repose_core/

dnd.rs

use crate::Vec2;
use crate::color::{Brush, Color};
use crate::geometry::Rect;
use crate::input::{Modifiers, PointerKind};
use crate::runtime::{Frame, HitRegion};
use crate::shortcuts::DragAction;
use crate::text::{FontStyle, FontWeight, TextAlign, TextDecoration};
use crate::view::{Scene, SceneNode};
use std::cell::RefCell;
use std::{any::Any, path::PathBuf, rc::Rc, sync::Arc};
use web_time::Instant;

/// Opaque payload moved during internal drag & drop.
/// Use [`downcast_drag_payload`] on the receiver side to recover a typed value.
pub type DragPayload = Rc<dyn Any>;

/// Wrap a typed value into a [`DragPayload`] for a drag source.
///
/// ```ignore
/// Modifier::new().on_drag_start(|_start| Some(drag_payload(MyItem { id: 1 })))
/// ```
pub fn drag_payload<T: 'static>(value: T) -> DragPayload {
    Rc::new(value)
}

/// Try to downcast a drag payload to a typed reference. Used on the drop side.
///
/// ```ignore
/// if let Some(item) = downcast_drag_payload::<MyItem>(&ev.payload) {
///     // handle item
/// }
/// ```
pub fn downcast_drag_payload<T: 'static>(payload: &DragPayload) -> Option<&T> {
    payload.as_ref().downcast_ref::<T>()
}

/// Block-style convenience for [`Modifier::on_drag_start`] with a typed payload.
///
/// ```ignore
/// use repose_core::{Modifier, drag_and_drop_source};
/// struct MyItem { id: i32 }
/// let m = drag_and_drop_source(Modifier::new(), |_start| Some(MyItem { id: 1 }));
/// ```
///
/// is equivalent to:
///
/// ```ignore
/// Modifier::new().on_drag_start(|_start| Some(drag_payload(MyItem { id: 1 })))
/// ```
pub fn drag_and_drop_source<T, F>(mut modifier: crate::Modifier, on_start: F) -> crate::Modifier
where
    T: 'static,
    F: Fn(DragStart) -> Option<T> + 'static,
{
    modifier = modifier.on_drag_start(move |start| on_start(start).map(drag_payload::<T>));
    modifier
}

/// Typed source + custom drag decoration in one call.
pub fn drag_and_drop_source_with_preview<T, F>(
    mut modifier: crate::Modifier,
    preview: DragPreview,
    on_start: F,
) -> crate::Modifier
where
    T: 'static,
    F: Fn(DragStart) -> Option<T> + 'static,
{
    modifier = modifier
        .draw_drag_decoration_rc(preview)
        .on_drag_start(move |start| on_start(start).map(drag_payload::<T>));
    modifier
}

/// Block-style convenience for [`Modifier::on_drop`] with a typed payload. The
/// drop is accepted when the closure returns `true`. The typed payload is
/// downcast before the closure is invoked.
///
/// ```ignore
/// use repose_core::{Modifier, drag_and_drop_target};
/// struct MyItem { id: i32 }
/// let m = drag_and_drop_target(Modifier::new(), |_ev, item: &MyItem| {
///     println!("got id {}", item.id);
///     true
/// });
/// ```
pub fn drag_and_drop_target<T, F>(mut modifier: crate::Modifier, on_drop: F) -> crate::Modifier
where
    T: 'static,
    F: Fn(&DropEvent, &T) -> bool + 'static,
{
    modifier = modifier.on_drop(move |ev| match downcast_drag_payload::<T>(&ev.payload) {
        Some(v) => on_drop(&ev, v),
        None => false,
    });
    modifier
}

/// Compose-like typed drag/drop modifier helpers.
pub trait DragDropModifierExt: Sized {
    /// Make this node a typed drag source.
    fn drag_source<T>(
        self,
        make_payload: impl Fn(DragStart) -> Option<T> + 'static,
    ) -> crate::Modifier
    where
        T: 'static;

    /// Typed drag-enter.
    fn on_drag_enter_typed<T>(self, f: impl Fn(&DragOver, &T) + 'static) -> crate::Modifier
    where
        T: 'static;

    /// Typed drag-over.
    fn on_drag_over_typed<T>(self, f: impl Fn(&DragOver, &T) + 'static) -> crate::Modifier
    where
        T: 'static;

