BFRImageContainerViewController.m

//
//  BFRImageContainerViewController.m
//  Buffer
//
//  Created by Jordan Morgan on 11/10/15.
//
//

#import "BFRImageContainerViewController.h"

#import <DACircularProgress/DACircularProgressView.h>
#import "AFNetworking.h"

@interface BFRImageContainerViewController () <UIScrollViewDelegate, UIGestureRecognizerDelegate>
@property (strong, nonatomic) UIScrollView *scrollView;
@property (strong, nonatomic) UIImageView *imgView;
@property (strong, nonatomic) UIImage *imgLoaded;
@property (strong, nonatomic) DACircularProgressView *progressView;
@property (strong, nonatomic) UIDynamicAnimator *animator;
@property (strong, nonatomic) UIAttachmentBehavior *imgAttatchment;
@end

@implementation BFRImageContainerViewController

#pragma mark - Lifecycle
//With peeking and popping, setting up your subviews in loadView will throw an exception
- (void)viewDidLoad {
    [super viewDidLoad];
    
    //View setup
    self.automaticallyAdjustsScrollViewInsets = NO;
    self.view.backgroundColor = [UIColor clearColor];
    
    //Scrollview (for pinching in and out of image)
    self.scrollView = [self createScrollView];
    [self.view addSubview:self.scrollView];
    
    //Fetch image - or just display it
    if ([self.imgSrc isKindOfClass:[NSURL class]]) {
        //Loading view
        self.progressView = [self createProgressView];
        [self.view addSubview:self.progressView];
        [self retrieveImageFromURL];
    } else {
        self.imgLoaded = (UIImage *)self.imgSrc;
        [self addImageToScrollView];
    }
    
    //Animator - used to snap the image back to the center when done dragging
    self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.scrollView];
}

- (void)viewWillLayoutSubviews {
    //Scrollview
    [self.scrollView setFrame:self.view.bounds];
    
    //Set the aspect ration of the image
    float hfactor = self.imgLoaded.size.width / self.view.bounds.size.width;
    float vfactor = self.imgLoaded.size.height /  self.view.bounds.size.height;
    float factor = fmax(hfactor, vfactor);
    
    //Divide the size by the greater of the vertical or horizontal shrinkage factor
    float newWidth = self.imgLoaded.size.width / factor;
    float newHeight = self.imgLoaded.size.height / factor;
    
    //Then figure out offset to center vertically or horizontally
    float leftOffset = (self.view.bounds.size.width - newWidth) / 2;
    float topOffset = ( self.view.bounds.size.height - newHeight) / 2;
    
    //Reposition image view
    CGRect newRect = CGRectMake(leftOffset, topOffset, newWidth, newHeight);
    self.imgView.frame = newRect;
}

#pragma mark - UI Methods
- (UIScrollView *)createScrollView {
    UIScrollView *sv = [[UIScrollView alloc] initWithFrame:self.view.bounds];
    sv.delegate = self;
    sv.showsHorizontalScrollIndicator = NO;
    sv.showsVerticalScrollIndicator = NO;
    sv.decelerationRate = UIScrollViewDecelerationRateFast;
    sv.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    
    //For UI Toggling
    UITapGestureRecognizer *singleSVTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(dismissUI)];
    singleSVTap.numberOfTapsRequired = 1;
    singleSVTap.cancelsTouchesInView = NO;
    [sv addGestureRecognizer:singleSVTap];
    
    return sv;
}

- (DACircularProgressView *)createProgressView {
    CGFloat screenWidth = self.view.bounds.size.width;
    CGFloat screenHeight = self.view.bounds.size.height;
    
    DACircularProgressView *progressView = [[DACircularProgressView alloc] initWithFrame:CGRectMake((screenWidth-35.)/2., (screenHeight-35.)/2, 35.0f, 35.0f)];
    [progressView setProgress:0.0f];
    progressView.thicknessRatio = 0.1;
    progressView.roundedCorners = NO;
    progressView.trackTintColor = [UIColor colorWithWhite:0.2 alpha:1];
    progressView.progressTintColor = [UIColor colorWithWhite:1.0 alpha:1];
    
    return progressView;
}

- (UIImageView *)createImageView {
    UIImageView *resizableImageView = [[UIImageView alloc] initWithImage:self.imgLoaded];
    resizableImageView.frame = self.view.bounds;
    resizableImageView.clipsToBounds = YES;
    resizableImageView.contentMode = UIViewContentModeScaleAspectFill;
    resizableImageView.backgroundColor = [UIColor colorWithWhite:0 alpha:1];
    
