🍰 Layered Cakewalk [Swift] - AttributesStyle

0. NSAttributedString+AttributesStyle.swift

import UIKit
import PlaygroundSupport

/// 
/// 🍰 Layered Cakewalk - AttributesStyle
///
/// Allows you to structure style classes used to modify an `NSAttributedString`s.
///

//
// 🚗 Demo
//

func exampleLines() -> [NSAttributedString]
{
    let base   = NSAttributedString.AttributesStyle().defaults() /// 🦄 base/defaults style is required to process the `fragments`.
    let style1 = NSAttributedString.AttributesStyle(foregroundColor: .red)
    let style2 = NSAttributedString.AttributesStyle(fontFragment: .init(size: 40), foregroundColor: .blue)
    let style3 = NSAttributedString.AttributesStyle(underlineStyle: .double)

    return 
        [
            "Hello World!"
            +  base
            +  style1 ///  `full range`
            + (style: style2, range: NSRange(location: 0, length: 4))
            + (style: style3, range: NSRange(location: 3, length: 4))
        ]
}

//
// 🍰 Implementation
//

extension NSAttributedString
{
    public typealias Attributes = [Key: Any]
}

/// 📍`Meta tags`
///
extension NSAttributedString.Key
{
    public static let fontFragment           = NSAttributedString.Key("@fontFragment")
    public static let paragraphStyleFragment = NSAttributedString.Key("@paragraphStyleFragment")
}

extension NSAttributedString.Attributes
{
    public func with(_ attributesStyle: NSAttributedString.AttributesStyle) -> NSAttributedString.Attributes
    {
        var result = self

        /// 🎛 `font` or `fontFragment`
        /// 📍
        if let fontFragment = attributesStyle.fontFragment
        {
            let currentFontFragment = result[.fontFragment] as! NSAttributedString.FontFragment?
            let newFontFragment     = currentFontFragment?.with(fontFragment) ?? fontFragment
            
            if let currentFont = result[.font] as! UIFont? ?? attributesStyle.defaultFont
            {
                result[.font]         = newFontFragment.font(basedOn: currentFont.fontDescriptor)
                result[.fontFragment] = nil
            }
            else
            {
                result[.fontFragment] = newFontFragment
            }
        }
        else
        if let defaultFont = attributesStyle.defaultFont
        {
            if let currentFontFragment = result[.fontFragment] as! NSAttributedString.FontFragment?
            {
                result[.font]         = currentFontFragment.font(basedOn: defaultFont.fontDescriptor)
                result[.fontFragment] = nil
            }
            else
            if result[.font] == nil
            {
                result[.font] = defaultFont
            }
        }
        
        /// 🎛 `paragraphStyle` or `paragraphStyleFragment`
        /// 📍
        if let paragraphStyleFragment = attributesStyle.paragraphStyleFragment
        {
            let currentParagraphStyleFragment = result[.paragraphStyleFragment] as! NSAttributedString.ParagraphStyleFragment?
            let newParagraphStyleFragment     = currentParagraphStyleFragment?.with(paragraphStyleFragment) ?? paragraphStyleFragment
            
            if let currentParagraphStyle = result[.paragraphStyle] as! NSParagraphStyle? ?? attributesStyle.defaultParagraphStyle
            {
                result[.paragraphStyle]         = newParagraphStyleFragment.paragraphStyle(basedOn: currentParagraphStyle)
                result[.paragraphStyleFragment] = nil
            }
            else
            {
                result[.paragraphStyleFragment] = newParagraphStyleFragment
            }
        }
        else
        if let defaultParagraphStyle = attributesStyle.defaultParagraphStyle
        {
            if let currentParagraphStyleFragment = result[.paragraphStyleFragment] as! NSAttributedString.ParagraphStyleFragment?
            {
                result[.paragraphStyle]         = currentParagraphStyleFragment.paragraphStyle(basedOn: defaultParagraphStyle)
                result[.paragraphStyleFragment] = nil
            }
            else
            if result[.paragraphStyle] == nil
            {
                result[.paragraphStyle] = defaultParagraphStyle
            }
        }

