use std::{
    collections::BTreeMap,
    fmt::Write as _,
    io::{self, Stdout},
    panic::{self, AssertUnwindSafe, PanicHookInfo},
    sync::{Arc, Mutex},
};

use crossterm::{
    cursor::Show,
    event::{
        self, DisableBracketedPaste, EnableBracketedPaste, Event, KeyCode, KeyEvent, KeyEventKind,
        KeyModifiers,
    },
    execute,
    terminal::{EnterAlternateScreen, LeaveAlternateScreen, disable_raw_mode, enable_raw_mode},
};
use ratatui::{
    Frame, Terminal,
    backend::CrosstermBackend,
    layout::{Constraint, Layout, Rect},
    style::{Color, Modifier, Style},
    text::Line,
    widgets::{Block, Borders, Clear, Paragraph},
};
use unicode_segmentation::UnicodeSegmentation;
use unicode_width::UnicodeWidthStr;

use crate::{
    editor::{Editor, Input, Mode, Palette},
    files::{DockSide, FilePicker, FilePresentation},
    session::EditorSession,
};

pub const CAPABILITIES: &[&str] = &["text", "styled_text"];
const TAB_WIDTH: usize = 4;

type PanicHook = Box<dyn Fn(&PanicHookInfo<'_>) + Send + Sync + 'static>;

struct HookState {
    previous: Option<PanicHook>,
    active: bool,
}

struct TerminalSession {
    hook: Arc<Mutex<HookState>>,
}

fn restore_terminal() {
    let _ = disable_raw_mode();
    let _ = execute!(
        io::stdout(),
        DisableBracketedPaste,
        LeaveAlternateScreen,
        Show
    );
}

impl TerminalSession {
    fn run(body: impl FnOnce() -> io::Result<()>) -> io::Result<()> {
        let hook = Arc::new(Mutex::new(HookState {
            previous: Some(panic::take_hook()),
            active: false,
        }));
        let during_session = Arc::clone(&hook);
        panic::set_hook(Box::new(move |info| {
            let mut state = during_session
                .lock()
                .unwrap_or_else(|error| error.into_inner());
            if state.active {
                restore_terminal();
                state.active = false;
            }
            if let Some(previous) = &state.previous {
                previous(info);
            }
        }));
        let session = Self { hook };
        // set_hook is forbidden on a panicking thread. Catch first, drop the
        // owner while not panicking, then resume the original panic unchanged.
        let result = panic::catch_unwind(AssertUnwindSafe(|| {
            enable_raw_mode()?;
            session
                .hook
                .lock()
                .unwrap_or_else(|error| error.into_inner())
                .active = true;
            execute!(io::stdout(), EnterAlternateScreen, EnableBracketedPaste)?;
            body()
        }));
        drop(session);
        match result {
            Ok(result) => result,
            Err(payload) => panic::resume_unwind(payload),
        }
    }
}

impl Drop for TerminalSession {
    fn drop(&mut self) {
        let mut state = self.hook.lock().unwrap_or_else(|error| error.into_inner());
        if state.active {
            restore_terminal();
            state.active = false;
        }
        let previous = state
            .previous
            .take()
            .expect("terminal session owns its prior hook");
        drop(state);
        panic::set_hook(previous);
    }
}

#[derive(Default)]
struct BufferViewports {
    offsets: BTreeMap<usize, (usize, usize)>,
}

impl BufferViewports {
    fn draw(&mut self, frame: &mut Frame, editor: &Editor) {
        self.offsets.retain(|id, _| editor.has_buffer(*id));
        let (top, left) = self.offsets.entry(editor.buffer_id()).or_default();
        draw(frame, editor, top, left);
    }
}

/// Renders session state and translates terminal input; the session owns plugin
/// execution and retirement, so the adapter needs no lifecycle callback.
pub fn run(session: &mut EditorSession) -> io::Result<()> {
    TerminalSession::run(|| {
        let mut terminal: Terminal<CrosstermBackend<Stdout>> =
            Terminal::new(CrosstermBackend::new(io::stdout()))?;
        let mut viewports = BufferViewports::default();
        while !session.editor().should_quit() {
            terminal.draw(|frame| viewports.draw(frame, session.editor()))?;
            match event::read()? {
                Event::Key(key) if key.kind != KeyEventKind::Release => {
                    if let Some(input) = translate(key) {
                        session.handle(input);
                    }
                }
                Event::Paste(text) => session.handle(Input::Paste(text)),
                _ => {}
            }
        }
        Ok(())
    })
}

fn translate(key: KeyEvent) -> Option<Input> {
    if key
        .modifiers
        .intersects(KeyModifiers::ALT | KeyModifiers::SUPER)
    {
        return None;
    }
    Some(match key.code {
        KeyCode::Char(c) if key.modifiers.contains(KeyModifiers::CONTROL) => {
            Input::Ctrl(c.to_ascii_lowercase())
        }
        KeyCode::Char(c) => Input::Char(c),
        KeyCode::Esc => Input::Escape,
        KeyCode::Enter => Input::Enter,
        KeyCode::Backspace => Input::Backspace,
        KeyCode::Delete => Input::Delete,
        KeyCode::Left => Input::Left,
        KeyCode::Right => Input::Right,
        KeyCode::Up => Input::Up,
        KeyCode::Down => Input::Down,
        KeyCode::Home => Input::Home,
        KeyCode::End => Input::End,
        KeyCode::Tab => Input::Char('\t'),
        _ => return None,
    })
}

fn display_column(line: &str, grapheme_column: usize) -> usize {
    line.graphemes(true)
        .take(grapheme_column)
        .fold(0, |column, grapheme| {
            column
                + if grapheme == "\t" {
                    TAB_WIDTH - column % TAB_WIDTH
                } else {
                    UnicodeWidthStr::width(grapheme)
                }
        })
}

fn visible_line(line: &str, left: usize, width: usize) -> String {
    let mut visible = String::new();
    let mut column = 0;
    let right = left.saturating_add(width);
    for grapheme in line.graphemes(true) {
        let cells = if grapheme == "\t" {
            TAB_WIDTH - column % TAB_WIDTH
        } else {
            UnicodeWidthStr::width(grapheme)
        };
        let end = column + cells;
        if column >= right {
            break;
        }
        if end > left || (cells == 0 && column >= left) {
            if grapheme == "\t" || column < left || end > right {
                for _ in column.max(left)..end.min(right) {
                    visible.push(' ');
                }
            } else {
                visible.push_str(grapheme);
            }
        }
        column = end;
    }
    visible
}

