fc-gpui-core 0.11.2

use crate::{
    Axis, Bounds, Capslock, Context, Empty, IntoElement, IsZero, Keystroke, Modifiers, Pixels,
    Point, Render, Window, point, px, seal::Sealed,
};
use smallvec::SmallVec;
use std::{
    any::Any,
    fmt::Debug,
    ops::Deref,
    path::PathBuf,
    time::{Duration, Instant},
};

/// An event from a platform input source.
pub trait InputEvent: Sealed + 'static {
    /// Convert this event into the platform input enum.
    fn to_platform_input(self) -> PlatformInput;
}

/// A key event from the platform.
pub trait KeyEvent: InputEvent {}

/// A mouse event from the platform.
pub trait MouseEvent: InputEvent {}

/// A gesture event from the platform.
pub trait GestureEvent: InputEvent {}

/// The key down event equivalent for the platform.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct KeyDownEvent {
    /// The keystroke that was generated.
    pub keystroke: Keystroke,

    /// Whether the key is currently held down.
    pub is_held: bool,

    /// Whether to prefer character input over keybindings for this keystroke.
    /// In some cases, like AltGr on Windows, modifiers are significant for character input.
    pub prefer_character_input: bool,
}

impl Sealed for KeyDownEvent {}
impl InputEvent for KeyDownEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::KeyDown(self)
    }
}
impl KeyEvent for KeyDownEvent {}

/// The key up event equivalent for the platform.
#[derive(Clone, Debug)]
pub struct KeyUpEvent {
    /// The keystroke that was released.
    pub keystroke: Keystroke,
}

impl Sealed for KeyUpEvent {}
impl InputEvent for KeyUpEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::KeyUp(self)
    }
}
impl KeyEvent for KeyUpEvent {}

/// The modifiers changed event equivalent for the platform.
#[derive(Clone, Debug, Default)]
pub struct ModifiersChangedEvent {
    /// The new state of the modifier keys
    pub modifiers: Modifiers,
    /// The new state of the capslock key
    pub capslock: Capslock,
}

impl Sealed for ModifiersChangedEvent {}
impl InputEvent for ModifiersChangedEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::ModifiersChanged(self)
    }
}
impl KeyEvent for ModifiersChangedEvent {}

impl Deref for ModifiersChangedEvent {
    type Target = Modifiers;

    fn deref(&self) -> &Self::Target {
        &self.modifiers
    }
}

/// The phase of a touch motion event.
/// Based on the winit enum of the same name.
#[derive(Clone, Copy, Debug, Default)]
pub enum TouchPhase {
    /// The touch started.
    Started,
    /// The touch event is moving.
    #[default]
    Moved,
    /// The touch phase has ended
    Ended,
}

/// A mouse down event from the platform
#[derive(Clone, Debug, Default)]
pub struct MouseDownEvent {
    /// Which mouse button was pressed.
    pub button: MouseButton,

    /// The position of the mouse on the window.
    pub position: Point<Pixels>,

    /// The modifiers that were held down when the mouse was pressed.
    pub modifiers: Modifiers,

    /// The number of times the button has been clicked.
    pub click_count: usize,

    /// Whether this is the first, focusing click.
    pub first_mouse: bool,
}

impl Sealed for MouseDownEvent {}
impl InputEvent for MouseDownEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::MouseDown(self)
    }
}
impl MouseEvent for MouseDownEvent {}

/// A mouse up event from the platform
#[derive(Clone, Debug, Default)]
pub struct MouseUpEvent {
    /// Which mouse button was released.
    pub button: MouseButton,

    /// The position of the mouse on the window.
    pub position: Point<Pixels>,

    /// The modifiers that were held down when the mouse was released.
    pub modifiers: Modifiers,

    /// The number of times the button has been clicked.
    pub click_count: usize,
}

impl Sealed for MouseUpEvent {}
impl InputEvent for MouseUpEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::MouseUp(self)
    }
}
impl MouseEvent for MouseUpEvent {}

/// A click event, generated when a mouse button is pressed and released.
#[derive(Clone, Debug, Default)]
pub struct MouseClickEvent {
    /// The mouse event when the button was pressed.
    pub down: MouseDownEvent,

