/**缓存类型*/
typedef NS_ENUM(NSInteger, SDImageCacheType) {/*** The image wasn't available the SDWebImage caches, but was downloaded from the web.*/SDImageCacheTypeNone,  //不使用 SDWebImage 缓存，从网络下载/*** The image was obtained from the disk cache.*/SDImageCacheTypeDisk,  //使用磁盘缓存/*** The image was obtained from the memory cache.*/SDImageCacheTypeMemory  //使用内存缓存
};

/**查询回调Block@param image 图片@param data 图片数据@param cacheType 缓存类型*/
typedef void(^SDCacheQueryCompletedBlock)(UIImage * _Nullable image, NSData * _Nullable data, SDImageCacheType cacheType);/**磁盘缓存检查回调@param isInCache 是否在缓存中*/
typedef void(^SDWebImageCheckCacheCompletionBlock)(BOOL isInCache);/**磁盘缓存空间大小计算回调Block@param fileCount 文件数量@param totalSize 总大小*/
typedef void(^SDWebImageCalculateSizeBlock)(NSUInteger fileCount, NSUInteger totalSize);

//SDImageCacheConfig.h
@property (assign, nonatomic) BOOL shouldDecompressImages;  //!<是否在缓存之前解压图片，此项操作可以提升性能，但是会消耗较多的内存，默认是YES。注意:如果内存不足，可以置为NO
@property (assign, nonatomic) BOOL shouldDisableiCloud;  //!<是否禁止iCloud备份，默认是YES
@property (assign, nonatomic) BOOL shouldCacheImagesInMemory;  //!<是否启用内存缓存 默认是YES
@property (assign, nonatomic) NSInteger maxCacheAge;  //!<磁盘缓存保留的最长时间，默认为1周
@property (assign, nonatomic) NSUInteger maxCacheSize;  //!<磁盘缓存最大容量，以字节为单位，默认为0，表示不做限制//SDImageCache.h
@property (nonatomic, nonnull, readonly) SDImageCacheConfig *config;  //!<SDImageCacheConfig
@property (assign, nonatomic) NSUInteger maxMemoryCost;  //!<内存最大容量
@property (assign, nonatomic) NSUInteger maxMemoryCountLimit;  //!<缓存中可以存放缓存的最大数量，与NSCache相关//SDImageCache.m
@property (strong, nonatomic, nonnull) NSCache *memCache;  //!<内存缓存
@property (strong, nonatomic, nonnull) NSString *diskCachePath;  //!<磁盘缓存路径
@property (strong, nonatomic, nullable) NSMutableArray<NSString *> *customPaths;  //!<自定义的缓存路径
@property (SDDispatchQueueSetterSementics, nonatomic, nullable) dispatch_queue_t ioQueue;  //!<磁盘缓存操作的串行队列

/**单例方法，返回一个全局的缓存实例@return 缓存实例*/
+ (nonnull instancetype)sharedImageCache {static dispatch_once_t once;static id instance;dispatch_once(&once, ^{instance = [self new];});return instance;
}- (instancetype)init {return [self initWithNamespace:@"default"];
}/**使用指定的命名空间实例化一个新的缓存存储@param ns 命名空间@return 缓存实例*/
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns {NSString *path = [self makeDiskCachePath:ns];return [self initWithNamespace:ns diskCacheDirectory:path];
}/**使用指定的命名空间实例化一个新的缓存存储和目录@param ns 命名空间@param directory 缓存所在目录@return 缓存实例*/
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)nsdiskCacheDirectory:(nonnull NSString *)directory {if ((self = [super init])) {NSString *fullNamespace = [@"com.hackemist.SDWebImageCache." stringByAppendingString:ns];// Create IO serial queue_ioQueue = dispatch_queue_create("com.hackemist.SDWebImageCache", DISPATCH_QUEUE_SERIAL);//初始化缓存策略配置对象_config = [[SDImageCacheConfig alloc] init];// Init the memory cache// 初始化内存缓存对象_memCache = [[AutoPurgeCache alloc] init];_memCache.name = fullNamespace;// 初始化磁盘缓存路径if (directory != nil) {_diskCachePath = [directory stringByAppendingPathComponent:fullNamespace];} else {NSString *path = [self makeDiskCachePath:ns];_diskCachePath = path;}dispatch_sync(_ioQueue, ^{_fileManager = [NSFileManager new];});#if SD_UIKIT// Subscribe to app events//当应用收到内存警告的时候，清除内存缓存
