ViewController.swift

// generate a PDF with
//	a 6-inch vertical line crossed by a 6-inch horizontal line
//	vertical and horizontal "1-inch hash" lines
//	6-, 4- and 2-inch diameter circles

// see app image here: https://imgur.com/a/O9dmB9M

import PDFKit

class ViewController: UIViewController {
	
	let pdfView = PDFView()
	let createButton = UIButton()
	let shareButton = UIButton()

	var pdfData: Data?
	
	override func viewDidLoad() {
		super.viewDidLoad()
		
		view.backgroundColor = .systemYellow
		
		[pdfView, createButton, shareButton].forEach {
			$0.translatesAutoresizingMaskIntoConstraints = false
			view.addSubview($0)
		}
		
		let g = view.safeAreaLayoutGuide
		
		NSLayoutConstraint.activate([
			
			pdfView.heightAnchor.constraint(equalTo: g.heightAnchor, multiplier: 0.6),
			pdfView.widthAnchor.constraint(equalTo: pdfView.heightAnchor, multiplier: 8.5 / 11.0),
			pdfView.centerXAnchor.constraint(equalTo: g.centerXAnchor),
			pdfView.centerYAnchor.constraint(equalTo: g.centerYAnchor),
			
			createButton.bottomAnchor.constraint(equalTo: pdfView.topAnchor, constant: -20.0),
			createButton.leadingAnchor.constraint(equalTo: pdfView.leadingAnchor),
			createButton.trailingAnchor.constraint(equalTo: pdfView.trailingAnchor),

			shareButton.topAnchor.constraint(equalTo: pdfView.bottomAnchor, constant: 20.0),
			shareButton.leadingAnchor.constraint(equalTo: pdfView.leadingAnchor),
			shareButton.trailingAnchor.constraint(equalTo: pdfView.trailingAnchor),
			
		])
		
		createButton.backgroundColor = .blue
		createButton.setTitle("Create", for: [])
		createButton.setTitleColor(.white, for: .normal)
		createButton.setTitleColor(.gray, for: .highlighted)

		shareButton.backgroundColor = .red
		shareButton.setTitle("Share", for: [])
		shareButton.setTitleColor(.white, for: .normal)
		shareButton.setTitleColor(.gray, for: .highlighted)

		pdfView.autoScales = true

		createButton.addTarget(self, action: #selector(createTap(_:)), for: .touchUpInside)
		shareButton.addTarget(self, action: #selector(shareTap(_:)), for: .touchUpInside)

	}
	
	@objc func shareTap(_ sender: Any?) -> Void {
		if let data = pdfData {
			let vc = UIActivityViewController(activityItems: [data], applicationActivities: [])
			present(vc, animated: true, completion: nil)
		}
	}
	
	@objc func createTap(_ sender: Any?) -> Void {
		pdfData = createTest()
		if let data = pdfData {
			pdfView.document = PDFDocument(data: data)
		}
	}
	
	func createTest() -> Data {
		let format = UIGraphicsPDFRendererFormat()
		
		let pageWidth = 8.5 * 72.0
		let pageHeight = 11 * 72.0
		let pageRect = CGRect(x: 0, y: 0, width: pageWidth, height: pageHeight)
		
		let renderer = UIGraphicsPDFRenderer(bounds: pageRect, format: format)

		let data = renderer.pdfData { (context) in
			context.beginPage()
			let context = context.cgContext
			drawMajorLines(context, pageRect: pageRect)
			drawHashLines(context, pageRect: pageRect)
			drawCircles(context, pageRect: pageRect)
		}
		
		return data
	}
	
	func drawMajorLines(_ drawContext: CGContext, pageRect: CGRect) -> Void {
		
		let r = CGRect(x: pageRect.midX - (72.0 * 3.0),
					   y: pageRect.midY - (72.0 * 3.0),
					   width: 72.0 * 6.0,
					   height: 72.0 * 6.0)
		
		drawContext.saveGState()
		
		drawContext.move(to: CGPoint(x: r.minX, y: r.midY))
		drawContext.addLine(to: CGPoint(x: r.maxX, y: r.midY))
		
		drawContext.move(to: CGPoint(x: r.midX, y: r.minY))
		drawContext.addLine(to: CGPoint(x: r.midX, y: r.maxY))
		
		drawContext.setStrokeColor(UIColor.black.cgColor)
		
		drawContext.strokePath()
		
		drawContext.restoreGState()
		
	}
	
	func drawHashLines(_ drawContext: CGContext, pageRect: CGRect) -> Void {
		
		let r = CGRect(x: pageRect.midX - (72.0 * 3.0),
					   y: pageRect.midY - (72.0 * 3.0),
					   width: 72.0 * 6.0,
					   height: 72.0 * 6.0)
		
		drawContext.saveGState()
		
		var y: CGFloat = r.midY - 72.0 * 0.5
		var x: CGFloat = r.minX
		
		for i in 1...7 {
			if i != 4 {
				drawContext.move(to: CGPoint(x: x, y: y))
				drawContext.addLine(to: CGPoint(x: x, y: y + 72.0))
			}
			x += 72.0
		}
		
		y = r.minY
		x = r.midX - 72.0 * 0.5
		
		for i in 1...7 {
			if i != 4 {
				drawContext.move(to: CGPoint(x: x, y: y))
				drawContext.addLine(to: CGPoint(x: x + 72.0, y: y))
			}
			y += 72.0
		}
		
		drawContext.setStrokeColor(UIColor.blue.cgColor)
		
		drawContext.strokePath()
		
		drawContext.restoreGState()
		
	}
	
	func drawCircles(_ drawContext: CGContext, pageRect: CGRect) -> Void {
		
		var r = CGRect(x: pageRect.midX - (72.0 * 3.0),
					   y: pageRect.midY - (72.0 * 3.0),
					   width: 72.0 * 6.0,
					   height: 72.0 * 6.0)
		
		drawContext.saveGState()
		
		drawContext.addEllipse(in: r)
		
		r = r.insetBy(dx: 72.0, dy: 72.0)
		
		drawContext.addEllipse(in: r)
		
		r = r.insetBy(dx: 72.0, dy: 72.0)
		
		drawContext.addEllipse(in: r)
		
		drawContext.setStrokeColor(UIColor.red.cgColor)
		
		drawContext.strokePath()
		
		drawContext.restoreGState()
		
	}

}