//
//  GalleryDismissAnimationController.swift
//  GalleryVC
//
//  Created by Shadowfacts on 3/1/24.
//

import UIKit

class GalleryDismissAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
    private let sourceView: UIView
    private let interactiveTranslation: CGPoint?
    private let interactiveVelocity: CGPoint?
    
    init(sourceView: UIView, interactiveTranslation: CGPoint?, interactiveVelocity: CGPoint?) {
        self.sourceView = sourceView
        self.interactiveTranslation = interactiveTranslation
        self.interactiveVelocity = interactiveVelocity
    }
    
    func transitionDuration(using transitionContext: (any UIViewControllerContextTransitioning)?) -> TimeInterval {
        return 0.3
    }
    
    func animateTransition(using transitionContext: any UIViewControllerContextTransitioning) {
        guard let to = transitionContext.viewController(forKey: .to),
              let from = transitionContext.viewController(forKey: .from) as? GalleryViewController else {
            fatalError()
        }
        
        let itemViewController = from.currentItemViewController
        
        if !itemViewController.content.canAnimateFromSourceView || (UIAccessibility.prefersCrossFadeTransitions && interactiveVelocity == nil) {
            animateCrossFadeTransition(using: transitionContext)
            return
        }
        
        let container = transitionContext.containerView
        let sourceFrameInContainer = container.convert(sourceView.bounds, from: sourceView)
        let destFrameInContainer = container.convert(itemViewController.content.view.bounds, from: itemViewController.content.view)
        
        let origSourceTransform = sourceView.transform
        let appliedSourceToDestTransform: Bool
        if destFrameInContainer.width > 0 && destFrameInContainer.height > 0 {
            appliedSourceToDestTransform = true
            let scale = min(destFrameInContainer.width / sourceFrameInContainer.width, destFrameInContainer.height / sourceFrameInContainer.height)
            let sourceToDestTransform = origSourceTransform
                .translatedBy(x: destFrameInContainer.midX - sourceFrameInContainer.midX, y: destFrameInContainer.midY - sourceFrameInContainer.midY)
                .scaledBy(x: scale, y: scale)
            sourceView.transform = sourceToDestTransform
        } else {
            appliedSourceToDestTransform = false
        }
        
        // Moving `to.view` to the container is necessary when the presenting VC (i.e., `to`)
        // is in the window's root presentation.
        // But it breaks when the gallery is presented from a sheet-presented VC--in which case
        // `to.view` is already in the view hierarchy at this point; and adding it to the
        // container causees it to be removed when the transition completes.
        if to.view.superview == nil {
            to.view.frame = container.bounds
            container.addSubview(to.view)
        }
        
        from.view.frame = container.bounds
        container.addSubview(from.view)

        let content = itemViewController.takeContent()
        content.view.translatesAutoresizingMaskIntoConstraints = true
        content.view.layer.masksToBounds = true
        container.addSubview(content.view)
        
        content.view.frame = destFrameInContainer
        content.view.layer.opacity = 1
        
        container.layoutIfNeeded()
        
        let duration = self.transitionDuration(using: transitionContext)
        var initialVelocity: CGVector
        if let interactiveVelocity,
           let interactiveTranslation,
           // very short/fast flicks don't transfer their velocity, since it makes size change animation look wacky due to the springs initial undershoot
           sqrt(pow(interactiveTranslation.x, 2) + pow(interactiveTranslation.y, 2)) > 100,
           sqrt(pow(interactiveVelocity.x, 2) + pow(interactiveVelocity.y, 2)) < 2000 {
            let xDistance = sourceFrameInContainer.midX - destFrameInContainer.midX
            let yDistance = sourceFrameInContainer.midY - destFrameInContainer.midY
            initialVelocity = CGVector(
                dx: xDistance == 0 ? 0 : interactiveVelocity.x / xDistance,
                dy: yDistance == 0 ? 0 : interactiveVelocity.y / yDistance
            )
        } else {
            initialVelocity = .zero
        }
        initialVelocity.dx = max(-10, min(10, initialVelocity.dx))
        initialVelocity.dy = max(-10, min(10, initialVelocity.dy))
        // no bounce for the dismiss animation
        let spring = UISpringTimingParameters(mass: 1, stiffness: 439, damping: 42, initialVelocity: initialVelocity)
        let animator = UIViewPropertyAnimator(duration: duration, timingParameters: spring)
        
        animator.addAnimations {
            from.view.layer.opacity = 0
            
            if appliedSourceToDestTransform {
                self.sourceView.transform = origSourceTransform
            }
            content.view.frame = sourceFrameInContainer
            content.view.layer.opacity = 0
            
            itemViewController.setControlsVisible(false, animated: false, dueToUserInteraction: false)
        }
        
        animator.addCompletion { _ in
            transitionContext.completeTransition(true)
        }
        
        animator.startAnimation()
    }
    
    private func animateCrossFadeTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let fromVC = transitionContext.viewController(forKey: .from),
              let toVC = transitionContext.viewController(forKey: .to) else {
            return
        }
        
        toVC.view.frame = transitionContext.containerView.bounds
        fromVC.view.frame = transitionContext.containerView.bounds
        transitionContext.containerView.addSubview(toVC.view)
        transitionContext.containerView.addSubview(fromVC.view)
        
        let duration = transitionDuration(using: transitionContext)
        let animator = UIViewPropertyAnimator(duration: duration, curve: .easeInOut)
        animator.addAnimations {
            fromVC.view.alpha = 0
        }
        animator.addCompletion { _ in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
        animator.startAnimation()
    }
}