    /// Typed drag-leave.
    fn on_drag_leave_typed<T>(self, f: impl Fn(&DragOver, &T) + 'static) -> crate::Modifier
    where
        T: 'static;

    /// Typed drop target.
    fn on_drop_typed<T>(self, f: impl Fn(&DropEvent, &T) -> bool + 'static) -> crate::Modifier
    where
        T: 'static;

    /// Common case: typed drag-over + typed drop.
    fn drop_target<T>(self, on_drop: impl Fn(&DropEvent, &T) -> bool + 'static) -> crate::Modifier
    where
        T: 'static;
}

impl DragDropModifierExt for crate::Modifier {
    fn drag_source<T>(
        self,
        make_payload: impl Fn(DragStart) -> Option<T> + 'static,
    ) -> crate::Modifier
    where
        T: 'static,
    {
        self.on_drag_start(move |start| make_payload(start).map(drag_payload::<T>))
    }

    fn on_drag_enter_typed<T>(self, f: impl Fn(&DragOver, &T) + 'static) -> crate::Modifier
    where
        T: 'static,
    {
        self.on_drag_enter(move |ev| {
            if let Some(payload) = downcast_drag_payload::<T>(&ev.payload) {
                f(&ev, payload);
            }
        })
    }

    fn on_drag_over_typed<T>(self, f: impl Fn(&DragOver, &T) + 'static) -> crate::Modifier
    where
        T: 'static,
    {
        self.on_drag_over(move |ev| {
            if let Some(payload) = downcast_drag_payload::<T>(&ev.payload) {
                f(&ev, payload);
            }
        })
    }

    fn on_drag_leave_typed<T>(self, f: impl Fn(&DragOver, &T) + 'static) -> crate::Modifier
    where
        T: 'static,
    {
        self.on_drag_leave(move |ev| {
            if let Some(payload) = downcast_drag_payload::<T>(&ev.payload) {
                f(&ev, payload);
            }
        })
    }

    fn on_drop_typed<T>(self, f: impl Fn(&DropEvent, &T) -> bool + 'static) -> crate::Modifier
    where
        T: 'static,
    {
        self.on_drop(move |ev| {
            let Some(payload) = downcast_drag_payload::<T>(&ev.payload) else {
                return false;
            };
            f(&ev, payload)
        })
    }

    fn drop_target<T>(self, on_drop: impl Fn(&DropEvent, &T) -> bool + 'static) -> crate::Modifier
    where
        T: 'static,
    {
        self.on_drop_typed(on_drop)
    }
}

#[derive(Clone, Debug)]
pub struct DragStart {
    pub source_id: u64,
    pub position: Vec2,
    pub modifiers: Modifiers,
}

#[derive(Clone, Debug)]
pub struct DragOver {
    pub source_id: u64,
    pub target_id: u64,
    pub position: Vec2,
    pub modifiers: Modifiers,
    pub payload: DragPayload,
}

#[derive(Clone, Debug)]
pub struct DropEvent {
    pub source_id: u64,
    pub target_id: u64,
    pub position: Vec2,
    pub modifiers: Modifiers,
    pub payload: DragPayload,
}

/// Sent to the drag source when the drag ends (drop or cancel).
#[derive(Clone, Copy, Debug)]
pub struct DragEnd {
    pub accepted: bool,
}

/// Context passed to a drag preview painter each frame while dragging.
#[derive(Clone)]
pub struct DragPreviewCtx {
    /// Current pointer position (px).
    pub pointer: Vec2,
    /// Pointer position when the drag started (px).
    pub start_pointer: Vec2,
    /// Source hit-region rect at drag start (px).
    pub source_rect: Rect,
    /// `pointer_at_start - source_rect.origin` so the ghost sticks under the finger/cursor.
    pub grab_offset: Vec2,
    /// Active payload (clone of session payload).
    pub payload: DragPayload,
}

/// Painter for the floating drag decoration.
/// Coordinates are in **screen px**. Draw relative to `ctx.pointer` / `ctx.grab_offset`.
pub type DragPreview = Rc<dyn Fn(&mut Scene, &DragPreviewCtx)>;