    /// The mouse event when the button was released.
    pub up: MouseUpEvent,
}

/// A click event that was generated by a keyboard button being pressed and released.
#[derive(Clone, Debug, Default)]
pub struct KeyboardClickEvent {
    /// The keyboard button that was pressed to trigger the click.
    pub button: KeyboardButton,

    /// The bounds of the element that was clicked.
    pub bounds: Bounds<Pixels>,
}

/// A click event, generated when a mouse button or keyboard button is pressed and released.
#[derive(Clone, Debug)]
pub enum ClickEvent {
    /// A click event trigger by a mouse button being pressed and released.
    Mouse(MouseClickEvent),
    /// A click event trigger by a keyboard button being pressed and released.
    Keyboard(KeyboardClickEvent),
}

impl Default for ClickEvent {
    fn default() -> Self {
        ClickEvent::Keyboard(KeyboardClickEvent::default())
    }
}

impl ClickEvent {
    /// Returns the modifiers that were held during the click event
    ///
    /// `Keyboard`: The keyboard click events never have modifiers.
    /// `Mouse`: Modifiers that were held during the mouse key up event.
    pub fn modifiers(&self) -> Modifiers {
        match self {
            // Click events are only generated from keyboard events _without any modifiers_, so we know the modifiers are always Default
            ClickEvent::Keyboard(_) => Modifiers::default(),
            // Click events on the web only reflect the modifiers for the keyup event,
            // tested via observing the behavior of the `ClickEvent.shiftKey` field in Chrome 138
            // under various combinations of modifiers and keyUp / keyDown events.
            ClickEvent::Mouse(event) => event.up.modifiers,
        }
    }

    /// Returns the position of the click event
    ///
    /// `Keyboard`: The bottom left corner of the clicked hitbox
    /// `Mouse`: The position of the mouse when the button was released.
    pub fn position(&self) -> Point<Pixels> {
        match self {
            ClickEvent::Keyboard(event) => event.bounds.bottom_left(),
            ClickEvent::Mouse(event) => event.up.position,
        }
    }

    /// Returns the mouse position of the click event
    ///
    /// `Keyboard`: None
    /// `Mouse`: The position of the mouse when the button was released.
    pub fn mouse_position(&self) -> Option<Point<Pixels>> {
        match self {
            ClickEvent::Keyboard(_) => None,
            ClickEvent::Mouse(event) => Some(event.up.position),
        }
    }

    /// Returns if this was a right click
    ///
    /// `Keyboard`: false
    /// `Mouse`: Whether the right button was pressed and released
    pub fn is_right_click(&self) -> bool {
        match self {
            ClickEvent::Keyboard(_) => false,
            ClickEvent::Mouse(event) => {
                event.down.button == MouseButton::Right && event.up.button == MouseButton::Right
            }
        }
    }

    /// Returns whether the click was a standard click
    ///
    /// `Keyboard`: Always true
    /// `Mouse`: Left button pressed and released
    pub fn standard_click(&self) -> bool {
        match self {
            ClickEvent::Keyboard(_) => true,
            ClickEvent::Mouse(event) => {
                event.down.button == MouseButton::Left && event.up.button == MouseButton::Left
            }
        }
    }

    /// Returns whether the click focused the element
    ///
    /// `Keyboard`: false, keyboard clicks only work if an element is already focused
    /// `Mouse`: Whether this was the first focusing click
    pub fn first_focus(&self) -> bool {
        match self {
            ClickEvent::Keyboard(_) => false,
            ClickEvent::Mouse(event) => event.down.first_mouse,
        }
    }

    /// Returns the click count of the click event
    ///
    /// `Keyboard`: Always 1
    /// `Mouse`: Count of clicks from MouseUpEvent
    pub fn click_count(&self) -> usize {
        match self {
            ClickEvent::Keyboard(_) => 1,
            ClickEvent::Mouse(event) => event.up.click_count,
        }
    }

    /// Returns whether the click event is generated by a keyboard event
    pub fn is_keyboard(&self) -> bool {
        match self {
            ClickEvent::Mouse(_) => false,
            ClickEvent::Keyboard(_) => true,
        }
    }
}

