//
//  SheetContainerDismissAnimationController.swift
//  SheetController
//
//  Created by Shadowfacts on 9/24/19.
//  Copyright © 2019 Shadowfacts. All rights reserved.
//

import UIKit

class SheetContainerDismissAnimationController: NSObject, UIViewControllerAnimatedTransitioning {

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        if UIAccessibility.prefersCrossFadeTransitionsBackwardsCompat && (transitionContext?.viewController(forKey: .from) as? SheetContainerViewController)?.dismissAnimationInitialVelocity == nil {
            return 0.25
        } else {
            return 0.35
        }
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let fromVC = transitionContext.viewController(forKey: .from) as? SheetContainerViewController else {
            fatalError()
        }
        
        if UIAccessibility.prefersCrossFadeTransitionsBackwardsCompat && fromVC.dismissAnimationInitialVelocity == nil {
            animateCrossFadeTransition(using: transitionContext)
            return
        }
        
        fromVC.view.alpha = 1.0
        fromVC.dimmingView.isHidden = true
        
        // match the frame to the original dimming view's frame so that it doesn't go under the content
        let dimmingView = UIView(frame: fromVC.dimmingView.bounds)
        dimmingView.backgroundColor = fromVC.dimmingView.backgroundColor
        dimmingView.alpha = fromVC.dimmingView.alpha

        let container = transitionContext.containerView
        container.addSubview(dimmingView)
        container.addSubview(fromVC.view)

        let duration = transitionDuration(using: transitionContext)
        let animator: UIViewPropertyAnimator
        
        if let initialVelocity = fromVC.dismissAnimationInitialVelocity {
            let vector = CGVector(dx: initialVelocity, dy: 0)
            let damping = SheetContainerViewController.springDamping
            let parameters = UISpringTimingParameters(dampingRatio: damping, initialVelocity: vector)
            animator = UIViewPropertyAnimator(duration: duration, timingParameters: parameters)
        } else {
            animator = UIViewPropertyAnimator(duration: duration, curve: .easeInOut)
        }
        
        animator.addAnimations {
            dimmingView.frame = container.bounds
            dimmingView.alpha = 0
            fromVC.view.transform = CGAffineTransform(translationX: 0, y: fromVC.content.view.bounds.height)
        }
        animator.addCompletion { (position) in
            dimmingView.removeFromSuperview()

            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
        
        animator.startAnimation()
    }
    
    func animateCrossFadeTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let fromVC = transitionContext.viewController(forKey: .from) as? SheetContainerViewController else {
            fatalError()
        }
        
        transitionContext.containerView.addSubview(fromVC.view)
        
        let duration = transitionDuration(using: transitionContext)
        UIView.animate(withDuration: duration) {
            fromVC.view.alpha = 0
        } completion: { (finished) in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
    }
    
}