        [[NSNotificationCenter defaultCenter] addObserver:selfselector:@selector(clearMemory)name:UIApplicationDidReceiveMemoryWarningNotificationobject:nil];//当应用终止的时候，清除老数据
        [[NSNotificationCenter defaultCenter] addObserver:selfselector:@selector(deleteOldFiles)name:UIApplicationWillTerminateNotificationobject:nil];//当应用进入后台的时候，在后台删除老数据
        [[NSNotificationCenter defaultCenter] addObserver:selfselector:@selector(backgroundDeleteOldFiles)name:UIApplicationDidEnterBackgroundNotificationobject:nil];
#endif}return self;
}

/**以key为键值将图片image存储到缓存中@param image 图片@param key key@param completionBlock 回调Block*/
- (void)storeImage:(nullable UIImage *)imageforKey:(nullable NSString *)keycompletion:(nullable SDWebImageNoParamsBlock)completionBlock {[self storeImage:image imageData:nil forKey:key toDisk:YES completion:completionBlock];
}/**以key为键值将图片image存储到缓存中@param image 图片@param key key@param toDisk 是否写入磁盘缓存@param completionBlock 回调Block*/
- (void)storeImage:(nullable UIImage *)imageforKey:(nullable NSString *)keytoDisk:(BOOL)toDiskcompletion:(nullable SDWebImageNoParamsBlock)completionBlock {[self storeImage:image imageData:nil forKey:key toDisk:toDisk completion:completionBlock];
}/**把一张图片存入缓存的具体实现@param image 缓存的图片对象@param imageData 缓存的图片数据@param key 缓存对应的key@param toDisk 是否缓存到磁盘@param completionBlock 缓存完成回调*/
- (void)storeImage:(nullable UIImage *)imageimageData:(nullable NSData *)imageDataforKey:(nullable NSString *)keytoDisk:(BOOL)toDiskcompletion:(nullable SDWebImageNoParamsBlock)completionBlock {if (!image || !key) {if (completionBlock) {completionBlock();}return;}// if memory cache is enabled//缓存到内存if (self.config.shouldCacheImagesInMemory) {//计算缓存数据的大小NSUInteger cost = SDCacheCostForImage(image);//加入缓存
        [self.memCache setObject:image forKey:key cost:cost];}if (toDisk) {//在一个串行队列中做磁盘缓存操作dispatch_async(self.ioQueue, ^{@autoreleasepool {NSData *data = imageData;if (!data && image) {//获取图片的类型GIF/PNG等SDImageFormat imageFormatFromData = [NSData sd_imageFormatForImageData:data];//根据指定的SDImageFormat，把图片转换为对应的data数据data = [image sd_imageDataAsFormat:imageFormatFromData];}//把处理好了的数据存入磁盘
                [self storeImageDataToDisk:data forKey:key];}if (completionBlock) {dispatch_async(dispatch_get_main_queue(), ^{completionBlock();});}});} else {if (completionBlock) {completionBlock();}}
}/**把图片资源存入磁盘@param imageData 图片数据@param key key*/
- (void)storeImageDataToDisk:(nullable NSData *)imageData forKey:(nullable NSString *)key {if (!imageData || !key) {return;}[self checkIfQueueIsIOQueue];//缓存目录是否已经初始化if (![_fileManager fileExistsAtPath:_diskCachePath]) {[_fileManager createDirectoryAtPath:_diskCachePath withIntermediateDirectories:YES attributes:nil error:NULL];}// get cache Path for image key//获取key对应的完整缓存路径NSString *cachePathForKey = [self defaultCachePathForKey:key];// transform to NSUrlNSURL *fileURL = [NSURL fileURLWithPath:cachePathForKey];//把数据存入路径
    [_fileManager createFileAtPath:cachePathForKey contents:imageData attributes:nil];// disable iCloud backupif (self.config.shouldDisableiCloud) {[fileURL setResourceValue:@YES forKey:NSURLIsExcludedFromBackupKey error:nil];}
}

/**根据key判断磁盘缓存中是否存在图片@param key key@param completionBlock 回调Block*/