fn draw(frame: &mut Frame, editor: &Editor, top: &mut usize, left: &mut usize) {
    let area = frame.area();
    if area.width == 0 || area.height == 0 {
        return;
    }
    let prompting = matches!(editor.mode(), Mode::Command | Mode::Search);
    let dock_focused = editor
        .file_picker()
        .is_some_and(|picker| picker.focused && picker.presentation == FilePresentation::Docked);
    let [workspace, status_area, prompt_area] = Layout::vertical([
        Constraint::Fill(1),
        Constraint::Length(u16::from(area.height >= 3)),
        Constraint::Length(u16::from(area.height >= 2 || (prompting && !dock_focused))),
    ])
    .areas(area);
    let (viewport, dock) = match editor.file_picker() {
        Some(picker) if picker.presentation == FilePresentation::Docked => {
            dock_layout(workspace, editor.file_explorer_side(), picker.focused)
        }
        _ => (workspace, None),
    };
    let digits = editor.lines().len().ilog10() as usize + 1;
    let gutter_width = (digits + 1) as u16;
    let [gutter, viewport] = Layout::horizontal([
        Constraint::Length(if viewport.width > gutter_width {
            gutter_width
        } else {
            0
        }),
        Constraint::Fill(1),
    ])
    .areas(viewport);
    let height = usize::from(viewport.height);
    let width = usize::from(viewport.width);
    let cursor = editor.cursor();
    if height > 0 && width > 0 {
        if cursor.row < *top {
            *top = cursor.row;
        } else if cursor.row >= top.saturating_add(height) {
            *top = cursor.row + 1 - height;
        }
        let column = display_column(&editor.lines()[cursor.row], cursor.column);
        if column < *left {
            *left = column;
        } else if column >= left.saturating_add(width) {
            *left = column + 1 - width;
        }
        if gutter.width > 0 {
            let numbers: Vec<Line> = (*top..top.saturating_add(height).min(editor.lines().len()))
                .map(|row| {
                    let style = if row == cursor.row {
                        Style::default()
                            .fg(Color::Cyan)
                            .add_modifier(Modifier::BOLD)
                    } else {
                        Style::default().fg(Color::DarkGray)
                    };
                    let number = if row == cursor.row {
                        row + 1
                    } else {
                        row.abs_diff(cursor.row)
                    };
                    Line::styled(format!("{number:>digits$} "), style)
                })
                .collect();
            frame.render_widget(Paragraph::new(numbers), gutter);
        }
        let lines: Vec<Line> = editor
            .lines()
            .iter()
            .skip(*top)
            .take(height)
            .map(|line| Line::from(visible_line(line, *left, width)))
            .collect();
        frame.render_widget(Paragraph::new(lines), viewport);
        if let Some(found) = editor.search_match()
            && found.start.row >= *top
            && found.start.row < top.saturating_add(height)
        {
            let line = &editor.lines()[found.start.row];
            let start = display_column(line, found.start.column).max(*left);
            let end = display_column(line, found.end_column).min(left.saturating_add(width));
            let y = viewport.y + (found.start.row - *top) as u16;
            let style = Style::default().fg(Color::Black).bg(Color::Yellow);
            let buffer = frame.buffer_mut();
            for column in start..end {
                buffer[(viewport.x + (column - *left) as u16, y)].set_style(style);
            }
        }
        for selection in editor.selections() {
            let first = selection.start.row.max(*top);
            let last = selection.end.row.min(top.saturating_add(height - 1));
            let style = Style::default().fg(Color::White).bg(Color::Blue);
            for row in first..=last {
                let line = &editor.lines()[row];
                let start = if row == selection.start.row {
                    display_column(line, selection.start.column)
                } else {
                    0
                };
                let end = if row == selection.end.row {
                    display_column(line, selection.end.column)
                } else {
                    display_column(line, usize::MAX) + 1
                };
                let start = start.max(*left);
                let end = end.min(left.saturating_add(width));
                let y = viewport.y + (row - *top) as u16;
                let buffer = frame.buffer_mut();
                for column in start..end {
                    buffer[(viewport.x + (column - *left) as u16, y)].set_style(style);
                }
            }
        }
        for caret in editor.carets().into_iter().filter(|caret| *caret != cursor) {
            if caret.row < *top || caret.row >= top.saturating_add(height) {
                continue;
            }
            let column = display_column(&editor.lines()[caret.row], caret.column);
            if column >= *left && column < left.saturating_add(width) {
                frame.buffer_mut()[(
                    viewport.x + (column - *left) as u16,
                    viewport.y + (caret.row - *top) as u16,
                )]
                    .set_style(Style::default().fg(Color::Black).bg(Color::Magenta));
            }
        }
    }
    let path = editor
        .path()
        .map(|p| p.to_string_lossy().into_owned())
        .unwrap_or_else(|| "[No Name]".into());
    let path: String = path
        .chars()
        .map(|c| if c.is_control() { '�' } else { c })
        .collect();
    let mut status = format!(" {}", editor.mode());
    if let Some(sequence) = editor.leader_pending() {
        write!(status, "  leader: {sequence}").unwrap();
    }
    if editor.buffer_count() > 1 {
        write!(
            status,
            "  [buffer {}/{}]",
            editor.buffer_id(),
            editor.buffer_count()
        )
        .unwrap();
    }
    write!(
        status,
        "  {}{}  {}:{}",
        path,
        if editor.dirty() { " [+]" } else { "" },
        cursor.row + 1,
        cursor.column + 1,
    )
    .unwrap();
    if editor.selection_count() > 1 {
        write!(status, "  {} selections", editor.selection_count()).unwrap();
    }
    if let Some(count) = editor.count() {
        write!(status, "  count: {count}").unwrap();
    }
    frame.render_widget(
        Paragraph::new(status).style(Style::default().fg(Color::Black).bg(Color::Cyan)),
        status_area,
    );
    if prompting && prompt_area.height > 0 && prompt_area.width > 0 {
        let prefix = if editor.mode() == Mode::Search {
            '/'
        } else {
            ':'
        };
        let command = format!("{prefix}{}", editor.command_line());
        let command_width = display_column(&command, usize::MAX);
        let prompt_width = usize::from(prompt_area.width);
        let offset = command_width.saturating_sub(prompt_width.saturating_sub(1));
        frame.render_widget(
            Paragraph::new(visible_line(&command, offset, prompt_width)),
            prompt_area,
        );
        frame.set_cursor_position((
            prompt_area.x + (command_width - offset) as u16,
            prompt_area.y,
        ));
    } else {
        frame.render_widget(Paragraph::new(editor.message()), prompt_area);
        if height > 0 && width > 0 {
            let column = display_column(&editor.lines()[cursor.row], cursor.column);
            frame.set_cursor_position((
                viewport.x + (column - *left) as u16,
                viewport.y + (cursor.row - *top) as u16,
            ));
        }
    }
    if let Some(picker) = editor.file_picker() {
        if picker.presentation == FilePresentation::Floating {
            let [_, column, _] = Layout::horizontal([
                Constraint::Fill(1),
                Constraint::Length(area.width.min(84)),
                Constraint::Fill(1),
            ])
            .areas(area);
            let [_, panel, _] = Layout::vertical([
                Constraint::Fill(1),
                Constraint::Length(area.height.min(18)),
                Constraint::Fill(1),
            ])
            .areas(column);
            frame.render_widget(Clear, panel);
            draw_file_list(frame, picker, panel, editor.selection_navigation_hint());
        } else if let Some(panel) = dock {
            draw_file_list(frame, picker, panel, editor.selection_navigation_hint());
        }
    }
    if let Some(palette) = editor.palette() {
        draw_palette(
            frame,
            palette,
            editor.mode(),
            editor.selection_navigation_hint(),
        );
    }
}

fn dock_layout(area: Rect, side: DockSide, focused: bool) -> (Rect, Option<Rect>) {
    if area.width == 0 || area.height == 0 {
        return (area, None);
    }
    let horizontal = matches!(side, DockSide::Left | DockSide::Right);
    let available = if horizontal { area.width } else { area.height };
    if !focused && available < if horizontal { 24 } else { 8 } {
        return (area, None);
    }
    let extent = if available < if horizontal { 20 } else { 6 } {
        available
    } else if horizontal {
        (available / 3).clamp(12, 38).min(available - 8)
    } else {
        (available / 3).clamp(4, 12).min(available - 2)
    };
    let leading = matches!(side, DockSide::Left | DockSide::Top);
    let constraints = if leading {
        [Constraint::Length(extent), Constraint::Fill(1)]
    } else {
        [Constraint::Fill(1), Constraint::Length(extent)]
    };
    let [first, second] = if horizontal {
        Layout::horizontal(constraints).areas(area)
    } else {
        Layout::vertical(constraints).areas(area)
    };
    if leading {
        (second, Some(first))
    } else {
        (first, Some(second))
    }
}

fn display_text(text: &str) -> String {
    text.chars()
        .map(|ch| if ch.is_control() { '�' } else { ch })
        .collect()
}

fn draw_file_list(frame: &mut Frame, picker: &FilePicker, panel: Rect, navigation_hint: &str) {
    if panel.width == 0 || panel.height == 0 {
        return;
    }
    let color = if picker.focused {
        Color::Cyan
    } else {
        Color::DarkGray
    };
    let bordered = panel.width >= 4 && panel.height >= 4;
    let title = match picker.presentation {
        FilePresentation::Floating => " Files ",
        FilePresentation::Docked => " Explorer ",
    };
    let block = Block::default()
        .borders(if bordered {
            Borders::ALL
        } else {
            Borders::NONE
        })
        .border_style(Style::default().fg(color))
        .title(title);
    let content = if bordered { block.inner(panel) } else { panel };
    if bordered {
        frame.render_widget(block, panel);
    }
    let show_root = content.height >= 4;
    let show_error = picker.error.is_some() && content.height >= 2;
    let show_help = content.height >= 5 + u16::from(show_error);
    let [query_area, root_area, error_area, results_area, help_area] = Layout::vertical([
        Constraint::Length(1),
        Constraint::Length(u16::from(show_root)),
        Constraint::Length(u16::from(show_error)),
        Constraint::Fill(1),
        Constraint::Length(u16::from(show_help)),
    ])
    .areas(content);
    let query = format!("> {}", display_text(&picker.query));
    let query_width = display_column(&query, usize::MAX);
    let width = usize::from(query_area.width);
    let offset = query_width.saturating_sub(width.saturating_sub(1));
    frame.render_widget(
        Paragraph::new(visible_line(&query, offset, width)).style(Style::default().fg(
            if picker.focused {
                Color::Yellow
            } else {
                Color::DarkGray
            },
        )),
        query_area,
    );
    if picker.focused && query_area.width > 0 && query_area.height > 0 {
        frame.set_cursor_position((query_area.x + (query_width - offset) as u16, query_area.y));
    }
    if show_root {
        frame.render_widget(
            Paragraph::new(display_text(&picker.root.to_string_lossy()))
                .style(Style::default().fg(Color::DarkGray)),
            root_area,
        );
    }
    if show_error {
        frame.render_widget(
            Paragraph::new(display_text(picker.error.as_deref().unwrap()))
                .style(Style::default().fg(Color::Red)),
            error_area,
        );
    }
    let entries = picker.entries();
    if entries.len() == 0 {
        frame.render_widget(
            Paragraph::new(if picker.query.is_empty() {
                "No project files"
            } else {
                "No matching files"
            }),
            results_area,
        );
    } else if results_area.height > 0 {
        let count = usize::from(results_area.height);
        let first = picker.selected.saturating_sub(count - 1);
        let lines: Vec<Line> = entries
            .enumerate()
            .skip(first)
            .take(count)
            .map(|(index, entry)| {
                let selected = index == picker.selected;
                let style = if selected {
                    Style::default()
                        .bg(if picker.focused {
                            Color::Blue
                        } else {
                            Color::DarkGray
                        })
                        .add_modifier(Modifier::BOLD)
                } else {
                    Style::default()
                };
                Line::styled(
                    format!("{} {}", if selected { ">" } else { " " }, entry.label),
                    style,
                )
            })
            .collect();
        frame.render_widget(Paragraph::new(lines), results_area);
    }
    let help = if picker.focused {
        let controls = match picker.presentation {
            FilePresentation::Floating => "Enter · Esc/^W close · ^R scan",
            FilePresentation::Docked => "Enter · Esc/Tab edit · ^W · ^R",
        };
        format!("{navigation_hint} · {controls}")
    } else {
        "Editor focus · invoke explorer to search".into()
    };
    frame.render_widget(
        Paragraph::new(help).style(Style::default().fg(Color::DarkGray)),
        help_area,
    );
}

