class Previewer: UIViewController { ... }

public weak var delegate: Delegate?
public weak var dataSource: DataSource?

/// - Parameters:
///   - container: Tell Previewer which view component tirggers this display operation, all is for the display animation.
///   if nil, Previewer will provide a fade animate.
///   - fromSource: When displaying animate play, Previewer should known who is the animation acort.
///   Of course you can passing nil, then Previewer will get that from 'dataSource' by 'currentIndex'.
///   - index: Tell Previewer which resource you wanna show from the 'dataSource' at index
///   - controller: The controller which is presenting Previewer
public func display(fromImageContainer container: UIView? = nil, fromSource source: UIImage? = nil, presentingController: UIViewController? = nil, current index: Int = 0)

/// The base resource provider of ImageProvider and VideoProvider
public protocol ResourceProvider {}

public protocol ImageProvider: ResourceProvider, Kingfisher.ImageDataProvider {}

public protocol VideoProvider: ResourceProvider, AnyObject {
    
    /// Video Content View
    var videoView: CZImagePreviewer.VideoView? { get }
        
    // Previewer should lintening the video size's changing, returning the new size in this closure
    typealias VideoSizeProvider = (_ videoSize: CGSize) -> Void
    var videoSizeProvider: VideoSizeProvider? { get set }
    
    func play()
    func pause()
    
    func cellDidEndDisplay()
    
    // You can do some preparing opreation for the video resource right here
    func perload()
}

public protocol DataSource: AnyObject {
    
    func numberOfItems(in previewer: Previewer) -> Int
    
    func imagePreviewer(_ previewer: Previewer, resourceForItemAtIndex index: Int) -> ResourceProvider?
    
    func imagePreviewer(_ previewer: Previewer, imageLoadingStateDidChanged state: Previewer.ImageLoadingState, at index: Int, accessoryView: AccessoryView?)
    
    /// Provide the accessory view for Previewer, this accessory view is not a part of scrolling or zooming effect. 
    /// Will calling when the index changed.
    /// - imagePreviewer: Previewer
    /// - index: which index of item need accessory view
    func imagePreviewer(_ imagePreviewer: Previewer, consoleForItemAtIndex index: Int) -> AccessoryView?
    
    /// Provider the accessory view for Previewer on each cell item. this is not part of zooming effect, but scrolling is.
    /// This accessory view will cover on the cell.
    /// Will calling when the index changed.
    /// - imagePreviewer: Previewer
    /// - cell: which cell adding this AccessoryView as the subview.
    /// - index: which index of item need accessory view
    func imagePreviewer(_ imagePreviewer: Previewer, accessoryViewForCell cell: CollectionViewCell, at index: Int) -> AccessoryView?
    
}

public protocol Delegate: AnyObject {
    
    func imagePreviewer(_ previewer: Previewer, willDisplayAtIndex index: Int)
    
    func imagePreviewer(_ previewer: Previewer, didDisplayAtIndex index: Int)
    
    func imagePreviewer(_ previewer: Previewer, indexDidChangedTo newIndex: Int, fromOldIndex oldIndex: Int)
    
    func imagePreviewer(_ previewer: Previewer, willDismissWithCell cell: CollectionViewCell, at index: Int) -> UIView?
    
    func imagePreviewerDidDismiss(_ previewer: Previewer)

    /// longPress gesture event happened with Previewer
    func imagePreviewer(_ previewer: Previewer, didLongPressAtIndex index: Int)
    
    /// By default, Previewer did add two kinds of gesture for dismiss: UITapGesture and UIPanningGesture.
    /// Call when Tap or Panning gesture been trigger. The returning Boolean value is deciding this dismiss should be happen or not.
    func imagePreviewer(_ previewer: Previewer, shouldDismissWithGesture gesture: UIGestureRecognizer, at index: Int) -> Bool
    
    /// Call after Previewer executed method: `deleteItems(at indexs: [Int])`
    func imagePreviewer(_ previewer: Previewer, didFinishDeletedItems indexs: [Int])   
}