JSJP_Student/jiaPei/Modules/VideosModule/SingletonManger/RQDownloadManager/RQDownloadOperation.m

//
//  RQDownloadOperation.m
//  TEST
//
//  Created by 张嵘 on 2018/10/22.
//  Copyright © 2018 张嵘. All rights reserved.
//

#import "RQDownloadOperation.h"
#import "RQDownloadHeader.h"

#define kKVOBlock(KEYPATH,BLOCK)\
[self willChangeValueForKey:KEYPATH];\
BLOCK();\
[self didChangeValueForKey:KEYPATH];

@interface RQDownloadOperation (){
	
	BOOL _executing;
	BOOL _finished;
}

@property (nonatomic, strong) NSLock *lock;

@property (nonatomic, assign) BOOL taskIsFinished;

@end

static const NSTimeInterval kTimeoutInterval = 60;

static NSString * const kIsExecuting = @"isExecuting";

static NSString * const kIsCancelled = @"isCancelled";

static NSString * const kIsFinished = @"isFinished";

@implementation RQDownloadOperation
MJCodingImplementation

- (instancetype)initWithDownloadModel:(RQDownloadModel *)downloadModel andSession:(NSURLSession *)session{
	self = [super init];
	if (self) {
		self.downloadModel = downloadModel;
		self.session = session;
		self.downloadModel.status = RQDownloadStatus_Waiting;
	}
	return self;
}


- (void)dealloc{
	NSLog(@"任务已销毁");
}


#pragma mark - Public Method
- (void)startRequest{
	
	//已下载完成 || 任务未就绪 --> 则直接返回
	if (self.downloadModel.isFinished || !self.isReady) {
		return;
	}
	// 创建请求
	NSURL *url = [NSURL URLWithString:self.downloadModel.urlString];
	NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:kTimeoutInterval];
	
	// 设置请求头
	NSString *range = [NSString stringWithFormat:@"bytes=%d-", self.downloadModel.fileDownloadSize];
	[request setValue:range forHTTPHeaderField:@"Range"];
	
	if(!self.downloadTask){
		self.downloadTask = [self.session dataTaskWithRequest:request];
	}
	
	self.downloadTask.downloadModel = self.downloadModel;
	[self addObserver];
	
	[self.downloadTask resume];
}

// 进行检索获取Key
- (BOOL)observerKeyPath:(NSString *)key observer:(id )observer{
	
	id info = self.downloadTask.observationInfo;
	NSArray *array = [info valueForKey:@"_observances"];
	for (id objc in array) {
		id Properties = [objc valueForKeyPath:@"_property"];
		id newObserver = [objc valueForKeyPath:@"_observer"];
		
		NSString *keyPath = [Properties valueForKeyPath:@"_keyPath"];
		if ([key isEqualToString:keyPath] && [newObserver isEqual:observer]) {
			return YES;
		}
	}
	return NO;
}

- (void)addObserver{
	
	if (![self observerKeyPath:@"state" observer:self]) {
		[self.downloadTask addObserver:self
							forKeyPath:@"state"
							   options:NSKeyValueObservingOptionNew
							   context:nil];
	}
}

- (void)removeObserver{
	
	if ([self observerKeyPath:@"state" observer:self]){
		[self.downloadTask removeObserver:self forKeyPath:@"state"];
	}
}

/** 挂起任务 */
- (void)suspend{
	
	NSLog(@"%@: currentThread = %@", NSStringFromSelector(_cmd), [NSThread currentThread]);
	
	kKVOBlock(kIsExecuting, ^{
		[self.downloadTask suspend];
		_executing = NO;
	});
}

