StringInterpolation.swift

//#! Swift 5

import Foundation
import AppKit

////////////////////////////////////////////////////////////////////
//: ## Type Definition

struct AttrString {
  let attributedString: NSAttributedString
}

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

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

////////////////////////////////////////////////////////////////////
//: ## StringInterpolation Support (Designated methods)

extension AttrString: ExpressibleByStringInterpolation {
  init(stringInterpolation: StringInterpolation) {
    self.attributedString = NSAttributedString(attributedString: stringInterpolation.attributedString)
  }

  struct StringInterpolation: StringInterpolationProtocol {
    var attributedString: NSMutableAttributedString

    init(literalCapacity: Int, interpolationCount: Int) {
      self.attributedString = NSMutableAttributedString()
    }

    func appendLiteral(_ literal: String) {
      let astr = NSAttributedString(string: literal)
      self.attributedString.append(astr)
    }

    func appendInterpolation(_ string: String, attributes: [NSAttributedString.Key: Any]) {
      let astr = NSAttributedString(string: string, attributes: attributes)
      self.attributedString.append(astr)
    }
  }
}

////////////////////////////////////////////////////////////////////
//: ## StringInterpolation : Style convenience methods

extension AttrString.StringInterpolation {
  struct Style {
    let attributes: [NSAttributedString.Key: Any]
    static func font(_ font: NSFont) -> Style {
      return Style(attributes: [.font: font])
    }
    static func color(_ color: NSColor) -> Style {
      return Style(attributes: [.foregroundColor: color])
    }
    static func bgColor(_ color: NSColor) -> Style {
      return Style(attributes: [.backgroundColor: color])
    }
    static func link(_ link: String) -> Style {
      return .link(URL(string: link)!)
    }
    static func link(_ link: URL) -> Style {
      return Style(attributes: [.link: link])
    }
    static let bold = Style(attributes: [.strokeWidth: -3.0])
    static let oblique = Style(attributes: [.obliqueness: 0.1])
    static func underline(_ color: NSColor, _ style: NSUnderlineStyle) -> Style {
      return Style(attributes: [
        .underlineColor: color,
        .underlineStyle: style.rawValue
      ])
    }
    static func alignment(_ alignment: NSTextAlignment) -> Style {
      let ps = NSMutableParagraphStyle()
      ps.alignment = alignment
      return Style(attributes: [.paragraphStyle: ps])
    }
  }

  func appendInterpolation(_ string: String, _ style: Style...) {
    var attrs: [NSAttributedString.Key: Any] = [:]
    style.forEach { attrs.merge($0.attributes, uniquingKeysWith: {$1}) }
    let astr = NSAttributedString(string: string, attributes: attrs)
    self.attributedString.append(astr)
  }

  func appendInterpolation(image: NSImage, scale: CGFloat = 1.0) {
    let attachment = NSTextAttachment()
    let size = NSSize(
      width: image.size.width * scale,
      height: image.size.height * scale
    )
    attachment.image = NSImage(size: size, flipped: false, drawingHandler: { (rect: NSRect) -> Bool in
      NSGraphicsContext.current?.cgContext.translateBy(x: 0, y: size.height)
      NSGraphicsContext.current?.cgContext.scaleBy(x: 1, y: -1)
      image.draw(in: rect)
      return true
    })
    self.attributedString.append(NSAttributedString(attachment: attachment))
  }
}


//////////////////////////////////
//: ## Demo


let str: AttrString = """
  Hello \("world", .color(.red)), isn't this \("cool", .color(.blue), .bold, .oblique, .underline(.purple, .single))?

  \(" Yay! ", .font(.systemFont(ofSize: 36)), .color(.blue), .bgColor(.yellow), .alignment(.center))

  \(image: #imageLiteral(resourceName: "Logo_Apple_Swift.png"), scale: 0.5)

  Oh, btw, here's a \("nice link", .link("http://swift.org"), .underline(.blue, .single))!
  """


//: Display

import PlaygroundSupport
let view = NSTextView(frame: NSRect(x: 0, y: 0, width: 300, height: 300))
view.textStorage?.setAttributedString(str.attributedString)
PlaygroundPage.current.liveView = view