//!
//! Extension for [ratatui::List](https://docs.rs/ratatui/latest/ratatui/widgets/struct.List.html)
//!

use crate::_private::NonExhaustive;
use crate::event::util::{row_at_clicked, row_at_drag, MouseFlags};
use crate::list::selection::{RowSelection, RowSetSelection};
use rat_focus::{FocusFlag, HasFocusFlag};
use rat_scrolled::{layout_scroll, Scroll, ScrollState};
use ratatui::buffer::Buffer;
use ratatui::layout::Rect;
use ratatui::prelude::StatefulWidget;
use ratatui::style::Style;
use ratatui::widgets::{Block, ListDirection, ListItem, StatefulWidgetRef, WidgetRef};
use std::cmp::min;
use std::collections::HashSet;
use std::marker::PhantomData;

/// Trait for list-selection.
pub trait ListSelection {
    /// Is selected.
    fn is_selected(&self, n: usize) -> bool;

    /// Selection lead.
    fn lead_selection(&self) -> Option<usize>;

    /// Scroll the selection instead of the offset.
    fn scroll_selected(&self) -> bool {
        false
    }
}

#[derive(Debug, Default, Clone)]
pub struct RList<'a, Selection> {
    block: Option<Block<'a>>,
    scroll: Option<Scroll<'a>>,

    items: Vec<ListItem<'a>>,

    style: Style,
    select_style: Style,
    focus_style: Style,
    direction: ListDirection,

    _phantom: PhantomData<Selection>,
}

#[derive(Debug, Clone)]
pub struct ListStyle {
    /// Style
    pub style: Style,
    /// Style for selection
    pub select_style: Style,
    /// Style for selection when focused.
    pub focus_style: Style,

    pub non_exhaustive: NonExhaustive,
}

#[derive(Debug, Default, Clone, PartialEq, Eq)]
pub struct RListState<Selection> {
    /// Length in items.
    pub rows: usize,
    /// Offset
    pub scroll: ScrollState,

    /// Total area
    pub area: Rect,
    /// Area inside the block.
    pub inner: Rect,
    /// Areas for the rendered items.
    pub item_areas: Vec<Rect>,

    /// Focus
    pub focus: FocusFlag,
    /// Selection model
    pub selection: Selection,

    /// Helper for mouse events.
    pub mouse: MouseFlags,
}

impl Default for ListStyle {
    fn default() -> Self {
        Self {
            style: Default::default(),
            select_style: Default::default(),
            focus_style: Default::default(),
            non_exhaustive: NonExhaustive,
        }
    }
}

impl<'a, Selection> RList<'a, Selection> {
    pub fn new<T>(items: T) -> Self
    where
        T: IntoIterator,
        T::Item: Into<ListItem<'a>>,
    {
        let items = items.into_iter().map(|v| v.into()).collect();

        Self {
            block: None,
            scroll: None,
            items,
            style: Default::default(),
            select_style: Default::default(),
            focus_style: Default::default(),
            direction: Default::default(),
            _phantom: Default::default(),
        }
    }

    pub fn items<T>(mut self, items: T) -> Self
    where
        T: IntoIterator,
        T::Item: Into<ListItem<'a>>,
    {
        let items = items.into_iter().map(|v| v.into()).collect();
        self.items = items;
        self
    }

    #[inline]
    pub fn block(mut self, block: Block<'a>) -> Self {
        self.block = Some(block);
        self
    }

    #[inline]
    pub fn styles(mut self, styles: ListStyle) -> Self {
        self.style = styles.style;
        self.select_style = styles.select_style;
        self.focus_style = styles.focus_style;
        self
    }

    #[inline]
    pub fn style<S: Into<Style>>(mut self, style: S) -> Self {
        self.style = style.into();
        self
    }

    #[inline]
    pub fn select_style<S: Into<Style>>(mut self, select_style: S) -> Self {
        self.select_style = select_style.into();
        self
    }

    #[inline]
    pub fn focus_style<S: Into<Style>>(mut self, focus_style: S) -> Self {
        self.focus_style = focus_style.into();
        self
    }

    #[inline]
    pub fn direction(mut self, direction: ListDirection) -> Self {
        self.direction = direction;
        self
    }

