import UIKit

extension RDEpubReaderView: UICollectionViewDataSource, RDEpubReaderFlowLayoutDelegate, RDEpubReaderFlowLayoutDataSoure {

    public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        if let identifer = pageReuseIdentifier(for: indexPath.row) {
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: identifer, for: IndexPath(item: indexPath.row, section: 0)) as! RDEpubReaderContentCell
            let preloadedView = preloadController.takePreloadedView(for: indexPath.row)
            let reusableView = cell.containerView ?? preloadedView
            let contentView = contentViewForPage(indexPath.row, reusableView: reusableView)
            (contentView as? RDEpubReaderPageVisibilityHandling)?
                .readerPageVisibilityDidChange(isVisible: false)
            cell.containerView = contentView
            DispatchQueue.main.async { [weak self] in
                self?.updatePageContentVisibility()
            }
            
            if pageDirection == .rightToLeft && currentDisplayType != .verticalScroll {
                cell.contentView.transform = CGAffineTransform(scaleX: -1, y: 1)
            } else {
                cell.contentView.transform = .identity
            }
            return cell
        }

        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: NSStringFromClass(UICollectionViewCell.self), for: indexPath)

        return cell
    }

    public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return numberOfPages()
    }

    public func pageNum(flowLayout: RDEpubReaderFlowLayout, pageIndex: Int) {
        if currentPage >= 0, currentPage != pageIndex {
            predictedPageDirection = pageIndex >= currentPage
        }
        currentPage = pageIndex
        primePageCache(around: pageIndex, preferredForward: predictedPageDirection)
    }

    public func heigtOfVerticalScrollPage(flowLayout: RDEpubReaderFlowLayout, pageIndex: Int) -> CGFloat? {
        return nil
    }
}