- (void)diskImageExistsWithKey:(nullable NSString *)key completion:(nullable SDWebImageCheckCacheCompletionBlock)completionBlock {dispatch_async(_ioQueue, ^{BOOL exists = [_fileManager fileExistsAtPath:[self defaultCachePathForKey:key]];// fallback because of https://github.com/rs/SDWebImage/pull/976 that added the extension to the disk file name// checking the key with and without the extensionif (!exists) {exists = [_fileManager fileExistsAtPath:[self defaultCachePathForKey:key].stringByDeletingPathExtension];}if (completionBlock) {dispatch_async(dispatch_get_main_queue(), ^{completionBlock(exists);});}});
}/**根据key获取缓存在内存中的图片@param key key@return 缓存的图片*/
- (nullable UIImage *)imageFromMemoryCacheForKey:(nullable NSString *)key {return [self.memCache objectForKey:key];
}/**根据key获取缓存在磁盘中的图片@param key key@return 缓存的图片*/
- (nullable UIImage *)imageFromDiskCacheForKey:(nullable NSString *)key {UIImage *diskImage = [self diskImageForKey:key];if (diskImage && self.config.shouldCacheImagesInMemory) {NSUInteger cost = SDCacheCostForImage(diskImage);[self.memCache setObject:diskImage forKey:key cost:cost];}return diskImage;
}/**根据key获取缓存图片(先从内存中搜索，再去磁盘中搜索)@param key key@return 缓存的图片*/
- (nullable UIImage *)imageFromCacheForKey:(nullable NSString *)key {// First check the in-memory cache...UIImage *image = [self imageFromMemoryCacheForKey:key];if (image) {return image;}// Second check the disk cache...image = [self imageFromDiskCacheForKey:key];return image;
}/**根据指定的key，获取存储在磁盘上的数据@param key 图片对应的key@return 返回图片数据*/
- (nullable NSData *)diskImageDataBySearchingAllPathsForKey:(nullable NSString *)key {//获取key对应的pathNSString *defaultPath = [self defaultCachePathForKey:key];NSData *data = [NSData dataWithContentsOfFile:defaultPath];if (data) {return data;}// fallback because of https://github.com/rs/SDWebImage/pull/976 that added the extension to the disk file name// checking the key with and without the extension//如果key没有后缀名，则会走到这里通过这里读取data = [NSData dataWithContentsOfFile:defaultPath.stringByDeletingPathExtension];if (data) {return data;}//如果在默认路径没有找到图片，则在自定义路径迭代查找NSArray<NSString *> *customPaths = [self.customPaths copy];for (NSString *path in customPaths) {NSString *filePath = [self cachePathForKey:key inPath:path];NSData *imageData = [NSData dataWithContentsOfFile:filePath];if (imageData) {return imageData;}// fallback because of https://github.com/rs/SDWebImage/pull/976 that added the extension to the disk file name// checking the key with and without the extensionimageData = [NSData dataWithContentsOfFile:filePath.stringByDeletingPathExtension];if (imageData) {return imageData;}}return nil;
}/**根据指定的key获取image对象@param key key@return image对象*/
- (nullable UIImage *)diskImageForKey:(nullable NSString *)key {//获取磁盘数据NSData *data = [self diskImageDataBySearchingAllPathsForKey:key];if (data) {UIImage *image = [UIImage sd_imageWithData:data];image = [self scaledImageForKey:key image:image];if (self.config.shouldDecompressImages) {image = [UIImage decodedImageWithImage:image];}return image;}else {return nil;}
}- (nullable UIImage *)scaledImageForKey:(nullable NSString *)key image:(nullable UIImage *)image {return SDScaledImageForKey(key, image);
}/**在缓存中查询对应key的数据@param key 要查询的key@param doneBlock 查询结束以后的回调Block@return 返回做查询操作的NSOperation*/