fn draw_palette(frame: &mut Frame, palette: &Palette, mode: Mode, navigation_hint: &str) {
    let area = frame.area();
    if area.width == 0 || area.height == 0 {
        return;
    }
    let [_, column, _] = Layout::horizontal([
        Constraint::Fill(1),
        Constraint::Length(area.width.min(100)),
        Constraint::Fill(1),
    ])
    .areas(area);
    let [_, panel, _] = Layout::vertical([
        Constraint::Fill(1),
        Constraint::Length(area.height.min(16)),
        Constraint::Fill(1),
    ])
    .areas(column);
    frame.render_widget(Clear, panel);
    let bordered = panel.height >= 4 && panel.width >= 4;
    let block = Block::default()
        .borders(if bordered {
            Borders::ALL
        } else {
            Borders::NONE
        })
        .title(format!(" Commands · {mode} "));
    let content = if bordered { block.inner(panel) } else { panel };
    if bordered {
        frame.render_widget(block, panel);
    }
    let [query_area, results_area, help_area] = Layout::vertical([
        Constraint::Length(1),
        Constraint::Fill(1),
        Constraint::Length(u16::from(content.height >= 4)),
    ])
    .areas(content);
    let query = format!("> {}", palette.query);
    let query_width = display_column(&query, usize::MAX);
    let width = usize::from(query_area.width);
    let offset = query_width.saturating_sub(width - 1);
    frame.render_widget(
        Paragraph::new(visible_line(&query, offset, width))
            .style(Style::default().fg(Color::Yellow)),
        query_area,
    );
    frame.set_cursor_position((query_area.x + (query_width - offset) as u16, query_area.y));
    if palette.entries.is_empty() {
        frame.render_widget(Paragraph::new("No matching commands"), results_area);
    } else if results_area.height > 0 {
        let row_height = usize::from(results_area.height >= 2) + 1;
        let count = usize::from(results_area.height) / row_height;
        let first = palette.selected.saturating_sub(count - 1);
        let mut lines = Vec::with_capacity(count * row_height);
        for (index, entry) in palette.entries.iter().enumerate().skip(first).take(count) {
            let mut style = Style::default();
            if !entry.enabled {
                style = style.add_modifier(Modifier::DIM);
            }
            if index == palette.selected {
                style = style.bg(Color::Blue).add_modifier(Modifier::BOLD);
            }
            let bindings = if entry.bindings.is_empty() {
                "unbound".into()
            } else {
                entry.bindings.join(", ")
            };
            let modes = entry
                .modes
                .iter()
                .map(ToString::to_string)
                .collect::<Vec<_>>()
                .join("/");
            let metadata = format!("{} | {bindings} | {modes}", entry.owner);
            let label = format!(
                "{} {} ({})",
                if index == palette.selected { ">" } else { " " },
                entry.label,
                entry.name
            );
            if row_height == 2 {
                lines.push(Line::from(label).style(style));
                lines.push(Line::from(format!("  {metadata}")).style(style));
            } else {
                lines.push(Line::from(format!("{label} | {metadata}")).style(style));
            }
        }
        frame.render_widget(Paragraph::new(lines), results_area);
    }
    frame.render_widget(
        Paragraph::new(format!(
            "{mode} · {navigation_hint} · Enter accept · Esc/Ctrl+p cancel"
        )),
        help_area,
    );
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::{
        fs,
        path::PathBuf,
        sync::atomic::{AtomicUsize, Ordering},
    };

    struct Directory(PathBuf);

    impl Directory {
        fn new() -> Self {
            static NEXT_ID: AtomicUsize = AtomicUsize::new(0);
            let id = NEXT_ID.fetch_add(1, Ordering::Relaxed);
            let path =
                std::env::temp_dir().join(format!("vamp-tui-test-{}-{id}", std::process::id()));
            fs::create_dir(&path).unwrap();
            Self(path)
        }

        fn file(&self, name: &str, text: &str) -> PathBuf {
            let path = self.0.join(name);
            fs::write(&path, text).unwrap();
            path
        }
    }

    impl Drop for Directory {
        fn drop(&mut self) {
            let _ = fs::remove_dir_all(&self.0);
        }
    }

    fn screen_text(terminal: &Terminal<ratatui::backend::TestBackend>) -> String {
        let buffer = terminal.backend().buffer();
        let area = buffer.area;
        (area.y..area.bottom())
            .map(|y| {
                (area.x..area.right())
                    .map(|x| buffer[(x, y)].symbol())
                    .collect::<String>()
            })
            .collect::<Vec<_>>()
            .join("\n")
    }

    #[test]
    fn translate_distinguishes_control_j_from_enter_and_normalizes_control_letters() {
        for (code, modifiers, expected) in [
            (
                KeyCode::Char('j'),
                KeyModifiers::CONTROL,
                Some(Input::Ctrl('j')),
            ),
            (
                KeyCode::Char('J'),
                KeyModifiers::CONTROL | KeyModifiers::SHIFT,
                Some(Input::Ctrl('j')),
            ),
            (
                KeyCode::Char('k'),
                KeyModifiers::CONTROL,
                Some(Input::Ctrl('k')),
            ),
            (KeyCode::Enter, KeyModifiers::NONE, Some(Input::Enter)),
            (KeyCode::Enter, KeyModifiers::CONTROL, Some(Input::Enter)),
            (
                KeyCode::Char('J'),
                KeyModifiers::SHIFT,
                Some(Input::Char('J')),
            ),
            (KeyCode::Char('j'), KeyModifiers::ALT, None),
        ] {
            assert_eq!(translate(KeyEvent::new(code, modifiers)), expected);
        }
    }

    #[test]
    fn file_list_window_follows_control_j_k_selection() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor.handle(Input::Char(' '));
        editor.handle(Input::Char('o'));
        let count = editor.file_picker().unwrap().entries().len();
        assert!(count > 1);
        for _ in 0..count - 1 {
            editor.handle(
                translate(KeyEvent::new(KeyCode::Char('j'), KeyModifiers::CONTROL)).unwrap(),
            );
        }
        assert_eq!(editor.file_picker().unwrap().selected, count - 1);
        editor.handle(translate(KeyEvent::new(KeyCode::Char('k'), KeyModifiers::CONTROL)).unwrap());
        assert_eq!(editor.file_picker().unwrap().selected, count - 2);
        let picker = editor.file_picker().unwrap();
        let label = picker.entries().nth(picker.selected).unwrap().label.clone();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(100, 9)).unwrap();
        terminal
            .draw(|frame| {
                draw_file_list(
                    frame,
                    picker,
                    frame.area(),
                    editor.selection_navigation_hint(),
                )
            })
            .unwrap();
        let text = screen_text(&terminal);
        assert!(text.contains(&format!("> {label}")), "{text}");
        let buffer = terminal.backend().buffer();
        let selected_y = (3..8).find(|&y| buffer[(1, y)].symbol() == ">").unwrap();
        assert_eq!(buffer[(1, selected_y)].bg, Color::Blue);
    }

    #[test]
    fn list_footers_show_remapped_and_disabled_selection_keys() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        for key in ["ctrl+j", "ctrl+n", "down", "ctrl+k", "up"] {
            editor.bind("selection", key, None).unwrap();
        }
        editor
            .bind("selection", "x", Some("core.down".into()))
            .unwrap();
        let hint = editor.selection_navigation_hint().to_owned();
        assert_eq!(hint, "x next · unbound previous");
        editor.set_file_explorer_side("bottom").unwrap();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(100, 24)).unwrap();
        let (mut top, mut left) = (0, 0);
        for key in ['o', 'e'] {
            editor.handle(Input::Char(' '));
            editor.handle(Input::Char(key));
            terminal
                .draw(|frame| draw(frame, &editor, &mut top, &mut left))
                .unwrap();
            let text = screen_text(&terminal);
            assert!(text.contains(&hint), "{text}");
            assert!(!text.contains("Ctrl+j"), "{text}");
            editor.handle(Input::Escape);
        }
        editor.handle(Input::Ctrl('p'));
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let text = screen_text(&terminal);
        assert!(text.contains(&hint), "{text}");
        assert!(!text.contains("Ctrl+j"), "{text}");
    }

    #[test]
    fn file_list_scrolls_selection_and_sanitizes_display_without_losing_paths() {
        let directory = Directory::new();
        for index in 0..18 {
            directory.file(&format!("file-{index:02}"), "text");
        }
        let special = directory.file("界e\u{301} space\nname", "text");
        let editor = Editor::open(None, vec![]).unwrap();
        let mut picker = FilePicker::scan(directory.0.clone(), FilePresentation::Floating).unwrap();
        assert!(
            picker
                .entries()
                .any(|entry| directory.0.join(&entry.path) == special)
        );
        let count = picker.entries().len();
        picker.selected = count - 1;
        let label = picker.entries().last().unwrap().label.clone();
        assert_eq!(label, "界e\u{301} space�name");
        picker.query = "long\t界e\u{301}z".into();
        let area = Rect::new(3, 2, 24, 9);
        let mut terminal = Terminal::with_options(
            ratatui::backend::TestBackend::new(40, 15),
            ratatui::TerminalOptions {
                viewport: ratatui::Viewport::Fixed(area),
            },
        )
        .unwrap();
        terminal
            .draw(|frame| draw_file_list(frame, &picker, area, editor.selection_navigation_hint()))
            .unwrap();
        let text = screen_text(&terminal);
        assert!(!text.contains("file-00"), "{text}");
        let cursor = terminal.get_cursor_position().unwrap();
        let buffer = terminal.backend().buffer();
        assert_eq!(buffer[(area.x + 7, area.y + 1)].symbol(), "�");
        assert_eq!(buffer[(area.x + 8, area.y + 1)].symbol(), "界");
        assert_eq!(buffer[(area.x + 10, area.y + 1)].symbol(), "e\u{301}");
        let selected_y = (area.y + 2..area.bottom() - 1)
            .find(|&y| buffer[(area.x + 1, y)].symbol() == ">")
            .unwrap();
        assert_eq!(buffer[(area.x + 3, selected_y)].symbol(), "界");
        assert_eq!(buffer[(area.x + 5, selected_y)].symbol(), "e\u{301}");
        assert_eq!(buffer[(area.x + 1, selected_y)].bg, Color::Blue);
        assert!(
            buffer[(area.x + 1, selected_y)]
                .modifier
                .contains(Modifier::BOLD)
        );
        assert_eq!(cursor.y, area.y + 1);
        assert_eq!(buffer[(0, 0)].symbol(), " ");
    }

