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

import UIKit

class GalleryPresentationAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
    private let sourceView: UIView
    private var completionHandlers: [() -> Void] = []
    
    init(sourceView: UIView) {
        self.sourceView = sourceView
    }
    
    func addCompletionHandler(_ block: @escaping () -> Void) {
        completionHandlers.append(block)
    }
    
    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()
        }
        
        to.presentationAnimationController = self
        
        let itemViewController = to.currentItemViewController

        if !itemViewController.content.canAnimateFromSourceView || UIAccessibility.prefersCrossFadeTransitions {
            animateCrossFadeTransition(using: transitionContext)
            return
        }
        
        let container = transitionContext.containerView
        itemViewController.view.layoutIfNeeded()
        
        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 {
            sourceToDestTransform = origSourceTransform
                .translatedBy(x: destFrameInContainer.midX - sourceFrameInContainer.midX, y: destFrameInContainer.midY - sourceFrameInContainer.midY)
                .scaledBy(x: destFrameInContainer.width / sourceFrameInContainer.width, y: destFrameInContainer.height / sourceFrameInContainer.height)
        } else {
            sourceToDestTransform = nil
        }
        
        let content = itemViewController.takeContent()
        content.view.translatesAutoresizingMaskIntoConstraints = true
        
        container.addSubview(to.view)
        container.addSubview(content.view)
        
        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: 0.4, bounce: 0.3
        let spring = UISpringTimingParameters(mass: 1, stiffness: 247, damping: 22, initialVelocity: .zero)
        let animator = UIViewPropertyAnimator(duration: duration, timingParameters: spring)
        
        animator.addAnimations {
            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
            if sourceToDestTransform != nil {
                self.sourceView.transform = origSourceTransform
            }
            
            itemViewController.addContent()
            
            transitionContext.completeTransition(true)
            
            for block in self.completionHandlers {
                block()
            }
            
            to.presentationAnimationController = nil
        }
        
        animator.startAnimation()
    }
    
    private func animateCrossFadeTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard let to = transitionContext.viewController(forKey: .to) as? GalleryViewController else {
            return
        }
        
        transitionContext.containerView.addSubview(to.view)
        to.view.alpha = 0
        
        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)
            
            for block in self.completionHandlers {
                block()
            }
            
            to.presentationAnimationController = nil
        }
        animator.startAnimation()
    }
}