- (nullable NSOperation *)queryCacheOperationForKey:(nullable NSString *)key done:(nullable SDCacheQueryCompletedBlock)doneBlock {if (!key) {if (doneBlock) {doneBlock(nil, nil, SDImageCacheTypeNone);}return nil;}// First check the in-memory cache...//首先从内存中查找图片UIImage *image = [self imageFromMemoryCacheForKey:key];if (image) {NSData *diskData = nil;if ([image isGIF]) {diskData = [self diskImageDataBySearchingAllPathsForKey:key];}if (doneBlock) {doneBlock(image, diskData, SDImageCacheTypeMemory);}return nil;}//新建一个NSOperation来获取磁盘图片NSOperation *operation = [NSOperation new];dispatch_async(self.ioQueue, ^{if (operation.isCancelled) {// do not call the completion if cancelledreturn;}//在一个自动释放池中处理图片从磁盘加载
        @autoreleasepool {NSData *diskData = [self diskImageDataBySearchingAllPathsForKey:key];UIImage *diskImage = [self diskImageForKey:key];if (diskImage && self.config.shouldCacheImagesInMemory) {NSUInteger cost = SDCacheCostForImage(diskImage);//把从磁盘取出的缓存图片加入内存缓存中
                [self.memCache setObject:diskImage forKey:key cost:cost];}//图片处理完成以后回调Blockif (doneBlock) {dispatch_async(dispatch_get_main_queue(), ^{doneBlock(diskImage, diskData, SDImageCacheTypeDisk);});}}});return operation;
}

#pragma mark - Remove Ops/**通过key从磁盘和内存中移除缓存@param key key@param completion 回调Block*/
- (void)removeImageForKey:(nullable NSString *)key withCompletion:(nullable SDWebImageNoParamsBlock)completion {[self removeImageForKey:key fromDisk:YES withCompletion:completion];
}/**移除指定key对应的缓存数据@param key key@param fromDisk 是否也清除磁盘缓存@param completion 回调*/
- (void)removeImageForKey:(nullable NSString *)key fromDisk:(BOOL)fromDisk withCompletion:(nullable SDWebImageNoParamsBlock)completion {if (key == nil) {return;}//移除内存缓存if (self.config.shouldCacheImagesInMemory) {[self.memCache removeObjectForKey:key];}//移除磁盘缓存if (fromDisk) {dispatch_async(self.ioQueue, ^{[_fileManager removeItemAtPath:[self defaultCachePathForKey:key] error:nil];if (completion) {dispatch_async(dispatch_get_main_queue(), ^{completion();});}});} else if (completion){completion();}}#pragma mark - Cache clean Ops 内存缓存清理相关操作/**清理当前SDImageCache对象的内存缓存*/
- (void)clearMemory {[self.memCache removeAllObjects];
}/**移除所有的磁盘缓存图片数据@param completion 移除完成以后回调*/
- (void)clearDiskOnCompletion:(nullable SDWebImageNoParamsBlock)completion {dispatch_async(self.ioQueue, ^{[_fileManager removeItemAtPath:self.diskCachePath error:nil];[_fileManager createDirectoryAtPath:self.diskCachePathwithIntermediateDirectories:YESattributes:nilerror:NULL];if (completion) {dispatch_async(dispatch_get_main_queue(), ^{completion();});}});
}- (void)deleteOldFiles {[self deleteOldFilesWithCompletionBlock:nil];
}/**当应用终止或者进入后台都会调用这个方法来清除缓存图片这里会根据图片存储时间来清理图片，默认是一周，从最老的图片开始清理。如果图片缓存空间小于一个规定值，则不考虑@param completionBlock 清除完成以后的回调*/
- (void)deleteOldFilesWithCompletionBlock:(nullable SDWebImageNoParamsBlock)completionBlock {dispatch_async(self.ioQueue, ^{//获取磁盘缓存的默认根目录NSURL *diskCacheURL = [NSURL fileURLWithPath:self.diskCachePath isDirectory:YES];NSArray<NSString *> *resourceKeys = @[NSURLIsDirectoryKey, NSURLContentModificationDateKey, NSURLTotalFileAllocatedSizeKey];// This enumerator prefetches useful properties for our cache files.NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtURL:diskCacheURLincludingPropertiesForKeys:resourceKeysoptions:NSDirectoryEnumerationSkipsHiddenFileserrorHandler:NULL];NSDate *expirationDate = [NSDate dateWithTimeIntervalSinceNow:-self.config.maxCacheAge];NSMutableDictionary<NSURL *, NSDictionary<NSString *, id> *> *cacheFiles = [NSMutableDictionary dictionary];NSUInteger currentCacheSize = 0;// Enumerate all of the files in the cache directory.  