import AppKit
import AVFoundation

/// A borderless window covering one screen, above the menu bar, that shows a video layer.
@MainActor
public final class OutputWindow: NSWindow {
    public let sink: VideoSink
    /// Called when the operator presses Esc on the output.
    public var onCancel: (() -> Void)?

    public init(screen: NSScreen) {
        let view = VideoView()
        sink = VideoSink(renderer: view.displayLayer.sampleBufferRenderer)
        super.init(contentRect: screen.frame, styleMask: .borderless, backing: .buffered, defer: false)

        contentView = view
        setFrame(screen.frame, display: false)
        level = .screenSaver
        collectionBehavior = [.canJoinAllSpaces, .stationary, .ignoresCycle, .fullScreenNone]
        backgroundColor = .black
        isOpaque = true
        hasShadow = false
        isReleasedWhenClosed = false
        animationBehavior = .none
    }

    public override var canBecomeKey: Bool { true }

    public override func orderFrontRegardless() {
        super.orderFrontRegardless()
        (contentView as? VideoView)?.hideCursorIfInside()
    }

    public override func orderOut(_ sender: Any?) {
        (contentView as? VideoView)?.showCursor()
        super.orderOut(sender)
    }

    public override func cancelOperation(_ sender: Any?) {
        onCancel?()
    }
}

/// Layer-hosting view backed by `AVSampleBufferDisplayLayer`; hides the cursor while it is inside.
@MainActor
final class VideoView: NSView {
    let displayLayer = AVSampleBufferDisplayLayer()
    private var cursorHidden = false

    init() {
        super.init(frame: .zero)
        displayLayer.videoGravity = .resizeAspect
        displayLayer.backgroundColor = NSColor.black.cgColor
        layer = displayLayer
        wantsLayer = true
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError() }

    override func updateTrackingAreas() {
        super.updateTrackingAreas()
        trackingAreas.forEach(removeTrackingArea)
        addTrackingArea(NSTrackingArea(rect: .zero, options: [.mouseEnteredAndExited, .activeAlways, .inVisibleRect], owner: self))
    }

    override func mouseEntered(with event: NSEvent) { hideCursor() }
    override func mouseExited(with event: NSEvent) { showCursor() }

    /// The cursor may already rest on the screen when the output opens; no enter event comes then.
    func hideCursorIfInside() {
        guard let window, window.frame.contains(NSEvent.mouseLocation) else { return }
        hideCursor()
    }

    // NSCursor.hide/unhide are counted, so keep them balanced.
    private func hideCursor() {
        guard !cursorHidden else { return }
        NSCursor.hide()
        cursorHidden = true
    }

    func showCursor() {
        guard cursorHidden else { return }
        NSCursor.unhide()
        cursorHidden = false
    }
}