/*

Copyright (C) 2017 Apple Inc. All Rights Reserved.

See LICENSE.txt for this sample’s licensing information

Abstract:

UIScrollView subclass that handles the user input to zoom the PDF page.  This class handles swapping the TiledPDFViews when the zoom level changes.

*/

import UIKit

class TiledPDFScrollView: UIScrollView, UIScrollViewDelegate {

    // Frame of the PDF

    var pageRect = CGRect()

    // A low resolution image of the PDF page that is displayed until the TiledPDFView renders its content.

    var backgroundImageView: UIView!

    // The TiledPDFView that is currently front most.

    var tiledPDFView: TiledPDFView!

    // The old TiledPDFView that we draw on top of when the zooming stops.

    var oldTiledPDFView: TiledPDFView!

    // Current PDF zoom scale.

    var PDFScale = CGFloat()

    // a reference to the page being drawn

    var tiledPDFPage: CGPDFPage!

    func initialize()

    {

        decelerationRate = UIScrollViewDecelerationRateFast

        delegate = self

        layer.borderColor = UIColor.lightGray.cgColor

        layer.borderWidth = 5

        minimumZoomScale = 0.25

        maximumZoomScale = 5

        backgroundImageView = UIView(frame: frame)

        oldTiledPDFView = TiledPDFView(frame: pageRect, scale: PDFScale)

    }

    required init?(coder aDecoder: NSCoder)

    {

        super.init(coder: aDecoder)

        initialize()

    }

    override init(frame: CGRect)

    {

        super.init(frame: frame)

        initialize()

    }

    func setPDFPage(_ newPDFPage: CGPDFPage?)

    {

        // note: calls to CGPDFPageRetain and CGPDFPageRelease in the Objective-C version are not necessary here because CF objects are automatically memory managed in Swift.

        tiledPDFPage = newPDFPage

        // PDFPage is null if we're requested to draw a padded blank page by the parent UIPageViewController

        if tiledPDFPage == nil

        {

            pageRect = bounds

        }

        else

        {

            pageRect = tiledPDFPage.getBoxRect(CGPDFBox.mediaBox)

            PDFScale = frame.size.width / pageRect.size.width

            pageRect = CGRect(x: pageRect.origin.x, y: pageRect.origin.y, width: pageRect.size.width * PDFScale, height: pageRect.size.height * PDFScale)

        }

        // Create the TiledPDFView based on the size of the PDF page and scale it to fit the view.

        replaceTiledPDFViewWithFrame(pageRect)

    }

    // Use layoutSubviews to center the PDF page in the view.

    override func layoutSubviews()

    {

        super.layoutSubviews()

        // Center the image as it becomes smaller than the size of the screen.

        let boundsSize:CGSize = bounds.size

        var frameToCenter:CGRect = tiledPDFView.frame

        // Center horizontally.

        if frameToCenter.size.width < boundsSize.width

        {

            frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2

        }

        else

        {

            frameToCenter.origin.x = 0

        }

        // Center vertically.

        if frameToCenter.size.height < boundsSize.height

        {

            frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2

        }

        else

        {

            frameToCenter.origin.y = 0

        }

        tiledPDFView.frame = frameToCenter

        backgroundImageView.frame = frameToCenter

        /*

         To handle the interaction between CATiledLayer and high resolution screens, set the tiling view's contentScaleFactor to 1.0.

         If this step were omitted, the content scale factor would be 2.0 on high resolution screens, which would cause the CATiledLayer to ask for tiles of the wrong scale.

         */

        tiledPDFView.contentScaleFactor = 1.0

    }

    /*

     A UIScrollView delegate callback, called when the user starts zooming.

     Return the current TiledPDFView.

     */

    func viewForZooming(in scrollView: UIScrollView) -> UIView?

    {

       return tiledPDFView

    }

    func scrollViewWillBeginZooming(_ scrollView: UIScrollView, with view: UIView?)

    {

        // Remove back tiled view.

        oldTiledPDFView.removeFromSuperview()

        // Set the current TiledPDFView to be the old view.

        oldTiledPDFView = tiledPDFView

    }

    /*

     A UIScrollView delegate callback, called when the user begins zooming.

     When the user begins zooming, remove the old TiledPDFView and set the current TiledPDFView to be the old view so we can create a new TiledPDFView when the zooming ends.

     */

    func scrollViewDidEndZooming(_ scrollView: UIScrollView, with view: UIView?, atScale scale: CGFloat)

    {

        // Set the new scale factor for the TiledPDFView.

        PDFScale *= scale

        replaceTiledPDFViewWithFrame(oldTiledPDFView.frame)

    }

    func replaceTiledPDFViewWithFrame(_ frame: CGRect)

    {

        // Create a new tiled PDF View at the new scale

        let newTiledPDFView = TiledPDFView(frame: frame, scale: PDFScale)

        newTiledPDFView.pdfPage = tiledPDFPage

        // Add the new TiledPDFView to the PDFScrollView.

        addSubview(newTiledPDFView)

        tiledPDFView = newTiledPDFView

    }

}