    //Scale to keep its aspect ration
    CGRect screenBound = [[UIScreen mainScreen] bounds];
    CGFloat screenWidth = screenBound.size.width;
    CGFloat screenHeight = screenBound.size.height;
    float scaleFactor = (self.imgLoaded ? self.imgLoaded.size.width : screenWidth) / screenWidth;
    CGRect finalImageViewFrame = CGRectMake(0, (screenHeight/2)-((self.imgLoaded.size.height / scaleFactor)/2), screenWidth, self.imgLoaded.size.height / scaleFactor);
    resizableImageView.layer.frame = finalImageViewFrame;
    
    //Toggle UI controls
    UITapGestureRecognizer *singleImgTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(dismissUI)];
    singleImgTap.numberOfTapsRequired = 1;
    [resizableImageView setUserInteractionEnabled:YES];
    [resizableImageView addGestureRecognizer:singleImgTap];
    
    //Recent the image on double tap
    UITapGestureRecognizer *doubleImgTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(recenterImageOriginOrZoomToPoint:)];
    doubleImgTap.numberOfTapsRequired = 2;
    [resizableImageView addGestureRecognizer:doubleImgTap];
    
    //Ensure the single tap doesn't fire when a user attempts to double tap
    [singleImgTap requireGestureRecognizerToFail:doubleImgTap];
    
    //Dragging to dismiss
    UIPanGestureRecognizer *panImg = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handleDrag:)];
    if (self.shouldDisableHorizontalDrag) {
        panImg.delegate = self;
    }
    [resizableImageView addGestureRecognizer:panImg];
    
    return resizableImageView;
}

- (void)addImageToScrollView {
    if (!self.imgView) {
        self.imgView = [self createImageView];
        [self.scrollView addSubview:self.imgView];
        [self setMaxMinZoomScalesForCurrentBounds];
    }
}

#pragma mark - Gesture Recognizer Delegate
//If we have more than one image, this will cancel out dragging horizontally to make it easy to navigate between images
- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer {
    CGPoint velocity = [(UIPanGestureRecognizer *)gestureRecognizer velocityInView:self.scrollView];
    return fabs(velocity.y) > fabs(velocity.x);
}

#pragma mark - Scrollview Delegate
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    return self.scrollView.subviews.firstObject;
}

- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
    [self.animator removeAllBehaviors];
    [self centerScrollViewContents];
}

#pragma mark - Scrollview Util Methods
/*! This calculates the correct zoom scale for the scrollview once we have the image's size */
- (void)setMaxMinZoomScalesForCurrentBounds {
    // Sizes
    CGSize boundsSize = self.scrollView.bounds.size;
    CGSize imageSize = self.imgView.frame.size;
    
    // Calculate Min
    CGFloat xScale = boundsSize.width / imageSize.width;
    CGFloat yScale = boundsSize.height / imageSize.height;
    CGFloat minScale = MIN(xScale, yScale);
    
    // Calculate Max
    CGFloat maxScale = 4.0;
    if ([UIScreen instancesRespondToSelector:@selector(scale)]) {
        maxScale = maxScale / [[UIScreen mainScreen] scale];
        
        if (maxScale < minScale) {
            maxScale = minScale * 2;
        }
    }
    
    //Apply zoom
    self.scrollView.maximumZoomScale = maxScale;
    self.scrollView.minimumZoomScale = minScale;
    self.scrollView.zoomScale = minScale;
}

/*! Called during zooming of the image to ensure it stays centered */
- (void)centerScrollViewContents {
    CGSize boundsSize = self.scrollView.bounds.size;
    CGRect contentsFrame = self.imgView.frame;
    
    if (contentsFrame.size.width < boundsSize.width) {
        contentsFrame.origin.x = (boundsSize.width - contentsFrame.size.width) / 2.0f;
    } else {
        contentsFrame.origin.x = 0.0f;
    }
    
    if (contentsFrame.size.height < boundsSize.height) {
        contentsFrame.origin.y = (boundsSize.height - contentsFrame.size.height) / 2.0f;
    } else {
        contentsFrame.origin.y = 0.0f;
    }
    
    self.imgView.frame = contentsFrame;
}

/*! Called when an image is double tapped. Either zooms out or to specific point */
- (void)recenterImageOriginOrZoomToPoint:(UITapGestureRecognizer *)tap {
    if (self.scrollView.zoomScale == self.scrollView.maximumZoomScale) {
        //Zoom out since we zoomed in here
        [self.scrollView setZoomScale:self.scrollView.minimumZoomScale animated:YES];
    } else {
        //Zoom to a point
        CGPoint touchPoint = [tap locationInView:self.scrollView];
        [self.scrollView zoomToRect:CGRectMake(touchPoint.x, touchPoint.y, 1, 1) animated:YES];
    }
}


