import Cocoa
import FlutterMacOS

// Hides the OS cursor and keeps it pinned in place for the duration of a
// drag, streaming raw pointer deltas back to Dart ourselves.
//
// Why not just let Flutters own pointer events drive this: Flutter computes
// PointerEvent.delta from the ABSOLUTE cursor position of consecutive
// events, not from raw hardware deltaX/deltaY. An earlier version tried to
// keep the cursor pinned by warping it back to an anchor point after every
// move while staying associated in between - that still let the OS visibly
// move the cursor between warps, and the warps themselves raced against
// real movement over the async Dart<->native round trip.
//
// The actual fix: CGAssociateMouseAndMouseCursorPosition(false) for the
// WHOLE gesture, not toggled per-event. WindowServer then simply stops
// moving the on-screen cursor at all in response to hardware input - no
// per-frame warping needed. mouseDragged events keep firing completely
// normally while disassociated, with correct deltaX/deltaY reflecting real
// HID movement (its only locationInWindow that freezes) - which is exactly
// why we read deltaX/deltaY here instead of position. Re-associating on
// unlock resumes normal 1:1 tracking from wherever the cursor was frozen,
// so it naturally reappears back where the drag started.
final class CursorLock {
  static let shared = CursorLock()

  private var locked = false
  private var monitor: Any?
  // strong on purpose - CursorLock.shared is a permanent singleton, theres
  // no retain cycle risk, and a weak ref here previously meant the channel
  // (whose only other strong reference was a local `let` in awakeFromNib)
  // got deallocated the moment that function returned, silently breaking
  // delta forwarding.
  private var channel: FlutterMethodChannel?

  func attach(channel: FlutterMethodChannel) {
    self.channel = channel
  }

  func lock() {
    guard !locked else { return }
    locked = true
    NSCursor.hide()
    CGAssociateMouseAndMouseCursorPosition(0)
    monitor = NSEvent.addLocalMonitorForEvents(matching: [.leftMouseDragged]) { [weak self] event in
      guard let self, self.locked else { return event }
      self.channel?.invokeMethod("scrubDelta", arguments: ["dx": event.deltaX, "dy": event.deltaY])
      // swallowed - Flutters own position for this event is frozen (and
      // therefore meaningless) while disassociated, no point forwarding it.
      return nil
    }
  }

  func unlock() {
    guard locked else { return }
    locked = false
    if let monitor {
      NSEvent.removeMonitor(monitor)
    }
    monitor = nil
    CGAssociateMouseAndMouseCursorPosition(1)
    NSCursor.unhide()
  }
}