    #[test]
    fn file_list_renders_root_empty_filter_errors_and_idle_focus() {
        let directory = Directory::new();
        let editor = Editor::open(None, vec![]).unwrap();
        let mut picker = FilePicker::scan(directory.0.clone(), FilePresentation::Docked).unwrap();
        let area = Rect::new(0, 0, 100, 12);
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(100, 12)).unwrap();
        terminal
            .draw(|frame| draw_file_list(frame, &picker, area, editor.selection_navigation_hint()))
            .unwrap();
        let text = screen_text(&terminal);
        assert!(text.contains("Explorer"), "{text}");
        assert!(
            text.contains(&directory.0.to_string_lossy().to_string()),
            "{text}"
        );
        assert!(text.contains("No project files"), "{text}");
        assert!(text.contains("Esc/Tab"), "{text}");
        picker.query = "missing".into();
        picker.error = Some("Unreadable\npath\u{1b}".into());
        picker.focused = false;
        terminal
            .draw(|frame| {
                frame.set_cursor_position((99, 11));
                draw_file_list(frame, &picker, area, editor.selection_navigation_hint());
            })
            .unwrap();
        let text = screen_text(&terminal);
        assert!(text.contains("No matching files"), "{text}");
        assert!(text.contains("Unreadable�path�"), "{text}");
        assert!(text.contains("Editor focus"), "{text}");
        assert_eq!(terminal.backend().buffer()[(1, 3)].fg, Color::Red);
        assert_eq!(terminal.backend().buffer()[(0, 0)].fg, Color::DarkGray);
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(99, 11)
        );
        picker.presentation = FilePresentation::Floating;
        picker.focused = true;
        terminal
            .draw(|frame| draw_file_list(frame, &picker, area, editor.selection_navigation_hint()))
            .unwrap();
        assert!(screen_text(&terminal).contains("Files"));
        assert!(screen_text(&terminal).contains("Esc/^W"));
        assert_eq!(terminal.backend().buffer()[(0, 0)].fg, Color::Cyan);
    }

    #[test]
    fn file_query_cursor_and_dock_layout_survive_tiny_offset_resizes() {
        let directory = Directory::new();
        let editor = Editor::open(None, vec![]).unwrap();
        let mut picker = FilePicker::scan(directory.0.clone(), FilePresentation::Docked).unwrap();
        picker.query = "long界e\u{301}z".into();
        for (width, height) in [(12, 6), (8, 2), (1, 1), (1, 2), (8, 1), (12, 6)] {
            let area = Rect::new(3, 2, width, height);
            let mut terminal = Terminal::with_options(
                ratatui::backend::TestBackend::new(24, 12),
                ratatui::TerminalOptions {
                    viewport: ratatui::Viewport::Fixed(area),
                },
            )
            .unwrap();
            terminal
                .draw(|frame| {
                    draw_file_list(frame, &picker, area, editor.selection_navigation_hint())
                })
                .unwrap();
            let cursor = terminal.get_cursor_position().unwrap();
            assert!(area.contains(cursor), "{area:?}: {cursor:?}");
            let bordered = width >= 4 && height >= 4;
            let query_x = area.x + u16::from(bordered);
            let query_y = area.y + u16::from(bordered);
            let query_width = width - 2 * u16::from(bordered);
            assert_eq!(cursor.x, query_x + query_width - 1);
            assert_eq!(cursor.y, query_y);
            let query = format!("> {}", picker.query);
            let offset =
                display_column(&query, usize::MAX).saturating_sub(usize::from(query_width) - 1);
            let mut expected =
                ratatui::buffer::Buffer::empty(Rect::new(query_x, query_y, query_width, 1));
            use ratatui::widgets::Widget;
            Paragraph::new(visible_line(&query, offset, usize::from(query_width)))
                .render(expected.area, &mut expected);
            for x in query_x..query_x + query_width {
                assert_eq!(
                    terminal.backend().buffer()[(x, query_y)].symbol(),
                    expected[(x, query_y)].symbol()
                );
            }
            assert_eq!(terminal.backend().buffer()[(0, 0)].symbol(), " ");
            for side in [
                DockSide::Left,
                DockSide::Right,
                DockSide::Top,
                DockSide::Bottom,
            ] {
                for focused in [false, true] {
                    let (editor, panel) = dock_layout(area, side, focused);
                    for rect in [Some(editor), panel].into_iter().flatten() {
                        assert!(rect.x >= area.x && rect.y >= area.y);
                        assert!(rect.right() <= area.right() && rect.bottom() <= area.bottom());
                    }
                    if focused {
                        assert!(panel.is_some());
                    } else {
                        assert!(panel.is_none());
                    }
                }
            }
        }
        for (width, height) in [(0, 1), (1, 0), (0, 0)] {
            let mut terminal =
                Terminal::new(ratatui::backend::TestBackend::new(width, height)).unwrap();
            terminal
                .draw(|frame| {
                    draw_file_list(
                        frame,
                        &picker,
                        frame.area(),
                        editor.selection_navigation_hint(),
                    )
                })
                .unwrap();
            assert!(
                dock_layout(Rect::new(3, 2, width, height), DockSide::Right, true)
                    .1
                    .is_none()
            );
        }
    }

    #[test]
    fn all_dock_sides_clip_editor_gutter_selection_carets_and_cursor() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(
                vec!["word ".repeat(40); 20].join("\n"),
            )])
            .unwrap();
        editor.handle(Input::Char('v'));
        editor.handle(Input::Ctrl('a'));
        assert!(editor.selection_count() > 1);
        let area = Rect::new(3, 2, 90, 26);
        let mut terminal = Terminal::with_options(
            ratatui::backend::TestBackend::new(100, 32),
            ratatui::TerminalOptions {
                viewport: ratatui::Viewport::Fixed(area),
            },
        )
        .unwrap();
        let (mut top, mut left) = (0, 0);
        editor.handle(Input::Char(' '));
        editor.handle(Input::Char('e'));
        assert!(editor.file_picker().unwrap().focused);
        for (name, side) in [
            ("left", DockSide::Left),
            ("right", DockSide::Right),
            ("top", DockSide::Top),
            ("bottom", DockSide::Bottom),
        ] {
            editor.set_file_explorer_side(name).unwrap();
            terminal
                .draw(|frame| draw(frame, &editor, &mut top, &mut left))
                .unwrap();
            let workspace = Rect::new(area.x, area.y, area.width, area.height - 2);
            let (editor_area, panel) = dock_layout(workspace, side, true);
            let panel = panel.unwrap();
            assert_eq!(editor_area.area() + panel.area(), workspace.area());
            assert_eq!(editor_area.intersection(panel).area(), 0);
            match side {
                DockSide::Left => assert_eq!(panel.right(), editor_area.x),
                DockSide::Right => assert_eq!(editor_area.right(), panel.x),
                DockSide::Top => assert_eq!(panel.bottom(), editor_area.y),
                DockSide::Bottom => assert_eq!(editor_area.bottom(), panel.y),
            }
            assert!(panel.contains(terminal.get_cursor_position().unwrap()));
            editor.handle(Input::Escape);
            terminal
                .draw(|frame| draw(frame, &editor, &mut top, &mut left))
                .unwrap();
            assert!(editor_area.contains(terminal.get_cursor_position().unwrap()));
            let buffer = terminal.backend().buffer();
            for y in panel.y..panel.bottom() {
                for x in panel.x..panel.right() {
                    assert!(
                        !matches!(
                            buffer[(x, y)].bg,
                            Color::Blue | Color::Magenta | Color::Yellow
                        ),
                        "{side:?}: {x},{y}"
                    );
                }
            }
            assert_eq!(buffer[(editor_area.x + 3, editor_area.y)].symbol(), "w");
            assert!(matches!(
                buffer[(editor_area.x + 3, editor_area.y)].bg,
                Color::Blue | Color::Magenta
            ));
            for y in editor_area.y..editor_area.bottom() {
                for x in editor_area.x..editor_area.x + 3 {
                    assert_eq!(buffer[(x, y)].bg, Color::Reset);
                }
            }
            for x in area.x..area.right() {
                assert_eq!(buffer[(x, area.bottom() - 2)].bg, Color::Cyan);
            }
            assert_eq!(buffer[(0, 0)].symbol(), " ");
            editor.handle(Input::Char(' '));
            editor.handle(Input::Char('e'));
            assert!(editor.file_picker().unwrap().focused);
        }
    }

