@class YYAsyncLayerDisplayTask;

/**
The YYAsyncLayer class is a subclass of CALayer used for render contents asynchronously.

@discussion When the layer need update it's contents, it will 
ask the delegate for a async display task to render the 
contents in a background queue.
*/
@interface YYAsyncLayer : CALayer
// Whether the render code is executed in background. Default is YES
@property BOOL displaysAsychronously;
@end

/**
The YYAsyncLayer's delegate protocol. The delegate of the 
YYAsyncLayer (typically a UIView) must implements the
method in this protocol
*/
@protocol YYAsyncLayerDelegate <NSObject>
@required
// This method is called to return a new display task when
// the layer's contents need update.
- (YYAsyncLayerDisplayTask *)newAsyncDisplayTask;
@end

/**
A display task used by YYAsyncLayer to render the 
contenets in background queue.
*/
@interface YYAsyncLayerDisplayTask : NSObject

/**
This block will be called before the asynchronous drawing 
begins.
It will be called on the main thread.
*/
@property (nullable, nonatomic, copy) void (^willDisplay)(CALayer *layer);

/**
This block will be called after the asynchronous drawing finished. It will be called on the main thread.
*/
@property (nullable, nonatomic, copy) void (^didDisplay)(CALayer *layer, BOOL finished);

/**
This block is called to draw the layer's contents.

This block may be called on the main thread or background thread so is should be thread-safe.
*/
@property (nullable, nonatomic, copy) void (^display)(CGContextRef context, CGSize size, BOOL(%isCancelled)(void)));
@end

static dispatch_quque_t YYAsyncLayerGetDisplayQueue() {
  #ifdef YYDispatchQueuePool_h
    return YYDispatchQueueGetForQOS(NSQualityOfServiceUserInitiated);
  #else 
  #define MAX_QUEUE_COUNT 16
    static int queueCount;
    static dispatch_queue_t queues[MAX_QUEUE_COUNT];
    static dispatch_once_t onceToken;
    static int32_t counter = 0;
dispatch_once(&onceToken, ^{
    queueCount = (int)[NSProcessInfo processInfo].activeProcessorCount;
    queueCount = queueCount < 1 ? 1 : queueCount > MAX_QUEUE_COUNT ? MAX_QUEUE_COUNT : queueCount;
    if ([UIDevice currentDevice].systemVersion.floatValue >= 8.0) {
        for (NSUInteger i = 0; i < queueCount; i++) {
            dispatch_queue_attr_t attr = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_USER_INITIATED, 0);
            queues[i] = dispatch_queue_create("com.ibireme.yykit.render", attr);
        }
    } else {
        for (NSUInteger i = 0; i < queueCount; i++) {
            queues[i] = dispatch_queue_create("com.ibireme.yykit.render", DISPATCH_QUEUE_SERIAL);
            dispatch_set_target_queue(queues[i], dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0));
        }
    }
});
int32_t cur = OSAtomicIncrement32(&counter);
if (cur < 0) cur = -cur;
return queues[(cur) % queueCount];
  #enddef MAX_QUEUE_COUNT
  #endif
}

static dispatch_queue_t YYAsyncLayerGetReleaseQueue() {
  #ifdef YYDispatchQueuePool_h
    return  YYDispatchQueueGetForQOS(NSQualityOfServiceDefault);
  #else
      return dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);
  #endif
}

@implementation YYAsyncLayerDisplayTask
@end

@implementation YYAsyncLayer {
    YYSentinel *_sentinel;
}

#pragma mark - Override

+ (id)defaultValueForKey:(NSString *)key {
    if ([key isEqualToString:@"displaysAsynchronously"]) {
        return @(YES);
    } else {
        return [super defaultValueForKey:key];
    }
}

- (instancetype)init {
    self = [super init];
    static CGFloat scale; //global
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        scale = [UIScreen mainScreen].scale;
    });
    self.contentsScale = scale;
    _sentinel = [YYSentinel new];
    _displaysAsynchronously = YES;
    return self;
}

- (void)dealloc {
    [_sentinel increase];
}

- (void)setNeedsDisplay {
    [self _cancelAsyncDisplay];
    [super setNeedsDisplay];
}

- (void)display {
    super.contents = super.contents;
    [self _displayAsync:_displaysAsynchronously];
}