        /// 🎛 `foregroundColor`
        
        if let foregroundColor = attributesStyle.foregroundColor
        {
            result[.foregroundColor] = foregroundColor
        }
        else
        if let defaultForegroundColor = attributesStyle.defaultForegroundColor, result[.foregroundColor] == nil
        {
            result[.foregroundColor] = defaultForegroundColor
        }
        
        /// 🎛 `underlineStyle`
        
        if let underlineStyle = attributesStyle.underlineStyle
        {
            result[.underlineStyle] = underlineStyle.rawValue
        }
        else
        if let defaultUnderlineStyle = attributesStyle.defaultUnderlineStyle, result[.underlineStyle] == nil
        {
            result[.underlineStyle] = defaultUnderlineStyle.rawValue
        }
        
        /// 🎛 `shadow`
        
        if let shadow = attributesStyle.shadow
        {
            result[.shadow] = shadow
        }

        return result
    }
}

extension NSAttributedString
{
    public struct FontFragment
    {
        static let systemFontPrefix = ".SFUI-"
        
        public var font:                 UIFont?
        public var name:                 String?
        public var family:               String?
        public var size:                 CGFloat?
        public var weight:               UIFont.Weight?
        public var symbolicTraits:       UIFontDescriptor.SymbolicTraits?
        public var addSymbolicTraits:    UIFontDescriptor.SymbolicTraits?
        public var removeSymbolicTraits: UIFontDescriptor.SymbolicTraits?
        
        public init(font: UIFont? = nil, name: String? = nil, family: String? = nil, size: CGFloat? = nil, weight: UIFont.Weight? = nil, removeWeight: Bool? = nil,
                    symbolicTraits: UIFontDescriptor.SymbolicTraits? = nil, addSymbolicTraits: UIFontDescriptor.SymbolicTraits? = nil, removeSymbolicTraits: UIFontDescriptor.SymbolicTraits? = nil)
        {
            self.font                 = font
            self.name                 = name
            self.family               = family
            self.size                 = size
            self.weight               = weight
            self.symbolicTraits       = symbolicTraits
            self.addSymbolicTraits    = addSymbolicTraits
            self.removeSymbolicTraits = removeSymbolicTraits
        }
        
        public func with(_ other: FontFragment) -> FontFragment
        {
            return FontFragment(font:                 other.font                 ?? self.font,
                                name:                 other.name                 ?? self.name,
                                family:               other.family               ?? self.family,
                                size:                 other.size                 ?? self.size,
                                weight:               other.weight               ?? self.weight,
                                symbolicTraits:       other.symbolicTraits       ?? self.symbolicTraits,
                                addSymbolicTraits:    other.addSymbolicTraits    ?? self.addSymbolicTraits,
                                removeSymbolicTraits: other.removeSymbolicTraits ?? self.removeSymbolicTraits)
        }
        
        public func fontDescriptor(basedOn: UIFontDescriptor) -> UIFontDescriptor
        {
            var result = self.font?.fontDescriptor ?? basedOn
            
            if let name = self.name, name != basedOn.postscriptName
            {
                /// Compiler warning:
                /// CoreText note: Client requested name `".SFUI-Regular"`, it will get `TimesNewRomanPSMT` rather than the intended font.
                /// All system UI font access should be through proper APIs such as `CTFontCreateUIFontForLanguage()` or `+[UIFont systemFontOfSize:]`.
                ///
                if name.hasPrefix(Self.systemFontPrefix)
                {
                    result = UIFont.systemFont(ofSize: basedOn.pointSize).fontDescriptor
                }
                else
                {
                    result = UIFont(name: name, size: basedOn.pointSize)!.fontDescriptor
                }
                
                result = result.withSymbolicTraits(basedOn.symbolicTraits) ?? result
            }
            
            if let weight = self.weight
            {
                result = result.addingAttributes([.traits : [UIFontDescriptor.TraitKey.weight : weight]])
            }
            