    #[inline]
    pub fn len(&self) -> usize {
        self.items.len()
    }

    #[inline]
    pub fn is_empty(&self) -> bool {
        self.items.is_empty()
    }
}

impl<'a, Item, Selection> FromIterator<Item> for RList<'a, Selection>
where
    Item: Into<ListItem<'a>>,
{
    fn from_iter<Iter: IntoIterator<Item = Item>>(iter: Iter) -> Self {
        Self::new(iter)
    }
}

impl<'a, Selection: ListSelection> StatefulWidget for RList<'a, Selection> {
    type State = RListState<Selection>;

    fn render(mut self, area: Rect, buf: &mut Buffer, state: &mut Self::State) {
        state.area = area;
        state.rows = self.len();

        let (_, scroll_area, inner_area) =
            layout_scroll(area, self.block.as_ref(), None, self.scroll.as_ref());
        state.inner = inner_area;

        // area for each item
        state.item_areas.clear();
        let mut item_area = Rect::new(state.inner.x, state.inner.y, state.inner.width, 1);
        for item in self.items.iter().skip(state.offset()) {
            item_area.height = item.height() as u16;

            state.item_areas.push(item_area);

            item_area.y += item_area.height;
            if item_area.y >= state.inner.y + state.inner.height {
                break;
            }
        }
        state.scroll.set_page_len(state.item_areas.len());

        // max_v_offset
        let mut n = 0;
        let mut height = 0;
        for item in self.items.iter().rev() {
            height += item.height();
            if height > state.inner.height as usize {
                break;
            }
            n += 1;
        }
        state.scroll.set_max_offset(state.rows.saturating_sub(n));

        let (style, select_style) = if state.is_focused() {
            (self.style, self.focus_style)
        } else {
            (self.style, self.select_style)
        };

        self.block.render_ref(area, buf);
        if let Some(scroll) = self.scroll.as_ref() {
            scroll.render_ref(scroll_area, buf, &mut state.scroll);
        }

        // rendering
        self.items = self
            .items
            .into_iter()
            .enumerate()
            .map(|(i, v)| {
                if state.selection.is_selected(i) {
                    v.style(select_style)
                } else {
                    v.style(style)
                }
            })
            .collect();

        let mut list_state =
            ratatui::widgets::ListState::default().with_offset(state.scroll.offset());

        ratatui::widgets::List::default()
            .items(self.items)
            .style(self.style)
            .direction(self.direction)
            .render(area, buf, &mut list_state);
    }
}

impl<Selection> HasFocusFlag for RListState<Selection> {
    #[inline]
    fn focus(&self) -> &FocusFlag {
        &self.focus
    }

    #[inline]
    fn area(&self) -> Rect {
        self.area
    }
}

impl<Selection: ListSelection> RListState<Selection> {
    #[inline]
    pub fn clear_offset(&mut self) {
        self.scroll.set_offset(0);
    }

    #[inline]
    pub fn max_offset(&self) -> usize {
        self.scroll.max_offset()
    }

    #[inline]
    pub fn offset(&self) -> usize {
        self.scroll.offset()
    }

    #[inline]
    pub fn set_offset(&mut self, offset: usize) -> bool {
        self.scroll.set_offset(offset)
    }

    #[inline]
    pub fn page_len(&self) -> usize {
        self.scroll.page_len()
    }

    pub fn scroll_by(&self) -> usize {
        self.scroll.scroll_by()
    }

    /// Scroll to selected.
    #[inline]
    pub fn scroll_to_selected(&mut self) -> bool {
        if let Some(selected) = self.selection.lead_selection() {
            self.scroll_to(selected)
        } else {
            false
        }
    }

    #[inline]
    pub fn scroll_to(&mut self, pos: usize) -> bool {
        if pos >= self.offset() + self.page_len() {
            self.set_offset(pos - self.page_len() + 1)
        } else if pos < self.offset() {
            self.set_offset(pos)
        } else {
            false
        }
    }

    #[inline]
    pub fn scroll_up(&mut self, n: usize) -> bool {
        self.scroll.scroll_up(n)
    }

    #[inline]
    pub fn scroll_down(&mut self, n: usize) -> bool {
        self.scroll.scroll_down(n)
    }
}

impl<Selection: ListSelection> RListState<Selection> {
    #[inline]
    pub fn row_at_clicked(&self, pos: (u16, u16)) -> Option<usize> {
        row_at_clicked(&self.item_areas, pos.1).map(|v| self.scroll.offset() + v)
    }