    #[test]
    fn floating_picker_clears_a_centered_overlay_without_moving_editor_regions() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(
                vec!["x".repeat(120); 30].join("\n"),
            )])
            .unwrap();
        let area = Rect::new(3, 2, 110, 26);
        let mut terminal = Terminal::with_options(
            ratatui::backend::TestBackend::new(120, 32),
            ratatui::TerminalOptions {
                viewport: ratatui::Viewport::Fixed(area),
            },
        )
        .unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let before = (top, left);
        editor.handle(Input::Char(' '));
        editor.handle(Input::Char('o'));
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let panel = Rect::new(area.x + 13, area.y + 4, 84, 18);
        assert_eq!((top, left), before);
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(panel.x + 3, panel.y + 1)
        );
        let buffer = terminal.backend().buffer();
        assert_eq!(buffer[(panel.x, panel.y)].fg, Color::Cyan);
        assert_eq!(buffer[(panel.right() - 2, panel.y + 1)].symbol(), " ");
        assert_eq!(buffer[(area.x + 3, area.y)].symbol(), "x");
        assert_eq!(buffer[(area.x, area.bottom() - 2)].bg, Color::Cyan);
        assert_eq!(buffer[(0, 0)].symbol(), " ");
    }

    #[test]
    fn picker_conversion_focus_palette_and_closure_preserve_buffer_viewport_cache() {
        let directory = Directory::new();
        let a = directory.file("a", &vec!["a".repeat(80); 30].join("\n"));
        let b = directory.file("b", "other");
        let mut editor = Editor::open(Some(a), vec![]).unwrap();
        let a_id = editor.buffer_id();
        for _ in 0..20 {
            editor.handle(Input::Down);
        }
        editor.handle(Input::End);
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(50, 10)).unwrap();
        let mut viewports = BufferViewports::default();
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        let before = viewports.offsets[&a_id];
        editor.handle(Input::Char(' '));
        editor.handle(Input::Char('o'));
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(viewports.offsets[&a_id], before);
        assert!(screen_text(&terminal).contains("Files"));
        editor.handle(Input::Escape);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(viewports.offsets[&a_id], before);
        editor.handle(Input::Char(' '));
        editor.handle(Input::Char('e'));
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert!(screen_text(&terminal).contains("Explorer"));
        editor.handle(Input::Escape);
        let docked = editor.file_picker().unwrap();
        assert!(!docked.focused);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        let dock_offsets = viewports.offsets[&a_id];
        editor.handle(Input::Ctrl('p'));
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert!(screen_text(&terminal).contains("Commands"));
        assert_eq!(terminal.get_cursor_position().unwrap().y, 1);
        assert_eq!(viewports.offsets[&a_id], dock_offsets);
        editor.handle(Input::Escape);
        editor.execute(&format!("edit {}", b.display()));
        let b_id = editor.buffer_id();
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert!(editor.file_picker().is_some());
        assert_eq!(viewports.offsets[&b_id], (0, 0));
        editor.execute(&format!("buffer {a_id}"));
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(viewports.offsets[&a_id], dock_offsets);
        editor.handle(Input::Char(' '));
        editor.handle(Input::Char('o'));
        assert_eq!(
            editor.file_picker().unwrap().presentation,
            FilePresentation::Floating
        );
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert!(screen_text(&terminal).contains("Files"));
        editor.handle(Input::Ctrl('w'));
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert!(editor.file_picker().is_none());
        assert_eq!(viewports.offsets[&b_id], (0, 0));
        assert!(screen_text(&terminal).contains("a"));
    }

    #[test]
    fn docked_search_highlight_and_cursor_survive_focus_and_offset_resizes() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(
                "0123456789界e\u{301}z\nsecond".into(),
            )])
            .unwrap();
        editor.handle(Input::Char('/'));
        editor.handle(Input::Char('界'));
        editor.handle(Input::Enter);
        assert!(editor.search_match().is_some());
        editor.handle(Input::Char(' '));
        editor.handle(Input::Char('e'));
        let mut terminal = Terminal::with_options(
            ratatui::backend::TestBackend::new(100, 32),
            ratatui::TerminalOptions {
                viewport: ratatui::Viewport::Fixed(Rect::new(3, 2, 90, 26)),
            },
        )
        .unwrap();
        let (mut top, mut left) = (0, 0);
        for (name, side) in [
            ("left", DockSide::Left),
            ("right", DockSide::Right),
            ("top", DockSide::Top),
            ("bottom", DockSide::Bottom),
        ] {
            editor.set_file_explorer_side(name).unwrap();
            for (width, height) in [
                (90, 26),
                (12, 6),
                (8, 2),
                (1, 1),
                (1, 2),
                (0, 1),
                (1, 0),
                (90, 26),
            ] {
                let area = Rect::new(3, 2, width, height);
                terminal.resize(area).unwrap();
                let area = terminal.get_frame().area();
                terminal
                    .draw(|frame| draw(frame, &editor, &mut top, &mut left))
                    .unwrap();
                if width > 0 && height > 0 {
                    let workspace = Rect::new(
                        area.x,
                        area.y,
                        width,
                        height - u16::from(height >= 3) - u16::from(height >= 2),
                    );
                    let (_, panel) = dock_layout(workspace, side, true);
                    let cursor = terminal.get_cursor_position().unwrap();
                    assert!(
                        panel.unwrap().contains(cursor),
                        "{side:?} {area:?} {panel:?}: {cursor:?}"
                    );
                }
                editor.handle(Input::Escape);
                terminal
                    .draw(|frame| draw(frame, &editor, &mut top, &mut left))
                    .unwrap();
                if width > 0 && height > 0 {
                    let cursor = terminal.get_cursor_position().unwrap();
                    assert!(area.contains(cursor), "{side:?} {area:?}: {cursor:?}");
                    let workspace = Rect::new(
                        area.x,
                        area.y,
                        width,
                        height - u16::from(height >= 3) - u16::from(height >= 2),
                    );
                    let (editor_area, panel) = dock_layout(workspace, side, false);
                    assert!(editor_area.contains(cursor), "{side:?}: {cursor:?}");
                    let buffer = terminal.backend().buffer();
                    if width == 90 {
                        let mut yellow = 0;
                        for y in editor_area.y..editor_area.bottom() {
                            for x in editor_area.x..editor_area.right() {
                                yellow += usize::from(buffer[(x, y)].bg == Color::Yellow);
                            }
                        }
                        assert!(yellow > 0);
                    }
                    if let Some(panel) = panel {
                        for y in panel.y..panel.bottom() {
                            for x in panel.x..panel.right() {
                                assert_ne!(buffer[(x, y)].bg, Color::Yellow);
                            }
                        }
                    }
                    assert_eq!(buffer[(0, 0)].symbol(), " ");
                }
                editor.handle(Input::Char(' '));
                editor.handle(Input::Char('e'));
                assert!(editor.file_picker().unwrap().focused);
            }
        }
    }

    #[test]
    fn pending_leader_is_visible_before_long_paths_and_unknown_keys_do_not_edit() {
        let directory = Directory::new();
        let path = directory.file(&"long-path-".repeat(12), "keep");
        let mut editor = Editor::open(Some(path), vec![]).unwrap();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(40, 6)).unwrap();
        let (mut top, mut left) = (0, 0);
        editor.handle(Input::Char(' '));
        editor.handle(Input::Char('b'));
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert!(screen_text(&terminal).contains("leader: Space b"));
        editor.handle(Input::Char('x'));
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert!(!screen_text(&terminal).contains("leader:"));
        assert_eq!(editor.lines(), &["keep"]);
        assert_eq!(editor.cursor(), crate::editor::Cursor::default());
        assert_eq!(editor.mode(), Mode::Normal);
    }

    #[test]
    fn palette_advertises_effective_leader_sequences_after_remapping() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor.set_leader(",").unwrap();
        editor.handle(Input::Ctrl('p'));
        for ch in "bnext".chars() {
            editor.handle(Input::Char(ch));
        }
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(100, 10)).unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert!(screen_text(&terminal).contains(", b n"));
        assert!(!screen_text(&terminal).contains("Space b n"));
        editor
            .bind("normal", ",", Some("core.command".into()))
            .unwrap();
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert!(screen_text(&terminal).contains("unbound"));
        assert!(!screen_text(&terminal).contains(", b n"));
    }

    #[test]
    fn buffer_switches_restore_independent_vertical_and_horizontal_viewports() {
        let directory = Directory::new();
        let a = directory.file("a", &vec!["a".repeat(50); 20].join("\n"));
        let b = directory.file("b", &vec!["b".repeat(40); 20].join("\n"));
        let mut editor = Editor::open(Some(a), vec![]).unwrap();
        let a_id = editor.buffer_id();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(16, 6)).unwrap();
        let mut viewports = BufferViewports::default();
        for _ in 0..14 {
            editor.handle(Input::Down);
        }
        editor.handle(Input::End);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(viewports.offsets[&a_id], (11, 37));
        for _ in 0..2 {
            editor.handle(Input::Up);
        }
        for _ in 0..3 {
            editor.handle(Input::Left);
        }
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        let a_viewport = viewports.offsets[&a_id];
        let a_cursor = terminal.get_cursor_position().unwrap();
        assert_eq!(a_viewport, (11, 37));

        editor.execute(&format!("edit {}", b.display()));
        let b_id = editor.buffer_id();
        assert_ne!(a_id, b_id);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(viewports.offsets[&b_id], (0, 0));
        for _ in 0..8 {
            editor.handle(Input::Down);
        }
        editor.handle(Input::End);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        editor.handle(Input::Up);
        editor.handle(Input::Left);
        editor.handle(Input::Left);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        let b_viewport = viewports.offsets[&b_id];
        let b_cursor = terminal.get_cursor_position().unwrap();
        assert_eq!(b_viewport, (5, 27));

        editor.execute(&format!("buffer {a_id}"));
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(viewports.offsets[&a_id], a_viewport);
        assert_eq!(terminal.get_cursor_position().unwrap(), a_cursor);
        assert_eq!(
            terminal.backend().buffer()[(a_cursor.x, a_cursor.y)].symbol(),
            "a"
        );
        editor.execute("bnext");
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(editor.buffer_id(), b_id);
        assert_eq!(viewports.offsets[&b_id], b_viewport);
        assert_eq!(terminal.get_cursor_position().unwrap(), b_cursor);
    }

