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?
    
    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!
            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)
            
            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
        }
    }
}