PNGScale.swift

#!/usr/bin/swift

import Foundation
import Cocoa

extension String: ErrorType {}

extension NSImage {
    
    public func writeToURL(url: NSURL, size: NSSize) throws {
        
        let bitmap = NSBitmapImageRep(bitmapDataPlanes: nil, pixelsWide: Int(size.width), pixelsHigh: Int(size.height), bitsPerSample: 8, samplesPerPixel: 4, hasAlpha: true, isPlanar: false, colorSpaceName: NSDeviceRGBColorSpace, bytesPerRow: 0, bitsPerPixel: 0)!
        bitmap.size = NSSize(width: size.width, height: size.height)
        
        NSGraphicsContext.saveGraphicsState()
        
        NSGraphicsContext.setCurrentContext(NSGraphicsContext(bitmapImageRep: bitmap))
        self.drawInRect(NSRect(origin: NSPoint(), size: size), fromRect: NSRect(), operation: .CompositeCopy, fraction: 1)
        NSGraphicsContext.restoreGraphicsState()
        
        try bitmap.representationUsingType(NSBitmapImageFileType.NSPNGFileType, properties: [NSImageCompressionFactor: 1.0])?.writeToURL(url, options: [])
    }
}

extension NSSize {
    
    func scaleDown(scale: CGFloat) -> CGSize {
        
        return CGSize(width: self.width / scale, height: self.height / scale)
    }
    
    func scaleUp(scale: CGFloat) -> CGSize {
        
        return CGSize(width: self.width * scale, height: self.height * scale)
    }
}

extension NSURL {
    
    var fileName: String? {
        
        return self.URLByDeletingPathExtension?.lastPathComponent ?? self.lastPathComponent
    }
    
    func URLByRenamingFileName(name: String, ext: String? = nil) -> NSURL? {
        
        let baseURL = self.URLByDeletingLastPathComponent
        
        var result = baseURL?.URLByAppendingPathComponent(name)
        
        if let ext = ext ?? self.pathExtension  {
            
            result = result?.URLByAppendingPathExtension(ext)
        }
        
        return result
    }
}

do {
    
    guard Process.arguments.count > 1 else {
        
        throw "You must provide a path to a directory as first argiment"
    }
    
    let path = Process.arguments[1]
    let dir = NSURL(fileURLWithPath: path)
    
    var files = try NSFileManager.defaultManager().contentsOfDirectoryAtURL(dir, includingPropertiesForKeys: nil, options: [.SkipsHiddenFiles, .SkipsPackageDescendants, .SkipsSubdirectoryDescendants])
    
    files = files.filter({ $0.pathExtension == "png" })
    
    try files.forEach({ (file) in
        
        var file  = file
        let baseFileName = file.fileName!.stringByReplacingOccurrencesOfString("@3x", withString: "")
        
        //rename to @3x if not named already
        if file.lastPathComponent?.containsString("@3x") == false {
            
            let newName = baseFileName + "@3x"
            
            let renamedFile = file.URLByRenamingFileName(newName)!
            
            try NSFileManager.defaultManager().moveItemAtURL(file, toURL: renamedFile)
            
            file = renamedFile
        }
        
        let firstScreenScaleFactor = NSScreen.screens()?.first?.backingScaleFactor
        let mainScreenScaleFactor =  NSScreen.mainScreen()?.backingScaleFactor
        let scaleFactor = firstScreenScaleFactor ?? mainScreenScaleFactor ?? 1
        
        let _3xImage = NSImage(contentsOfFile: file.path!)!
        let _3xImageRepresentation = NSBitmapImageRep(data: _3xImage.TIFFRepresentation!)!
        let _3xSize = NSSize(width: _3xImageRepresentation.pixelsWide, height: _3xImageRepresentation.pixelsHigh)
        
        //generate @1x
        let _1xSize = _3xSize.scaleDown(3)
        let _1xFile = file.URLByRenamingFileName(baseFileName)!
        try _3xImage.writeToURL(_1xFile, size: _1xSize)
        
        //generate @2x
        let _2xSize = _1xSize.scaleUp(2)
        let _2xFile = file.URLByRenamingFileName(baseFileName + "@2x")!
        try _3xImage.writeToURL(_2xFile, size: _2xSize)
    })
}
catch let e {
    
    print(e)
}