    #[test]
    fn closing_inactive_buffer_retires_its_viewport_without_moving_active_buffer() {
        let directory = Directory::new();
        let a = directory.file("a", &vec!["a".repeat(50); 20].join("\n"));
        let b = directory.file("b", &vec!["b".repeat(40); 20].join("\n"));
        let c = directory.file("c", "new buffer");
        let mut editor = Editor::open(Some(a), vec![]).unwrap();
        let a_id = editor.buffer_id();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(16, 6)).unwrap();
        let mut viewports = BufferViewports::default();
        for _ in 0..14 {
            editor.handle(Input::Down);
        }
        editor.handle(Input::End);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        editor.execute(&format!("edit {}", b.display()));
        let b_id = editor.buffer_id();
        for _ in 0..8 {
            editor.handle(Input::Down);
        }
        editor.handle(Input::End);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        let b_viewport = viewports.offsets[&b_id];
        let b_cursor = terminal.get_cursor_position().unwrap();
        assert_eq!(viewports.offsets.len(), 2);

        editor.execute(&format!("bdelete {a_id}"));
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(editor.buffer_id(), b_id);
        assert!(!editor.has_buffer(a_id));
        assert!(!viewports.offsets.contains_key(&a_id));
        assert_eq!(viewports.offsets.len(), 1);
        assert_eq!(viewports.offsets[&b_id], b_viewport);
        assert_eq!(terminal.get_cursor_position().unwrap(), b_cursor);
        editor.execute(&format!("edit {}", c.display()));
        let c_id = editor.buffer_id();
        assert!(c_id > b_id);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(viewports.offsets[&c_id], (0, 0));
        assert!(!viewports.offsets.contains_key(&a_id));
    }

    #[test]
    fn restoring_buffer_after_narrow_resize_clamps_caret_inside_text_region() {
        let directory = Directory::new();
        let a = directory.file("a", &vec!["a".repeat(50); 20].join("\n"));
        let b = directory.file("b", "other");
        let mut editor = Editor::open(Some(a), vec![]).unwrap();
        let a_id = editor.buffer_id();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(24, 8)).unwrap();
        let mut viewports = BufferViewports::default();
        for _ in 0..14 {
            editor.handle(Input::Down);
        }
        editor.handle(Input::End);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(viewports.offsets[&a_id], (9, 29));
        editor.execute(&format!("edit {}", b.display()));
        let b_id = editor.buffer_id();
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        terminal.backend_mut().resize(4, 4);
        terminal
            .resize(ratatui::layout::Rect::new(0, 0, 4, 4))
            .unwrap();
        editor.execute(&format!("buffer {a_id}"));
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert_eq!(viewports.offsets[&a_id], (13, 49));
        assert_eq!(viewports.offsets[&b_id], (0, 0));
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(3, 1)
        );

        for (width, height) in [(1, 1), (24, 8)] {
            let area = ratatui::layout::Rect::new(0, 0, width, height);
            terminal.backend_mut().resize(width, height);
            terminal.resize(area).unwrap();
            terminal
                .draw(|frame| viewports.draw(frame, &editor))
                .unwrap();
            let cursor = terminal.get_cursor_position().unwrap();
            assert!(area.contains(cursor), "{area:?}: {cursor:?}");
            assert_eq!(
                terminal.backend().buffer()[(cursor.x, cursor.y)].symbol(),
                "a"
            );
            assert_eq!(viewports.offsets[&b_id], (0, 0));
        }
    }

    #[test]
    fn status_identifies_active_buffer_and_restored_visual_selection_count() {
        let directory = Directory::new();
        let a = directory.file("a", "word\nword\nword");
        let b = directory.file("b", "other");
        let mut editor = Editor::open(Some(a), vec![]).unwrap();
        let a_id = editor.buffer_id();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(240, 6)).unwrap();
        let mut viewports = BufferViewports::default();
        editor.handle(Input::Char('v'));
        editor.handle(Input::Ctrl('a'));
        assert_eq!(editor.selection_count(), 3);
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        assert!(!screen_text(&terminal).contains("[buffer"));
        editor.execute(&format!("edit {}", b.display()));
        let b_id = editor.buffer_id();
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        let text = screen_text(&terminal);
        assert!(
            text.contains(&format!("NORMAL  [buffer {b_id}/2]")),
            "{text}"
        );
        assert!(!text.contains("3 selections"), "{text}");
        editor.execute(&format!("buffer {a_id}"));
        terminal
            .draw(|frame| viewports.draw(frame, &editor))
            .unwrap();
        let text = screen_text(&terminal);
        assert!(
            text.contains(&format!("VISUAL  [buffer {a_id}/2]")),
            "{text}"
        );
        assert!(text.contains("3 selections"), "{text}");
        let (top, left) = viewports.offsets[&a_id];
        for selection in editor.selections() {
            let x = 2 + (selection.start.column - left) as u16;
            let y = (selection.start.row - top) as u16;
            assert!(matches!(
                terminal.backend().buffer()[(x, y)].bg,
                Color::Blue | Color::Magenta
            ));
        }
    }

    #[test]
    fn pending_motion_count_is_visible_and_escape_cancels_without_moving() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(["row"; 12].join("\n"))])
            .unwrap();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(60, 6)).unwrap();
        let (mut top, mut left) = (0, 0);
        editor.handle(Input::Char('1'));
        editor.handle(Input::Char('0'));
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert!(screen_text(&terminal).contains("count: 10"));
        editor.handle(Input::Escape);
        editor.handle(Input::Down);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert!(!screen_text(&terminal).contains("count:"));
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(3, 1)
        );
    }

    #[test]
    fn gutter_tracks_scrolled_rows_without_scrolling_with_text() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(
                "0123456789界z\n".repeat(11),
            )])
            .unwrap();
        for _ in 0..10 {
            editor.handle(Input::Down);
        }
        editor.handle(Input::End);
        let area = ratatui::layout::Rect::new(3, 2, 8, 5);
        let mut terminal = Terminal::with_options(
            ratatui::backend::TestBackend::new(20, 10),
            ratatui::TerminalOptions {
                viewport: ratatui::Viewport::Fixed(area),
            },
        )
        .unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert_eq!((top, left), (8, 8));
        let buffer = terminal.backend().buffer();
        for (y, expected) in [(2, " 2 "), (3, " 1 "), (4, "11 ")] {
            let number: String = (3..6).map(|x| buffer[(x, y)].symbol()).collect();
            assert_eq!(number, expected);
            assert_eq!(buffer[(6, y)].symbol(), "8");
            assert_eq!(buffer[(3, y)].bg, Color::Reset);
        }
        assert!(buffer[(3, 4)].modifier.contains(Modifier::BOLD));
        assert!(!buffer[(3, 3)].modifier.contains(Modifier::BOLD));
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(10, 4)
        );
        editor.handle(Input::Down);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        let last_number: String = (3..6).map(|x| buffer[(x, 4)].symbol()).collect();
        assert_eq!(last_number, "12 ");
        assert_eq!(buffer[(6, 4)].symbol(), " ");
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(6, 4)
        );
        editor.handle(Input::Up);
        editor.handle(Input::Up);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        for (y, expected) in [(2, "10 "), (3, " 1 "), (4, " 2 ")] {
            let number: String = (3..6).map(|x| buffer[(x, y)].symbol()).collect();
            assert_eq!(number, expected);
        }
        editor.handle(Input::Ctrl('e'));
        assert_eq!(editor.selection_count(), 2);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        for (y, expected) in [(2, " 1 "), (3, "11 "), (4, " 1 ")] {
            let number: String = (3..6).map(|x| buffer[(x, y)].symbol()).collect();
            assert_eq!(number, expected);
        }
    }

    #[test]
    fn gutter_resizes_at_digit_boundaries_and_yields_to_narrow_text() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        let (mut top, mut left) = (0, 0);
        for count in [9usize, 10, 100] {
            editor
                .apply(vec![crate::editor::Effect::Replace(
                    vec!["x"; count].join("\n"),
                )])
                .unwrap();
            let digits = count.ilog10() as u16 + 1;
            let gutter_width = digits + 1;
            for width in [12, gutter_width, gutter_width + 1, 1] {
                let mut terminal =
                    Terminal::new(ratatui::backend::TestBackend::new(width, 4)).unwrap();
                terminal
                    .draw(|frame| draw(frame, &editor, &mut top, &mut left))
                    .unwrap();
                let cursor = terminal.get_cursor_position().unwrap();
                let buffer = terminal.backend().buffer();
                let text_x = if width > gutter_width {
                    gutter_width
                } else {
                    0
                };
                assert_eq!(buffer[(text_x, 0)].symbol(), "x");
                assert_eq!(cursor, ratatui::layout::Position::new(text_x, 0));
                if text_x > 0 {
                    let number: String = (0..text_x).map(|x| buffer[(x, 0)].symbol()).collect();
                    assert_eq!(
                        number,
                        format!("{:>digits$} ", 1, digits = usize::from(digits))
                    );
                }
            }
        }
        editor
            .apply(vec![crate::editor::Effect::Replace(String::new())])
            .unwrap();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(8, 5)).unwrap();
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        assert_eq!(buffer[(0, 0)].symbol(), "1");
        assert_eq!(buffer[(0, 1)].symbol(), " ");
        assert_eq!(buffer[(0, 2)].symbol(), " ");
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(2, 0)
        );
    }

