Simple attributed string styles

SimpleAttributedStringStyles.swift

import Cocoa

/// Enumerates the types of fonts supported for attributed strings.
enum TextFontType {

    case System
    case Named(String)

}

/// Describes font attributes that can be applied to attributed strings.
struct TextFont {

    let type: TextFontType
    let size: Float
    let bold: Bool
    let italic: Bool

}

/// Describes colors that can be applied to text in attributed strings.
struct TextColor {

    let foreground: NSColor?
    let background: NSColor?

}

/// Aggregates all style attributes that can be applied to text in attributed strings.
struct TextStyle {

    let font: TextFont
    let color: TextColor
    let underline: Bool
    let strikethrough: Bool

}

/// Protocol for composing text styles in a fluent manner.
protocol TextStyleConfigurable {

    func font(type: TextFontType, size: Float, bold: Bool, italic: Bool) -> Self
    func font(font: NSFont) -> Self
    func underline() -> Self
    func strikethrough() -> Self
    func foreground(color: NSColor) -> Self
    func background(color: NSColor) -> Self

}

final class AttributedTextStyle: TextStyleConfigurable {

    private var attributes: [String: NSObject] = [:]

    func font(type: TextFontType = .System,
              size: Float = Float(NSFont.systemFontSize()),
              bold: Bool = false,
              italic: Bool = false) -> Self {
        let pointSize = CGFloat(size)
        let systemFont = NSFont.systemFontOfSize(pointSize)
        var font: NSFont
        switch type {
        case .System:
            font = systemFont
        case let .Named(name):
            font = NSFont(name: name, size: pointSize) ?? systemFont
        }
        let fontManager = NSFontManager.sharedFontManager()
        if bold {
            font = fontManager.convertFont(font, toHaveTrait: .BoldFontMask)
        }
        if italic {
            font = fontManager.convertFont(font, toHaveTrait: .ItalicFontMask)
        }
        self.font(font)
        return self
    }

    func font(font: NSFont) -> Self {
        attributes[NSFontAttributeName] = font
        return self
    }

    func underline() -> Self {
        attributes[NSUnderlineStyleAttributeName] = 1
        return self
    }

    func strikethrough() -> Self {
        attributes[NSStrikethroughStyleAttributeName] = 1
        return self
    }

    func foreground(color: NSColor) -> Self {
        attributes[NSForegroundColorAttributeName] = color
        return self
    }

    func background(color: NSColor) -> Self {
        attributes[NSBackgroundColorAttributeName] = color
        return self
    }

}

typealias AttributedTextStyleBlock = AttributedTextStyle -> Void

extension NSMutableAttributedString {

    /// Appends a string to this attributed string, after applying the styles provided by the
    /// configuration block, if any.
    func append(string: String, _ styleConfigurationBlock: AttributedTextStyleBlock? = nil) {
        let style = AttributedTextStyle()
        styleConfigurationBlock?(style)
        appendAttributedString(NSMutableAttributedString(string: string, attributes: style.attributes))
    }
    
}


let boldWhiteAvenirOnRed: AttributedTextStyleBlock = { style in
    style
        .font(.Named("Avenir"), size: 18, bold: true)
        .background(NSColor.redColor())
        .foreground(NSColor.whiteColor())
}

// Let's try!
let string = NSMutableAttributedString()
string.append("CocoaPods", boldWhiteAvenirOnRed)