/// An enum representing the keyboard button that was pressed for a click event.
#[derive(Hash, PartialEq, Eq, Copy, Clone, Debug, Default)]
pub enum KeyboardButton {
    /// Enter key was clicked
    #[default]
    Enter,
    /// Space key was clicked
    Space,
}

/// An enum representing the mouse button that was pressed.
#[derive(Hash, PartialEq, Eq, Copy, Clone, Debug, Default)]
pub enum MouseButton {
    /// The left mouse button.
    #[default]
    Left,

    /// The right mouse button.
    Right,

    /// The middle mouse button.
    Middle,

    /// A navigation button, such as back or forward.
    Navigate(NavigationDirection),
}

impl MouseButton {
    /// Get all the mouse buttons in a list.
    pub fn all() -> Vec<Self> {
        vec![
            MouseButton::Left,
            MouseButton::Right,
            MouseButton::Middle,
            MouseButton::Navigate(NavigationDirection::Back),
            MouseButton::Navigate(NavigationDirection::Forward),
        ]
    }
}

/// A navigation direction, such as back or forward.
#[derive(Hash, PartialEq, Eq, Copy, Clone, Debug, Default)]
pub enum NavigationDirection {
    /// The back button.
    #[default]
    Back,

    /// The forward button.
    Forward,
}

/// A mouse move event from the platform
#[derive(Clone, Debug, Default)]
pub struct MouseMoveEvent {
    /// The position of the mouse on the window.
    pub position: Point<Pixels>,

    /// The mouse button that was pressed, if any.
    pub pressed_button: Option<MouseButton>,

    /// The modifiers that were held down when the mouse was moved.
    pub modifiers: Modifiers,
}

impl Sealed for MouseMoveEvent {}
impl InputEvent for MouseMoveEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::MouseMove(self)
    }
}
impl MouseEvent for MouseMoveEvent {}

impl MouseMoveEvent {
    /// Returns true if the left mouse button is currently held down.
    pub fn dragging(&self) -> bool {
        self.pressed_button == Some(MouseButton::Left)
    }
}

/// A mouse wheel event from the platform
#[derive(Clone, Debug, Default)]
pub struct ScrollWheelEvent {
    /// The position of the mouse on the window.
    pub position: Point<Pixels>,

    /// The change in scroll wheel position for this event.
    pub delta: ScrollDelta,

    /// The modifiers that were held down when the mouse was moved.
    pub modifiers: Modifiers,

    /// The phase of the touch event.
    pub touch_phase: TouchPhase,
}

impl Sealed for ScrollWheelEvent {}
impl InputEvent for ScrollWheelEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::ScrollWheel(self)
    }
}
impl MouseEvent for ScrollWheelEvent {}

impl Deref for ScrollWheelEvent {
    type Target = Modifiers;

    fn deref(&self) -> &Self::Target {
        &self.modifiers
    }
}

/// The scroll delta for a scroll wheel event.
#[derive(Clone, Copy, Debug)]
pub enum ScrollDelta {
    /// An exact scroll delta in pixels.
    Pixels(Point<Pixels>),
    /// An inexact scroll delta in lines.
    Lines(Point<f32>),
}

impl Default for ScrollDelta {
    fn default() -> Self {
        Self::Lines(Default::default())
    }
}

/// A pinch gesture event from the platform, generated when the user performs
/// a pinch-to-zoom gesture.
#[derive(Clone, Debug, Default)]
pub struct PinchEvent {
    /// The position of the pinch center on the window.
    pub position: Point<Pixels>,

    /// The zoom delta for this event. Positive values indicate zooming in,
    /// negative values indicate zooming out. Native pinch gestures report
    /// the change in scale since the previous event. Wheel-based synthetic
    /// pinch gestures report the normalized wheel-notch delta.
    pub delta: f32,

    /// The modifiers that were held down during the pinch gesture.
    pub modifiers: Modifiers,