            if let family = self.family
            {
                result = result.withFamily(family)
            }
            if let size = self.size
            {
                result = result.withSize(size)
            }
            
            if self.symbolicTraits != nil || self.addSymbolicTraits != nil || self.removeSymbolicTraits != nil
            {
                var newTraits = self.symbolicTraits ?? result.symbolicTraits
            
                if let addSymbolicTraits = self.addSymbolicTraits
                {
                    newTraits.insert(addSymbolicTraits)
                }
                if let removeSymbolicTraits = self.removeSymbolicTraits
                {
                    newTraits.remove(removeSymbolicTraits)
                }
                
                result = result.withSymbolicTraits(newTraits) ?? result
            }

            return result
        }
        
        public func font(basedOn: UIFontDescriptor) -> UIFont
        {
            let newFontDescriptor = self.fontDescriptor(basedOn: basedOn)
            
            return UIFont(descriptor: newFontDescriptor, size: newFontDescriptor.pointSize)
        }
    }
}

extension NSAttributedString
{

    public struct ParagraphStyleFragment
    {
        public var alignment:          NSTextAlignment?
        public var lineBreakMode:      NSLineBreakMode?
        public var lineSpacing:        CGFloat?
        public var lineHeightMultiple: CGFloat?
        public var paragraphSpacingBefore: CGFloat?
        public var headIndent:         CGFloat?
        public var tailIndent:         CGFloat?

        public init(alignment: NSTextAlignment? = nil, lineBreakMode: NSLineBreakMode? = nil, lineSpacing: CGFloat? = nil, lineHeightMultiple: CGFloat? = nil,
                    //
                    paragraphSpacingBefore: CGFloat? = nil, headIndent: CGFloat? = nil, tailIndent: CGFloat? = nil)
        {
            self.alignment              = alignment
            self.lineBreakMode          = lineBreakMode
            self.lineSpacing            = lineSpacing
            self.lineHeightMultiple     = lineHeightMultiple
            self.paragraphSpacingBefore = paragraphSpacingBefore
            self.headIndent             = headIndent
            self.tailIndent             = tailIndent
        }
        
        public func with(_ other: ParagraphStyleFragment) -> ParagraphStyleFragment
        {
            return ParagraphStyleFragment(alignment:              other.alignment              ?? self.alignment,
                                          lineBreakMode:          other.lineBreakMode          ?? self.lineBreakMode,
                                          lineSpacing:            other.lineSpacing            ?? self.lineSpacing,
                                          lineHeightMultiple:     other.lineHeightMultiple     ?? self.lineHeightMultiple,
                                          paragraphSpacingBefore: other.paragraphSpacingBefore ?? self.paragraphSpacingBefore,
                                          headIndent:             other.headIndent             ?? self.headIndent,
                                          tailIndent:             other.tailIndent             ?? self.tailIndent)
        }
        
        public func paragraphStyle(basedOn: NSParagraphStyle) -> NSParagraphStyle
        {
            let result = NSMutableParagraphStyle()
                //
                result.alignment              = self.alignment              ?? basedOn.alignment
                result.lineBreakMode          = self.lineBreakMode          ?? basedOn.lineBreakMode
                result.lineSpacing            = self.lineSpacing            ?? basedOn.lineSpacing
                result.lineHeightMultiple     = self.lineHeightMultiple     ?? basedOn.lineHeightMultiple
                result.paragraphSpacingBefore = self.paragraphSpacingBefore ?? basedOn.paragraphSpacingBefore
                result.headIndent             = self.headIndent             ?? basedOn.headIndent
                result.tailIndent             = self.tailIndent             ?? basedOn.tailIndent
            
            return result
        }
    }
}

extension NSAttributedString
{
    public struct AttributesStyle
    {
        public var defaultFont:            UIFont?
        public var fontFragment:           FontFragment?
        //
        public var defaultParagraphStyle:  NSParagraphStyle?
        public var paragraphStyleFragment: ParagraphStyleFragment?
        //
        public var defaultForegroundColor: UIColor?
        public var foregroundColor:        UIColor?
        public var defaultUnderlineStyle:  NSUnderlineStyle?
        public var underlineStyle:         NSUnderlineStyle?
        //
        public var shadow:                 NSShadow?
        