    /// Row when dragging. Can go outside the area.
    #[inline]
    pub fn row_at_drag(&self, pos: (u16, u16)) -> usize {
        match row_at_drag(self.inner, &self.item_areas, pos.1) {
            Ok(v) => self.scroll.offset() + v,
            Err(v) if v <= 0 => self.scroll.offset().saturating_sub((-v) as usize),
            Err(v) => self.scroll.offset() + self.item_areas.len() + v as usize,
        }
    }
}

impl RListState<RowSelection> {
    /// When scrolling the table, change the selection instead of the offset.
    #[inline]
    pub fn set_scroll_selection(&mut self, scroll: bool) {
        self.selection.set_scroll_selected(scroll);
    }

    /// Scroll delivers a value between 0 and max_offset as offset.
    /// This remaps the ratio to the selection with a range 0..row_len.
    ///
    pub(crate) fn remap_offset_selection(&self, offset: usize) -> usize {
        if self.scroll.max_offset() > 0 {
            (self.rows * offset) / self.scroll.max_offset()
        } else {
            0 // ???
        }
    }

    /// Clear the selection.
    #[inline]
    pub fn clear_selection(&mut self) {
        self.selection.clear();
    }

    /// Anything selected?
    #[inline]
    pub fn has_selection(&mut self) -> bool {
        self.selection.has_selection()
    }

    /// Returns the lead selection.
    #[inline]
    pub fn selected(&self) -> Option<usize> {
        self.selection.lead_selection()
    }

    #[inline]
    pub fn select(&mut self, row: Option<usize>) -> bool {
        if let Some(row) = row {
            self.selection
                .select(Some(min(row, self.rows.saturating_sub(1))))
        } else {
            self.selection.select(None)
        }
    }

    /// Move the selection to the given row.
    /// Ensures the row is visible afterwards.
    #[inline]
    pub fn move_to(&mut self, row: usize) -> bool {
        let r = self.selection.move_to(row, self.rows.saturating_sub(1));
        let s = self.scroll_to(self.selection.selected().expect("row"));
        r || s
    }

    /// Move the selection up n rows.
    /// Ensures the row is visible afterwards.
    #[inline]
    pub fn move_up(&mut self, n: usize) -> bool {
        let r = self.selection.move_up(n, self.rows.saturating_sub(1));
        let s = self.scroll_to(self.selection.selected().expect("row"));
        r || s
    }

    /// Move the selection down n rows.
    /// Ensures the row is visible afterwards.
    #[inline]
    pub fn move_down(&mut self, n: usize) -> bool {
        let r = self.selection.move_down(n, self.rows.saturating_sub(1));
        let s = self.scroll_to(self.selection.selected().expect("row"));
        r || s
    }
}

impl RListState<RowSetSelection> {
    /// Clear the selection.
    #[inline]
    pub fn clear_selection(&mut self) {
        self.selection.clear();
    }

    /// Anything selected?
    #[inline]
    pub fn has_selection(&mut self) -> bool {
        self.selection.has_selection()
    }

    #[inline]
    pub fn selected(&self) -> HashSet<usize> {
        self.selection.selected()
    }

    /// Change the lead-selection. Limits the value to the number of rows.
    /// If extend is false the current selection is cleared and both lead and
    /// anchor are set to the given value.
    /// If extend is true, the anchor is kept where it is and lead is changed.
    /// Everything in the range `anchor..lead` is selected. It doesn't matter
    /// if anchor < lead.
    #[inline]
    pub fn set_lead(&mut self, row: Option<usize>, extend: bool) -> bool {
        if let Some(row) = row {
            self.selection
                .set_lead(Some(min(row, self.rows.saturating_sub(1))), extend)
        } else {
            self.selection.set_lead(None, extend)
        }
    }

    /// Current lead.
    #[inline]
    pub fn lead(&self) -> Option<usize> {
        self.selection.lead()
    }

    /// Current anchor.
    #[inline]
    pub fn anchor(&self) -> Option<usize> {
        self.selection.anchor()
    }

    /// Set a new lead, at the same time limit the lead to max.
    #[inline]
    pub fn set_lead_clamped(&mut self, lead: usize, max: usize, extend: bool) {
        self.selection.move_to(lead, max, extend);
    }

    /// Retire the current anchor/lead selection to the set of selected rows.
    /// Resets lead and anchor and starts a new selection round.
    #[inline]
    pub fn retire_selection(&mut self) {
        self.selection.retire_selection();
    }

