Attributed String builder for Swift

StringAttributes

// Playground - noun: a place where people can play

import Cocoa

enum StringAttribute {
    case List([StringAttribute])
    case Font(NSFont)
    case BgColor(NSColor)
    case FgColor(NSColor)
    
    
    func append(attr:StringAttribute) -> StringAttribute {
        switch (self, attr) {
        case let (.List(a), .List(b)):
            var temp = a
            temp.extend(b)
            return .List(temp)
        case let (.List(a), _):
            return self.append(.List([attr]))
        case let (_, .List(b)):
            var temp = [self]
            temp.extend(b)
            return .List(temp)
        default:
            return .List([self, attr])
        }
    }
    
    private func key() -> NSString {
        switch self {
        case .Font(_): return NSFontAttributeName
        case .BgColor(_): return NSBackgroundColorAttributeName
        case .FgColor(_): return NSForegroundColorAttributeName
        default: return ""
        }
    }
    
    private func value() -> AnyObject {
        switch self {
        case let .Font(v): return v
        case let .BgColor(v): return v
        case let .FgColor(v): return v
        default: return ""
        }
    }
    
    private func makeAttribute() -> (String, AnyObject) {
        switch self {
        case let .Font(v): return (self.key(), v)
        case let .BgColor(v): return (self.key(), v)
        case let .FgColor(v): return (self.key(), v)
        default: return ("", "")
        }
    }
    
    
    private func makeAttributeDict() -> [String : AnyObject] {
        var dict = [String : AnyObject]()
        switch self {
        case let .List(a):
            for x in a {
                let (key, val):(String, AnyObject) = x.makeAttribute()
                dict[key] = val
            }
            
        case let .Font(f): dict.updateValue(f, forKey: self.key())
        case let .BgColor(c): dict.updateValue(c, forKey: self.key())
        case let .FgColor(c): dict.updateValue(c, forKey: self.key())
        }
        return dict
    }
    
    func build(s:String) -> NSAttributedString {
        let dict = self.makeAttributeDict()
        return NSAttributedString(string: s, attributes: dict)
    }
}


@infix func +(lhs:StringAttribute, rhs:StringAttribute) -> StringAttribute {
    return lhs.append(rhs)
}

let attributes = .Font(NSFont(name: "Papyrus", size: 12)) + .BgColor(NSColor.redColor()) + .FgColor(NSColor.greenColor())
attributes.build("this is a string")