import AppKit

final class OverlayWindow: NSPanel {
    init(screen: NSScreen, onComplete: @escaping (NSRect) -> Void, onCancel: @escaping () -> Void, onWindowPick: @escaping (NSRect) -> Void) {
        let content = OverlayView(onComplete: onComplete, onCancel: onCancel, onWindowPick: onWindowPick)
        super.init(
            contentRect: screen.frame,
            styleMask: [.borderless, .nonactivatingPanel],
            backing: .buffered,
            defer: false
        )
        contentView = content
        level = .screenSaver
        collectionBehavior = [.canJoinAllSpaces, .fullScreenAuxiliary, .stationary, .transient]
        backgroundColor = .clear
        isOpaque = false
        hasShadow = false
        isReleasedWhenClosed = false
        acceptsMouseMovedEvents = true
    }

    override var canBecomeKey: Bool { true }
}

final class OverlayView: NSView {
    private let onComplete: (NSRect) -> Void
    private let onCancel: () -> Void
    private let onWindowPick: (NSRect) -> Void

    private var startPoint: NSPoint?
    private(set) var selection: NSRect?
    private var isDragging = false

    // Window detection
    private var trackedWindows: [(id: CGWindowID, frame: NSRect)] = []
    private var hoveredWindowFrame: NSRect?
    private var excludedIDs: [Int] = []

    init(onComplete: @escaping (NSRect) -> Void, onCancel: @escaping () -> Void, onWindowPick: @escaping (NSRect) -> Void) {
        self.onComplete = onComplete
        self.onCancel = onCancel
        self.onWindowPick = onWindowPick
        super.init(frame: .zero)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override var acceptsFirstResponder: Bool { true }

    override func acceptsFirstMouse(for event: NSEvent?) -> Bool { true }

    override func resetCursorRects() {
        addCursorRect(bounds, cursor: .crosshair)
    }

    // MARK: - Window detection

    /// Rebuild the list of capturable windows intersecting this screen.
    /// Called lazily on mouse moves; cheap enough for interactive hover.
    private func refreshTrackedWindows() {
        guard let window = window else { return }
        let screenFrame = window.convertToScreen(NSRect(origin: .zero, size: bounds.size))
        // Exclude this overlay's own window (the other overlays don't intersect
        // this screen, so the on-screen filter handles them).
        let ownID = window.windowNumber

        guard let list = CGWindowListCopyWindowInfo(
            [ .optionOnScreenOnly, .excludeDesktopElements ], kCGNullWindowID
        ) as? [[String: Any]] else { trackedWindows = []; return }

        var found: [(CGWindowID, NSRect)] = []
        for info in list {
            guard let cid = info[kCGWindowNumber as String] as? CGWindowID,
                  let bounds = info[kCGWindowBounds as String] as? [String: CGFloat],
                  let layer = info[kCGWindowLayer as String] as? Int,
                  layer == 0
            else { continue }
            // Skip our own overlays
            if Int(cid) == ownID { continue }
            let rect = NSRect(
                x: bounds["X"] ?? 0,
                y: bounds["Y"] ?? 0,
                width: bounds["Width"] ?? 0,
                height: bounds["Height"] ?? 0
            )
            guard rect.width >= 80, rect.height >= 60 else { continue }
            // Skip tiny/utility windows
            guard rect.width < screenFrame.width || rect.height < screenFrame.height else { continue }
            // Only windows intersecting this screen
            guard rect.intersects(screenFrame) else { continue }
            found.append((cid, rect))
        }
        trackedWindows = found
    }

    private func windowFrame(at point: NSPoint) -> NSRect? {
        guard let window = window else { return nil }
        // convertToScreen gives AppKit-global coordinates; convert tracked
        // CG frames to the same space and pick the frontmost containing it.
        let screenPoint = window.convertToScreen(NSRect(origin: point, size: .zero)).origin
        for (_, frame) in trackedWindows {
            if Self.cgToAppKit(rect: frame).contains(screenPoint) {
                return frame
            }
        }
        return nil
    }

    /// Convert a CGWindowList (top-left origin, CG global space) frame into
    /// AppKit screen coordinates (bottom-left origin) for capture.
    private static func cgToAppKit(rect: NSRect) -> NSRect {
        guard let mainScreen = NSScreen.screens.first else { return rect }
        let y = mainScreen.frame.height - rect.origin.y - rect.height
        return NSRect(x: rect.origin.x, y: y, width: rect.width, height: rect.height)
    }