    /// Add to selection.
    #[inline]
    pub fn add_selected(&mut self, idx: usize) {
        self.selection.add(idx);
    }

    /// Remove from selection. Only works for retired selections, not for the
    /// active anchor-lead range.
    #[inline]
    pub fn remove_selected(&mut self, idx: usize) {
        self.selection.remove(idx);
    }

    /// Move the selection to the given row.
    /// Ensures the row is visible afterwards.
    #[inline]
    pub fn move_to(&mut self, row: usize, extend: bool) -> bool {
        let r = self
            .selection
            .move_to(row, self.rows.saturating_sub(1), extend);
        let s = self.scroll_to(self.selection.lead().expect("row"));
        r || s
    }

    /// Move the selection up n rows.
    /// Ensures the row is visible afterwards.
    #[inline]
    pub fn move_up(&mut self, n: usize, extend: bool) -> bool {
        let r = self
            .selection
            .move_up(n, self.rows.saturating_sub(1), extend);
        let s = self.scroll_to(self.selection.lead().expect("row"));
        r || s
    }

    /// Move the selection down n rows.
    /// Ensures the row is visible afterwards.
    #[inline]
    pub fn move_down(&mut self, n: usize, extend: bool) -> bool {
        let r = self
            .selection
            .move_down(n, self.rows.saturating_sub(1), extend);
        let s = self.scroll_to(self.selection.lead().expect("row"));
        r || s
    }
}

pub mod selection {
    use crate::event::{ct_event, flow, FocusKeys, HandleEvent, MouseOnly, Outcome};
    use crate::list::{ListSelection, RListState};
    use crossterm::event::KeyModifiers;
    use rat_focus::HasFocusFlag;
    use rat_ftable::TableSelection;
    use rat_scrolled::event::ScrollOutcome;
    use rat_scrolled::ScrollArea;
    use std::mem;

    /// No selection
    pub type NoSelection = rat_ftable::selection::NoSelection;

    impl ListSelection for NoSelection {
        #[inline]
        fn is_selected(&self, _n: usize) -> bool {
            false
        }

        #[inline]
        fn lead_selection(&self) -> Option<usize> {
            None
        }
    }

    impl HandleEvent<crossterm::event::Event, FocusKeys, Outcome> for RListState<NoSelection> {
        fn handle(&mut self, event: &crossterm::event::Event, _keymap: FocusKeys) -> Outcome {
            let res = if self.is_focused() {
                match event {
                    ct_event!(keycode press Down) => self.scroll_down(1).into(),
                    ct_event!(keycode press Up) => self.scroll_up(1).into(),
                    ct_event!(keycode press CONTROL-Down) | ct_event!(keycode press End) => {
                        self.scroll_to(self.max_offset()).into()
                    }
                    ct_event!(keycode press CONTROL-Up) | ct_event!(keycode press Home) => {
                        self.scroll_to(0).into()
                    }
                    ct_event!(keycode press PageUp) => {
                        self.scroll_up(self.page_len().saturating_sub(1)).into()
                    }
                    ct_event!(keycode press PageDown) => {
                        self.scroll_down(self.page_len().saturating_sub(1)).into()
                    }
                    _ => Outcome::NotUsed,
                }
            } else {
                Outcome::NotUsed
            };

            if res == Outcome::NotUsed {
                self.handle(event, MouseOnly)
            } else {
                res
            }
        }
    }

    impl HandleEvent<crossterm::event::Event, MouseOnly, Outcome> for RListState<NoSelection> {
        fn handle(&mut self, event: &crossterm::event::Event, _keymap: MouseOnly) -> Outcome {
            let r = match ScrollArea(self.inner, None, Some(&mut self.scroll))
                .handle(event, MouseOnly)
            {
                ScrollOutcome::Up(v) => self.scroll_up(v),
                ScrollOutcome::Down(v) => self.scroll_down(v),
                ScrollOutcome::VPos(v) => self.scroll_to(v),
                ScrollOutcome::Left(_) => false,
                ScrollOutcome::Right(_) => false,
                ScrollOutcome::HPos(_) => false,

                ScrollOutcome::NotUsed => false,
                ScrollOutcome::Unchanged => false,
                ScrollOutcome::Changed => true,
            };
            if r {
                return Outcome::Changed;
            }

