clock.swift

//
//  ViewController.swift
//  storyboardtest2
//
//  Created by Johan Dahlin on 2022-07-08.
//

import Cocoa

// https://developer.apple.com/documentation/appkit/nsviewcontroller
class ViewController: NSViewController {
    var dateformat = DateFormatter()
    var currentDate = ""
    @IBOutlet weak var mainLabel: NSTextField!

    // https://developer.apple.com/documentation/appkit/nsviewcontroller/1434476-viewdidload
    override func viewDidLoad() {
        super.viewDidLoad()
        // https://unicode-org.github.io/icu/userguide/format_parse/datetime/#datetime-format-syntax
        self.dateformat.dateFormat = "HH:mm" // 12h as "hh:mm a"

        self.timerInitialize()
        self.textFieldInitialize()
    }
    
    // https://developer.apple.com/documentation/appkit/nsviewcontroller/1434415-viewwillappear
    override func viewWillAppear() {
        self.mainWindowInitialize(window: view.window!)
        super.viewWillAppear()
    }

    // https://developer.apple.com/documentation/appkit/nsevent/1532495-mouseevent
    override public func mouseDown(with event: NSEvent) {
        // Dragging should move the window, forward events to the window
        event.window?.performDrag(with: event)
    }

    private func mainWindowInitialize(window: NSWindow) {
        // Do not render background, leave it transparent
        // https://developer.apple.com/documentation/appkit/nswindow/1419751-backgroundcolor
        // https://developer.apple.com/documentation/appkit/nscolor/1527217-clear
        window.backgroundColor = .clear

        // Make the window appear on all workspaces
        // https://developer.apple.com/documentation/appkit/nswindow/collectionbehavior
        window.collectionBehavior = [.canJoinAllSpaces]

        // Ensure the window is always on top, clicking on another application will
        // not cause it to be hidden.
        // https://developer.apple.com/documentation/appkit/nswindow/level
        window.level = .floating

        // Do not render window title and decoration
        // https://developer.apple.com/documentation/appkit/nswindow/stylemask/1644698-borderless
        window.styleMask = .borderless
    }
    
    private func textFieldInitialize() {
        self.mainLabel.font = NSFont.systemFont(ofSize: 80)
        self.mainLabel.textColor = NSColor.systemGreen
    }
    
    private func timerInitialize() {
        // Every second dispatch a timer, this means the clock is at most 1s out of sync.
        // FIXME: Schedule a timer exactly when each minute changes
        // https://developer.apple.com/documentation/foundation/timer/2091889-scheduledtimer
        let _ = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { timer in
            // Has the minute changed since last time
            let date = self.dateformat.string(from: Date())
            if (date != self.currentDate) {
                self.textFieldUpdate(date: date)
            }
        }
    }

    private func textFieldUpdate(date: String) {
        // Update the label with current time of the day, e.g: `12:34`
        self.mainLabel.stringValue = date
        // https://developer.apple.com/documentation/appkit/nsview/1483360-needsdisplay
        self.mainLabel.needsDisplay = true
        self.currentDate = date
    }

}