import AppKit

@MainActor
final class LauncherAlignmentGuides {
    private let view = AlignmentGuideView()
    private lazy var overlay: NSPanel = {
        let panel = NSPanel(contentRect: .zero, styleMask: [.borderless, .nonactivatingPanel], backing: .buffered, defer: false)
        panel.backgroundColor = .clear
        panel.isOpaque = false
        panel.hasShadow = false
        panel.ignoresMouseEvents = true
        panel.isReleasedWhenClosed = false
        panel.collectionBehavior = [.moveToActiveSpace, .fullScreenAuxiliary]
        panel.contentView = view
        panel.setAccessibilityElement(false)
        return panel
    }()
    private var dragging = false

    func begin(for window: NSWindow) {
        guard window.screen != nil else { return }
        dragging = true
        update(for: window)
        overlay.level = window.level
        overlay.order(.below, relativeTo: window.windowNumber)
    }

    func update(for window: NSWindow) {
        guard dragging, let screen = window.screen else { return }
        let frame = screen.visibleFrame
        if overlay.frame != frame {
            overlay.setFrame(frame, display: false)
        }
        view.launcherFrame = window.frame.offsetBy(dx: -frame.minX, dy: -frame.minY)
        view.alignmentTolerance = 1 / screen.backingScaleFactor
        view.needsDisplay = true
    }

    func end() {
        guard dragging else { return }
        dragging = false
        overlay.orderOut(nil)
    }
}

@MainActor
private final class AlignmentGuideView: NSView {
    var launcherFrame = NSRect.zero
    var alignmentTolerance: CGFloat = 0.5
    private static let dash: [CGFloat] = [1, 5]
    private static let muted = SunsetPalette.accent.withAlphaComponent(0.4).cgColor
    private static let aligned = SunsetPalette.accent.withAlphaComponent(0.95).cgColor
    private static let shadow = NSColor.black.withAlphaComponent(0.6).cgColor

    override func hitTest(_ point: NSPoint) -> NSView? { nil }

    override func draw(_ dirtyRect: NSRect) {
        guard let context = NSGraphicsContext.current?.cgContext else { return }
        context.saveGState()
        defer { context.restoreGState() }
        context.addRect(bounds)
        context.addRect(launcherFrame.insetBy(dx: -8, dy: -8))
        context.clip(using: .evenOdd)
        context.setLineWidth(1.5)
        context.setLineCap(.round)
        context.setLineDash(phase: 0, lengths: Self.dash)
        context.setShadow(offset: .zero, blur: 2, color: Self.shadow)

        let centeredX = abs(launcherFrame.midX - bounds.midX) <= alignmentTolerance
        context.setStrokeColor(centeredX ? Self.aligned : Self.muted)
        context.move(to: NSPoint(x: bounds.midX, y: bounds.minY))
        context.addLine(to: NSPoint(x: bounds.midX, y: bounds.maxY))
        context.strokePath()

        let centeredY = abs(launcherFrame.midY - bounds.midY) <= alignmentTolerance
        context.setStrokeColor(centeredY ? Self.aligned : Self.muted)
        context.move(to: NSPoint(x: bounds.minX, y: bounds.midY))
        context.addLine(to: NSPoint(x: bounds.maxX, y: bounds.midY))
        context.strokePath()
    }
}