Swift Attributed String Construction Helpers

AttributeConstructor.swift

import UIKit

public enum AttributeConstructor {
    public enum Attribute {
        case lineHeight(CGFloat)
        case lineHeightMultiple(CGFloat)
        case alignment(NSTextAlignment)
        case font(UIFont)
        case kern(CGFloat)
        case color(UIColor)
        case baselineOffset(CGFloat)
        case lineBreakMode(NSLineBreakMode)
        case underline
        case strikeThrough(UIColor)
    }

    public static func construct(_ attributes: [Attribute]) -> [NSAttributedString.Key: Any] {
        let paragraphStyle = NSMutableParagraphStyle()
        var attributesDic = [NSAttributedString.Key: Any]()
        attributes.forEach {
            switch $0 {
            case let .lineHeight(value):
                paragraphStyle.minimumLineHeight = value

            case let .lineHeightMultiple(value):
                paragraphStyle.lineHeightMultiple = value

            case let .alignment(alignment):
                paragraphStyle.alignment = alignment

            case let .font(font):
                attributesDic[.font] = font

            case let .kern(kern):
                attributesDic[.kern] = kern

            case let .color(color):
                attributesDic[.foregroundColor] = color

            case let .baselineOffset(baselineOffset):
                attributesDic[.baselineOffset] = baselineOffset

            case let .lineBreakMode(lineBreakMode):
                paragraphStyle.lineBreakMode = lineBreakMode

            case .underline:
                attributesDic[.underlineStyle] = NSUnderlineStyle.single.rawValue

            case let .strikeThrough(color):
                attributesDic[.strikethroughColor] = color
                attributesDic[.strikethroughStyle] = NSUnderlineStyle.single.rawValue
            }
        }
        attributesDic[.paragraphStyle] = paragraphStyle
        return attributesDic
    }
}

extension NSAttributedString {
    convenience init(string: String, attributes: [AttributeConstructor.Attribute]) {
        let attributes = AttributeConstructor.construct(attributes)
        self.init(string: string, attributes: attributes)
    }

    public func highlight(
        substring: String,
        attributes: AttributeConstructor.Attribute...
        ) -> NSAttributedString {
        let resultString = NSMutableAttributedString(attributedString: self)
        let nsText = string as NSString
        let range = nsText.range(of: substring)

        let attributes = AttributeConstructor.construct(attributes)
        resultString.addAttributes(attributes, range: range)

        return resultString
    }

    public var mutable: NSMutableAttributedString {
        return .init(attributedString: self)
    }
}

extension NSMutableAttributedString {
    public func addAttributes(_ attrs: AttributeConstructor.Attribute..., range: NSRange) {
        let attributes = AttributeConstructor.construct(attrs)
        addAttributes(attributes, range: range)
    }
}

extension String {
    public typealias Attribute = AttributeConstructor.Attribute

    public func withAttributes(_ attributes: Attribute...) -> NSAttributedString {
        let attributes = AttributeConstructor.construct(attributes)
        return NSAttributedString(string: self, attributes: attributes)
    }
    
    public func withAttributes(_ attributes: [Attribute]) -> NSAttributedString {
        let attributes = AttributeConstructor.construct(attributes)
        return NSAttributedString(string: self, attributes: attributes)
    }
}

// Usage example
"some string".withAttributes(
    .font(AppFonts.regular.fontWithSize(12.0)),
    .color(UIColor.blue),
    .kern(0.4),
    .lineHeight(18)
)