            Outcome::Unchanged
        }
    }

    /// Single element selection.
    pub type RowSelection = rat_ftable::selection::RowSelection;

    impl ListSelection for RowSelection {
        #[inline]
        fn is_selected(&self, n: usize) -> bool {
            self.lead_row == Some(n)
        }

        #[inline]
        fn lead_selection(&self) -> Option<usize> {
            self.lead_row
        }
    }

    impl HandleEvent<crossterm::event::Event, FocusKeys, Outcome> for RListState<RowSelection> {
        fn handle(&mut self, event: &crossterm::event::Event, _keymap: FocusKeys) -> Outcome {
            let res = if self.is_focused() {
                match event {
                    ct_event!(keycode press Down) => self.move_down(1).into(),
                    ct_event!(keycode press Up) => self.move_up(1).into(),
                    ct_event!(keycode press CONTROL-Down) | ct_event!(keycode press End) => {
                        self.move_to(self.rows.saturating_sub(1)).into()
                    }
                    ct_event!(keycode press CONTROL-Up) | ct_event!(keycode press Home) => {
                        self.move_to(0).into()
                    }
                    ct_event!(keycode press PageUp) => {
                        self.move_up(self.page_len().saturating_sub(1)).into()
                    }
                    ct_event!(keycode press PageDown) => {
                        self.move_down(self.page_len().saturating_sub(1)).into()
                    }
                    _ => Outcome::NotUsed,
                }
            } else {
                Outcome::NotUsed
            };

            if res == Outcome::NotUsed {
                self.handle(event, MouseOnly)
            } else {
                res
            }
        }
    }

    impl HandleEvent<crossterm::event::Event, MouseOnly, Outcome> for RListState<RowSelection> {
        fn handle(&mut self, event: &crossterm::event::Event, _keymap: MouseOnly) -> Outcome {
            flow!(match event {
                ct_event!(mouse any for m) if self.mouse.drag(self.inner, m) => {
                    self.move_to(self.row_at_drag((m.column, m.row))).into()
                }
                ct_event!(mouse down Left for column, row) => {
                    if self.inner.contains((*column, *row).into()) {
                        if let Some(new_row) = self.row_at_clicked((*column, *row)) {
                            self.move_to(new_row).into()
                        } else {
                            Outcome::NotUsed
                        }
                    } else {
                        Outcome::NotUsed
                    }
                }

                _ => Outcome::NotUsed,
            });

            let r = match ScrollArea(self.inner, None, Some(&mut self.scroll))
                .handle(event, MouseOnly)
            {
                ScrollOutcome::Up(v) => {
                    if ListSelection::scroll_selected(&self.selection) {
                        self.move_up(1)
                    } else {
                        self.scroll_up(v)
                    }
                }
                ScrollOutcome::Down(v) => {
                    if ListSelection::scroll_selected(&self.selection) {
                        self.move_down(1)
                    } else {
                        self.scroll_down(v)
                    }
                }
                ScrollOutcome::VPos(v) => {
                    if ListSelection::scroll_selected(&self.selection) {
                        self.move_to(self.remap_offset_selection(v))
                    } else {
                        self.scroll_to(v)
                    }
                }
                ScrollOutcome::Left(_) => false,
                ScrollOutcome::Right(_) => false,
                ScrollOutcome::HPos(_) => false,

                ScrollOutcome::NotUsed => false,
                ScrollOutcome::Unchanged => false,
                ScrollOutcome::Changed => true,
            };
            if r {
                return Outcome::Changed;
            }

            Outcome::NotUsed
        }
    }

    pub type RowSetSelection = rat_ftable::selection::RowSetSelection;

    impl ListSelection for RowSetSelection {
        fn is_selected(&self, n: usize) -> bool {
            if let Some(mut anchor) = self.anchor_row {
                if let Some(mut lead) = self.lead_row {
                    if lead < anchor {
                        mem::swap(&mut lead, &mut anchor);
                    }

                    if n >= anchor && n <= lead {
                        return true;
                    }
                }
            } else {
                if let Some(lead) = self.lead_row {
                    if n == lead {
                        return true;
                    }
                }
            }

            self.selected.contains(&n)
        }

        fn lead_selection(&self) -> Option<usize> {
            self.lead_row
        }
    }