/// Call from `on_drag_start` to supply a session-specific preview.
///
/// ```ignore
/// .on_drag_start(move |_s| {
///     provide_drag_preview(drag_preview_label(title.clone(), Color::from_hex("#44AAFF")));
///     Some(drag_payload(MyItem { .. }))
/// })
/// ```
pub fn provide_drag_preview(preview: DragPreview) {
    with_dnd_state(|state| state.pending_preview = Some(preview));
}

fn take_pending_preview() -> Option<DragPreview> {
    with_dnd_state(|state| state.pending_preview.take())
}

/// Simple floating label chip (good default for tabs / list rows).
pub fn drag_preview_label(label: impl Into<String>, accent: Color) -> DragPreview {
    let label = label.into();
    Rc::new(move |scene: &mut Scene, ctx: &DragPreviewCtx| {
        draw_label_chip(scene, ctx.pointer, &label, accent, false);
    })
}

/// Label chip with a slightly larger "elevated" look (shadow-ish fill).
pub fn drag_preview_chip(label: impl Into<String>, accent: Color) -> DragPreview {
    let label = label.into();
    Rc::new(move |scene: &mut Scene, ctx: &DragPreviewCtx| {
        draw_label_chip(scene, ctx.pointer, &label, accent, true);
    })
}

fn draw_label_chip(scene: &mut Scene, pointer: Vec2, label: &str, accent: Color, elevated: bool) {
    use crate::units::{Px, UnitExt as _};
    // Paint-space: Dp/Sp converted at the boundary (Compose `Density.toPx`).
    // `Rect` carries px magnitudes; scalar node fields take `Px`.
    let pad_x = 10.0.dp().to_px();
    let pad_y = 6.0.dp().to_px();
    let font_px = 13.0.sp().to_px();
    // Approximate width: ~0.55em per char (good enough without measuring).
    let text_w = Px((label.chars().count() as f32 * font_px.0 * 0.55).max(24.0.dp().to_px().0));
    let w = text_w.0 + pad_x.0 * 2.0;
    let h = font_px.0 + pad_y.0 * 2.0;
    let r = 8.0.dp().to_px();

    let origin = Vec2 {
        x: pointer.x + 14.0.dp().to_px().0,
        y: pointer.y + 14.0.dp().to_px().0,
    };
    let rect = Rect {
        x: origin.x,
        y: origin.y,
        w,
        h,
    };

    if elevated {
        // Soft "shadow"
        scene.nodes.push(SceneNode::Rect {
            rect: Rect {
                x: rect.x + 2.0.dp().to_px().0,
                y: rect.y + 3.0.dp().to_px().0,
                w: rect.w,
                h: rect.h,
            },
            brush: Brush::Solid(Color::from_rgba(0, 0, 0, 50)),
            radius: [r; 4],
        });
    }

    let bg = accent.with_alpha(0xDD);
    scene.nodes.push(SceneNode::Rect {
        rect,
        brush: Brush::Solid(bg),
        radius: [r; 4],
    });
    scene.nodes.push(SceneNode::Border {
        rect,
        brush: Brush::Solid(accent.with_alpha(0xFF)),
        width: 1.0.dp().to_px(),
        radius: [r; 4],
    });
    scene.nodes.push(SceneNode::Text {
        rect: Rect {
            x: rect.x + pad_x.0,
            y: rect.y + pad_y.0,
            w: text_w.0,
            h: font_px.0,
        },
        text: Arc::<str>::from(label),
        color: Color::WHITE,
        size: font_px,
        font_family: None,
        text_align: TextAlign::Unspecified,
        font_weight: FontWeight::MEDIUM,
        font_style: FontStyle::Normal,
        text_decoration: TextDecoration::default(),
        letter_spacing: Px::ZERO,
        line_height: Px::ZERO,
        extra_style: Default::default(),
        url: None,
        font_variation_settings: None,
    });
}

/// Default ghost: translucent clone of the source bounds, locked to grab offset.
fn draw_default_source_ghost(scene: &mut Scene, ctx: &DragPreviewCtx, accent: Color) {
    use crate::units::UnitExt as _;
    let w = ctx.source_rect.w.max(24.0.dp().to_px().0);
    let h = ctx.source_rect.h.max(16.0.dp().to_px().0);
    let rect = Rect {
        x: ctx.pointer.x - ctx.grab_offset.x,
        y: ctx.pointer.y - ctx.grab_offset.y,
        w,
        h,
    };
    let r = 6.0.dp().to_px();
    scene.nodes.push(SceneNode::Rect {
        rect,
        brush: Brush::Solid(accent.with_alpha(0x55)),
        radius: [r; 4],
    });
    scene.nodes.push(SceneNode::Border {
        rect,
        brush: Brush::Solid(accent.with_alpha(0xCC)),
        width: 1.5.dp().to_px(),
        radius: [r; 4],
    });
}