    // MARK: - Events

    override func mouseMoved(with event: NSEvent) {
        guard !isDragging else { return }
        refreshTrackedWindows()
        let p = convert(event.locationInWindow, from: nil)
        let frame = windowFrame(at: p)
        if frame != hoveredWindowFrame {
            hoveredWindowFrame = frame
            needsDisplay = true
        }
    }

    override func mouseDown(with event: NSEvent) {
        let p = convert(event.locationInWindow, from: nil)
        startPoint = p
        selection = NSRect(origin: p, size: .zero)
        needsDisplay = true
    }

    override func mouseDragged(with event: NSEvent) {
        guard let start = startPoint else { return }
        isDragging = true
        hoveredWindowFrame = nil
        let p = convert(event.locationInWindow, from: nil)
        selection = NSRect(
            x: min(start.x, p.x),
            y: min(start.y, p.y),
            width: abs(p.x - start.x),
            height: abs(p.y - start.y)
        )
        needsDisplay = true
    }

    override func mouseUp(with event: NSEvent) {
        if isDragging {
            guard let sel = selection else { return }
            if sel.width >= 2, sel.height >= 2 {
                onComplete(window!.convertToScreen(sel))
            } else {
                onCancel()
            }
            return
        }

        // No drag: it was a click. If a window is hovered, capture it with
        // rounded corners; otherwise treat as an empty marquee (cancel).
        if let frame = hoveredWindowFrame {
            onWindowPick(Self.cgToAppKit(rect: frame))
        } else {
            onCancel()
        }
    }

    override func keyDown(with event: NSEvent) {
        if event.keyCode == 53 {
            onCancel()
        } else {
            super.keyDown(with: event)
        }
    }

    override func draw(_ dirtyRect: NSRect) {
        NSColor.black.withAlphaComponent(0.35).setFill()
        NSBezierPath(rect: bounds).fill()

        // Highlight the hovered window (rounded, like the real window corners)
        if let frame = hoveredWindowFrame {
            // Convert the CG frame to AppKit-global, then to this view's space.
            guard let window = window else { return }
            let screenFrame = window.convertToScreen(NSRect(origin: .zero, size: bounds.size))
            let appKitFrame = Self.cgToAppKit(rect: frame)
            let viewFrame = NSRect(
                x: appKitFrame.origin.x - screenFrame.origin.x,
                y: appKitFrame.origin.y - screenFrame.origin.y,
                width: frame.width,
                height: frame.height
            )
            NSGraphicsContext.current?.saveGraphicsState()
            NSGraphicsContext.current?.compositingOperation = .clear
            NSColor.black.setFill()
            NSBezierPath(roundedRect: viewFrame, xRadius: 10, yRadius: 10).fill()
            NSGraphicsContext.current?.restoreGraphicsState()

            let border = NSBezierPath(roundedRect: viewFrame, xRadius: 10, yRadius: 10)
            border.lineWidth = 2
            NSColor.controlAccentColor.setStroke()
            border.stroke()
            return
        }

        guard let sel = selection, sel.width > 0, sel.height > 0 else { return }

        NSGraphicsContext.current?.saveGraphicsState()
        NSGraphicsContext.current?.compositingOperation = .clear
        NSColor.black.setFill()
        NSBezierPath(rect: sel).fill()
        NSGraphicsContext.current?.restoreGraphicsState()

        let border = NSBezierPath(rect: sel)
        border.lineWidth = 1.5
        NSColor.controlAccentColor.setStroke()
        border.stroke()

        let label = "\(Int(sel.width)) × \(Int(sel.height))"
        let attrs: [NSAttributedString.Key: Any] = [
            .font: NSFont.monospacedDigitSystemFont(ofSize: 12, weight: .medium),
            .foregroundColor: NSColor.white,
        ]
        let labelSize = label.size(withAttributes: attrs)
        let labelRect = NSRect(
            x: sel.maxX - labelSize.width - 8,
            y: sel.minY - labelSize.height - 10,
            width: labelSize.width + 8,
            height: labelSize.height + 6
        )
        NSColor.black.withAlphaComponent(0.6).setFill()
        NSBezierPath(roundedRect: labelRect, xRadius: 4, yRadius: 4).fill()
        label.draw(
            at: NSPoint(x: labelRect.minX + 4, y: labelRect.minY + 3),
            withAttributes: attrs
        )
    }
}