Tusker/Packages/GalleryVC/Sources/GalleryVC/GalleryDismissInteraction.swift

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

import UIKit

@MainActor
class GalleryDismissInteraction: NSObject {
    
    private unowned let viewController: GalleryViewController
    
    private var content: GalleryContentViewController?
    private var origContentFrameInGallery: CGRect?
    private var origControlsVisible: Bool?

    private(set) var isActive = false
    private(set) var dismissVelocity: CGPoint?
    private(set) var dismissTranslation: CGPoint?
    
    private var cancelAnimator: UIViewPropertyAnimator?
    
    init(viewController: GalleryViewController) {
        self.viewController = viewController
        super.init()
        let panRecognizer = UIPanGestureRecognizer(target: self, action: #selector(panRecognized))
        panRecognizer.delegate = self
        panRecognizer.allowedScrollTypesMask = .continuous
        viewController.view.addGestureRecognizer(panRecognizer)
    }
    
    @objc private func panRecognized(_ recognizer: UIPanGestureRecognizer) {
        switch recognizer.state {
        case .began:
            isActive = true
            
            origContentFrameInGallery = viewController.view.convert(viewController.currentItemViewController.content.view.bounds, from: viewController.currentItemViewController.content.view)
            content = viewController.currentItemViewController.takeContent()
            content!.view.translatesAutoresizingMaskIntoConstraints = true
            content!.view.frame = origContentFrameInGallery!
            // Make sure the context remains behind the controls
            content!.view.layer.zPosition = -1000
            viewController.view.addSubview(content!.view)
            
            origControlsVisible = viewController.currentItemViewController.controlsVisible
            if origControlsVisible! {
                viewController.currentItemViewController.setControlsVisible(false, animated: true, dueToUserInteraction: false)
            }
            
        case .changed:
            let translation = recognizer.translation(in: viewController.view)
            content!.view.frame = origContentFrameInGallery!.offsetBy(dx: translation.x, dy: translation.y)
            
        case .ended:
            let translation = recognizer.translation(in: viewController.view)
            let velocity = recognizer.velocity(in: viewController.view)
            
            let translationMagnitude = sqrt(translation.x.magnitudeSquared + translation.y.magnitudeSquared)
            let velocityMagnitude = sqrt(velocity.x.magnitudeSquared + velocity.y.magnitudeSquared)
            
            if translationMagnitude < 150 && velocityMagnitude < 500 {
                isActive = false
                
                cancelAnimator?.stopAnimation(true)
                
                let spring = UISpringTimingParameters(mass: 1, stiffness: 439, damping: 42, initialVelocity: .zero)
                cancelAnimator = UIViewPropertyAnimator(duration: 0.2, timingParameters: spring)
                cancelAnimator!.addAnimations {
                    self.content!.view.frame = self.origContentFrameInGallery!
                    self.viewController.currentItemViewController.setControlsVisible(self.origControlsVisible!, animated: false, dueToUserInteraction: false)
                }
                cancelAnimator!.addCompletion { _ in
                    guard !self.isActive else {
                        // bail in case the animation finishing raced with the user's interaction
                        return
                    }
                    self.content!.view.layer.zPosition = 0
                    self.content!.view.removeFromSuperview()
                    self.viewController.currentItemViewController.addContent()
                    self.content = nil
                    self.origContentFrameInGallery = nil
                    self.origControlsVisible = nil
                }
                cancelAnimator!.startAnimation()

            } else {
                dismissVelocity = velocity
                dismissTranslation = translation
                viewController.dismiss(animated: true)
                
                // don't unset this until after dismiss is called, so that the dismiss animation controller can read it
                isActive = false
            }
            
        default:
            break
        }
    }
    
}

extension GalleryDismissInteraction: UIGestureRecognizerDelegate {
    func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
        let itemVC = viewController.currentItemViewController
        if viewController.galleryDataSource.galleryContentTransitionSourceView(forItemAt: itemVC.itemIndex) == nil {
            return false
        } else if itemVC.scrollView.zoomScale > itemVC.scrollView.minimumZoomScale {
            return false
        } else if !itemVC.scrollAndZoomEnabled {
            return false
        } else {
            return true
        }
    }
}