/// A single dropped file descriptor.
/// - On desktop: `path` is `Some(PathBuf)`.
/// - On web: `path` is usually `None` (browser doesn't expose local paths).
#[derive(Clone, Debug)]
pub struct DroppedFile {
    pub name: String,
    pub path: Option<PathBuf>,
}

/// Payload type for file drag/drop coming from the OS/browser.
#[derive(Clone, Debug)]
pub struct DroppedFiles {
    pub files: Vec<DroppedFile>,
}

/// Tracks an active drag session (internal widget-to-widget DnD).
#[derive(Clone)]
pub struct DragSession {
    pub source_id: u64,
    pub payload: DragPayload,
    pub start_px: (f32, f32),
    pub over_id: Option<u64>,
    /// Source hit rect at drag start (px).
    pub source_rect: Rect,
    /// Pointer - source origin at drag start.
    pub grab_offset: Vec2,
    /// Optional custom decoration (Compose `drawDragDecoration`).
    pub preview: Option<DragPreview>,
}

// Manual Debug (Rc<dyn Fn> is not Debug)
impl std::fmt::Debug for DragSession {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("DragSession")
            .field("source_id", &self.source_id)
            .field("start_px", &self.start_px)
            .field("over_id", &self.over_id)
            .field("source_rect", &self.source_rect)
            .field("grab_offset", &self.grab_offset)
            .field("preview", &self.preview.as_ref().map(|_| "…"))
            .finish_non_exhaustive()
    }
}

#[derive(Clone)]
struct MouseDownState {
    position: Vec2,
    capture_id: u64,
}

#[derive(Clone)]
struct TouchDownState {
    time: Instant,
    position: Vec2,
    capture_id: u64,
    long_press_pending: bool,
}

const LONG_PRESS_MS: u128 = 400;

#[derive(Default)]
struct DndStorage {
    frame: Option<Rc<Frame>>,
    scale: f32,
    session: Option<DragSession>,
    mouse_down: Option<MouseDownState>,
    touch_down: Option<TouchDownState>,
    pending_preview: Option<DragPreview>,
}

#[derive(Clone)]
pub struct DndContext {
    storage: Rc<RefCell<DndStorage>>,
}

impl Default for DndContext {
    fn default() -> Self {
        Self {
            storage: Rc::new(RefCell::new(DndStorage {
                scale: 1.0,
                ..DndStorage::default()
            })),
        }
    }
}

pub struct DndContextGuard {
    previous: Option<DndContext>,
}

impl DndContext {
    pub fn enter(&self) -> DndContextGuard {
        let previous = ACTIVE_DND_CONTEXT.with(|slot| slot.borrow_mut().replace(self.clone()));
        DndContextGuard { previous }
    }
}

impl Drop for DndContextGuard {
    fn drop(&mut self) {
        ACTIVE_DND_CONTEXT.with(|slot| {
            *slot.borrow_mut() = self.previous.take();
        });
    }
}

thread_local! {
    static GLOBAL_DND: RefCell<DndStorage> = RefCell::new(DndStorage {
        scale: 1.0,
        ..DndStorage::default()
    });
    static ACTIVE_DND_CONTEXT: RefCell<Option<DndContext>> = const { RefCell::new(None) };
}

fn with_dnd_state<R>(f: impl FnOnce(&mut DndStorage) -> R) -> R {
    if let Some(context) = ACTIVE_DND_CONTEXT.with(|slot| slot.borrow().clone()) {
        let mut storage = context.storage.borrow_mut();
        f(&mut storage)
    } else {
        GLOBAL_DND.with(|storage| f(&mut storage.borrow_mut()))
    }
}

fn dnd_frame() -> Option<Rc<Frame>> {
    with_dnd_state(|state| state.frame.clone())
}

fn dnd_scale() -> f32 {
    with_dnd_state(|state| state.scale)
}

fn mouse_down() -> Option<MouseDownState> {
    with_dnd_state(|state| state.mouse_down.clone())
}

fn set_mouse_down(state: Option<MouseDownState>) {
    with_dnd_state(|storage| storage.mouse_down = state);
}

