#if os(macOS)
import AppKit
import SwiftUI

struct SheetResizeHandle: NSViewRepresentable {
  let vertical: Bool
  let canBegin: () -> Bool
  let change: (Double) -> Void
  let finish: () -> Void
  let cancel: () -> Void
  var fit: (() -> Void)? = nil
  func makeNSView(context: Context) -> Handle { Handle() }
  func updateNSView(_ view: Handle, context: Context) { view.actions = self }
  final class Handle: NSControl {
    override func draw(_ dirtyRect: NSRect) {
      NSColor.secondaryLabelColor.withAlphaComponent(0.15).setFill()
      // Keep the 8-point mouse target, but paint only the grid boundary.
      let pixel = 1 / (window?.backingScaleFactor ?? 2)
      let rule = actions?.vertical == true
        ? NSRect(x: bounds.minX, y: bounds.minY, width: bounds.width, height: pixel)
        : NSRect(x: bounds.maxX - pixel, y: bounds.minY, width: pixel, height: bounds.height)
      rule.fill()
    }
    var actions: SheetResizeHandle?
    private var start: NSPoint?
    private var moved = false
    private weak var previousResponder: NSResponder?
    override var acceptsFirstResponder: Bool { true }
    override func acceptsFirstMouse(for event: NSEvent?) -> Bool { true }
    override func resetCursorRects() {
      addCursorRect(bounds, cursor: actions?.vertical == true ? .resizeUpDown : .resizeLeftRight)
    }
    override func mouseDown(with event: NSEvent) {
      guard actions?.canBegin() == true else { return }
      if event.clickCount == 2, let fit = actions?.fit { fit(); return }
      previousResponder = window?.firstResponder
      window?.makeFirstResponder(self)
      start = event.locationInWindow; moved = false
    }
    override func mouseDragged(with event: NSEvent) {
      guard let start else { return }
      let amount = actions?.vertical == true ? start.y - event.locationInWindow.y : event.locationInWindow.x - start.x
      guard moved || abs(amount) >= 2 else { return }
      moved = true; actions?.change(amount)
    }
    override func mouseUp(with event: NSEvent) {
      guard start != nil else { return }
      if moved { actions?.finish() }
      reset()
    }
    override func keyDown(with event: NSEvent) {
      if event.keyCode == 53 { actions?.cancel(); reset() } else { super.keyDown(with: event) }
    }
    override func viewWillMove(toWindow newWindow: NSWindow?) {
      if newWindow == nil, start != nil { actions?.cancel(); reset() }
      super.viewWillMove(toWindow: newWindow)
    }
    private func reset() {
      start = nil; moved = false
      if window?.firstResponder === self { window?.makeFirstResponder(previousResponder) }
      previousResponder = nil
    }
  }
}
#endif