Add overlay to the macOS app in runtime

NSApp+AppIconOverlay.swift

//
//  NSApp+AppIconOverlay.swift
//
//  Created by Daniel on 12/01/2023.
//

import AppKit

extension NSApplication {
    /// Checks if the app is launched from Xcode with attached debugger.
    ///
    /// [Found on StackOverflow.](https://stackoverflow.com/questions/27252898/ios-detect-if-app-is-running-from-xcode)
    var isDebuggerAttached: Bool {
        // Buffer for "sysctl(...)" call's result.
        var info = kinfo_proc()
        // Counts buffer's size in bytes (like C/C++'s `sizeof`).
        var size = MemoryLayout.stride(ofValue: info)
        // Tells we want info about own process.
        var mib: [Int32] = [CTL_KERN, KERN_PROC, KERN_PROC_PID, getpid()]
        // Call the API (and assert success).
        let junk = sysctl(&mib, UInt32(mib.count), &info, &size, nil, 0)
        assert(junk == 0, "sysctl failed")
        // Finally, checks if debugger's flag is present yet.
        return (info.kp_proc.p_flag & P_TRACED) != 0
    }
    
    ///
    /// Adds an overlay to the app'a icon with a given text and optional background color.
    /// Uses `NSColor.controlAccentColor` as a default background color.
    ///
    /// Usage example:
    /// ```
    /// func applicationDidFinishLaunching(_: Notification) {
    /// ...
    ///     if NSApp.isDebuggerAttached {
    ///         NSApp.addAppIconOverlay(with: "debug")
    ///     }
    /// ...
    /// }
    /// ```
    func addAppIconOverlay(with text: String, background: NSColor = NSColor.controlAccentColor) {
        if let image = applicationIconImage {
            self.applicationIconImage = NSImage(size: image.size, flipped: false) { rect in
                let shadow = NSShadow()
                shadow.shadowColor = NSColor.black
                shadow.shadowOffset = NSSize(width: 0, height: 0)
                shadow.shadowBlurRadius = 2

                let attributes: [NSAttributedString.Key: Any] = [
                    .shadow: shadow,
                    .font: NSFont.boldSystemFont(ofSize: 20.0),
                    .foregroundColor: NSColor.white,
                ]
                let textSize = text.size(withAttributes: attributes)

                // Make the backdrop behind the text a bit taller to have a space for the shadow
                let heightOffset = textSize.height * 0.2
                let height = textSize.height + heightOffset

                let textCoords = CGPoint(x: (image.size.width - textSize.width) / 2, y: heightOffset / 2.0)

                // Draw the orignal app's icon
                image.draw(in: rect)

                // Draw the background for text
                let rect = NSRect(x: 0, y: 0, width: image.size.width, height: textSize.height + heightOffset)
                let path = NSBezierPath(roundedRect: rect, xRadius: height / 2, yRadius: height / 2)
                background.withAlphaComponent(0.75).setFill()
                path.fill()

                // Draw the text
                text.draw(at: textCoords, withAttributes: attributes)
                return true
            }
        }
    }
}