fn touch_down() -> Option<TouchDownState> {
    with_dnd_state(|state| state.touch_down.clone())
}

fn set_touch_down(state: Option<TouchDownState>) {
    with_dnd_state(|storage| storage.touch_down = state);
}

fn update_touch_down(f: impl FnOnce(&mut TouchDownState)) {
    with_dnd_state(|state| {
        if let Some(touch) = state.touch_down.as_mut() {
            f(touch);
        }
    });
}

fn with_session_mut<R>(f: impl FnOnce(&mut Option<DragSession>) -> R) -> R {
    with_dnd_state(|state| f(&mut state.session))
}

fn take_session() -> Option<DragSession> {
    with_dnd_state(|state| state.session.take())
}

fn set_session(session: DragSession) {
    with_dnd_state(|state| state.session = Some(session));
}

/// Set the current frame for DnD hit-testing. Called by platform after each render.
pub fn set_dnd_frame(frame: Option<Frame>) {
    set_shared_dnd_frame(frame.map(Rc::new));
}

pub fn set_shared_dnd_frame(frame: Option<Rc<Frame>>) {
    with_dnd_state(|state| state.frame = frame);
}

/// Set the display scale for DnD slop calculation.
pub fn set_dnd_scale(scale: f32) {
    with_dnd_state(|state| state.scale = scale);
}

/// Check if a drag session is currently active.
pub fn is_dragging() -> bool {
    with_dnd_state(|state| state.session.is_some())
}

/// Current drag session snapshot (if any).
pub fn current_drag_session() -> Option<DragSession> {
    with_dnd_state(|state| state.session.clone())
}

fn touch_slop_px(scale: f32) -> f32 {
    6.0 * scale
}

fn hit_index_by_id(frame: &Frame, id: u64) -> Option<usize> {
    frame.hit_regions.iter().position(|h| h.id == id)
}

fn is_dnd_target(hit: &HitRegion) -> bool {
    hit.on_drop.is_some()
        || hit.on_drag_enter.is_some()
        || hit.on_drag_over.is_some()
        || hit.on_drag_leave.is_some()
}

pub fn dnd_target_id_at(frame: &Frame, pos: Vec2) -> Option<u64> {
    frame
        .hit_regions
        .iter()
        .rev()
        .filter(|h| h.rect.contains(pos))
        .find(|h| is_dnd_target(h))
        .map(|h| h.id)
}

fn dnd_update_over(frame: &Frame, session: &mut DragSession, modifiers: Modifiers, pos: Vec2) {
    let new_over = dnd_target_id_at(frame, pos);

    if new_over != session.over_id {
        if let Some(prev) = session.over_id
            && let Some(i) = hit_index_by_id(frame, prev)
            && let Some(cb) = &frame.hit_regions[i].on_drag_leave
        {
            cb(DragOver {
                source_id: session.source_id,
                target_id: prev,
                position: pos,
                modifiers,
                payload: session.payload.clone(),
            });
        }

        if let Some(now) = new_over
            && let Some(i) = hit_index_by_id(frame, now)
            && let Some(cb) = &frame.hit_regions[i].on_drag_enter
        {
            cb(DragOver {
                source_id: session.source_id,
                target_id: now,
                position: pos,
                modifiers,
                payload: session.payload.clone(),
            });
        }

        session.over_id = new_over;
    }

    if let Some(over) = session.over_id
        && let Some(i) = hit_index_by_id(frame, over)
        && let Some(cb) = &frame.hit_regions[i].on_drag_over
    {
        cb(DragOver {
            source_id: session.source_id,
            target_id: over,
            position: pos,
            modifiers,
            payload: session.payload.clone(),
        });
    }
}

