AttributedStringBuilder.swift

struct AttributedStringBuilder {
    
    // MARK: - Types
    
    enum Attribute {
        case Font(UIFont)
        case ParagraphStyle(NSParagraphStyle)
        case ForegroundColor(UIColor)
        case BackgroundColor(UIColor)
        case Ligature(UInt)
        case Kerning(Double)
        case StrikethroughStyle(NSNumber)
        case UnderlineStyle(NSNumber)
        case StrokeColor(UIColor)
        case StrokeWidth(Double)
        case Shadow(NSShadow)
        case TextEffect(String)
        case Attachment(NSTextAttachment)
        case Link(NSURL)
        case BaselineOffset(Double)
        case UnderlineColor(UIColor)
        case StrikethroughColor(UIColor)
        case Obliqueness(Double)
        case Expansion(Double)
        case WritingDirections([UInt])
        case VerticalGlyphForm(UInt)
        
        var value: AnyObject {
            switch self {
            case let .Font(font): return font
            case let .ParagraphStyle(paragraphStyle): return paragraphStyle
            case let .ForegroundColor(foregroundColor): return foregroundColor
            case let .BackgroundColor(backgroundColor): return backgroundColor
            case let .Ligature(ligature): return ligature
            case let .Kerning(kerning): return kerning
            case let .StrikethroughStyle(strikethroughStyle): return strikethroughStyle
            case let .UnderlineStyle(underlineStyle): return underlineStyle
            case let .StrokeColor(strokeColor): return strokeColor
            case let .StrokeWidth(strokeWidth): return strokeWidth
            case let .Shadow(shadow): return shadow
            case let .TextEffect(textEffect): return textEffect
            case let .Attachment(attachment): return attachment
            case let .Link(link): return link
            case let .BaselineOffset(baselineOffset): return baselineOffset
            case let .UnderlineColor(underlineColor): return underlineColor
            case let .StrikethroughColor(strikethroughColor): return strikethroughColor
            case let .Obliqueness(obliqueness): return obliqueness
            case let .Expansion(expansion): return expansion
            case let .WritingDirections(writingDirections): return writingDirections
            case let .VerticalGlyphForm(verticalGlyphForm): return verticalGlyphForm
            }
        }
        
        var name: String {
            switch self {
            case .Font(_): return NSFontAttributeName
            case .ParagraphStyle(_): return NSParagraphStyleAttributeName
            case .ForegroundColor(_): return NSForegroundColorAttributeName
            case .BackgroundColor(_): return NSBackgroundColorAttributeName
            case .Ligature(_): return NSLigatureAttributeName
            case .Kerning(_): return NSKernAttributeName
            case .StrikethroughStyle(_): return NSStrikethroughStyleAttributeName
            case .UnderlineStyle(_): return NSUnderlineStyleAttributeName
            case .StrokeColor(_): return NSStrokeColorAttributeName
            case .StrokeWidth(_): return NSStrokeWidthAttributeName
            case .Shadow(_): return NSShadowAttributeName
            case .TextEffect(_): return NSTextEffectAttributeName
            case .Attachment(_): return NSAttachmentAttributeName
            case .Link(_): return NSLinkAttributeName
            case .BaselineOffset(_): return NSBaselineOffsetAttributeName
            case .UnderlineColor(_): return NSUnderlineColorAttributeName
            case .StrikethroughColor(_): return NSStrikethroughColorAttributeName
            case .Obliqueness(_): return NSObliquenessAttributeName
            case .Expansion(_): return NSExpansionAttributeName
            case .WritingDirections(_): return NSWritingDirectionAttributeName
            case .VerticalGlyphForm(_): return NSVerticalGlyphFormAttributeName
            }
        }
    }
    
    
    // MARK: - Initialization
    
    init(string: String) {
        workingString = NSMutableAttributedString(string: string)
        fullRange = NSRange(location: 0, length: NSString(string: workingString.string).length)
    }
    
    
    // MARK: - Methods
    
    func set(attribute: Attribute, range: NSRange? = nil) -> AttributedStringBuilder {
        addValue(attribute.value, forAttribute: attribute.name, onRange: range)
        return self
    }
    
    func build() -> NSAttributedString {
        return NSAttributedString(attributedString: workingString)
    }
    
    
    // MARK: - Private
    
    private let workingString: NSMutableAttributedString
    private let fullRange: NSRange
    
    private func addValue(value: AnyObject, forAttribute attribute: String, onRange range: NSRange? = nil) {
        workingString.addAttribute(attribute, value: value, range: range ?? fullRange)
    }
}