article-programmaticalstyling6.swift

import UIKit

// MARK: Image helpers

extension UIImage {
    struct Constants {
        static let defaultTraits = [UITraitCollection(userInterfaceStyle: .dark),
                                    UITraitCollection(userInterfaceStyle: .light)]
    }

    static func buttonBackground(color: UIColor,
                                 borderColor: UIColor,
                                 borderWidth: CGFloat,
                                 cornerRadius: CGFloat,
                                 traitCollections: [UITraitCollection] = Constants.defaultTraits) -> UIImage {
        let set = UIImageAsset()

        for trait in traitCollections {
            let image = buttonBackground(color: color.resolvedColor(with: trait),
                                         borderColor: borderColor.resolvedColor(with: trait),
                                         borderWidth: borderWidth,
                                         cornerRadius: cornerRadius)
            let insets = image.size.width / 2
            set.register(image.resizableImage(withCapInsets: UIEdgeInsets(top: insets, left: insets,
                                                                          bottom: insets, right: insets)),
                         with: UITraitCollection(traitsFrom: [trait, UITraitCollection(displayScale: image.scale)]))
        }

        return set.image(with: UITraitCollection())
    }

    private static func from(color: UIColor,
                             size: CGSize = CGSize(width: 1, height: 1)) -> UIImage {
        return UIGraphicsImageRenderer(size: size).image { context in
            color.setFill()
            context.fill(CGRect(origin: .zero, size: size))
        }
    }

    private static func buttonBackground(color: UIColor,
                                         borderColor: UIColor,
                                         borderWidth: CGFloat,
                                         cornerRadius: CGFloat) -> UIImage {
        let width = max(2, cornerRadius * 2)
        let size = CGSize(width: width, height: width)

        return UIGraphicsImageRenderer(size: size).image { context in
            color.setFill()
            context.fill(CGRect(origin: .zero, size: size))
        }.roundedBorder(color: borderColor,
                        width: borderWidth,
                        radius: cornerRadius)!
    }

    private func roundedBorder(color: UIColor, width: CGFloat, radius: CGFloat) -> UIImage? {
        let format = imageRendererFormat
        format.opaque = false

        return UIGraphicsImageRenderer(size: size, format: format).image { _ in
            let ovalPath = UIBezierPath(roundedRect: CGRect(origin: .zero, size: size), cornerRadius: radius)
            ovalPath.addClip()
            draw(at: .zero)
            color.setStroke()
            ovalPath.lineWidth = width
            ovalPath.stroke()
        }
    }
}

// MARK: Implementation example

let backgroundColor = UIColor {
    $0.userInterfaceStyle == .dark ?
        UIColor(red: 10.0 / 255, green: 40.0 / 255, blue: 58.0 / 255, alpha: 1) :
        UIColor(red: 183.0 / 255, green: 228.0 / 255, blue: 255.0 / 255, alpha: 1)
}


let borderColour = UIColor {
    $0.userInterfaceStyle == .dark ?
        UIColor(red: 197.0 / 255, green: 197.0 / 255, blue: 197.0 / 255, alpha: 1) :
        UIColor(red: 0, green: 27.0 / 255, blue: 67.0 / 255, alpha: 1)
}

// MARK: Usage
let someImage = UIImage.buttonBackground(color: backgroundColor,
                                         borderColor: borderColour,
                                         borderWidth: 2,
                                         cornerRadius: 8,
                                         traitCollections: UIImage.Constants.defaultTraits)