InternetReachable.swift

// swiftc -o /tmp/InternetReachable ~/Temp/InternetReachable.swift && /tmp/InternetReachable

import AppKit
import Cocoa
import Foundation
import Network

private var window: NSWindow = {
    let w = NSWindow(
        contentRect: NSRect(x: 0, y: 0, width: NSScreen.main!.frame.width, height: 20),
        styleMask: [.fullSizeContentView, .borderless],
        backing: .buffered,
        defer: false
    )
    w.backgroundColor = .clear
    w.level = NSWindow.Level(Int(CGShieldingWindowLevel()))

    w.isOpaque = false
    w.hasShadow = false
    w.hidesOnDeactivate = false
    w.ignoresMouseEvents = true
    w.isReleasedWhenClosed = false
    w.isMovableByWindowBackground = false

    w.sharingType = .none
    w.setAccessibilityRole(.popover)
    w.setAccessibilitySubrole(.unknown)

    w.collectionBehavior = [.canJoinAllSpaces, .stationary, .ignoresCycle, .fullScreenDisallowsTiling]

    return w
}()
private var windowController = NSWindowController(window: window)
private var fader: DispatchWorkItem? { didSet { oldValue?.cancel() } }
private var closer: DispatchWorkItem? { didSet { oldValue?.cancel() } }

private func mainAsyncAfter(_ duration: TimeInterval, _ action: @escaping () -> Void) -> DispatchWorkItem {
    let workItem = DispatchWorkItem { action() }
    DispatchQueue.main.asyncAfter(deadline: .now() + duration, execute: workItem)

    return workItem
}

private func drawColoredTopLine(_ color: NSColor, hideAfter: TimeInterval = 5) {
    DispatchQueue.main.async {
        lastColor = color
        lastHideAfter = hideAfter

        let box = NSBox()
        box.boxType = .custom
        box.fillColor = color
        box.frame = NSRect(x: 0, y: 10, width: NSScreen.main!.frame.width + 10, height: 3)

        box.shadow = NSShadow()
        box.shadow!.shadowColor = color
        box.shadow!.shadowBlurRadius = 3
        box.shadow!.shadowOffset = .init(width: 0, height: -2)

        let containerView = NSView()
        containerView.frame = NSRect(x: 0, y: 0, width: NSScreen.main!.frame.width + 10, height: 20)
        containerView.addSubview(box)

        window.contentView = containerView
        window.setFrameOrigin(NSPoint(x: NSScreen.main!.frame.minX - 5, y: NSScreen.main!.frame.maxY - 12))

        windowController.showWindow(nil)
        NSAnimationContext.runAnimationGroup { ctx in
            ctx.duration = 1.0
            window.animator().alphaValue = 0.5
        }

        fader?.cancel()
        closer?.cancel()
        guard hideAfter > 0 else { return }

        fader = mainAsyncAfter(hideAfter) {
            NSAnimationContext.runAnimationGroup { ctx in
                ctx.duration = 2.0
                window.animator().alphaValue = 0.01
            }

            closer = mainAsyncAfter(2.0) {
                window.alphaValue = 0.0
                lastColor = nil
                lastHideAfter = nil
            }
        }
    }
}

private var lastColor: NSColor?
private var lastHideAfter: TimeInterval?
private var lastStatus: NWPath.Status?

NotificationCenter.default.addObserver(forName: NSApplication.didChangeScreenParametersNotification, object: nil, queue: nil) { n in
    guard let color = lastColor, let hideAfter = lastHideAfter else {
        return
    }
    drawColoredTopLine(color, hideAfter: hideAfter)
}

let monitor = NWPathMonitor()
monitor.pathUpdateHandler = { path in
    guard path.status != lastStatus else {
        return
    }
    lastStatus = path.status

    switch path.status {
    case .satisfied:
        print("Internet connection: ON")
        drawColoredTopLine(.systemGreen, hideAfter: 5)
    case .unsatisfied:
        print("Internet connection: OFF")
        drawColoredTopLine(.systemRed, hideAfter: 0)
    case .requiresConnection:
        print("Internet connection: MAYBE")
        drawColoredTopLine(.systemOrange, hideAfter: 5)
    @unknown default:
        print("Internet connection: UNKNOWN")
        drawColoredTopLine(.systemYellow, hideAfter: 5)
    }
}
monitor.start(queue: DispatchQueue.global())
signal(SIGINT) { _ in
    monitor.cancel()
    exit(0)
}

RunLoop.main.run()