ImageDownsampleTest

import Foundation
import SwiftUI

class ViewModel: ObservableObject {
    
    var downloadURL = URL(string: "https://i.redd.it/dwlyzl73nv071.jpg")!
    @Published var downsampledImage: Image?
    
    func downloadResourceToURL(optimize: Bool, width: CGFloat) {
        
        let downloadTask = URLSession.shared.downloadTask(with: downloadURL) { url, response, error in
            
            if let tempURL = url {
                self.downsampleResource(at: tempURL, optimize: optimize, width: width)
            }
        }
        
        downloadTask.resume()
    }
    
    func downloadResourceToData(width: CGFloat) {
        
        let dataTask = URLSession.shared.dataTask(with: downloadURL) { data, response, error in
            if let resourceData = data {
                self.downsampleResource(data: resourceData, width: width)
            }
        }
        
        dataTask.resume()
    }
    
    func downsampleResource(at url: URL, optimize: Bool, width: CGFloat) {
        
        let options = (optimize ? [kCGImageSourceShouldCache: false] : [kCGImageSourceShouldCache: true]) as CFDictionary
        
        if let source = CGImageSourceCreateWithURL(url as CFURL, options) {
         
            let targetDimension = width
            
            var thumbnailOptions: CFDictionary {
                
                if optimize {
                    return [kCGImageSourceCreateThumbnailFromImageAlways: true,
                            kCGImageSourceCreateThumbnailWithTransform: true,
                            kCGImageSourceShouldCacheImmediately: true,
                            kCGImageSourceThumbnailMaxPixelSize: targetDimension] as CFDictionary
                }
                
                return [kCGImageSourceCreateThumbnailFromImageAlways: true,
                        kCGImageSourceCreateThumbnailWithTransform: true,
                        kCGImageSourceShouldCacheImmediately: false,
                        kCGImageSourceThumbnailMaxPixelSize: targetDimension] as CFDictionary
                
            }
            
            guard let thumbnail = CGImageSourceCreateThumbnailAtIndex(source, 0, thumbnailOptions) else { return }
            
            DispatchQueue.main.async {
                self.downsampledImage = Image.init(decorative: thumbnail, scale: 1.0)
                print(thumbnail)
            }
        }
    }
    
    func downsampleResource(data: Data, width: CGFloat) {
        
        let optimize = false
        let options = (optimize ? [kCGImageSourceShouldCache: false] : [kCGImageSourceShouldCache: true]) as CFDictionary

        if let source = CGImageSourceCreateWithData(data as CFData, options) {
         
            let targetDimension = width
            let thumbnailOptions = [kCGImageSourceCreateThumbnailFromImageAlways: true,
                                    kCGImageSourceCreateThumbnailWithTransform: true,
                                    kCGImageSourceShouldCacheImmediately: true,
                                    kCGImageSourceThumbnailMaxPixelSize: targetDimension] as CFDictionary

            guard let thumbnail = CGImageSourceCreateThumbnailAtIndex(source, 0,thumbnailOptions) else { return }
            
            DispatchQueue.main.async {
                self.downsampledImage = Image.init(decorative: thumbnail, scale: 1.0)
                print(thumbnail)
            }
        }
    }
}

struct ContentView: View {
    
    @ObservedObject var viewModel: ViewModel
    
    var body: some View {
        
        GeometryReader { proxy in
            VStack(spacing:8) {
                
                Button("Downsample URL Optimized Exact") { viewModel.downloadResourceToURL(optimize: true, width: proxy.size.width) }
                Button("Downsample URL Optimized 700") { viewModel.downloadResourceToURL(optimize: true, width: 700) }
                Button("Downsample URL Exact") { viewModel.downloadResourceToURL(optimize: false, width: proxy.size.width) }
                Button("Downsample URL 700") { viewModel.downloadResourceToURL(optimize: false, width: proxy.size.width) }
                Button("Downsample Data") { viewModel.downloadResourceToData(width: proxy.size.width) }
                
                if let image = viewModel.downsampledImage {
                    image
                        .resizable()
                        .aspectRatio(contentMode: .fit)
                } else {
                    Image(systemName: "photo")
                        .resizable()
                        .aspectRatio(contentMode: .fit)
                }
            }
        }
    }
}

@main
struct ImageIOApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView(viewModel: ViewModel())
        }
    }
}