/*

     File: ProgressObserver.m

 Abstract: 

    This model class uses Key Value Observeration (KVO) to monitor the NSProgress for Multipeer Connectivity API resource sending/receiving completion progress (or cancellation). 

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 */

#import "ProgressObserver.h"

// KVO path strings for observing changes to properties of NSProgress

static NSString * const kProgressCancelledKeyPath          = @"cancelled";

static NSString * const kProgressCompletedUnitCountKeyPath = @"completedUnitCount";

// This class implement KVO on the NSProgress class so that we can track the progress of the incoming or outgoing resource transfer

@implementation ProgressObserver

- (id)initWithName:(NSString *)name progress:(NSProgress *)progress

{

    if ((self = [super init])) {

        _name = [name copy];

        _progress = progress;

        // Add KVO observer for the cancelled and completed unit count properties of NSProgress

        [_progress addObserver:self forKeyPath:kProgressCancelledKeyPath options:NSKeyValueObservingOptionNew context:NULL];

        [_progress addObserver:self forKeyPath:kProgressCompletedUnitCountKeyPath options:NSKeyValueObservingOptionNew context:NULL];

    }

    return self;

}

- (void)dealloc

{

    // stop KVO

    [_progress removeObserver:self forKeyPath:kProgressCancelledKeyPath];

    [_progress removeObserver:self forKeyPath:kProgressCompletedUnitCountKeyPath];

    _progress = nil;

}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

{

    NSProgress *progress = object;

    // Check which KVO key change has fired

    if ([keyPath isEqualToString:kProgressCancelledKeyPath]) {

        // Notify the delegate that the progress was cancelled

        [self.delegate observerDidCancel:self];

    }

    else if ([keyPath isEqualToString:kProgressCompletedUnitCountKeyPath]) {

        // Notify the delegate of our progress change

        [self.delegate observerDidChange:self];

        if (progress.completedUnitCount == progress.totalUnitCount) {

            // Progress completed, notify delegate

            [self.delegate observerDidComplete:self];

        }

    }

}

@end