    /// The phase of the pinch gesture.
    pub phase: TouchPhase,
}

impl Sealed for PinchEvent {}
impl InputEvent for PinchEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::Pinch(self)
    }
}
impl GestureEvent for PinchEvent {}
impl MouseEvent for PinchEvent {}

impl Deref for PinchEvent {
    type Target = Modifiers;

    fn deref(&self) -> &Self::Target {
        &self.modifiers
    }
}

impl ScrollDelta {
    /// Returns true if this is a precise scroll delta in pixels.
    pub fn precise(&self) -> bool {
        match self {
            ScrollDelta::Pixels(_) => true,
            ScrollDelta::Lines(_) => false,
        }
    }

    /// Converts this scroll event into exact pixels.
    pub fn pixel_delta(&self, line_height: Pixels) -> Point<Pixels> {
        match self {
            ScrollDelta::Pixels(delta) => *delta,
            ScrollDelta::Lines(delta) => point(line_height * delta.x, line_height * delta.y),
        }
    }

    /// Combines two scroll deltas into one.
    /// If the signs of the deltas are the same (both positive or both negative),
    /// the deltas are added together. If the signs are opposite, the second delta
    /// (other) is used, effectively overriding the first delta.
    pub fn coalesce(self, other: ScrollDelta) -> ScrollDelta {
        match (self, other) {
            (ScrollDelta::Pixels(a), ScrollDelta::Pixels(b)) => {
                let x = if a.x.signum() == b.x.signum() {
                    a.x + b.x
                } else {
                    b.x
                };

                let y = if a.y.signum() == b.y.signum() {
                    a.y + b.y
                } else {
                    b.y
                };

                ScrollDelta::Pixels(point(x, y))
            }

            (ScrollDelta::Lines(a), ScrollDelta::Lines(b)) => {
                let x = if a.x.signum() == b.x.signum() {
                    a.x + b.x
                } else {
                    b.x
                };

                let y = if a.y.signum() == b.y.signum() {
                    a.y + b.y
                } else {
                    b.y
                };

                ScrollDelta::Lines(point(x, y))
            }

            _ => other,
        }
    }
}

const SCROLL_EVENT_SEPARATION: Duration = Duration::from_millis(28);

/// Tracks the dominant axis across the events in a scroll gesture.
#[derive(Clone, Copy, Debug, Default)]
pub struct OngoingScroll {
    last_event: Option<Instant>,
    axis: Option<Axis>,
}

impl OngoingScroll {
    /// Filters the given delta to the dominant axis of the current scroll gesture.
    ///
    /// Gestures are delimited by their touch phase when available, with a timeout
    /// fallback for platforms that only emit [`TouchPhase::Moved`].
    pub fn filter(&mut self, delta: &mut Point<Pixels>, touch_phase: TouchPhase) {
        self.filter_at(delta, touch_phase, Instant::now())
    }

    fn filter_at(&mut self, delta: &mut Point<Pixels>, touch_phase: TouchPhase, now: Instant) {
        const UNLOCK_PERCENT: f32 = 1.9;
        const UNLOCK_LOWER_BOUND: Pixels = px(6.);

        if matches!(touch_phase, TouchPhase::Ended) {
            self.last_event = None;
            self.axis = None;
            return;
        }

        let x = delta.x.abs();
        let y = delta.y.abs();
        if x.is_zero() && y.is_zero() {
            if matches!(touch_phase, TouchPhase::Started) {
                self.last_event = None;
                self.axis = None;
            }
            return;
        }

        let starts_new_gesture = matches!(touch_phase, TouchPhase::Started)
            || self
                .last_event
                .is_none_or(|last_event| now.duration_since(last_event) >= SCROLL_EVENT_SEPARATION);
        let mut axis = self.axis;
        if starts_new_gesture {
            axis = if x <= y {
                Some(Axis::Vertical)
            } else {
                Some(Axis::Horizontal)
            };
        } else if x.max(y) >= UNLOCK_LOWER_BOUND {
            match axis {
                Some(Axis::Vertical) if x > y && x >= y * UNLOCK_PERCENT => {
                    axis = None;
                }
                Some(Axis::Horizontal) if y > x && y >= x * UNLOCK_PERCENT => {
                    axis = None;
                }
                _ => {}
            }
        }

        self.last_event = Some(now);
        self.axis = axis;
        match axis {
            Some(Axis::Vertical) => delta.x = Pixels::ZERO,
            Some(Axis::Horizontal) => delta.y = Pixels::ZERO,
            None => {}
        }
    }
}

