import AppKit
import ConjureKit

@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.appearance = ThemePalette.appearance
        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 !dragging, window.screen != nil else { return }
        overlay.appearance = ThemePalette.appearance
        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
        let alignment = LauncherAlignment(windowFrame: window.frame, visibleFrame: frame)
        if overlay.frame != frame {
            overlay.setFrame(frame, display: false)
        }
        view.targetFrame = alignment.targetFrame.offsetBy(dx: -frame.minX, dy: -frame.minY)
        view.snapsHorizontally = alignment.snappedOrigin.x == alignment.targetFrame.minX
        view.snapsVertically = alignment.snappedOrigin.y == alignment.targetFrame.minY
        view.needsDisplay = true
    }

    func end(snapping window: NSWindow? = nil) {
        guard dragging else { return }
        dragging = false
        overlay.orderOut(nil)
        if let window, let screen = window.screen {
            let origin = LauncherAlignment(windowFrame: window.frame, visibleFrame: screen.visibleFrame).snappedOrigin
            if window.frame.origin != origin {
                window.setFrameOrigin(origin)
            }
        }
    }
}

@MainActor
private final class AlignmentGuideView: NSView {
    var targetFrame = NSRect.zero
    var snapsHorizontally = false
    var snapsVertically = false
    private static let dash: [CGFloat] = [1, 5]
    private var muted = ThemePalette.accent.withAlphaComponent(0.4).cgColor
    private var aligned = ThemePalette.accent.withAlphaComponent(0.95).cgColor
    private static let shadow = NSColor.black.withAlphaComponent(0.6).cgColor
    private var themeObservation: ThemeObservation?

    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)
        themeObservation = ThemeObservation { [weak self] in
            self?.window?.appearance = ThemePalette.appearance
            self?.muted = ThemePalette.accent.withAlphaComponent(0.4).cgColor
            self?.aligned = ThemePalette.accent.withAlphaComponent(0.95).cgColor
            self?.needsDisplay = true
        }
    }

    required init?(coder: NSCoder) { fatalError("Conjure creates alignment guides programmatically") }

    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.clip()
        context.setLineWidth(1.5)
        context.setLineCap(.round)
        context.setLineDash(phase: 0, lengths: Self.dash)
        context.setShadow(offset: .zero, blur: 2, color: Self.shadow)

        context.setStrokeColor(snapsHorizontally ? aligned : muted)
        context.move(to: NSPoint(x: targetFrame.minX, y: bounds.minY))
        context.addLine(to: NSPoint(x: targetFrame.minX, y: bounds.maxY))
        context.move(to: NSPoint(x: targetFrame.maxX, y: bounds.minY))
        context.addLine(to: NSPoint(x: targetFrame.maxX, y: bounds.maxY))
        context.strokePath()

        context.setStrokeColor(snapsVertically ? aligned : muted)
        context.move(to: NSPoint(x: bounds.minX, y: targetFrame.maxY))
        context.addLine(to: NSPoint(x: bounds.maxX, y: targetFrame.maxY))
        context.strokePath()
    }
}