This loop has two purposes:////  1. Removing files that are older than the expiration date.//  2. Storing file attributes for the size-based cleanup pass.//迭代缓存目录。有两个目的：//1 删除比指定日期更老的图片//2 记录文件的大小，以提供给后面删除使用NSMutableArray<NSURL *> *urlsToDelete = [[NSMutableArray alloc] init];for (NSURL *fileURL in fileEnumerator) {NSError *error;//获取指定url对应文件的指定三种属性的key和valueNSDictionary<NSString *, id> *resourceValues = [fileURL resourceValuesForKeys:resourceKeys error:&error];// Skip directories and errors.//如果是文件夹则返回if (error || !resourceValues || [resourceValues[NSURLIsDirectoryKey] boolValue]) {continue;}// Remove files that are older than the expiration date;//获取指定url文件对应的修改日期NSDate *modificationDate = resourceValues[NSURLContentModificationDateKey];//如果修改日期大于指定日期，则加入要移除的数组里if ([[modificationDate laterDate:expirationDate] isEqualToDate:expirationDate]) {[urlsToDelete addObject:fileURL];continue;}// Store a reference to this file and account for its total size.//获取指定的url对应的文件的大小，并且把url与对应大小存入一个字典中NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];currentCacheSize += totalAllocatedSize.unsignedIntegerValue;cacheFiles[fileURL] = resourceValues;}//删除所有最后修改日期大于指定日期的所有文件for (NSURL *fileURL in urlsToDelete) {[_fileManager removeItemAtURL:fileURL error:nil];}// If our remaining disk cache exceeds a configured maximum size, perform a second// size-based cleanup pass.  We delete the oldest files first.//如果当前缓存的大小超过了默认大小，则按照日期删除，直到缓存大小<默认大小的一半if (self.config.maxCacheSize > 0 && currentCacheSize > self.config.maxCacheSize) {// Target half of our maximum cache size for this cleanup pass.const NSUInteger desiredCacheSize = self.config.maxCacheSize / 2;// Sort the remaining cache files by their last modification time (oldest first).//根据文件创建的时间排序NSArray<NSURL *> *sortedFiles = [cacheFiles keysSortedByValueWithOptions:NSSortConcurrentusingComparator:^NSComparisonResult(id obj1, id obj2) {return [obj1[NSURLContentModificationDateKey] compare:obj2[NSURLContentModificationDateKey]];}];// Delete files until we fall below our desired cache size.//迭代删除缓存，直到缓存大小是默认缓存大小的一半for (NSURL *fileURL in sortedFiles) {if ([_fileManager removeItemAtURL:fileURL error:nil]) {NSDictionary<NSString *, id> *resourceValues = cacheFiles[fileURL];NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];currentCacheSize -= totalAllocatedSize.unsignedIntegerValue;if (currentCacheSize < desiredCacheSize) {break;}}}}//执行完毕，主线程回调if (completionBlock) {dispatch_async(dispatch_get_main_queue(), ^{completionBlock();});}});
}#if SD_UIKIT/**应用进入后台的时候，调用这个方法*/
- (void)backgroundDeleteOldFiles {Class UIApplicationClass = NSClassFromString(@"UIApplication");if(!UIApplicationClass || ![UIApplicationClass respondsToSelector:@selector(sharedApplication)]) {return;}UIApplication *application = [UIApplication performSelector:@selector(sharedApplication)];//如果backgroundTask对应的时间结束了，任务还没有处理完成，则直接终止任务__block UIBackgroundTaskIdentifier bgTask = [application beginBackgroundTaskWithExpirationHandler:^{// Clean up any unfinished task business by marking where you// stopped or ending the task outright.//当任务非正常终止的时候，做清理工作
