day-toolkit-appkit 0.6.2

// Copyright © The Daybrite Project
// SPDX-License-Identifier: MPL-2.0

// ---------------------------------------------------------------------------
// AppKit emulated-gesture glue: macOS has no native pull-to-refresh, but NSScrollView's elastic
// scrolling (trackpad rubber-band) exposes exactly the gesture: during an overscroll past the top
// the clip view's bounds origin goes negative (the document view is flipped, so top-of-content is
// y = 0). Observe NSViewBoundsDidChangeNotification on the clip view and fire once per pull when
// the overshoot crosses a threshold, re-arming when the scroll settles back to the top. Applied as
// a `Decorate::tweak` on the wrapped scrollable (docs/tweaks.md); inert when the child's realized
// view is not an NSScrollView.
//
// Safety: the observer does not run app logic directly; it routes a `pullrefresh:begin` Custom
// event through the backend's sink (`crate::emit`), queued and pumped with the framework's
// panic containment, exactly like a built-in control's event. The piece's `cx.on` wire on the host
// node turns it into the begin.
// ---------------------------------------------------------------------------

use std::cell::Cell;

use day_spec::{Event, NodeId};
use objc2::runtime::AnyObject;
use objc2_app_kit::{NSScrollView, NSViewBoundsDidChangeNotification};
use objc2_foundation::{NSNotification, NSNotificationCenter};

/// How far past the top (in points) the elastic overscroll must travel to count as a pull,
/// roughly UIRefreshControl's activation distance.
const PULL_THRESHOLD: f64 = 60.0;

pub(crate) fn attach(view: &objc2::rc::Retained<objc2_app_kit::NSView>, host: NodeId) {
    let Some(sv) = view.downcast_ref::<NSScrollView>() else {
        return; // not a scroll-backed child; gesture inert (spinner overlay still works)
    };
    let clip = sv.contentView();
    clip.setPostsBoundsChangedNotifications(true);

    // Fire once per gesture: armed while at/below the top, disarmed after firing until the
    // scroll returns to rest at the top.
    let armed = Cell::new(true);
    let clip_for_block = clip.clone();
    let block = block2::RcBlock::new(move |_: std::ptr::NonNull<NSNotification>| {
        let y = clip_for_block.bounds().origin.y;
        if y <= -PULL_THRESHOLD {
            if armed.get() {
                armed.set(false);
                crate::emit(host, Event::custom("pullrefresh:begin", ""));
            }
        } else if y >= 0.0 {
            armed.set(true);
        }
    });
    let center = NSNotificationCenter::defaultCenter();
    let clip_obj: &AnyObject = &clip;
    let token = unsafe {
        center.addObserverForName_object_queue_usingBlock(
            Some(NSViewBoundsDidChangeNotification),
            Some(clip_obj),
            None,
            &block,
        )
    };
    // Unregister when the piece's scope is disposed (the native_ref cleanup pattern).
    day_reactive::Scope::current().on_cleanup(move || {
        let center = NSNotificationCenter::defaultCenter();
        // The observer token is a ProtocolObject (no Deref to AnyObject); every ObjC object
        // shares representation, so the pointer cast is the standard bridge.
        let ptr = objc2::rc::Retained::as_ptr(&token) as *const AnyObject;
        unsafe { center.removeObserver(&*ptr) };
    });
}