/*

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

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 A transition animator that transitions between two view controllers in

  a tab bar controller by sliding both view controllers in a given

  direction.

 */

#import "AAPLSlideTransitionAnimator.h"

@implementation AAPLSlideTransitionAnimator

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

- (instancetype)initWithTargetEdge:(UIRectEdge)targetEdge

{

    self = [self init];

    if (self) {

        _targetEdge = targetEdge;

    }

    return self;

}

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

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

{

    return 0.35;

}

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

//  Custom transitions within a UITabBarController follow the same

//  conventions as those used for modal presentations.  Your animator will

//  be given the incoming and outgoing view controllers along with a container

//  view where both view controller's views will reside.  Your animator is

//  tasked with animating the incoming view controller's view into the

//  container view.  The frame of the incoming view controller's view is

//  is expected to match the value returned from calling

//  [transitionContext finalFrameForViewController:toViewController] when

//  the transition is complete.

//

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

{

    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];

    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

    UIView *containerView = transitionContext.containerView;

    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.

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

        fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];

        toView = [transitionContext viewForKey:UITransitionContextToViewKey];

    } else {

        fromView = fromViewController.view;

        toView = toViewController.view;

    }

    CGRect fromFrame = [transitionContext initialFrameForViewController:fromViewController];

    CGRect toFrame = [transitionContext finalFrameForViewController:toViewController];

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

    // be used to offset the frame of the view controllers.

    CGVector offset;

    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 UIRectEdgeLeft, or UIRectEdgeRight.");

    // The toView starts off-screen and slides in as the fromView slides out.

    fromView.frame = fromFrame;

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

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

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

    [containerView addSubview:toView];

    NSTimeInterval transitionDuration = [self transitionDuration:transitionContext];

    [UIView animateWithDuration:transitionDuration animations:^{

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

                                      fromFrame.size.height * offset.dy);

        toView.frame = toFrame;

    } completion:^(BOOL finished) {

        BOOL wasCancelled = [transitionContext transitionWasCancelled];

        // When we complete, tell the transition context

        // passing along the BOOL that indicates whether the transition

        // finished or not.

        [transitionContext completeTransition:!wasCancelled];

    }];

}

@end