import AppKit

class EdgeGradientView: NSView {
    var intensity: CGFloat = 0.4

    override func draw(_ dirtyRect: NSRect) {
        guard let ctx = NSGraphicsContext.current?.cgContext else { return }
        let w = bounds.width, h = bounds.height, edge: CGFloat = 220
        let color = NSColor.systemTeal
        let colors = [color.withAlphaComponent(intensity).cgColor, color.withAlphaComponent(0.0).cgColor] as CFArray
        guard let grad = CGGradient(colorsSpace: CGColorSpaceCreateDeviceRGB(), colors: colors, locations: [0, 1]) else { return }

        ctx.saveGState(); ctx.clip(to: CGRect(x: 0, y: h - edge, width: w, height: edge))
        ctx.drawLinearGradient(grad, start: CGPoint(x: w/2, y: h), end: CGPoint(x: w/2, y: h - edge), options: []); ctx.restoreGState()

        ctx.saveGState(); ctx.clip(to: CGRect(x: 0, y: 0, width: w, height: edge))
        ctx.drawLinearGradient(grad, start: CGPoint(x: w/2, y: 0), end: CGPoint(x: w/2, y: edge), options: []); ctx.restoreGState()

        ctx.saveGState(); ctx.clip(to: CGRect(x: 0, y: 0, width: edge, height: h))
        ctx.drawLinearGradient(grad, start: CGPoint(x: 0, y: h/2), end: CGPoint(x: edge, y: h/2), options: []); ctx.restoreGState()

        ctx.saveGState(); ctx.clip(to: CGRect(x: w - edge, y: 0, width: edge, height: h))
        ctx.drawLinearGradient(grad, start: CGPoint(x: w, y: h/2), end: CGPoint(x: w - edge, y: h/2), options: []); ctx.restoreGState()
    }
}