    impl HandleEvent<crossterm::event::Event, FocusKeys, Outcome> for RListState<RowSetSelection> {
        fn handle(&mut self, event: &crossterm::event::Event, _: FocusKeys) -> Outcome {
            let res = if self.is_focused() {
                match event {
                    ct_event!(keycode press Down) => self.move_down(1, false).into(),
                    ct_event!(keycode press SHIFT-Down) => self.move_down(1, true).into(),
                    ct_event!(keycode press Up) => self.move_up(1, false).into(),
                    ct_event!(keycode press SHIFT-Up) => self.move_up(1, true).into(),
                    ct_event!(keycode press CONTROL-Down) | ct_event!(keycode press End) => {
                        self.move_to(self.rows.saturating_sub(1), false).into()
                    }
                    ct_event!(keycode press SHIFT-End) => {
                        self.move_to(self.rows.saturating_sub(1), true).into()
                    }
                    ct_event!(keycode press CONTROL-Up) | ct_event!(keycode press Home) => {
                        self.move_to(0, false).into()
                    }
                    ct_event!(keycode press SHIFT-Home) => self.move_to(0, true).into(),

                    ct_event!(keycode press PageUp) => self
                        .move_up(self.page_len().saturating_sub(1), false)
                        .into(),
                    ct_event!(keycode press SHIFT-PageUp) => {
                        self.move_up(self.page_len().saturating_sub(1), true).into()
                    }
                    ct_event!(keycode press PageDown) => self
                        .move_down(self.page_len().saturating_sub(1), false)
                        .into(),
                    ct_event!(keycode press SHIFT-PageDown) => self
                        .move_down(self.page_len().saturating_sub(1), true)
                        .into(),
                    _ => Outcome::NotUsed,
                }
            } else {
                Outcome::NotUsed
            };

            if res == Outcome::NotUsed {
                self.handle(event, MouseOnly)
            } else {
                res
            }
        }
    }

    impl HandleEvent<crossterm::event::Event, MouseOnly, Outcome> for RListState<RowSetSelection> {
        fn handle(&mut self, event: &crossterm::event::Event, _: MouseOnly) -> Outcome {
            flow!(match event {
                ct_event!(mouse any for m) | ct_event!(mouse any CONTROL for m)
                    if self.mouse.drag(self.inner, m)
                        || self.mouse.drag2(self.inner, m, KeyModifiers::CONTROL) =>
                {
                    self.move_to(self.row_at_drag((m.column, m.row)), true)
                        .into()
                }
                ct_event!(mouse down Left for column, row) => {
                    let pos = (*column, *row);
                    if self.inner.contains(pos.into()) {
                        if let Some(new_row) = self.row_at_clicked(pos) {
                            self.move_to(new_row, false).into()
                        } else {
                            Outcome::NotUsed
                        }
                    } else {
                        Outcome::NotUsed
                    }
                }
                ct_event!(mouse down ALT-Left for column, row) => {
                    let pos = (*column, *row);
                    if self.area.contains(pos.into()) {
                        if let Some(new_row) = self.row_at_clicked(pos) {
                            self.move_to(new_row, true).into()
                        } else {
                            Outcome::NotUsed
                        }
                    } else {
                        Outcome::NotUsed
                    }
                }
                ct_event!(mouse down CONTROL-Left for column, row) => {
                    let pos = (*column, *row);
                    if self.area.contains(pos.into()) {
                        if let Some(new_row) = self.row_at_clicked(pos) {
                            self.retire_selection();
                            if self.selection.is_selected_row(new_row) {
                                self.selection.remove(new_row);
                            } else {
                                self.move_to(new_row, true);
                            }
                            Outcome::Changed
                        } else {
                            Outcome::NotUsed
                        }
                    } else {
                        Outcome::NotUsed
                    }
                }
                _ => Outcome::NotUsed,
            });

            let r = match ScrollArea(self.inner, None, Some(&mut self.scroll))
                .handle(event, MouseOnly)
            {
                ScrollOutcome::Up(v) => self.scroll_up(v),
                ScrollOutcome::Down(v) => self.scroll_down(v),
                ScrollOutcome::VPos(v) => self.scroll_to(v),
                ScrollOutcome::Left(_) => false,
                ScrollOutcome::Right(_) => false,
                ScrollOutcome::HPos(_) => false,

                ScrollOutcome::NotUsed => false,
                ScrollOutcome::Unchanged => false,
                ScrollOutcome::Changed => true,
            };
            if r {
                return Outcome::Changed;
            }

            Outcome::Unchanged
        }
    }
}