        public init(defaultFont: UIFont? = nil, fontFragment: NSAttributedString.FontFragment? = nil,
                    //
                    defaultParagraphStyle: NSParagraphStyle? = nil, paragraphStyleFragment: NSAttributedString.ParagraphStyleFragment? = nil,
                    //
                    defaultForegroundColor: UIColor? = nil, foregroundColor: UIColor? = nil,
                    defaultUnderlineStyle:  NSUnderlineStyle? = nil, underlineStyle: NSUnderlineStyle? = nil,
                    //
                    shadow: NSShadow? = nil)
        {
            self.defaultFont            = defaultFont
            self.fontFragment           = fontFragment
            //
            self.defaultParagraphStyle  = defaultParagraphStyle
            self.paragraphStyleFragment = paragraphStyleFragment
            //
            self.defaultForegroundColor = defaultForegroundColor
            self.foregroundColor        = foregroundColor
            self.defaultUnderlineStyle  = defaultUnderlineStyle
            self.underlineStyle         = underlineStyle
            //
            self.shadow                 = shadow
        }
        
        public func with(_ other: AttributesStyle) -> AttributesStyle
        {
            return AttributesStyle(defaultFont:            other.defaultFont             ?? self.defaultFont,
                                   fontFragment:           other.fontFragment            .map { self.fontFragment?.with($0) ?? $0 }           ?? self.fontFragment,
                                   //
                                   defaultParagraphStyle:  other.defaultParagraphStyle   ?? self.defaultParagraphStyle,
                                   paragraphStyleFragment: other.paragraphStyleFragment  .map { self.paragraphStyleFragment?.with($0) ?? $0 } ?? self.paragraphStyleFragment,
                                   //
                                   defaultForegroundColor: other.defaultForegroundColor  ?? self.defaultForegroundColor,
                                   foregroundColor:        other.foregroundColor         ?? self.foregroundColor,
                                   defaultUnderlineStyle:  other.defaultUnderlineStyle   ?? self.defaultUnderlineStyle,
                                   underlineStyle:         other.underlineStyle          ?? self.underlineStyle,
                                   //
                                   shadow:                 other.shadow                  ?? self.shadow)
        }
        
        public func defaults() -> AttributesStyle
        {
            AttributesStyle(defaultFont: self.defaultFont ?? .preferredFont(forTextStyle: .body),
                            //
                            defaultParagraphStyle:  self.defaultParagraphStyle ?? .default,
                            //
                            defaultForegroundColor: self.defaultForegroundColor,
                            defaultUnderlineStyle:  self.defaultUnderlineStyle)
        }
        
        public func attributes(basedOn: Attributes = [:]) -> Attributes
        {
            basedOn.with(self)
        }
    }
    
    public func with(_ attributesStyle: AttributesStyle, in range: NSRange? = nil) -> NSAttributedString
    {
        let result = NSMutableAttributedString()
        
        let replacementRange = range ?? NSRange(self.string.startIndex..., in: self.string)
        
        if  replacementRange.location > 0
        {
            result.append(self.attributedSubstring(from: NSRange(location: 0, length: replacementRange.location)))
        }
        
        self.enumerateAttributes(in: replacementRange, options: [])
        {
            rangeAttributes, range, _ in

            let subString = (self.string as NSString).substring(with: range)
            
            result.append(NSAttributedString(string: subString, attributes: rangeAttributes.with(attributesStyle)))
        }
        
        if replacementRange.upperBound < self.length
        {
            result.append(self.attributedSubstring(from: NSRange(location: replacementRange.upperBound, length: self.length - replacementRange.upperBound)))
        }

        return result
    }
}

///
/// `AttributedStyle Operators`
///

@inlinable public func + (left: NSAttributedString.AttributesStyle, right: NSAttributedString.AttributesStyle) -> NSAttributedString.AttributesStyle
{
    return left.with(right)
}