    #[test]
    fn palette_renders_query_no_matches_and_restores_underlying_prompt() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor.handle(Input::Char('/'));
        for ch in "saved search".chars() {
            editor.handle(Input::Char(ch));
        }
        editor.handle(Input::Ctrl('p'));
        for ch in "no-such-command".chars() {
            editor.handle(Input::Char(ch));
        }
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(100, 16)).unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let text = screen_text(&terminal);
        assert!(text.contains("> no-such-command"), "{text}");
        assert!(text.contains("No matching commands"), "{text}");
        assert!(text.contains("SEARCH"), "{text}");
        assert_eq!(terminal.get_cursor_position().unwrap().y, 1);
        editor.handle(Input::Enter);
        assert!(editor.palette().is_some());
        editor.handle(Input::Escape);
        assert_eq!(editor.mode(), Mode::Search);
        assert_eq!(editor.command_line(), "saved search");
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert!(screen_text(&terminal).contains("/saved search"));
    }

    #[test]
    fn palette_window_follows_keyboard_selection() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor.handle(Input::Ctrl('p'));
        for _ in 0..20 {
            editor.handle(Input::Ctrl('j'));
        }
        editor.handle(Input::Ctrl('k'));
        editor.handle(Input::Ctrl('n'));
        let palette = editor.palette().unwrap();
        assert_eq!(palette.selected, 20);
        let selected = &palette.entries[palette.selected];
        let first_name = palette.entries[0].name.clone();
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(100, 10)).unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let text = screen_text(&terminal);
        assert!(text.contains(&selected.name), "{text}");
        assert!(!text.contains(&format!("({first_name})")), "{text}");
        let buffer = terminal.backend().buffer();
        let selected_y = (2..10).find(|&y| buffer[(1, y)].symbol() == ">").unwrap();
        assert_eq!(buffer[(1, selected_y)].bg, Color::Blue);
        assert!(buffer[(1, selected_y)].modifier.contains(Modifier::BOLD));
        assert_eq!(terminal.get_cursor_position().unwrap().y, 1);
    }

    #[test]
    fn palette_shows_effective_bindings_and_dimmed_mode_ineligible_commands() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .register(crate::editor::Feature {
                name: "sample".into(),
                required_capabilities: vec![],
                commands: vec!["greet".into()],
                core: false,
            })
            .unwrap();
        editor.bind("normal", "g", Some("greet".into())).unwrap();
        editor.bind("normal", "g", None).unwrap();
        editor
            .bind("normal", "ctrl+x", Some("greet".into()))
            .unwrap();
        editor.handle(Input::Ctrl('p'));
        for ch in "greet".chars() {
            editor.handle(Input::Char(ch));
        }
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(100, 10)).unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let text = screen_text(&terminal);
        assert!(text.contains("sample | Ctrl+x | NORMAL"), "{text}");
        assert!(!text.contains("unbound"), "{text}");
        editor.handle(Input::Escape);
        editor.handle(Input::Char('i'));
        editor.handle(Input::Ctrl('p'));
        for ch in "greet".chars() {
            editor.handle(Input::Char(ch));
        }
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let text = screen_text(&terminal);
        assert!(text.contains("sample | unbound | NORMAL"), "{text}");
        assert!(text.contains("INSERT"), "{text}");
        let cell = &terminal.backend().buffer()[(1, 2)];
        assert!(cell.modifier.contains(Modifier::DIM));
        assert_eq!(cell.bg, Color::Blue);
        editor.handle(Input::Enter);
        assert!(editor.palette().is_some());
        assert_eq!(editor.mode(), Mode::Insert);
    }

    #[test]
    fn palette_query_scrolls_graphemes_tabs_and_wide_cells_on_tiny_offset_areas() {
        let editor = Editor::open(None, vec![]).unwrap();
        let palette = Palette {
            query: "long\t界e\u{301}z".into(),
            entries: vec![],
            selected: 0,
        };
        for (width, height) in [(12, 6), (8, 2), (1, 1), (1, 2), (8, 1), (12, 6)] {
            let area = ratatui::layout::Rect::new(3, 2, width, height);
            let mut terminal = Terminal::with_options(
                ratatui::backend::TestBackend::new(24, 12),
                ratatui::TerminalOptions {
                    viewport: ratatui::Viewport::Fixed(area),
                },
            )
            .unwrap();
            terminal
                .draw(|frame| {
                    draw_palette(
                        frame,
                        &palette,
                        Mode::Visual,
                        editor.selection_navigation_hint(),
                    )
                })
                .unwrap();
            let cursor = terminal.get_cursor_position().unwrap();
            assert!(area.contains(cursor), "{area:?}: {cursor:?}");
            let bordered = height >= 4 && width >= 4;
            let query_x = area.x + u16::from(bordered);
            let query_y = area.y + u16::from(bordered);
            let query_width = width - 2 * u16::from(bordered);
            assert_eq!(cursor.x, query_x + query_width - 1);
            assert_eq!(cursor.y, query_y);
            let query = format!("> {}", palette.query);
            let offset =
                display_column(&query, usize::MAX).saturating_sub(usize::from(query_width) - 1);
            let mut expected = ratatui::buffer::Buffer::empty(ratatui::layout::Rect::new(
                query_x,
                query_y,
                query_width,
                1,
            ));
            use ratatui::widgets::Widget;
            Paragraph::new(visible_line(&query, offset, usize::from(query_width)))
                .render(expected.area, &mut expected);
            for x in query_x..query_x + query_width {
                assert_eq!(
                    terminal.backend().buffer()[(x, query_y)].symbol(),
                    expected[(x, query_y)].symbol()
                );
            }
            assert_eq!(terminal.backend().buffer()[(0, 0)].symbol(), " ");
        }
        for (width, height) in [(0, 1), (1, 0), (0, 0)] {
            let mut terminal =
                Terminal::new(ratatui::backend::TestBackend::new(width, height)).unwrap();
            terminal
                .draw(|frame| {
                    draw_palette(
                        frame,
                        &palette,
                        Mode::Normal,
                        editor.selection_navigation_hint(),
                    )
                })
                .unwrap();
        }
    }

    #[test]
    fn opening_palette_does_not_scroll_underlying_editor_viewport() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(
                "first\nsecond\n0123456789界z".into(),
            )])
            .unwrap();
        editor.handle(Input::Down);
        editor.handle(Input::Down);
        editor.handle(Input::End);
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(8, 4)).unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let viewport = (top, left);
        editor.handle(Input::Ctrl('p'));
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert_eq!((top, left), viewport);
        editor.handle(Input::Ctrl('p'));
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert_eq!((top, left), viewport);
        let cursor = terminal.get_cursor_position().unwrap();
        assert_eq!(
            terminal.backend().buffer()[(cursor.x, cursor.y)].symbol(),
            "z"
        );
    }

    #[test]
    fn layout_keeps_scrolled_content_and_prompts_inside_offset_regions() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(
                "first\nsecond\n0123456789界z".into(),
            )])
            .unwrap();
        editor.handle(Input::Down);
        editor.handle(Input::Down);
        editor.handle(Input::End);
        let (mut top, mut left) = (0, 0);
        for prompting in [false, true] {
            if prompting {
                editor.handle(Input::Char('/'));
                for ch in "long query".chars() {
                    editor.handle(Input::Char(ch));
                }
            }
            for height in [4, 2, 1, 4] {
                let area = ratatui::layout::Rect::new(3, 2, 8, height);
                let mut terminal = Terminal::with_options(
                    ratatui::backend::TestBackend::new(20, 10),
                    ratatui::TerminalOptions {
                        viewport: ratatui::Viewport::Fixed(area),
                    },
                )
                .unwrap();
                terminal
                    .draw(|frame| draw(frame, &editor, &mut top, &mut left))
                    .unwrap();
                let cursor = terminal.get_cursor_position().unwrap();
                assert!(area.contains(cursor), "{area:?}: {cursor:?}");
                let buffer = terminal.backend().buffer();
                if prompting {
                    assert_eq!(cursor.y, area.bottom() - 1);
                    assert_eq!(buffer[(area.x, cursor.y)].symbol(), "g");
                } else {
                    assert_eq!(buffer[(cursor.x, cursor.y)].symbol(), "z");
                }
                if height >= 3 {
                    assert_eq!(buffer[(area.x, area.bottom() - 2)].bg, Color::Cyan);
                } else {
                    for y in area.y..area.bottom() {
                        assert_ne!(buffer[(area.x, y)].bg, Color::Cyan);
                    }
                }
                assert_eq!(buffer[(0, 0)].symbol(), " ");
            }
        }
    }

    #[test]
    fn tabs_and_wide_graphemes_scroll_in_terminal_cells() {
        let text = "a\t界e\u{301}z";
        assert_eq!(display_column(text, 4), 7);
        assert_eq!(visible_line(text, 2, 5), "  界e\u{301}");
        assert_eq!(visible_line(text, 5, 2), " e\u{301}");
    }

