PDF imposition in Swift

//---------------------------------------------------------------------------------------
// Copyright (c) 2001-2019 by PDFTron Systems Inc. All Rights Reserved.
// Consult legal.txt regarding legal and license information.
//---------------------------------------------------------------------------------------

import PDFNet
import Foundation

//-----------------------------------------------------------------------------------
// The sample illustrates how multiple pages can be combined/imposed
// using PDFNet. Page imposition can be used to arrange/order pages
// prior to printing or to assemble a 'master' page from several 'source'
// pages. Using PDFNet API it is possible to write applications that can
// re-order the pages such that they will display in the correct order
// when the hard copy pages are compiled and folded correctly.
//-----------------------------------------------------------------------------------
func runImpositionTest() -> Int {
    return autoreleasepool {
        var ret: Int = 0
        
        
        // Relative path to the folder containing test files.
        let input_path: String? = Bundle.main.path(forResource: "newsletter", ofType: "pdf")
        let output_path: String = URL(fileURLWithPath: NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]).appendingPathComponent("newsletter_booklet.pdf").path
        
        do {
            try PTPDFNet.catchException {
                print("-------------------------------------------------")
                print("Opening the input pdf...")
                
                let filein: String? = input_path
                let fileout: String = output_path
                
                let in_doc: PTPDFDoc = PTPDFDoc(filepath: filein)
                in_doc.initSecurityHandler()
                
                // Create a list of pages to import from one PDF document to another.
                let import_pages: PTVectorPage = PTVectorPage()
                let itr: PTPageIterator = in_doc.getPageIterator(1)
                while itr.hasNext() {
                    import_pages.add(itr.current())
                    itr.next()
                }
                
                let new_doc: PTPDFDoc = PTPDFDoc()
                let imported_pages: PTVectorPage = new_doc.importPages(import_pages, import_bookmarks: false)
                
                // Paper dimension for A3 format in points. Because one inch has
                // 72 points, 11.69 inch 72 = 841.69 points
                let media_box: PTPDFRect = PTPDFRect(x1: 0, y1: 0, x2: 1190.88, y2: 841.69)
                let mid_point: Double = media_box.width() / 2
                
                let builder: PTElementBuilder = PTElementBuilder()
                let writer: PTElementWriter = PTElementWriter()
                
                var i: Int32 = 0
                while i < imported_pages.size() {
                    // Create a blank new A3 page and place on it two pages from the input document.
                    let new_page: PTPage = new_doc.pageCreate(media_box)
                    
                    writer.writerBegin(with: new_page, placement: e_ptoverlay, page_coord_sys: true, compress: true, resources: nil)
                
                    // Place the first page
                    var src_page: PTPage = imported_pages.get(i)
                    var element: PTElement = builder.createForm(with: src_page)
                    
                    var sc_x: Double = mid_point / src_page.getWidth(e_ptcrop)
                    var sc_y: Double = media_box.height() / src_page.getHeight(e_ptcrop)
                    var scale: Double = sc_x < sc_y ? sc_x : sc_y // min(sc_x, sc_y)
                    element.getGState().setTransform(scale, b: 0, c: 0, d: scale, h: 0, v: 0)
                    writer.writePlacedElement(element)
                    
                    // Place the second page
                    i += 1
                    if i < imported_pages.size() {
                        src_page = imported_pages.get(i)
                        element = builder.createForm(with: src_page)
                        sc_x = mid_point / src_page.getWidth(e_ptcrop)
                        sc_y = media_box.height() / src_page.getHeight(e_ptcrop)
                        scale = sc_x < sc_y ? sc_x : sc_y
                        // min(sc_x, sc_y)
                        element.getGState().setTransform(scale, b: 0, c: 0, d: scale, h: mid_point, v: 0)
                        writer.writePlacedElement(element)
                    }
                    
                    writer.end()
                    new_doc.pagePushBack(new_page)
                    i += 1
                }
                
                new_doc.save(toFile: fileout, flags: e_ptlinearized.rawValue)
                print("Done. Result saved in newsletter_booklet.pdf...")
            }
        } catch let e as NSError {
            print("\(e)")
            ret = 1
        }
        
        print("Done.")
        return ret
    }
}