/*

 Copyright (C) 2016 Apple Inc. All Rights Reserved.

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 A transition animator that slides the incoming view controller over the

  presenting view controller.

 */

#import "AAPLSwipeTransitionAnimator.h"

@implementation AAPLSwipeTransitionAnimator

//| ----------------------------------------------------------------------------

- (instancetype)initWithTargetEdge:(UIRectEdge)targetEdge

{

    self = [self init];

    if (self) {

        _targetEdge = targetEdge;

    }

    return self;

}

//| ----------------------------------------------------------------------------

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext

{

    return 0.35;

}

//| ----------------------------------------------------------------------------

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext

{

    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];

    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

    UIView *containerView = transitionContext.containerView;

    // For a Presentation:

    //      fromView = The presenting view.

    //      toView   = The presented view.

    // For a Dismissal:

    //      fromView = The presented view.

    //      toView   = The presenting view.

    UIView *fromView;

    UIView *toView;

    // In iOS 8, the viewForKey: method was introduced to get views that the

    // animator manipulates.  This method should be preferred over accessing

    // the view of the fromViewController/toViewController directly.

    // It may return nil whenever the animator should not touch the view

    // (based on the presentation style of the incoming view controller).

    // It may also return a different view for the animator to animate.

    //

    // Imagine that you are implementing a presentation similar to form sheet.

    // In this case you would want to add some shadow or decoration around the

    // presented view controller's view. The animator will animate that

    // decoration instead and the presented view controller's view will be a

    // child of the decoration.

    if ([transitionContext respondsToSelector:@selector(viewForKey:)]) {

        fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];

        toView = [transitionContext viewForKey:UITransitionContextToViewKey];

    } else {

        fromView = fromViewController.view;

        toView = toViewController.view;

    }

    // If this is a presentation, toViewController corresponds to the presented

    // view controller and its presentingViewController will be

    // fromViewController.  Otherwise, this is a dismissal.

    BOOL isPresenting = (toViewController.presentingViewController == fromViewController);

    CGRect fromFrame = [transitionContext initialFrameForViewController:fromViewController];

    CGRect toFrame = [transitionContext finalFrameForViewController:toViewController];

    // Based on our configured targetEdge, derive a normalized vector that will

    // be used to offset the frame of the presented view controller.

    CGVector offset;

    if (self.targetEdge == UIRectEdgeTop)

        offset = CGVectorMake(0.f, 1.f);

    else if (self.targetEdge == UIRectEdgeBottom)

        offset = CGVectorMake(0.f, -1.f);

    else if (self.targetEdge == UIRectEdgeLeft)

        offset = CGVectorMake(1.f, 0.f);

    else if (self.targetEdge == UIRectEdgeRight)

        offset = CGVectorMake(-1.f, 0.f);

    else

        NSAssert(NO, @"targetEdge must be one of UIRectEdgeTop, UIRectEdgeBottom, UIRectEdgeLeft, or UIRectEdgeRight.");

    if (isPresenting) {

        // For a presentation, the toView starts off-screen and slides in.

        fromView.frame = fromFrame;

        toView.frame = CGRectOffset(toFrame, toFrame.size.width * offset.dx * -1,

                                             toFrame.size.height * offset.dy * -1);

    } else {

        fromView.frame = fromFrame;

        toView.frame = toFrame;

    }

    // We are responsible for adding the incoming view to the containerView

    // for the presentation.

    if (isPresenting)

        [containerView addSubview:toView];

    else

        // -addSubview places its argument at the front of the subview stack.

        // For a dismissal animation we want the fromView to slide away,

        // revealing the toView.  Thus we must place toView under the fromView.

        [containerView insertSubview:toView belowSubview:fromView];

    NSTimeInterval transitionDuration = [self transitionDuration:transitionContext];

    [UIView animateWithDuration:transitionDuration animations:^{

        if (isPresenting) {

            toView.frame = toFrame;

        } else {

            // For a dismissal, the fromView slides off the screen.

            fromView.frame = CGRectOffset(fromFrame, fromFrame.size.width * offset.dx,

                                                     fromFrame.size.height * offset.dy);

        }

    } completion:^(BOOL finished) {

        BOOL wasCancelled = [transitionContext transitionWasCancelled];

        // Due to a bug with unwind segues targeting a view controller inside

        // of a navigation controller, we must remove the toView in cases where

        // an interactive dismissal was cancelled.  This bug manifests as a

        // soft UI lockup after canceling the first interactive modal

        // dismissal; further invocations of the unwind segue have no effect.

        //

        // The navigation controller's implementation of

        // -segueForUnwindingToViewController:fromViewController:identifier:

        // returns a segue which only dismisses the currently presented

        // view controller if it determines that the navigation controller's

        // view is not in the view hierarchy at the time the segue is invoked.

        // The system does not remove toView when we invoke -completeTransition:

        // with a value of NO if this is a dismissal transition.

        //

        // Note that it is not necessary to check for further conditions

        // specific to this bug (e.g. isPresenting==NO &&

        // [toViewController isKindOfClass:UINavigationController.class])

        // because removing toView is a harmless operation in all scenarios

        // except for a successfully completed presentation transition, where

        // it would result in a blank screen.

        if (wasCancelled)

            [toView removeFromSuperview];

        // When we complete, tell the transition context

        // passing along the BOOL that indicates whether the transition

        // finished or not.

        [transitionContext completeTransition:!wasCancelled];

    }];

}

@end