/*

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

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 The delegate of the tab bar controller for the Slide demo.  Manages the

  gesture recognizer used for the interactive transition.  Vends

  instances of AAPLSlideTransitionAnimator and 

  AAPLSlideTransitionInteractionController.

 */

#import "AAPLSlideTransitionDelegate.h"

#import "AAPLSlideTransitionAnimator.h"

#import "AAPLSlideTransitionInteractionController.h"

#import <objc/runtime.h>

//! They key used to associate an instance of AAPLSlideTransitionDelegate with

//! the tab bar controller for which it is the delegate.

const char * AAPLSlideTabBarControllerDelegateAssociationKey = "AAPLSlideTabBarControllerDelegateAssociation";

@interface AAPLSlideTransitionDelegate ()

@property (nonatomic, strong) UIPanGestureRecognizer *panGestureRecognizer;

@end

@implementation AAPLSlideTransitionDelegate

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

//  Custom implementation of the setter for the tabBarController property.

//

//  An instance of the AAPLSlideTransitionDelegate class is defined in the

//  Tab Bar Controller's scene in the storyboard, and its tabBarControllerOutlet

//  connected to the tab bar controller.  At unarchive time this method will

//  be called, providing an opportunity to perform the necessary setup.

//

- (void)setTabBarController:(UITabBarController *)tabBarController

{

    if (tabBarController != _tabBarController) {

        // Remove all associations of this object from the old tab bar

        // controller.

        objc_setAssociatedObject(_tabBarController, AAPLSlideTabBarControllerDelegateAssociationKey, nil, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

        [_tabBarController.view removeGestureRecognizer:self.panGestureRecognizer];

        if (_tabBarController.delegate == self) _tabBarController.delegate = nil;

        _tabBarController = tabBarController;

        _tabBarController.delegate = self;

        [_tabBarController.view addGestureRecognizer:self.panGestureRecognizer];

        // Associate this object with the new tab bar controller.  This ensures

        // that this object wil not be deallocated prior to the tab bar

        // controller being deallocated.

        objc_setAssociatedObject(_tabBarController, AAPLSlideTabBarControllerDelegateAssociationKey, self, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

    }

}

#pragma mark -

#pragma mark Gesture Recognizer

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

//  Custom implementation of the getter for the panGestureRecognizer property.

//  Lazily creates the pan gesture recognizer for the tab bar controller.

//

- (UIPanGestureRecognizer*)panGestureRecognizer

{

    if (_panGestureRecognizer == nil)

        _panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panGestureRecognizerDidPan:)];

    return _panGestureRecognizer;

}

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

//! Action method for the panGestureRecognizer.

//

- (IBAction)panGestureRecognizerDidPan:(UIPanGestureRecognizer*)sender

{

    // Do not attempt to begin an interactive transition if one is already

    // ongoing

    if (self.tabBarController.transitionCoordinator)

        return;

    if (sender.state == UIGestureRecognizerStateBegan || sender.state == UIGestureRecognizerStateChanged)

        [self beginInteractiveTransitionIfPossible:sender];

    // Remaining cases are handled by the vended

    // AAPLSlideTransitionInteractionController.

}

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

//! Begins an interactive transition with the provided gesture recognizer, if

//! there is a view controller to transition to.

//

- (void)beginInteractiveTransitionIfPossible:(UIPanGestureRecognizer *)sender

{

    CGPoint translation = [sender translationInView:self.tabBarController.view];

    if (translation.x > 0.f && self.tabBarController.selectedIndex > 0) {

        // Panning right, transition to the left view controller.

        self.tabBarController.selectedIndex--;

    } else if (translation.x < 0.f && self.tabBarController.selectedIndex + 1 < self.tabBarController.viewControllers.count) {

        // Panning left, transition to the right view controller.

        self.tabBarController.selectedIndex++;

    } else {

        // Don't reset the gesture recognizer if we skipped starting the

        // transition because we don't have a translation yet (and thus, could

        // not determine the transition direction).

        if (!CGPointEqualToPoint(translation, CGPointZero)) {

            // There is not a view controller to transition to, force the

            // gesture recognizer to fail.

            sender.enabled = NO;

            sender.enabled = YES;

        }

    }

    // We must handle the case in which the user begins panning but then

    // reverses direction without lifting their finger.  The transition

    // should seamlessly switch to revealing the correct view controller

    // for the new direction.

    //

    // The approach presented in this demonstration relies on coordination

    // between this object and the AAPLSlideTransitionInteractionController

    // it vends.  If the AAPLSlideTransitionInteractionController detects

    // that the current position of the user's touch along the horizontal

    // axis has crossed over the initial position, it cancels the

    // transition.  A completion block is attached to the tab bar

    // controller's transition coordinator.  This block will be called when

    // the transition completes or is cancelled.  If the transition was

    // cancelled but the gesture recgonzier has not transitioned to the

    // ended or failed state, a new transition to the proper view controller

    // is started, and new animation + interaction controllers are created.

    //

    [self.tabBarController.transitionCoordinator animateAlongsideTransition:NULL completion:^(id<UIViewControllerTransitionCoordinatorContext> context) {

        if ([context isCancelled] && sender.state == UIGestureRecognizerStateChanged)

            [self beginInteractiveTransitionIfPossible:sender];

    }];

}

#pragma mark -

#pragma mark UITabBarControllerDelegate

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

//  The tab bar controller tries to invoke this method on its delegate to

//  retrieve an animator object to be used for animating the transition to the

//  incoming view controller.  Your implementation is expected to return an

//  object that conforms to the UIViewControllerAnimatedTransitioning protocol,

//  or nil if the transition should not be animated.

//

- (id<UIViewControllerAnimatedTransitioning>)tabBarController:(UITabBarController *)tabBarController animationControllerForTransitionFromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC

{

    NSAssert(tabBarController == self.tabBarController, @"%@ is not the tab bar controller currently associated with %@", tabBarController, self);

    NSArray *viewControllers = tabBarController.viewControllers;

    if ([viewControllers indexOfObject:toVC] > [viewControllers indexOfObject:fromVC]) {

        // The incoming view controller succeeds the outgoing view controller,

        // slide towards the left.

        return [[AAPLSlideTransitionAnimator alloc] initWithTargetEdge:UIRectEdgeLeft];

    } else {

        // The incoming view controller precedes the outgoing view controller,

        // slide towards the right.

        return [[AAPLSlideTransitionAnimator alloc] initWithTargetEdge:UIRectEdgeRight];

    }

}

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

//  If an id<UIViewControllerAnimatedTransitioning> was returned from

//  -tabBarController:animationControllerForTransitionFromViewController:toViewController:,

//  the tab bar controller tries to invoke this method on its delegate to

//  retrieve an interaction controller for the transition.  Your implementation

//  is expected to return an object that conforms to the

//  UIViewControllerInteractiveTransitioning protocol, or nil if the transition

//  should not be a interactive.

//

- (id<UIViewControllerInteractiveTransitioning>)tabBarController:(UITabBarController *)tabBarController interactionControllerForAnimationController:(id<UIViewControllerAnimatedTransitioning>)animationController

{

    NSAssert(tabBarController == self.tabBarController, @"%@ is not the tab bar controller currently associated with %@", tabBarController, self);

    if (self.panGestureRecognizer.state == UIGestureRecognizerStateBegan || self.panGestureRecognizer.state == UIGestureRecognizerStateChanged) {

        return [[AAPLSlideTransitionInteractionController alloc] initWithGestureRecognizer:self.panGestureRecognizer];

    } else {

        // You must not return an interaction controller from this method unless

        // the transition will be interactive.

        return nil;

    }

}

@end