/*

Copyright (C) 2016 Apple Inc. All Rights Reserved.

See LICENSE.txt for this sample’s licensing information

Abstract:

A view controller that shows text about this app, using readable margins.

*/

import UIKit

class AboutViewController: UIViewController {

    // MARK: Properties

    var headlineLabel: UILabel?

    var label: UILabel?

    // MARK: View Controller

    override func loadView() {

        let view = UIView()

        view.backgroundColor = UIColor.white

        let headlineLabel = UILabel()

        headlineLabel.font = UIFont.preferredFont(forTextStyle: UIFontTextStyle.headline)

        headlineLabel.numberOfLines = 1

        headlineLabel.translatesAutoresizingMaskIntoConstraints = false

        view.addSubview(headlineLabel)

        self.headlineLabel = headlineLabel

        let label = UILabel()

        label.font = UIFont.preferredFont(forTextStyle: UIFontTextStyle.body)

        label.numberOfLines = 0

        if let url = Bundle.main.url(forResource: "Text", withExtension: "txt") {

            do {

                var usedEncoding: String.Encoding = .utf8

                let text = try String(contentsOf: url, usedEncoding: &usedEncoding)

                label.text = text

            } catch let error {

                print("Error loading text: \(error)")

            }

        }

        label.translatesAutoresizingMaskIntoConstraints = false

        view.addSubview(label)

        self.label = label

        self.view = view

        var constraints = [NSLayoutConstraint]()

        let viewsAndGuides: [String: AnyObject] = [

            "topLayoutGuide":       topLayoutGuide,

            "bottomLayoutGuide":    bottomLayoutGuide,

            "headlineLabel":        headlineLabel,

            "label":                label

        ]

        // Position our labels in the center, respecting the readableContentGuide if it is available

        constraints += NSLayoutConstraint.constraints(withVisualFormat: "V:[topLayoutGuide]-[headlineLabel]-[label]-[bottomLayoutGuide]|", options: [], metrics: nil, views: viewsAndGuides)

        if #available(iOS 9.0, *) {

            // Use `readableContentGuide` on iOS 9.

            let readableContentGuide = view.readableContentGuide

            constraints += [

                label.leadingAnchor.constraint(equalTo: readableContentGuide.leadingAnchor),

                label.trailingAnchor.constraint(equalTo: readableContentGuide.trailingAnchor),

                headlineLabel.leadingAnchor.constraint(equalTo: readableContentGuide.leadingAnchor),

                headlineLabel.trailingAnchor.constraint(equalTo: readableContentGuide.trailingAnchor)

            ]

        }

        else {

            // Fallback on earlier versions.

            constraints += NSLayoutConstraint.constraints(withVisualFormat: "20-[label]-20|", options: [], metrics:nil, views: viewsAndGuides)

            constraints += NSLayoutConstraint.constraints(withVisualFormat: "20-[headlineLabel]-20|", options: [], metrics:nil, views: viewsAndGuides)

        }

        NSLayoutConstraint.activate(constraints)

        updateLabelsForTraitCollection(traitCollection)

    }

    // MARK: Transition

    override func willTransition(to newCollection: UITraitCollection, with coordinator: UIViewControllerTransitionCoordinator) {

        super.willTransition(to: newCollection, with:coordinator)

        updateLabelsForTraitCollection(newCollection)

    }

    fileprivate func updateLabelsForTraitCollection(_ collection: UITraitCollection) {

        if collection.horizontalSizeClass == .regular {

            headlineLabel?.text = "Regular Width"

        }

        else {

            headlineLabel?.text = "Compact Width"

        }

    }

}