /**
   * Allows you to instantiate a prefetcher with any arbitrary image manager.
   */
  - (nonnull instancetype)initWithImageManager:(nonnull SDWebImageManager *)manager NS_DESIGNATED_INITIALIZER;
  
  /**
   * Assign list of URLs to let SDWebImagePrefetcher to queue the prefetching. It based on the image manager so the image may from the cache and network according to the `options` property.
   * Prefetching is seperate to each other, which means the progressBlock and completionBlock you provide is bind to the prefetching for the list of urls.
   * Attention that call this will not cancel previous fetched urls. You should keep the token return by this to cancel or cancel all the prefetch.
   *
   * @param urls list of URLs to prefetch
   * @return the token to cancel the current prefetching.
   */
  - (nullable SDWebImagePrefetchToken *)prefetchURLs:(nullable NSArray<NSURL *> *)urls;
  
  /**
   * Assign list of URLs to let SDWebImagePrefetcher to queue the prefetching. It based on the image manager so the image may from the cache and network according to the `options` property.
   * Prefetching is seperate to each other, which means the progressBlock and completionBlock you provide is bind to the prefetching for the list of urls.
   * Attention that call this will not cancel previous fetched urls. You should keep the token return by this to cancel or cancel all the prefetch.
   *
   * @param urls            list of URLs to prefetch
   * @param progressBlock   block to be called when progress updates; 
   *                        first parameter is the number of completed (successful or not) requests, 
   *                        second parameter is the total number of images originally requested to be prefetched
   * @param completionBlock block to be called when the current prefetching is completed
   *                        first param is the number of completed (successful or not) requests,
   *                        second parameter is the number of skipped requests
   * @return the token to cancel the current prefetching.
   */
  - (nullable SDWebImagePrefetchToken *)prefetchURLs:(nullable NSArray<NSURL *> *)urls
                                            progress:(nullable SDWebImagePrefetcherProgressBlock)progressBlock
                                           completed:(nullable SDWebImagePrefetcherCompletionBlock)completionBlock;
  
  /**
   * Remove and cancel all the prefeching for the prefetcher.
   */
  - (void)cancelPrefetching;
  
  
  @end
  