ReadViewSDK/Sources/RDEpubReaderView/ReaderView/Paging/RDEpubReaderPagingController.swift

import UIKit

struct RDEpubReaderPagingController {

    struct PageTransitionRequest: Equatable {
        let pageNum: Int
        let animated: Bool
    }

    var pendingTransitionRequest: PageTransitionRequest?

    var isTransitioning: Bool = false

    var didBuildUI = false

    static func createPageViewController(isDualPage: Bool) -> UIPageViewController {
        let options: [UIPageViewController.OptionsKey: Any]?
        if isDualPage {
            options = [.spineLocation: NSNumber(value: UIPageViewController.SpineLocation.mid.rawValue)]
        } else {
            options = nil
        }
        let pageVC = UIPageViewController(transitionStyle: .pageCurl, navigationOrientation: .horizontal, options: options)
        pageVC.isDoubleSided = isDualPage
        return pageVC
    }

    mutating func shouldQueuePageTransition(_ request: PageTransitionRequest, currentDisplayType: RDEpubReaderView.DisplayType) -> Bool {
        guard currentDisplayType == .pageCurl, isTransitioning else { return false }
        pendingTransitionRequest = request
        return true
    }

    mutating func finishPageCurlTransition() -> PageTransitionRequest? {
        isTransitioning = false
        guard let pending = pendingTransitionRequest else { return nil }
        pendingTransitionRequest = nil
        return pending
    }

    mutating func resetPendingState() {
        isTransitioning = false
        pendingTransitionRequest = nil
    }
}