/// Finish a drag-and-drop session.
fn dnd_finish(
    frame: &Frame,
    session: DragSession,
    modifiers: Modifiers,
    pos: Vec2,
    accept_if_possible: bool,
) -> bool {
    let mut accepted = false;
    if accept_if_possible {
        let drop_target = dnd_target_id_at(frame, pos);
        if let Some(tid) = drop_target
            && let Some(i) = hit_index_by_id(frame, tid)
            && let Some(cb) = &frame.hit_regions[i].on_drop
        {
            accepted = cb(DropEvent {
                source_id: session.source_id,
                target_id: tid,
                position: pos,
                modifiers,
                payload: session.payload.clone(),
            });
        }
    }

    if let Some(i) = hit_index_by_id(frame, session.source_id)
        && let Some(cb) = &frame.hit_regions[i].on_drag_end
    {
        cb(DragEnd { accepted });
    }

    accepted
}

fn initiate_drag(
    frame: &Frame,
    capture_id: u64,
    start_pos: Vec2,
    current_pos: Vec2,
    modifiers: Modifiers,
) -> bool {
    let Some(i) = hit_index_by_id(frame, capture_id) else {
        return false;
    };
    let Some(cb) = &frame.hit_regions[i].on_drag_start else {
        return false;
    };

    // Clear any stale pending preview from a previous aborted start.
    let _ = take_pending_preview();

    let payload = cb(DragStart {
        source_id: capture_id,
        position: current_pos,
        modifiers,
    });
    let Some(payload) = payload else {
        let _ = take_pending_preview();
        return false;
    };

    // Prefer provide_drag_preview(...) from on_drag_start; else modifier decoration.
    let preview = take_pending_preview().or_else(|| frame.hit_regions[i].drag_preview.clone());

    let source_rect = frame.hit_regions[i].rect;
    let grab_offset = Vec2 {
        x: start_pos.x - source_rect.x,
        y: start_pos.y - source_rect.y,
    };

    set_session(DragSession {
        source_id: capture_id,
        payload,
        start_px: (start_pos.x, start_pos.y),
        over_id: None,
        source_rect,
        grab_offset,
        preview,
    });
    true
}

/// Handle a DragAction from the platform. Returns true if the action was consumed.
pub fn handle_drag_action(action: &DragAction) -> bool {
    let scale = dnd_scale();
    let slop = touch_slop_px(scale);

    match *action {
        DragAction::Press {
            position,
            capture_id,
            kind,
            ..
        } => {
            match kind {
                PointerKind::Mouse => {
                    set_mouse_down(Some(MouseDownState {
                        position,
                        capture_id,
                    }));
                }
                _ => {
                    set_touch_down(Some(TouchDownState {
                        time: web_time::Instant::now(),
                        position,
                        capture_id,
                        long_press_pending: true,
                    }));
                }
            }
            false
        }

        DragAction::Move {
            position,
            modifiers,
        } => {
            // If already dragging, update
            if is_dragging() {
                if let Some(frame) = dnd_frame() {
                    with_session_mut(|session| {
                        if let Some(session) = session.as_mut() {
                            dnd_update_over(&frame, session, modifiers, position);
                        }
                    });
                }
                return true;
            }

            // Mouse: try drag initiation (drag past slop)
            if let Some(down) = mouse_down() {
                let dx = position.x - down.position.x;
                let dy = position.y - down.position.y;
                let dist = (dx * dx + dy * dy).sqrt();
                if dist >= slop {
                    if let Some(frame) = dnd_frame()
                        && initiate_drag(
                            &frame,
                            down.capture_id,
                            down.position,
                            position,
                            modifiers,
                        )
                    {
                        with_session_mut(|session| {
                            if let Some(session) = session.as_mut() {
                                dnd_update_over(&frame, session, modifiers, position);
                            }
                        });
                        set_mouse_down(None);
                        return true;
                    }
                    set_mouse_down(None);
                }
                return true; // consumed: mouse is pressed, don't fall through to scroll
            }

            // Touch: try long-press initiation
            if let Some(touch) = touch_down() {
                if touch.long_press_pending {
                    let elapsed_ms = (Instant::now() - touch.time).as_millis();
                    let dx = position.x - touch.position.x;
                    let dy = position.y - touch.position.y;
                    let dist = (dx * dx + dy * dy).sqrt();

                    if elapsed_ms >= LONG_PRESS_MS
                        && dist <= slop
                        && let Some(frame) = dnd_frame()
                    {
                        if initiate_drag(
                            &frame,
                            touch.capture_id,
                            touch.position,
                            position,
                            modifiers,
                        ) {
                            with_session_mut(|session| {
                                if let Some(session) = session.as_mut() {
                                    dnd_update_over(&frame, session, modifiers, position);
                                }
                            });
                            set_touch_down(None);
                            return true;
                        }
                        update_touch_down(|touch| touch.long_press_pending = false);
                    }
                    if dist > slop {
                        update_touch_down(|touch| touch.long_press_pending = false);
                    }
                }
                // Only consume if still waiting for long-press (within slop, timer not yet expired).
                // If long-press was cancelled (moved past slop), let scroll handle the event.
                let still_pending = touch_down().is_some_and(|touch| touch.long_press_pending);
                if still_pending {
                    return true;
                }
            }