/// A mouse exit event from the platform, generated when the mouse leaves the window.
#[derive(Clone, Debug, Default)]
pub struct MouseExitEvent {
    /// The position of the mouse relative to the window.
    pub position: Point<Pixels>,
    /// The mouse button that was pressed, if any.
    pub pressed_button: Option<MouseButton>,
    /// The modifiers that were held down when the mouse was moved.
    pub modifiers: Modifiers,
}

impl Sealed for MouseExitEvent {}
impl InputEvent for MouseExitEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::MouseExited(self)
    }
}
impl MouseEvent for MouseExitEvent {}

impl Deref for MouseExitEvent {
    type Target = Modifiers;

    fn deref(&self) -> &Self::Target {
        &self.modifiers
    }
}

/// A collection of paths from the platform, such as from a file drop.
#[derive(Debug, Clone, Default)]
#[allow(missing_docs)]
pub struct ExternalPaths(pub SmallVec<[PathBuf; 2]>);

impl ExternalPaths {
    /// Convert this collection of paths into a slice.
    pub fn paths(&self) -> &[PathBuf] {
        &self.0
    }
}

impl Render for ExternalPaths {
    fn render(&mut self, _: &mut Window, _: &mut Context<Self>) -> impl IntoElement {
        // the platform will render icons for the dragged files
        Empty
    }
}

/// A file drop event from the platform, generated when files are dragged and dropped onto the window.
#[derive(Debug, Clone)]
pub enum FileDropEvent {
    /// The files have entered the window.
    Entered {
        /// The position of the mouse relative to the window.
        position: Point<Pixels>,
        /// The paths of the files that are being dragged.
        paths: ExternalPaths,
    },
    /// The files are being dragged over the window
    Pending {
        /// The position of the mouse relative to the window.
        position: Point<Pixels>,
    },
    /// The files have been dropped onto the window.
    Submit {
        /// The position of the mouse relative to the window.
        position: Point<Pixels>,
    },
    /// The user has stopped dragging the files over the window.
    Exited,
}

impl Sealed for FileDropEvent {}
impl InputEvent for FileDropEvent {
    fn to_platform_input(self) -> PlatformInput {
        PlatformInput::FileDrop(self)
    }
}
impl MouseEvent for FileDropEvent {}

/// An enum corresponding to all kinds of platform input events.
#[derive(Clone, Debug)]
pub enum PlatformInput {
    /// A key was pressed.
    KeyDown(KeyDownEvent),
    /// A key was released.
    KeyUp(KeyUpEvent),
    /// The keyboard modifiers were changed.
    ModifiersChanged(ModifiersChangedEvent),
    /// The mouse was pressed.
    MouseDown(MouseDownEvent),
    /// The mouse was released.
    MouseUp(MouseUpEvent),
    /// The mouse was moved.
    MouseMove(MouseMoveEvent),
    /// The mouse exited the window.
    MouseExited(MouseExitEvent),
    /// The scroll wheel was used.
    ScrollWheel(ScrollWheelEvent),
    /// A pinch gesture was performed.
    Pinch(PinchEvent),
    /// Files were dragged and dropped onto the window.
    FileDrop(FileDropEvent),
}

impl PlatformInput {
    pub(crate) fn mouse_event(&self) -> Option<&dyn Any> {
        match self {
            PlatformInput::KeyDown { .. } => None,
            PlatformInput::KeyUp { .. } => None,
            PlatformInput::ModifiersChanged { .. } => None,
            PlatformInput::MouseDown(event) => Some(event),
            PlatformInput::MouseUp(event) => Some(event),
            PlatformInput::MouseMove(event) => Some(event),
            PlatformInput::MouseExited(event) => Some(event),
            PlatformInput::ScrollWheel(event) => Some(event),
            PlatformInput::Pinch(event) => Some(event),
            PlatformInput::FileDrop(event) => Some(event),
        }
    }

    pub(crate) fn keyboard_event(&self) -> Option<&dyn Any> {
        match self {
            PlatformInput::KeyDown(event) => Some(event),
            PlatformInput::KeyUp(event) => Some(event),
            PlatformInput::ModifiersChanged(event) => Some(event),
            PlatformInput::MouseDown(_) => None,
            PlatformInput::MouseUp(_) => None,
            PlatformInput::MouseMove(_) => None,
            PlatformInput::MouseExited(_) => None,
            PlatformInput::ScrollWheel(_) => None,
            PlatformInput::Pinch(_) => None,
            PlatformInput::FileDrop(_) => None,
        }
    }
}

