icon-sizes.swift

// Resizes an image file to necessary sizes for iOS application icons.
// Accepts the path to the file to be resized, e.g. `swift icons.swift icon.png`
// Created by Anthony Mattox on 2016-02-11

import Cocoa

extension NSImage {

  func resize(size: CGSize) -> NSImage {
    let cgImage = self.CGImageForProposedRect(nil, context: nil, hints: nil)

    let bitsPerComponent = CGImageGetBitsPerComponent(cgImage)
    let bytesPerRow = CGImageGetBytesPerRow(cgImage)
    let colorSpace = CGImageGetColorSpace(cgImage)
    let bitmapInfo = CGImageGetBitmapInfo(cgImage)

    let context = CGBitmapContextCreate(nil, Int(size.width), Int(size.height), bitsPerComponent, bytesPerRow, colorSpace, bitmapInfo.rawValue)

    CGContextSetInterpolationQuality(context, .High)
    CGContextDrawImage(context, CGRect(origin: CGPointZero, size: size), cgImage)

    let resizedCGImage = CGBitmapContextCreateImage(context)!
    return NSImage(CGImage: resizedCGImage, size: size)
  }

  func savePNG(file: String) -> Bool {
    guard let tiffData = TIFFRepresentation else { return false }
    guard let bitmap = NSBitmapImageRep(data:tiffData) else { return false }
    guard let pngData = bitmap.representationUsingType(.NSPNGFileType, properties: [:]) else { return false }
    pngData.writeToFile(file, atomically: false)
    return true
  }

}

struct IconFormat {
  let points: CGFloat
  let scale: CGFloat

  init(_ points: CGFloat, at scale: CGFloat) {
    self.points = points
    self.scale = scale
  }

  var pointSize: CGSize {
    return CGSize(width: points, height: points)
  }

  var pixelSize: CGSize {
    return CGSize(width: points * scale, height: points * scale)
  }

  var fileName: String {
    if scale > 1 {
      return String(format: "icon-%0.0f@%0.0fx.png", points, scale)
    }
    return String(format: "icon-%0.0f.png", points)
  }
}

// The specific icon formats that should be created. These could be expanded to include more icon types, or there could be a way to provide them as a parameter to this script.
let iconFormats = [
  IconFormat(29, at: 1),
  IconFormat(29, at: 2),
  IconFormat(29, at: 3),
  IconFormat(40, at: 1),
  IconFormat(40, at: 2),
  IconFormat(40, at: 3),
  IconFormat(60, at: 2),
  IconFormat(60, at: 3),
  IconFormat(29, at: 1),
  IconFormat(29, at: 2),
  IconFormat(40, at: 1),
  IconFormat(40, at: 2),
  IconFormat(76, at: 1),
  IconFormat(76, at: 2),
  IconFormat(83.5, at: 2)
]


guard Process.arguments.count == 2 else {
  print("Provide a filename to the original image.")
  exit(0)
}

let inputImage = Process.arguments[1]

guard let image = NSImage(contentsOfFile: inputImage) else {
  print("Unable to load image \"\(inputImage)\".")
  exit(0)
}

for format in iconFormats {
  let resizedImage = image.resize(format.pixelSize)

  let fileName = format.fileName
  if !resizedImage.savePNG(fileName) {
    print("Unable to save \"\(fileName)\".")
  }
}