- (void)_cancelAsyncDisplay {
    [_sentinel increase];
}

#pragma mark - Private

- (void)_displayAsync:(BOOL)async {
    __strong id<YYAsyncLayerDelegate> delegate = self.delegate;
    YYAsyncLayerDisplayTask *task = [delegate newAsyncDisplayTask];
    if (!task.display) {
        if (task.willDisplay) task.willDisplay(self);
        self.contents = nil;
        if (task.didDisplay) task.didDisplay(self, YES);
        return;
    }

    if (async) {
        if (task.willDisplay) task.willDisplay(self);
        YYSentinel *sentinel = _sentinel;
        int32_t value = sentinel.value;
        BOOL (^isCancelled)() = ^BOOL() {
            return value != sentinel.value;
        };
        CGSize size = self.bounds.size;
        BOOL opaque = self.opaque;
        CGFloat scale = self.contentsScale;
        CGColorRef backgroundColor = (opaque && self.backgroundColor) ? CGColorRetain(self.backgroundColor) : NULL;
        if (size.width < 1 || size.height < 1) {
            CGImageRef image = (__bridge_retained CGImageRef)(self.contents);
            self.contents = nil;
            if (image) {
                 dispatch_async(YYAsyncLayerGetReleaseQueue(), ^{
                    CFRelease(image);
                 });
            }
            if (task.didDisplay) task.didDisplay(self, YES);
            CGColorRelease(backgroundColor);
            return;
        }
    
        dispatch_async(YYAsyncLayerGetDisplayQueue(), ^{
            if (isCancelled()) {
                CGColorRelease(backgroundColor);
                return;
             }
            UIGraphicsBeginImageContextWithOptions(size, opaque, scale);
            CGContextRef context = UIGraphicsGetCurrentContext();
            if (opaque) {
                CGContextSaveGState(context); {
                    if (!backgroundColor || CGColorGetAlpha(backgroundColor) < 1) {
                        CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
                        CGContextAddRect(context, CGRectMake(0, 0, size.width * scale, size.height * scale));
                        CGContextFillPath(context);
                    }
                    if (backgroundColor) {
                        CGContextSetFillColorWithColor(context, backgroundColor);
                        CGContextAddRect(context, CGRectMake(0, 0, size.width * scale, size.height * scale));
                        CGContextFillPath(context);
                    }
                } CGContextRestoreGState(context);
                CGColorRelease(backgroundColor);
              }
              task.display(context, size, isCancelled);
              if (isCancelled()) {
                  UIGraphicsEndImageContext();
                  dispatch_async(dispatch_get_main_queue(), ^{
                    if (task.didDisplay) task.didDisplay(self, NO);
                });
                  return;
              }
              UIImage *image =     UIGraphicsGetImageFromCurrentImageContext();
              UIGraphicsEndImageContext();
              if (isCancelled()) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    if (task.didDisplay) task.didDisplay(self, NO);
                });
                return;
            }
            dispatch_async(dispatch_get_main_queue(), ^{
                if (isCancelled()) {
                    if (task.didDisplay) task.didDisplay(self, NO);
                } else {
                    self.contents = (__bridge id)(image.CGImage);
                    if (task.didDisplay) task.didDisplay(self, YES);
                }
            });
        });
    } else {
        [_sentinel increase];
        if (task.willDisplay) task.willDisplay(self);
        
  UIGraphicsBeginImageContextWithOptions(self.bounds.size,       
        self.opaque, self.contentsScale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    if (self.opaque) {
        CGSize size = self.bounds.size;
        size.width *= self.contentsScale;
        size.height *= self.contentsScale;
        CGContextSaveGState(context); {
            if (!self.backgroundColor || CGColorGetAlpha(self.backgroundColor) < 1) {
                CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
                CGContextAddRect(context, CGRectMake(0, 0, size.width, size.height));
                CGContextFillPath(context);
            }
            if (self.backgroundColor) {
                CGContextSetFillColorWithColor(context, self.backgroundColor);
                CGContextAddRect(context, CGRectMake(0, 0, size.width, size.height));
                CGContextFillPath(context);
            }
        } CGContextRestoreGState(context);
    }
    task.display(context, self.bounds.size, ^{return NO;});
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    self.contents = (__bridge id)(image.CGImage);
    if (task.didDisplay) task.didDisplay(self, YES);
}

}

@end