import UIKit

extension String {
    private var isURLString: Bool {
        return URL(string: self) != nil
    }
    
    private var isAssetURL: Bool {
        let asset = self.components(separatedBy: ".").last
        return asset == "png" || asset == "jpg" || asset == "pdf"
    }
    
    var scaledAssetURL: String {
        let scale = Int(UIScreen.main.scale)
        guard isURLString, isAssetURL, scale != 1 else { return self }
        
        var path = self
        let components = path.components(separatedBy: ".")
        let asset = components.last ?? "png"
        path = components.dropLast().joined(separator: ".")
        return "\(path)@\(scale)x.\(asset)"
    }
}

let path = "https://www.domain.com/app-assets/asset.png"
path.scaledAssetURL