Interpolated Attributed String Builder

AttributedStringBuilder.swift

// Example

var brown: AttributedStringSegment = "brown"
brown.foregroundColor = UIColor.brownColor()
brown.expansion = 1.1

var lazy: AttributedStringSegment = "lazy"
lazy.strikethroughStyle = NSUnderlineStyle.StyleDouble
lazy.strikethroughColor = UIColor.redColor()

let fox = UIImage(named: "fox.jpg")!

let text = attributedString("The quick \(brown) \(fox) jumped over the \(lazy) dog.")
// AND WE GET SOMETHING LIKE THIS!
// https://twitter.com/JadenGeller/status/614286532875194368

func attributedString(builder: AttributedStringBuilder) -> NSAttributedString {
    return builder.attributedString
}

struct AttributedStringBuilder : StringInterpolationConvertible, StringLiteralConvertible {
    private let attributedString: NSAttributedString
    
    init(stringInterpolation strings: AttributedStringBuilder...) {
        let builder = NSMutableAttributedString()
        for string in strings {
            builder.appendAttributedString(string.attributedString)
        }
        self.attributedString = NSAttributedString(attributedString: builder)
    }
    
    init<T>(stringInterpolationSegment expr: T) {
        attributedString = "\(expr)".attributedStringRepresentation
    }
    
    init<T : AttributedStringConvertible>(stringInterpolationSegment expr: T) {
        attributedString = expr.attributedStringRepresentation
    }
    
    init(string: String) {
        attributedString = NSAttributedString(string: string)
    }
    
    init(stringLiteral value: String) {
        attributedString = NSAttributedString(string: value)
    }
    
    init(extendedGraphemeClusterLiteral value: String) {
        attributedString = NSAttributedString(string: value)
    }
    
    init(unicodeScalarLiteral value: String) {
        attributedString = NSAttributedString(string: value)
    }
}

protocol AttributedStringConvertible {
    var attributedStringRepresentation: NSAttributedString { get }
}

extension NSAttributedString {
    var attributedStringRepresentation: NSAttributedString {
        get {
            return self
        }
    }
}

struct AttributedStringSegment : AttributedStringConvertible, StringLiteralConvertible {
    let text: String
    
    init(_ text: String) {
        self.text = text
    }
    
    init(stringLiteral value: String) {
        text = value
    }
    
    init(extendedGraphemeClusterLiteral value: String) {
        text = value
    }
    
    init(unicodeScalarLiteral value: String) {
        text = value
    }
    
    var font: UIFont!
    var paragraphStyle: NSParagraphStyle!
    var foregroundColor: UIColor!
    var backgroundColor: UIColor!
    var kern: Float!
    var strikethroughStyle: NSUnderlineStyle!
    var underlineStyle: NSUnderlineStyle!
    var strokeColor: UIColor!
    var strokeWidth: Float!
    var shadow: NSShadow!
    var link: NSURL!
    var baselineOffset: Float!
    var underlineColor: UIColor!
    var strikethroughColor: UIColor!
    var obliqueness: Float!
    var expansion: Float!
    var writingDirection: [NSWritingDirection]!
    var vertical: Bool!
    
    var attributedStringRepresentation: NSAttributedString {
        get {
            var attributes = [String : NSObject]()
            
            if let font = font {
                attributes[NSFontAttributeName] = font
            }
            if let paragraphStyle = paragraphStyle {
                attributes[NSParagraphStyleAttributeName] = paragraphStyle
            }
            if let foregroundColor = foregroundColor {
                attributes[NSForegroundColorAttributeName] = foregroundColor
            }
            if let backgroundColor = backgroundColor {
                attributes[NSBackgroundColorAttributeName] = backgroundColor
            }
            if let kern = kern {
                attributes[NSKernAttributeName] = kern
            }
            if let strikethroughStyle = strikethroughStyle {
                attributes[NSStrikethroughStyleAttributeName] = strikethroughStyle.rawValue
            }
            if let underlineStyle = underlineStyle {
                attributes[NSUnderlineStyleAttributeName] = underlineStyle.rawValue
            }
            if let strokeColor = strokeColor {
                attributes[NSStrokeColorAttributeName] = strokeColor
            }
            if let strokeWidth = strokeWidth {
                attributes[NSStrokeWidthAttributeName] = strokeWidth
            }
            if let shadow = shadow {
                attributes[NSShadowAttributeName] = shadow
            }
            if let link = link {
                attributes[NSLinkAttributeName] = link
            }
            if let baselineOffset = baselineOffset {
                attributes[NSBaselineOffsetAttributeName] = baselineOffset
            }
            if let underlineColor = underlineColor {
                attributes[NSUnderlineColorAttributeName] = underlineColor
            }
            if let strikethroughColor = strikethroughColor {
                attributes[NSStrikethroughColorAttributeName] = strikethroughColor
            }
            if let obliqueness = obliqueness {
                attributes[NSObliquenessAttributeName] = obliqueness
            }
            if let expansion = expansion {
                attributes[NSExpansionAttributeName] = expansion
            }
            if let writingDirection = writingDirection {
                attributes[NSWritingDirectionAttributeName] = writingDirection.map { $0.rawValue }
            }
            if let vertical = vertical {
                attributes[NSVerticalGlyphFormAttributeName] = vertical ? 1 : 0
            }
            
            return NSAttributedString(string: text, attributes: attributes)
        }
    }
}

extension NSURL : AttributedStringConvertible {
    var attributedStringRepresentation: NSAttributedString {
        get {
            var segment = AttributedStringSegment(absoluteString)
            segment.link = self
            return segment.attributedStringRepresentation
        }
    }
}

extension String : AttributedStringConvertible {
    var attributedStringRepresentation: NSAttributedString {
        get {
            return NSAttributedString(string: self)
        }
    }
}

extension NSTextAttachment {
    var attributedStringRepresentation: NSAttributedString {
        get {
            return NSAttributedString(attachment: self)
        }
    }
}

extension UIImage : AttributedStringConvertible {
    var attributedStringRepresentation: NSAttributedString {
        get {
            let attachment = NSTextAttachment()
            attachment.image = self
            return attachment.attributedStringRepresentation
        }
    }
}