            false
        }

        DragAction::Release {
            position,
            modifiers,
        } => {
            let mut consumed = false;

            if let Some(session) = take_session() {
                if let Some(frame) = dnd_frame() {
                    dnd_finish(&frame, session, modifiers, position, true);
                }
                consumed = true;
            }

            set_mouse_down(None);
            set_touch_down(None);

            consumed
        }

        DragAction::Cancel => {
            let mut consumed = false;
            if let Some(session) = take_session() {
                if let Some(frame) = dnd_frame() {
                    dnd_finish(
                        &frame,
                        session,
                        Modifiers::default(),
                        Vec2::default(),
                        false,
                    );
                }
                consumed = true;
            }
            set_mouse_down(None);
            set_touch_down(None);
            consumed
        }
    }
}

/// Draw drag overlay indicator on the scene.
/// `external_file_drag` enables orange styling for OS/browser file-drop overlays.
pub fn overlay_drag_indicator(
    scene: &mut Scene,
    mouse_pos_px: (f32, f32),
    external_file_drag: bool,
) {
    if !is_dragging() && !external_file_drag {
        return;
    }

    let pos = Vec2 {
        x: mouse_pos_px.0,
        y: mouse_pos_px.1,
    };

    let frame = dnd_frame();
    let Some(ref f) = frame else {
        return;
    };

    let accent = if external_file_drag {
        Color::from_hex("#FFAA00")
    } else {
        Color::from_hex("#44AAFF")
    };

    // Highlight best drop target under cursor
    if let Some(tid) = dnd_target_id_at(f, pos)
        && let Some(hit) = f.hit_regions.iter().find(|h| h.id == tid)
    {
        use crate::units::UnitExt as _;
        let r = 8.0.dp().to_px();
        scene.nodes.push(SceneNode::Border {
            rect: hit.rect,
            brush: Brush::Solid(accent),
            width: 2.0.dp().to_px(),
            radius: [r; 4],
        });
    }

    if external_file_drag {
        draw_label_chip(scene, pos, "Drop files", accent, true);
        return;
    }

    let Some(session) = current_drag_session() else {
        return;
    };
    let ctx = DragPreviewCtx {
        pointer: pos,
        start_pointer: Vec2 {
            x: session.start_px.0,
            y: session.start_px.1,
        },
        source_rect: session.source_rect,
        grab_offset: session.grab_offset,
        payload: session.payload.clone(),
    };

    if let Some(preview) = session.preview {
        preview(scene, &ctx);
    } else {
        draw_default_source_ghost(scene, &ctx, accent);
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::input::PointerKind;
    use crate::runtime::HitRegion;

    #[test]
    fn contexts_isolate_drag_sessions() {
        let frame = Frame {
            scene: Scene::default(),
            hit_regions: vec![HitRegion {
                id: 1,
                rect: Rect {
                    x: 0.0,
                    y: 0.0,
                    w: 100.0,
                    h: 100.0,
                },
                on_drag_start: Some(Rc::new(|_| Some(drag_payload(7u32)))),
                ..Default::default()
            }],
            semantics_nodes: Vec::new(),
            focus_chain: Vec::new(),
        };
        let a = DndContext::default();
        let b = DndContext::default();
        {
            let _guard = a.enter();
            set_dnd_frame(Some(frame.clone()));
            handle_drag_action(&DragAction::Press {
                position: Vec2 { x: 10.0, y: 10.0 },
                capture_id: 1,
                kind: PointerKind::Mouse,
                modifiers: Modifiers::default(),
            });
            handle_drag_action(&DragAction::Move {
                position: Vec2 { x: 40.0, y: 40.0 },
                modifiers: Modifiers::default(),
            });
            assert!(is_dragging());
        }
        {
            let _guard = b.enter();
            assert!(!is_dragging());
            set_dnd_frame(Some(frame.clone()));
        }
        {
            let _guard = a.enter();
            assert!(is_dragging());
            handle_drag_action(&DragAction::Cancel);
            assert!(!is_dragging());
        }
    }
}