//
//  GalleryPresentationAnimationController.swift
//  GalleryVC
//
//  Created by Shadowfacts on 12/28/23.
//

import UIKit

class GalleryPresentationAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
    private let sourceView: UIView
    
    init(sourceView: UIView) {
        self.sourceView = sourceView
    }
    
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.4
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let to = transitionContext.viewController(forKey: .to) as? GalleryViewController else {
            fatalError()
        }
        
        let itemViewController = to.currentItemViewController

        if !itemViewController.content.canAnimateFromSourceView || UIAccessibility.prefersCrossFadeTransitions {
            animateCrossFadeTransition(using: transitionContext)
            return
        }
        
        let container = transitionContext.containerView
        to.view.frame = container.bounds
        container.addSubview(to.view)
        
        container.layoutIfNeeded()
        // Make sure the zoom scale is updated before getting the content view frame, since it needs to take into account the correct transform.
        itemViewController.updateZoomScale(resetZoom: true)
        
        let sourceFrameInContainer = container.convert(sourceView.bounds, from: sourceView)
        let destFrameInContainer = container.convert(itemViewController.content.view.bounds, from: itemViewController.content.view)

        // Use a transformation to make the actual source view appear to move into the destination frame.
        // Doing this while having the content view fade-in papers over the z-index change when
        // there was something overlapping the source view.
        let origSourceTransform = sourceView.transform
        let sourceToDestTransform: CGAffineTransform?
        if destFrameInContainer.width > 0 && destFrameInContainer.height > 0 {
            // Scale evenly in both dimensions, to prevent the source view appearing to stretch/distort during the animation.
            let scale = min(destFrameInContainer.width / sourceFrameInContainer.width, destFrameInContainer.height / sourceFrameInContainer.height)
            sourceToDestTransform = origSourceTransform
                .translatedBy(x: destFrameInContainer.midX - sourceFrameInContainer.midX, y: destFrameInContainer.midY - sourceFrameInContainer.midY)
                .scaledBy(x: scale, y: scale)
        } else {
            sourceToDestTransform = nil
        }
        
        let content = itemViewController.takeContent()
        content.view.translatesAutoresizingMaskIntoConstraints = true
        container.insertSubview(content.view, belowSubview: to.view)

        // Use a separate dimming view from to.view, so that the gallery controls can be in front of the moving content.
        let dimmingView = UIView()
        dimmingView.backgroundColor = .black
        dimmingView.frame = container.bounds
        dimmingView.layer.opacity = 0
        container.insertSubview(dimmingView, belowSubview: content.view)

        to.view.backgroundColor = nil
        to.view.layer.opacity = 0
        content.view.frame = sourceFrameInContainer
        content.view.layer.opacity = 0
        
        container.layoutIfNeeded()
        
        // This needs to take place after the layout, so that the transform is correct.
        itemViewController.setControlsVisible(false, animated: false)

        let duration = self.transitionDuration(using: transitionContext)
        // rougly equivalent to duration: 0.35, bounce: 0.3
        let spring = UISpringTimingParameters(mass: 1, stiffness: 322, damping: 25, initialVelocity: .zero)
        let animator = UIViewPropertyAnimator(duration: duration, timingParameters: spring)
        
        animator.addAnimations {
            dimmingView.layer.opacity = 1
            
            to.view.layer.opacity = 1
            
            content.view.frame = destFrameInContainer
            content.view.layer.opacity = 1
            
            itemViewController.setControlsVisible(true, animated: false)

            if let sourceToDestTransform {
                self.sourceView.transform = sourceToDestTransform
            }
        }
        
        animator.addCompletion { _ in
            dimmingView.removeFromSuperview()
            
            to.view.backgroundColor = .black
            
            if sourceToDestTransform != nil {
                self.sourceView.transform = origSourceTransform
            }
            
            itemViewController.addContent()
            
            transitionContext.completeTransition(true)
        }
        
        animator.startAnimation()
    }
    
    private func animateCrossFadeTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let to = transitionContext.viewController(forKey: .to) as? GalleryViewController else {
            return
        }
        
        to.view.alpha = 0
        to.view.frame = transitionContext.containerView.bounds
        transitionContext.containerView.addSubview(to.view)
        
        let duration = transitionDuration(using: transitionContext)
        let animator = UIViewPropertyAnimator(duration: duration, curve: .easeInOut)
        animator.addAnimations {
            to.view.alpha = 1
        }
        animator.addCompletion { _ in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
        animator.startAnimation()
    }
}