/*

See LICENSE folder for this sample’s licensing information.

Abstract:

An example demonstrating adding accessibility to an NSView subclass that shows a hidden view

 on mouse over by implementing the NSAccessibilityContainsTransientUI protocol.

*/

import Cocoa

class TransientUITriggerView: NSView, NSAccessibilityContainsTransientUI {

    static let ShowHideTransientUIAnimationDuration = 0.2

    @IBOutlet var transientView: NSView!

    override func awakeFromNib() {

        super.awakeFromNib()

        createTrackingArea()

        transientView.alphaValue = 0.0

        transientView.isHidden = true

    }

    fileprivate func createTrackingArea() {

        // Track the mouse for enter and exit for proper highlighting.

        let trackingArea = NSTrackingArea(rect: bounds,

                                          options: [NSTrackingArea.Options.activeInActiveApp,

                                                    NSTrackingArea.Options.activeAlways,

                                                    NSTrackingArea.Options.mouseEnteredAndExited,

                                                    NSTrackingArea.Options.mouseMoved,

                                                    NSTrackingArea.Options.inVisibleRect],

                                          owner: self,

                                          userInfo: nil)

        addTrackingArea(trackingArea)

    }

    fileprivate func showTransientView() {

        setTransientViewIsHidden(hidden: false)

    }

    fileprivate func hideTransientView() {

        setTransientViewIsHidden(hidden: true)

    }

    fileprivate func setTransientViewIsHidden(hidden: Bool) {

        if hidden != transientView.isHidden {

            transientView.isHidden = hidden

            let animationContext = NSAnimationContext.current

            NSAnimationContext.beginGrouping()

            animationContext.duration = TransientUITriggerView.ShowHideTransientUIAnimationDuration

            transientView.animator().alphaValue = transientView.isHidden ? 0.0 : 1.0

            NSAnimationContext.endGrouping()

            sendTransientUIChangedNotification()

        }

    }

    // MARK: - Events

    override func mouseMoved(with event: NSEvent) {

        showTransientView()

    }

    override func mouseEntered(with event: NSEvent) {

        showTransientView()

    }

    override func mouseExited(with event: NSEvent) {

        hideTransientView()

    }

}

// MARK: -

extension TransientUITriggerView {

    // MARK: Accessibility

    override func isAccessibilityAlternateUIVisible() -> Bool {

        return !transientView.isHidden

    }

    override func accessibilityPerformShowAlternateUI() -> Bool {

        showTransientView()

        return true

    }

    override func accessibilityPerformShowDefaultUI() -> Bool {

        hideTransientView()

        return true

    }

    fileprivate func sendTransientUIChangedNotification() {

        let changedElements = NSAccessibilityUnignoredChildren(transientView.subviews)

        NSAccessibilityPostNotificationWithUserInfo(self, .layoutChanged, [NSAccessibilityNotificationUserInfoKey.uiElements: changedElements])

    }

}