@discardableResult
@inlinable public func += (left: inout NSAttributedString.AttributesStyle, right: NSAttributedString.AttributesStyle) -> NSAttributedString.AttributesStyle
{
           left = left + right
    return left
}

@inlinable public func + (left: NSAttributedString.Attributes, right: NSAttributedString.AttributesStyle) -> NSAttributedString.Attributes
{
    return left.with(right)
}

@inlinable public func += (left: inout NSAttributedString.Attributes, right: NSAttributedString.AttributesStyle) -> NSAttributedString.Attributes
{
           left = left + right
    return left
}

///
/// `NSAttributedString Operators`
///

@inlinable public func + (left: String, right: NSAttributedString.AttributesStyle) -> NSAttributedString
{
    return NSAttributedString(string: left).with(right)
}

@inlinable public func + (left: NSAttributedString, right: NSAttributedString.AttributesStyle) -> NSAttributedString
{
    return left.with(right)
}

@discardableResult
@inlinable public func += (left: inout NSAttributedString, right: NSAttributedString.AttributesStyle) -> NSAttributedString
{
           left = left + right
    return left
}

@inlinable public func + (left: NSAttributedString, right: (style: NSAttributedString.AttributesStyle, range: NSRange)) -> NSAttributedString
{
    return left.with(right.style, in: right.range)
}

@discardableResult
@inlinable public func += (left: inout NSAttributedString, right: (style: NSAttributedString.AttributesStyle, range: NSRange)) -> NSAttributedString
{
           left = left + right
    return left
}

//
// 🎡🎢🎠 Playground
//

class ExampleViewController : UIViewController
{
    
    override func loadView()
    {
        let view = UIView(frame: .zero)
            //
            view.backgroundColor = .white
        
        let stack = UIStackView(frame: .zero)
        
            stack.axis = .vertical
            //
            stack.spacing                            = 10
            stack.layoutMargins                      = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
            stack.isLayoutMarginsRelativeArrangement = true
        
        exampleLines()
            ///
            /// `Template`
            ///
            .map
            {
                let label = UILabel()
                    //
                    label.numberOfLines   = 0
                    //
                    label.attributedText  = $0
                
                return label
            }
            ///
            /// `Build`
            ///
            .forEach
            {
                stack.addArrangedSubview($0)
            }
        
        stack.addArrangedSubview(UIView()) // Spacer
        stack.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        
        view.addSubview(stack)
        
        self.view = view
    }
}
//
PlaygroundPage.current.liveView = ExampleViewController()

1. More-Examples.swift

//
// 👻 More examples
//

func exampleLines() -> [NSAttributedString]
{
    let base = NSAttributedString.AttributesStyle().defaults() /// 🦄 base/defaults style is required to process the `fragments`.
    
    let spacingStyle = NSAttributedString.AttributesStyle(paragraphStyleFragment: .init())
    
    let headerStyle  = NSAttributedString.AttributesStyle(foregroundColor: .gray)
    
    let codeStyle    = spacingStyle + NSAttributedString.AttributesStyle(
        //
        fontFragment:           .init(family: "Menlo",
                                      size:   11),
        paragraphStyleFragment: .init(lineHeightMultiple: 0.8),
        foregroundColor:        .darkGray)

    let style1        = NSAttributedString.AttributesStyle(foregroundColor: .red)
    let style3        = NSAttributedString.AttributesStyle(underlineStyle: .double)
    
    let fontSizeStyle = NSAttributedString.AttributesStyle(fontFragment: .init(size: 40), foregroundColor: .blue)
    let fontBoldStyle = NSAttributedString.AttributesStyle(fontFragment: .init(addSymbolicTraits: [.traitItalic]))
    let fontThinStyle = NSAttributedString.AttributesStyle(fontFragment: .init(weight: .thin))