#[cfg(test)]
mod test {

    use crate::{
        self as gpui, AppContext as _, Context, FocusHandle, InteractiveElement, IntoElement,
        KeyBinding, Keystroke, Modifiers, ParentElement, Render, TestAppContext, Window, div,
    };

    struct TestView {
        saw_key_down: bool,
        saw_action: bool,
        focus_handle: FocusHandle,
    }

    actions!(test_only, [TestAction]);

    impl Render for TestView {
        fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
            div().id("testview").child(
                div()
                    .key_context("parent")
                    .on_key_down(cx.listener(|this, _, _, cx| {
                        cx.stop_propagation();
                        this.saw_key_down = true
                    }))
                    .on_action(cx.listener(|this: &mut TestView, _: &TestAction, _, _| {
                        this.saw_action = true
                    }))
                    .child(
                        div()
                            .key_context("nested")
                            .track_focus(&self.focus_handle)
                            .into_element(),
                    ),
            )
        }
    }

    #[gpui::test]
    fn test_on_events(cx: &mut TestAppContext) {
        let window = cx.update(|cx| {
            cx.open_window(Default::default(), |_, cx| {
                cx.new(|cx| TestView {
                    saw_key_down: false,
                    saw_action: false,
                    focus_handle: cx.focus_handle(),
                })
            })
            .unwrap()
        });

        cx.update(|cx| {
            cx.bind_keys(vec![KeyBinding::new("ctrl-g", TestAction, Some("parent"))]);
        });

        window
            .update(cx, |test_view, window, _cx| {
                window.focus(&test_view.focus_handle)
            })
            .unwrap();

        cx.dispatch_keystroke(*window, Keystroke::parse("a").unwrap());
        cx.dispatch_keystroke(*window, Keystroke::parse("ctrl-g").unwrap());

        window
            .update(cx, |test_view, _, _| {
                assert!(test_view.saw_key_down || test_view.saw_action);
                assert!(test_view.saw_key_down);
                assert!(test_view.saw_action);
            })
            .unwrap();
    }

    #[gpui::test]
    fn test_multi_modifier_gesture_does_not_dispatch_standalone_modifier_binding(
        cx: &mut TestAppContext,
    ) {
        let (test_view, cx) = cx.add_window_view(|_, cx| TestView {
            saw_key_down: false,
            saw_action: false,
            focus_handle: cx.focus_handle(),
        });

        cx.update(|_, cx| {
            cx.bind_keys(vec![KeyBinding::new("shift", TestAction, None)]);
        });
        test_view.update_in(cx, |test_view, window, _cx| {
            window.focus(&test_view.focus_handle);
        });

        cx.simulate_modifiers_change(Modifiers::alt());
        cx.simulate_modifiers_change(Modifiers::alt() | Modifiers::shift());
        cx.simulate_modifiers_change(Modifiers::shift());
        cx.simulate_modifiers_change(Modifiers::none());
        assert!(!test_view.read_with(cx, |test_view, _| test_view.saw_action));

        cx.simulate_modifiers_change(Modifiers::shift());
        cx.simulate_modifiers_change(Modifiers::none());
        assert!(test_view.read_with(cx, |test_view, _| test_view.saw_action));
    }
}

#[cfg(test)]
mod ongoing_scroll_tests {
    use super::*;

    #[test]
    fn ongoing_scroll_locks_to_dominant_axis() {
        let now = Instant::now();
        let mut ongoing_scroll = OngoingScroll::default();
        let mut horizontal_delta = point(px(10.), px(2.));
        ongoing_scroll.filter_at(&mut horizontal_delta, TouchPhase::Started, now);
        assert_eq!(ongoing_scroll.axis, Some(Axis::Horizontal));
        assert_eq!(horizontal_delta, point(px(10.), px(0.)));

        let mut continued_delta = point(px(3.), px(2.));
        ongoing_scroll.filter_at(
            &mut continued_delta,
            TouchPhase::Moved,
            now + Duration::from_millis(1),
        );
        assert_eq!(ongoing_scroll.axis, Some(Axis::Horizontal));
        assert_eq!(continued_delta, point(px(3.), px(0.)));
    }

