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

import UIKit

public class GalleryViewController: UIPageViewController {
    
    let galleryDataSource: GalleryDataSource
    let initialItemIndex: Int
    private let _itemsCount: Int
    private var itemsCount: Int {
        get {
            precondition(_itemsCount == galleryDataSource.galleryItemsCount(), "GalleryDataSource item count cannot change")
            return _itemsCount
        }
    }
    
    var currentItemViewController: GalleryItemViewController {
        viewControllers![0] as! GalleryItemViewController
    }
    
    private var dismissInteraction: GalleryDismissInteraction!
    private var presentationAnimationCompletionHandlers: [() -> Void] = []
    
    override public var prefersStatusBarHidden: Bool {
        true
    }
    override public var preferredStatusBarUpdateAnimation: UIStatusBarAnimation {
        .none
    }
    override public var childForHomeIndicatorAutoHidden: UIViewController? {
        currentItemViewController
    }
    
    public init(dataSource: GalleryDataSource, initialItemIndex: Int) {
        self.galleryDataSource = dataSource
        self.initialItemIndex = initialItemIndex
        self._itemsCount = dataSource.galleryItemsCount()
        precondition(initialItemIndex >= 0 && initialItemIndex < _itemsCount, "initialItemIndex is out of bounds")
        
        super.init(transitionStyle: .scroll, navigationOrientation: .horizontal, options: [
            .interPageSpacing: 50
        ])
        
        modalPresentationStyle = .fullScreen
        transitioningDelegate = self
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    public override func viewDidLoad() {
        super.viewDidLoad()
        
        dismissInteraction = GalleryDismissInteraction(viewController: self)
        
        view.backgroundColor = .black
        overrideUserInterfaceStyle = .dark
        
        dataSource = self
        delegate = self
        
        setViewControllers([makeItemVC(index: initialItemIndex)], direction: .forward, animated: false)
    }
    
    public override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        if animated {
            // Wait until the transition is no longer in-progress, otherwise things will just get deferred again.
            DispatchQueue.main.async {
                self.presentationAnimationCompleted()
            }
        }
    }
    
    public override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        
        if isBeingDismissed {
            currentItemViewController.content.galleryContentWillDisappear()
        }
    }
    
    private func makeItemVC(index: Int) -> GalleryItemViewController {
        let content = galleryDataSource.galleryContentViewController(forItemAt: index)
        return GalleryItemViewController(delegate: self, itemIndex: index, content: content)
    }
    
    func presentationAnimationCompleted() {
        for block in presentationAnimationCompletionHandlers {
            block()
        }
        currentItemViewController.content.galleryContentDidAppear()
    }
}

extension GalleryViewController: UIPageViewControllerDataSource {
    public func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let viewController = viewController as? GalleryItemViewController else {
            preconditionFailure("VC must be GalleryItemViewController")
        }
        guard viewController.itemIndex > 0 else {
            return nil
        }
        return makeItemVC(index: viewController.itemIndex - 1)
    }
    
    public func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let viewController = viewController as? GalleryItemViewController else {
            preconditionFailure("VC must be GalleryItemViewController")
        }
        guard viewController.itemIndex < itemsCount - 1 else {
            return nil
        }
        return makeItemVC(index: viewController.itemIndex + 1)
    }
}

extension GalleryViewController: UIPageViewControllerDelegate {
    public func pageViewController(_ pageViewController: UIPageViewController, willTransitionTo pendingViewControllers: [UIViewController]) {
        currentItemViewController.content.galleryContentWillDisappear()
    }
    
    public func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        currentItemViewController.content.galleryContentDidAppear()
    }
}

extension GalleryViewController: GalleryItemViewControllerDelegate {
    func isGalleryBeingPresented() -> Bool {
        isBeingPresented
    }
    
    func addPresentationAnimationCompletion(_ block: @escaping () -> Void) {
        presentationAnimationCompletionHandlers.append(block)
    }
    
    func galleryItemClose(_ item: GalleryItemViewController) {
        dismiss(animated: true)
    }
    
    func galleryItemApplicationActivities(_ item: GalleryItemViewController) -> [UIActivity]? {
        galleryDataSource.galleryApplicationActivities(forItemAt: item.itemIndex)
    }
}

extension GalleryViewController: UIViewControllerTransitioningDelegate {
    public func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        if let sourceView = galleryDataSource.galleryContentTransitionSourceView(forItemAt: initialItemIndex) {
            return GalleryPresentationAnimationController(sourceView: sourceView)
        } else {
            return nil
        }
    }
    
    public func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        if let sourceView = galleryDataSource.galleryContentTransitionSourceView(forItemAt: currentItemViewController.itemIndex) {
            let translation: CGPoint?
            let velocity: CGPoint?
            if let dismissInteraction,
               dismissInteraction.isActive {
                translation = dismissInteraction.dismissTranslation
                velocity = dismissInteraction.dismissVelocity
            } else {
                translation = nil
                velocity = nil
            }
            return GalleryDismissAnimationController(sourceView: sourceView, interactiveTranslation: translation, interactiveVelocity: velocity)
        } else {
            return nil
        }
    }
}