NSAttributedString+Interpolation.swift

import UIKit

/* Example of how to use it:
import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var label: UILabel!
    @IBOutlet weak var textView: UITextView!

    override func viewDidLoad() {
        super.viewDidLoad()
        let style = NSAttributedStringStyle(font: .preferredFont(forTextStyle: .body))
        label.attributedText = .compose(
            style: style,
            """
            Please go to \(urlString: "https://google.com" ) for more details. \(systemImage: "globe")
            Also you can go to our \(link: "Website", urlString: "https://google.com").
            This is another line.
            """
        )
        textView.attributedText = .compose(
            style: style,
            """
            Please go to \(urlString: "https://google.com" ) for more details. \(systemImage: "globe")
            Also you can go to our \(link: "Website", urlString: "https://google.com").
            This is another line.
            """
        )
    }


}
*/

struct NSAttributedStringLiteral: ExpressibleByStringLiteral {
    let value: NSAttributedString
    init(stringLiteral value: String) {
        self.value = NSAttributedString(string: value)
    }
}

extension NSAttributedStringLiteral: ExpressibleByStringInterpolation {
    init(stringInterpolation: StringInterpolation) {
        self.value = stringInterpolation.output
    }
}

extension NSAttributedStringLiteral {
    struct StringInterpolation: StringInterpolationProtocol {

        var output = NSMutableAttributedString()

        init(literalCapacity: Int, interpolationCount: Int) {
            // DO NOTHING
            // this initializer is required, and can be used as a performance optimization
        }

        mutating func appendLiteral(_ literal: String) {
            output.append(NSAttributedString(string: literal))
        }

        mutating func appendInterpolation(link label: String? = nil, url: URL) {
            output.append(NSAttributedString(string: label ?? url.absoluteString, attributes: [.link: url]))
        }

        mutating func appendInterpolation(link label: String? = nil, urlString: String) {
            assert(URL(string: urlString) != nil)
            output.append(NSAttributedString(string: label ?? urlString, attributes: [.link: urlString]))
        }

        mutating func appendInterpolation(image: UIImage?, size: CGSize? = nil) {
            let attachment = NSTextAttachment()
            attachment.image = image
            if let size = size {
                attachment.bounds.size = size
            }
            output.append(NSAttributedString(attachment: attachment))
        }

        @available(iOS 13.0, *)
        mutating func appendInterpolation(systemImage name: String, tintColor: UIColor? = nil) {
            var image = UIImage(systemName: name)
            if let tintColor = tintColor {
                image = image?.withTintColor(tintColor)
            }
            appendInterpolation(image: image)
        }
    }
}

struct NSAttributedStringStyle {
    static let `default` = NSAttributedStringStyle()
    let font: UIFont?
    let foregroundColor: UIColor?
    let alignment: NSTextAlignment?
    let lineSpacing: CGFloat?
    let paragraphSpacing: CGFloat?

    init(font: UIFont? = nil, foregroundColor: UIColor? = nil, alignment: NSTextAlignment? = nil, lineSpacing: CGFloat? = nil, paragraphSpacing: CGFloat? = nil) {
        self.font = font
        self.foregroundColor = foregroundColor
        self.alignment = alignment
        self.lineSpacing = lineSpacing
        self.paragraphSpacing = paragraphSpacing
    }

    func attributes() -> [NSAttributedString.Key: Any] {
        var attributes: [NSAttributedString.Key: Any] = [:]
        attributes[.font] = font
        attributes[.foregroundColor] = foregroundColor
        let paragraphStyle = NSMutableParagraphStyle()
        if let alignment = alignment {
            paragraphStyle.alignment = alignment
        }
        if let lineSpacing = lineSpacing {
            paragraphStyle.lineSpacing = lineSpacing
        }
        if let paragraphSpacing = paragraphSpacing {
            paragraphStyle.paragraphSpacing = paragraphSpacing
        }
        attributes[.paragraphStyle] = paragraphStyle
        return attributes
    }
}

extension NSAttributedString {
    static func compose(style: NSAttributedStringStyle = .default, _ literal: NSAttributedStringLiteral) -> NSAttributedString {
        let mutableAttributedString = NSMutableAttributedString(attributedString: literal.value)
        let range = NSRange(location: 0, length: mutableAttributedString.length)
        mutableAttributedString.addAttributes(style.attributes(), range: range)
        return mutableAttributedString
    }
}