/** 开始执行任务 */
- (void)startExcuting{
	
	NSLog(@"%@: currentThread = %@", NSStringFromSelector(_cmd), [NSThread currentThread]);
	
	kKVOBlock(kIsExecuting, ^{
		[self startRequest];
		_executing = YES;
	});
}


/** 开始执行任务 */
- (void)resume{
	
	//等待中的任务交给队列调度
	if (self.downloadModel.status == RQDownloadStatus_Waiting)
	return;
	
	kKVOBlock(kIsExecuting, ^{
		[self startRequest];
		_executing = YES;
	});
}


/** 任务已完成 */
- (void)completeOperation{
	
	[self willChangeValueForKey:kIsFinished];
	[self willChangeValueForKey:kIsExecuting];
	
	_executing = NO;
	_finished = YES;
	
	[self didChangeValueForKey:kIsExecuting];
	[self didChangeValueForKey:kIsFinished];
}


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
	
	if ([keyPath isEqualToString:@"state"]) {
		
		NSInteger newState = [[change objectForKey:@"new"] integerValue];
		NSInteger oldState = [[change objectForKey:@"old"] integerValue];
		
		switch (newState) {
				case NSURLSessionTaskStateSuspended:
				self.downloadModel.status = RQDownloadStatus_Suspended;
				//为进行任务管理 暂停任务后 直接取消
				[self cancel];
				break;
				case NSURLSessionTaskStateCompleted:{
					if (self.downloadModel.isFinished) {
						self.downloadModel.status = RQDownloadStatus_Completed;
						[self cancel];
					}else{
						if (self.downloadModel.status == RQDownloadStatus_Suspended) {
						}else{// 下载失败
							self.downloadModel.status = RQDownloadStatus_Failed;
						}
					}
				}break;
				case NSURLSessionTaskStateRunning:
				self.downloadModel.status = RQDownloadStatus_Running;
				break;
				case NSURLSessionTaskStateCanceling:
				self.taskIsFinished = YES;
				break;
			default:
				break;
		}
		
		if (newState != oldState) {
			if (self.downloadStatusChangedBlock) {
				self.downloadStatusChangedBlock();
			}
		}
	}
}



#pragma mark - Override Methods
- (void)start{
	
	self.lock = [[NSLock alloc] init];
	[self.lock lock];
	//重写start方法时，要做好isCannelled的判断
	if ([self isCancelled]){
		//若已取消则设置状态已完成
		kKVOBlock(kIsFinished, ^{
			_finished = YES;
		});
		return;
	}
	
	kKVOBlock(kIsExecuting, ^{
		_executing = YES;
	});
	
	//未取消则调用main方法来执行任务
	//经测试 加入operationQueue中后会自动开启新的线程执行 无需手动开启
	[NSThread currentThread].name = self.downloadModel.downloadDesc;
	[NSThread mainThread].name = @"主线程";
	[self main];
	[self.lock unlock];
}


- (void)main{
	
	@try {
		// 必须为自定义的 operation 提供 autorelease pool，因为 operation 完成后需要销毁。
		@autoreleasepool {
			// 提供一个变量标识，来表示需要执行的操作是否完成了，当然，没开始执行之前，为NO
			_taskIsFinished = NO;
			
			//只有当没有执行完成和没有被取消，才执行自定义的相应操作
			if (self.taskIsFinished == NO && [self isCancelled] == NO) {
				[self startExcuting];
			}
			
		}
	}@catch (NSException * e) {
		NSLog(@"Exception %@", e);
	}
}

- (BOOL)isExecuting{
	return _executing;
}


- (BOOL)isFinished{
	return _finished;
}

- (BOOL)isAsynchronous{
	return YES;
}
/**
 *  1.cancel方法调用后 该operation将会取消并从queue中移除
 *  2.若队列中有等待中的任务，将会自动执行
 */
- (void)cancel{
	
	BOOL isWaiting = self.downloadModel.status == RQDownloadStatus_Waiting;
	[self.downloadTask cancel];
	[self removeObserver];
	[super cancel];
	//等待状态下取消时 无需将isFinished设置为已完成  等调用start方法时检测canceled来设置
	//参考：https://blog.csdn.net/loggerhuang/article/details/50015573
	if (!isWaiting) {
		[self completeOperation];
	}
}
@end