MKNavigationController

//
//  MKNavigationController.m
//  
//
//  Created by Mohammad Alatrash on 7/29/15.
//  Copyright (c) 2015 MKALatrash. All rights reserved.
//
/// A UINavigationController subclass allowing the interactive pop gesture to be recognized when the navigation bar is hidden or a custom back button is used.

#import "MKNavigationController.h"

@interface MKNavigationController ()<UINavigationControllerDelegate, UIGestureRecognizerDelegate>

/**
 *  A Boolean value indicating whether navigation controller is currently pushing a new view controller on the stack.
 */
@property (nonatomic, getter = isDuringPushAnimation) BOOL duringPushAnimation;

/**
 *  A real delegate of the class. `delegate` property is used only for keeping an internal state during
 *  animations – we need to know when the animation ended, and that info is available only 
 *  from `navigationController:didShowViewController:animated:`.
 */
@property (weak, nonatomic) id<UINavigationControllerDelegate> realDelegate;

@end

@implementation MKNavigationController

#pragma mark - NSObject

- (void)dealloc
{
    self.delegate = nil;
    self.interactivePopGestureRecognizer.delegate = nil;
}

#pragma mark - UIViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    if (!self.delegate) {
        self.delegate = self;
    }
    
    self.interactivePopGestureRecognizer.delegate = self;
}

#pragma mark - UINavigationController

- (void)setDelegate:(id<UINavigationControllerDelegate>)delegate
{
    [super setDelegate:delegate ? self : nil];
    self.realDelegate = delegate != self ? delegate : nil;
}

- (void)pushViewController:(UIViewController *)viewController
                  animated:(BOOL)animated __attribute__((objc_requires_super))
{
    self.duringPushAnimation = YES;
    [super pushViewController:viewController animated:animated];
}

#pragma mark UINavigationControllerDelegate

- (void)navigationController:(UINavigationController *)navigationController
       didShowViewController:(UIViewController *)viewController
                    animated:(BOOL)animated
{
    NSCAssert(self.interactivePopGestureRecognizer.delegate == self, @"MKNavigationController won't work correctly if you change interactivePopGestureRecognizer's delegate.");
    
    self.duringPushAnimation = NO;
    
    if ([self.realDelegate respondsToSelector:_cmd]) {
        [self.realDelegate navigationController:navigationController didShowViewController:viewController animated:animated];
    }
}

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController*)fromVC toViewController:(UIViewController*)toVC
{
    if ([self.realDelegate respondsToSelector:_cmd]) {
        return [self.realDelegate navigationController:navigationController animationControllerForOperation:operation fromViewController:fromVC toViewController:toVC];
    }
    return nil;
}

- (id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController*)navigationController interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>)animationController
{
    if ([self.realDelegate respondsToSelector:_cmd]) {
        return [self.realDelegate navigationController:navigationController interactionControllerForAnimationController:animationController];
    }
    return nil;
}

#pragma mark - UIGestureRecognizerDelegate

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
{
    if (gestureRecognizer == self.interactivePopGestureRecognizer) {
        // Disable pop gesture in two situations:
        // 1) when the pop animation is in progress
        // 2) when user swipes quickly a couple of times and animations don't have time to be performed
        return [self.viewControllers count] > 1 && !self.isDuringPushAnimation;
    } else {
        // default value
        return YES;
    }
}

#pragma mark - Delegate Forwarder

// Thanks for the idea goes to: https://github.com/steipete/PSPDFTextView/blob/ee9ce04ad04217efe0bc84d67f3895a34252d37c/PSPDFTextView/PSPDFTextView.m#L148-164

- (BOOL)respondsToSelector:(SEL)s
{
    return [super respondsToSelector:s] || [self.realDelegate respondsToSelector:s];
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)s
{
    return [super methodSignatureForSelector:s] ?: [(id)self.realDelegate methodSignatureForSelector:s];
}

- (void)forwardInvocation:(NSInvocation *)invocation
{
    id delegate = self.realDelegate;
    if ([delegate respondsToSelector:invocation.selector]) {
        [invocation invokeWithTarget:delegate];
    }
}

@end