#pragma mark - Dragging Methods
- (void)handleDrag:(UIPanGestureRecognizer *)recognizer {
    
    if (recognizer.state == UIGestureRecognizerStateBegan) {
        [self.animator removeAllBehaviors];
        
        CGPoint location = [recognizer locationInView:self.scrollView];
        CGPoint imgLocation = [recognizer locationInView:self.imgView];
        
        UIOffset centerOffset = UIOffsetMake(imgLocation.x - CGRectGetMidX(self.imgView.bounds),
                                             imgLocation.y - CGRectGetMidY(self.imgView.bounds));
        self.imgAttatchment = [[UIAttachmentBehavior alloc] initWithItem:self.imgView offsetFromCenter:centerOffset attachedToAnchor:location];
        [self.animator addBehavior:self.imgAttatchment];
    } else if (recognizer.state == UIGestureRecognizerStateChanged) {
        [self.imgAttatchment setAnchorPoint:[recognizer locationInView:self.scrollView]];
    } else if (recognizer.state == UIGestureRecognizerStateEnded) {
        CGPoint location = [recognizer locationInView:self.scrollView];
        CGRect closeTopThreshhold = CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height * .15);
        CGRect closeBottomThreshhold = CGRectMake(0, self.view.bounds.size.height - closeTopThreshhold.size.height, self.view.bounds.size.width, self.view.bounds.size.height * .15);
        
        //Check if we should close - or just snap back to the center
        if (CGRectContainsPoint(closeTopThreshhold, location) || CGRectContainsPoint(closeBottomThreshhold, location)) {
            [self.animator removeAllBehaviors];
            self.imgView.userInteractionEnabled = NO;
            self.scrollView.userInteractionEnabled = NO;
            
            UIGravityBehavior *exitGravity = [[UIGravityBehavior alloc] initWithItems:@[self.imgView]];
            if (CGRectContainsPoint(closeTopThreshhold, location)) {
                exitGravity.gravityDirection = CGVectorMake(0.0, -1.0);
            }
            exitGravity.magnitude = 15.0f;
            [self.animator addBehavior:exitGravity];
            
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.35f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                [self dismissUI];
            });
        } else {
            [self.scrollView setZoomScale:self.scrollView.minimumZoomScale animated:YES];
            UISnapBehavior *snapBack = [[UISnapBehavior alloc] initWithItem:self.imgView snapToPoint:self.scrollView.center];
            [self.animator addBehavior:snapBack];
        }
    }
}

#pragma mark - Misc. Methods
- (void)dismissUI {
    [[NSNotificationCenter defaultCenter] postNotificationName:@"DismissUI" object:nil];
}

- (void)retrieveImageFromURL {
    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:(NSURL *)self.imgSrc cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:0];
    
    AFHTTPRequestOperation *imgOperation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
    imgOperation.responseSerializer = [AFImageResponseSerializer serializer];
    
    [imgOperation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
        self.imgLoaded = responseObject;
        [self addImageToScrollView];
        [self.progressView removeFromSuperview];
    } failure:^(AFHTTPRequestOperation *operation, NSError *error){
        [self.progressView removeFromSuperview];
        [self showError];
    }];
    
    [imgOperation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {
        CGFloat progress = ((CGFloat)totalBytesRead)/((CGFloat)totalBytesExpectedToRead);
        [self.progressView setProgress:progress];
    }];
    
    [[NSOperationQueue mainQueue] addOperation:imgOperation];
}

- (void)showError {
    UIAlertController *controller = [UIAlertController alertControllerWithTitle:@"Whoops" message:@"Looks like we ran into an issue loading the image, sorry about that!" preferredStyle:UIAlertControllerStyleAlert];
    UIAlertAction *closeAction = [UIAlertAction actionWithTitle:@"Ok" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){
        [[NSNotificationCenter defaultCenter] postNotificationName:@"ImageLoadingError" object:nil];
    }];
    [controller addAction:closeAction];
    [self presentViewController:controller animated:YES completion:nil];
}
@end