    #[test]
    fn ongoing_scroll_unlocks_when_direction_changes() {
        let now = Instant::now();
        let mut ongoing_scroll = OngoingScroll::default();
        let mut horizontal_delta = point(px(10.), px(2.));
        ongoing_scroll.filter_at(&mut horizontal_delta, TouchPhase::Started, now);

        let mut vertical_delta = point(px(2.), px(10.));
        ongoing_scroll.filter_at(
            &mut vertical_delta,
            TouchPhase::Moved,
            now + Duration::from_millis(1),
        );
        assert_eq!(ongoing_scroll.axis, None);
        assert_eq!(vertical_delta, point(px(2.), px(10.)));
    }

    #[test]
    fn ongoing_scroll_starts_new_gesture_at_timeout_boundary() {
        let now = Instant::now();
        let mut ongoing_scroll = OngoingScroll::default();
        let mut horizontal_delta = point(px(10.), px(2.));
        ongoing_scroll.filter_at(&mut horizontal_delta, TouchPhase::Moved, now);

        let mut vertical_delta = point(px(2.), px(10.));
        ongoing_scroll.filter_at(
            &mut vertical_delta,
            TouchPhase::Moved,
            now + SCROLL_EVENT_SEPARATION,
        );
        assert_eq!(ongoing_scroll.axis, Some(Axis::Vertical));
        assert_eq!(vertical_delta, point(px(0.), px(10.)));
    }

    #[test]
    fn ongoing_scroll_ignores_zero_delta_and_resets_when_ended() {
        let now = Instant::now();
        let mut ongoing_scroll = OngoingScroll::default();
        let mut horizontal_delta = point(px(10.), px(2.));
        ongoing_scroll.filter_at(&mut horizontal_delta, TouchPhase::Started, now);

        let mut zero_delta = Point::default();
        ongoing_scroll.filter_at(
            &mut zero_delta,
            TouchPhase::Ended,
            now + Duration::from_millis(1),
        );
        assert_eq!(ongoing_scroll.axis, None);

        let mut vertical_delta = point(px(2.), px(3.));
        ongoing_scroll.filter_at(
            &mut vertical_delta,
            TouchPhase::Moved,
            now + Duration::from_millis(2),
        );
        assert_eq!(ongoing_scroll.axis, Some(Axis::Vertical));
        assert_eq!(vertical_delta, point(px(0.), px(3.)));
    }

    #[test]
    fn ongoing_scroll_ignores_zero_delta_movement() {
        let now = Instant::now();
        let mut ongoing_scroll = OngoingScroll::default();
        let mut horizontal_delta = point(px(10.), px(2.));
        ongoing_scroll.filter_at(&mut horizontal_delta, TouchPhase::Started, now);

        let mut zero_delta = Point::default();
        ongoing_scroll.filter_at(
            &mut zero_delta,
            TouchPhase::Moved,
            now + SCROLL_EVENT_SEPARATION,
        );

        let mut vertical_delta = point(px(2.), px(10.));
        ongoing_scroll.filter_at(
            &mut vertical_delta,
            TouchPhase::Moved,
            now + SCROLL_EVENT_SEPARATION,
        );
        assert_eq!(ongoing_scroll.axis, Some(Axis::Vertical));
        assert_eq!(vertical_delta, point(px(0.), px(10.)));
    }

    #[test]
    fn ongoing_scroll_supports_moved_only_platforms() {
        let now = Instant::now();
        let mut ongoing_scroll = OngoingScroll::default();
        let mut horizontal_delta = point(px(10.), px(2.));
        ongoing_scroll.filter_at(&mut horizontal_delta, TouchPhase::Moved, now);
        assert_eq!(ongoing_scroll.axis, Some(Axis::Horizontal));
        assert_eq!(horizontal_delta, point(px(10.), px(0.)));
    }
}