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

import UIKit

class SheetContainerPresentationAnimationController: NSObject, UIViewControllerAnimatedTransitioning {

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        if UIAccessibility.prefersCrossFadeTransitionsBackwardsCompat {
            return 0.25
        } else {
            return 0.5
        }
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let toVC = transitionContext.viewController(forKey: .to) as? SheetContainerViewController else {
            fatalError()
        }
        
        if UIAccessibility.prefersCrossFadeTransitionsBackwardsCompat {
            animateCrossFadeTransition(using: transitionContext)
            return
        }
        
        toVC.dimmingView.isHidden = true
        
        let finalFrame = transitionContext.finalFrame(for: toVC)

        let dimmingView = UIView(frame: finalFrame)
        dimmingView.backgroundColor = toVC.dimmingView.backgroundColor
        dimmingView.alpha = 0
        
        let container = transitionContext.containerView
        container.addSubview(dimmingView)
        container.addSubview(toVC.view)
        
        let initialConstant = toVC.initialConstant
        toVC.topConstraint.constant = toVC.view.bounds.height
        toVC.view.layoutIfNeeded()
        
        let duration = transitionDuration(using: transitionContext)
        let damping = SheetContainerViewController.springDamping
        let pointsPerSecond: CGFloat = 50
        let velocity = pointsPerSecond / initialConstant
        UIView.animate(withDuration: duration, delay: 0, usingSpringWithDamping: damping, initialSpringVelocity: velocity, options: []) {
            // we animate the dimming view's frame so that it doesn't go under the content view, in case there's a transparent background
            // we also extend the dimming view under any rounded corners the content view has
            dimmingView.frame = CGRect(x: 0, y: 0, width: dimmingView.bounds.width, height: initialConstant + toVC.content.view.layer.cornerRadius)
            dimmingView.alpha = toVC.dimmingView.alpha
            toVC.topConstraint.constant = initialConstant
            toVC.view.layoutIfNeeded()
        } completion: { (finished) in
            dimmingView.removeFromSuperview()
            toVC.dimmingView.isHidden = false
            
            toVC.view.frame = finalFrame
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }

    }
    
    func animateCrossFadeTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let toVC = transitionContext.viewController(forKey: .to) as? SheetContainerViewController else {
            fatalError()
        }
        
        transitionContext.containerView.addSubview(toVC.view)
        
        toVC.view.alpha = 0
        
        let duration = transitionDuration(using: transitionContext)
        UIView.animate(withDuration: duration) {
            toVC.view.alpha = 1
        } completion: { (finished) in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
        
    }
    
}