ali.swift

import AppKit

struct AttributableString {
  let attributedString: NSAttributedString
}

extension AttributableString: ExpressibleByStringLiteral {
  init(stringLiteral: String) {
    self.attributedString = NSAttributedString(string: stringLiteral)
  }
}

extension AttributableString: CustomPlaygroundDisplayConvertible {
  var playgroundDescription: Any {
    return attributedString
  }
}

extension AttributableString: CustomStringConvertible {
  var description: String {
    return String(describing: self.attributedString)
  }
}

extension AttributableString: ExpressibleByStringInterpolation {
  init(stringInterpolation: StringInterpolation) {
    self.attributedString = NSAttributedString(attributedString: stringInterpolation.attributedString)
  }
  
  struct StringInterpolation: StringInterpolationProtocol {
    var attributedString: NSMutableAttributedString
    
    init(literalCapacity: Int, interpolationCount: Int) {
      self.attributedString = NSMutableAttributedString()
    }
    
    mutating func appendLiteral(_ literal: String) {
      let astr = NSAttributedString(string: literal)
      self.attributedString.append(astr)
    }
    
    mutating func appendInterpolation(_ string: String, _ attributes: StringAttribute...) {
      var attributeDictionary: [NSAttributedString.Key: Any] = [:]
      for attribute in attributes {
        switch attribute {
        case .backgroundColor(let color), .foregroundColor(let color):
          attributeDictionary[attribute.key] = color
        case .font(let font):
          attributeDictionary[attribute.key] = font
        case .link(let url):
          attributeDictionary[attribute.key] = url as NSURL
        }
      }
      
      let attributedString = NSAttributedString(string: string, attributes: attributeDictionary)
      self.attributedString.append(attributedString)
    }
  }
}

public enum StringAttribute {
  case backgroundColor(NSColor) // / UIColor, default nil: no background
  case font(NSFont) // UIFont, default Helvetica(Neue) 12
  case foregroundColor(NSColor) // UIColor, default blackColor
  case link(NSURL) // // NSURL (preferred) or NSString
}

extension StringAttribute {
  public var key: NSAttributedString.Key {
    switch self {
    case .backgroundColor: return NSAttributedString.Key.backgroundColor
    case .font: return NSAttributedString.Key.font
    case .foregroundColor: return NSAttributedString.Key.foregroundColor
    case .link: return NSAttributedString.Key.link
    }
  }
}

let bigFont = NSFont.boldSystemFont(ofSize: 64)
let futura = NSFont(name: "Futura", size: 18)!
let s = AttributableString("""
  Hello \("world", .foregroundColor(.red))!
  \("This is big", .font(bigFont), .backgroundColor(.lightGray), .foregroundColor(.green))
  \("The end", .font(futura))
  """)

s