    let existingAttributedString = NSAttributedString(string: "Font has been pre-defined", attributes: [.font : UIFont.preferredFont(forTextStyle: .headline)])
    
    return
        [
            "\nexistingAttributedString looks like:"
                + base
                + headerStyle
            ,
            existingAttributedString
            ,
            "\nApply some styles:"
                + base
                + headerStyle
            ,
            """
            existingAttributedString
                + (style: fontSizeStyle, range: NSRange(location: 5,  length: 3))
                + (style: fontBoldStyle, range: NSRange(location: 14, length: 3))
                + (style: fontThinStyle, range: NSRange(location: 9,  length: 3))
            """ + base + codeStyle
            ,
            "\nNow it looks like:"
                + base
                + headerStyle
            ,
            existingAttributedString
                + (style: fontSizeStyle, range: NSRange(location: 5,  length: 3))
                + (style: fontBoldStyle, range: NSRange(location: 14, length: 3))
                + (style: fontThinStyle, range: NSRange(location: 9,  length: 3))
        ]
}

The Example 🚗...

func exampleLines() -> [NSAttributedString]
{
    let base   = NSAttributedString.AttributesStyle().defaults() /// 🦄 base/defaults style is required to process the `fragments`.
    let style1 = NSAttributedString.AttributesStyle(foregroundColor: .red)
    let style2 = NSAttributedString.AttributesStyle(fontFragment: .init(size: 40), foregroundColor: .blue)
    let style3 = NSAttributedString.AttributesStyle(underlineStyle: .double)

    return
        [
            "Hello World!"
            +  base
            +  style1 ///  `full range`
            + (style: style2, range: NSRange(location: 0, length: 4))
            + (style: style3, range: NSRange(location: 3, length: 4))
        ]
}

More Examples

func exampleLines() -> [NSAttributedString]
{
    let base = NSAttributedString.AttributesStyle().defaults() /// 🦄 base/defaults style is required to process the `fragments`.
    
    let spacingStyle = NSAttributedString.AttributesStyle(paragraphStyleFragment: .init())
    
    let headerStyle  = NSAttributedString.AttributesStyle(foregroundColor: .gray)
    
    let codeStyle    = spacingStyle + NSAttributedString.AttributesStyle(
        //
        fontFragment:           .init(family: "Menlo",
                                      size:   11),
        paragraphStyleFragment: .init(lineHeightMultiple: 0.8),
        foregroundColor:        .darkGray)

    let style1        = NSAttributedString.AttributesStyle(foregroundColor: .red)
    let style3        = NSAttributedString.AttributesStyle(underlineStyle: .double)
    
    let fontSizeStyle   = NSAttributedString.AttributesStyle(fontFragment: .init(size: 40), foregroundColor: .blue)
    let fontItalicStyle = NSAttributedString.AttributesStyle(fontFragment: .init(addSymbolicTraits: [.traitItalic]))
    let fontThinStyle   = NSAttributedString.AttributesStyle(fontFragment: .init(weight: .thin))

    let existingAttributedString = NSAttributedString(string: "Font has been pre-defined", attributes: [.font : UIFont.preferredFont(forTextStyle: .headline)])
    
    return
        [
            "\n The String existingAttributedString looks like:"
                + base
                + headerStyle
            ,
            existingAttributedString
            ,
            "\nApply some styles:"
                + base
                + headerStyle
            ,
            """
            existingAttributedString
                + (style: fontSizeStyle,   range: NSRange(location: 5,  length: 3))
                + (style: fontItalicStyle, range: NSRange(location: 14, length: 3))
                + (style: fontThinStyle,   range: NSRange(location: 9,  length: 3))
            """ + base + codeStyle
            ,
            "\nNow it looks like:"
                + base
                + headerStyle
            ,
            existingAttributedString
                + (style: fontSizeStyle,   range: NSRange(location: 5,  length: 3))
                + (style: fontItalicStyle, range: NSRange(location: 14, length: 3))
                + (style: fontThinStyle,   range: NSRange(location: 9,  length: 3))
        ]
}