        [application endBackgroundTask:bgTask];bgTask = UIBackgroundTaskInvalid;}];// Start the long-running task and return immediately.//图片清理结束以后，处理完成[self deleteOldFilesWithCompletionBlock:^{//清理完成以后，终止任务
        [application endBackgroundTask:bgTask];bgTask = UIBackgroundTaskInvalid;}];
}
#endif

#pragma mark - Cache paths/**添加只读的缓存路径@param path 路径*/
- (void)addReadOnlyCachePath:(nonnull NSString *)path {if (!self.customPaths) {self.customPaths = [NSMutableArray new];}if (![self.customPaths containsObject:path]) {[self.customPaths addObject:path];}
}/**获取指定key对应的完整缓存路径@param key 对应一张图片，比如图片的名字@param path 指定根目录@return 完整路径*/
- (nullable NSString *)cachePathForKey:(nullable NSString *)key inPath:(nonnull NSString *)path {NSString *filename = [self cachedFileNameForKey:key];return [path stringByAppendingPathComponent:filename];
}- (nullable NSString *)defaultCachePathForKey:(nullable NSString *)key {return [self cachePathForKey:key inPath:self.diskCachePath];
}/**MD5加密@param key key@return 加密后的数据*/
- (nullable NSString *)cachedFileNameForKey:(nullable NSString *)key {const char *str = key.UTF8String;if (str == NULL) {str = "";}unsigned char r[CC_MD5_DIGEST_LENGTH];CC_MD5(str, (CC_LONG)strlen(str), r);NSString *filename = [NSString stringWithFormat:@"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%@",r[0], r[1], r[2], r[3], r[4], r[5], r[6], r[7], r[8], r[9], r[10],r[11], r[12], r[13], r[14], r[15], [key.pathExtension isEqualToString:@""] ? @"" : [NSString stringWithFormat:@".%@", key.pathExtension]];return filename;
}/**图片缓存目录@param fullNamespace 自定义子目录名称@return 完整目录*/
- (nullable NSString *)makeDiskCachePath:(nonnull NSString*)fullNamespace {NSArray<NSString *> *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);return [paths[0] stringByAppendingPathComponent:fullNamespace];
}#pragma mark - Cache Info/**磁盘缓存使用的大小@return 磁盘缓存的大小*/
- (NSUInteger)getSize {__block NSUInteger size = 0;dispatch_sync(self.ioQueue, ^{NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtPath:self.diskCachePath];for (NSString *fileName in fileEnumerator) {NSString *filePath = [self.diskCachePath stringByAppendingPathComponent:fileName];NSDictionary<NSString *, id> *attrs = [[NSFileManager defaultManager] attributesOfItemAtPath:filePath error:nil];size += [attrs fileSize];}});return size;
}/**磁盘缓存的图片数量@return 缓存的图片数量*/
- (NSUInteger)getDiskCount {__block NSUInteger count = 0;dispatch_sync(self.ioQueue, ^{NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtPath:self.diskCachePath];count = fileEnumerator.allObjects.count;});return count;
}/**异步计算磁盘缓存的大小@param completionBlock 回调Block*/
- (void)calculateSizeWithCompletionBlock:(nullable SDWebImageCalculateSizeBlock)completionBlock {NSURL *diskCacheURL = [NSURL fileURLWithPath:self.diskCachePath isDirectory:YES];dispatch_async(self.ioQueue, ^{NSUInteger fileCount = 0;NSUInteger totalSize = 0;NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtURL:diskCacheURLincludingPropertiesForKeys:@[NSFileSize]options:NSDirectoryEnumerationSkipsHiddenFileserrorHandler:NULL];for (NSURL *fileURL in fileEnumerator) {NSNumber *fileSize;[fileURL getResourceValue:&fileSize forKey:NSURLFileSizeKey error:NULL];totalSize += fileSize.unsignedIntegerValue;fileCount += 1;}if (completionBlock) {dispatch_async(dispatch_get_main_queue(), ^{completionBlock(fileCount, totalSize);});}});
}