    #[test]
    fn selection_set_renders_all_ranges_and_counts_offscreen_targets() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(
                "界\n界\n界\n界\n界".into(),
            )])
            .unwrap();
        editor.handle(Input::Home);
        editor.handle(Input::Char('v'));
        editor.handle(Input::Ctrl('a'));
        assert_eq!(editor.selection_count(), 5);
        assert_eq!(editor.selections().len(), 5);
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(48, 4)).unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        for selection in editor.selections() {
            if selection.start.row >= top && selection.start.row < top + 2 {
                let y = (selection.start.row - top) as u16;
                assert!(matches!(buffer[(2, y)].bg, Color::Blue | Color::Magenta));
            }
        }
        let status: String = (0..48).map(|x| buffer[(x, 2)].symbol()).collect();
        assert!(status.contains("5 selections"), "{status}");
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(2, (editor.cursor().row - top) as u16)
        );
    }

    #[test]
    fn secondary_carets_render_on_empty_lines_and_at_line_end() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace("a\n\n界".into())])
            .unwrap();
        editor.handle(Input::Home);
        editor.handle(Input::Ctrl('e'));
        editor.handle(Input::Ctrl('e'));
        assert_eq!(editor.selection_count(), 3);
        editor.handle(Input::Char('A'));
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(48, 5)).unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        for caret in editor.carets() {
            let x = 2 + display_column(&editor.lines()[caret.row], caret.column) as u16;
            assert_eq!(buffer[(x, caret.row as u16)].symbol(), " ");
            if caret != editor.cursor() {
                assert_eq!(buffer[(x, caret.row as u16)].bg, Color::Magenta);
            }
        }
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(
                2 + display_column(&editor.lines()[editor.cursor().row], editor.cursor().column)
                    as u16,
                editor.cursor().row as u16
            )
        );
    }

    #[test]
    fn visual_selection_highlights_graphemes_newlines_and_clipped_ranges_over_search() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(
                "a\t界e\u{301}z\n\nxy".into(),
            )])
            .unwrap();
        editor.handle(Input::Char('/'));
        for ch in "界e\u{301}".chars() {
            editor.handle(Input::Char(ch));
        }
        editor.handle(Input::Enter);
        editor.handle(Input::Char('v'));
        editor.handle(Input::Left);
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(12, 6)).unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        for x in [1, 2, 3, 4] {
            assert_eq!(buffer[(2 + x, 0)].bg, Color::Blue);
        }
        assert_eq!(buffer[(6, 0)].symbol(), "界");
        assert_eq!(buffer[(8, 0)].bg, Color::Yellow);
        editor.handle(Input::Down);
        editor.handle(Input::Down);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        assert_eq!(buffer[(10, 0)].symbol(), " ");
        assert_eq!(buffer[(10, 0)].bg, Color::Blue);
        assert_eq!(buffer[(2, 1)].bg, Color::Blue);
        assert_eq!(buffer[(2, 2)].bg, Color::Blue);
        assert_ne!(buffer[(3, 2)].bg, Color::Blue);

        editor.handle(Input::Up);
        editor.handle(Input::Up);
        editor.handle(Input::End);
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(7, 6)).unwrap();
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        assert_eq!(left, 4);
        assert_eq!(buffer[(2, 0)].symbol(), "界");
        assert_eq!(buffer[(4, 0)].symbol(), "e\u{301}");
        assert_eq!(buffer[(6, 0)].symbol(), " ");
        for x in [0, 2, 3, 4] {
            assert_eq!(buffer[(2 + x, 0)].bg, Color::Blue);
        }
        assert_ne!(buffer[(2, 1)].bg, Color::Blue);
        editor.handle(Input::Escape);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        assert_eq!(buffer[(2, 0)].bg, Color::Yellow);
        assert_eq!(buffer[(4, 0)].bg, Color::Yellow);
        assert_ne!(buffer[(5, 0)].bg, Color::Blue);
        assert_ne!(buffer[(6, 0)].bg, Color::Blue);
    }

    #[test]
    fn active_search_highlight_uses_display_cells_and_clips_with_horizontal_scroll() {
        let mut editor = Editor::open(None, vec![]).unwrap();
        editor
            .apply(vec![crate::editor::Effect::Replace(
                "a\t界e\u{301}zz".into(),
            )])
            .unwrap();
        editor.handle(Input::Char('/'));
        for ch in "\t界e\u{301}".chars() {
            editor.handle(Input::Char(ch));
        }
        editor.handle(Input::Enter);
        editor.handle(Input::End);
        let mut terminal = Terminal::new(ratatui::backend::TestBackend::new(7, 5)).unwrap();
        let (mut top, mut left) = (0, 0);
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        assert_eq!(left, 4);
        assert_eq!(buffer[(2, 0)].symbol(), "界");
        assert_eq!(buffer[(4, 0)].symbol(), "e\u{301}");
        for x in [0, 2] {
            assert_eq!(buffer[(2 + x, 0)].bg, Color::Yellow);
        }
        for x in 3..5 {
            assert_ne!(buffer[(2 + x, 0)].bg, Color::Yellow);
        }
        editor.handle(Input::Char('/'));
        for ch in "界界".chars() {
            editor.handle(Input::Char(ch));
        }
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        let buffer = terminal.backend().buffer();
        assert_eq!(buffer[(1, 4)].symbol(), "界");
        assert_eq!(buffer[(3, 4)].symbol(), "界");
        editor.handle(Input::Backspace);
        editor.handle(Input::Backspace);
        editor.handle(Input::Char('\t'));
        terminal
            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
            .unwrap();
        assert_eq!(
            terminal.get_cursor_position().unwrap(),
            ratatui::layout::Position::new(4, 4)
        );
    }

    #[cfg(unix)]
    #[test]
    fn terminal_session_scopes_the_callers_panic_hook() {
        use std::io::Write;
        const CHILD: &str = "VAMP_TERMINAL_HOOK_PROBE";
        if let Ok(mode) = std::env::var(CHILD) {
            std::panic::set_hook(Box::new(|info| {
                assert!(!crossterm::terminal::is_raw_mode_enabled().unwrap());
                println!("CALLER_HOOK");
                eprintln!("{info}");
            }));
            if mode == "entry" {
                let mut editor = EditorSession::open(None, vec![], None).unwrap();
                assert!(run(&mut editor).is_err());
            } else {
                let result = panic::catch_unwind(AssertUnwindSafe(|| {
                    TerminalSession::run(|| {
                        assert!(crossterm::terminal::is_raw_mode_enabled().unwrap());
                        match mode.as_str() {
                            "normal" => Ok(()),
                            "error" => Err(io::Error::from(io::ErrorKind::BrokenPipe)),
                            "panic" => panic::panic_any(73_u64),
                            "keys" => {
                                let mut editor = Editor::open(None, vec![]).unwrap();
                                editor.handle(Input::Ctrl('p'));
                                let original = editor.lines().to_vec();
                                println!("READING_KEYS");
                                io::stdout().flush()?;
                                for (index, expected) in [
                                    Input::Ctrl('j'),
                                    Input::Ctrl('k'),
                                    Input::Ctrl('j'),
                                    Input::Ctrl('k'),
                                    Input::Enter,
                                    Input::Enter,
                                ]
                                .into_iter()
                                .enumerate()
                                {
                                    let Event::Key(key) = event::read()? else {
                                        panic!("expected a keyboard event");
                                    };
                                    let input = translate(key).unwrap();
                                    assert_eq!(input, expected);
                                    if index == 4 {
                                        for ch in "q!".chars() {
                                            editor.handle(Input::Char(ch));
                                        }
                                    }
                                    editor.handle(input);
                                    match index {
                                        0 | 2 => assert_eq!(editor.palette().unwrap().selected, 1),
                                        1 | 3 => assert_eq!(editor.palette().unwrap().selected, 0),
                                        4 => {
                                            assert!(editor.palette().is_none());
                                            assert_eq!(editor.mode(), Mode::Command);
                                            assert_eq!(editor.command_line(), "q! ");
                                            assert!(!editor.should_quit());
                                        }
                                        5 => assert!(editor.should_quit()),
                                        _ => unreachable!(),
                                    }
                                    assert_eq!(editor.lines(), original);
                                }
                                Ok(())
                            }
                            _ => unreachable!(),
                        }
                    })
                }));
                match mode.as_str() {
                    "normal" | "keys" => result.unwrap().unwrap(),
                    "error" => assert_eq!(
                        result.unwrap().unwrap_err().kind(),
                        io::ErrorKind::BrokenPipe
                    ),
                    "panic" => assert_eq!(result.unwrap_err().downcast_ref::<u64>(), Some(&73)),
                    _ => unreachable!(),
                }
            }
            assert!(!crossterm::terminal::is_raw_mode_enabled().unwrap());
            println!("AFTER_TERMINAL_RETURN");
            let _ = panic::catch_unwind(|| panic!("outside the terminal session"));
            return;
        }

        use std::os::unix::process::CommandExt;
        use std::process::{Command, Stdio};
        unsafe extern "C" {
            fn setsid() -> i32;
        }
        let mut command = Command::new(std::env::current_exe().unwrap());
        command
            .args([
                "--exact",
                "tui::tests::terminal_session_scopes_the_callers_panic_hook",
                "--nocapture",
                "--color",
                "never",
            ])
            .env(CHILD, "entry")
            .stdin(Stdio::null());
        // SAFETY: setsid is async-signal-safe and detaches the child from any
        // controlling terminal without touching inherited Rust state.
        unsafe {
            command.pre_exec(|| {
                if setsid() == -1 {
                    Err(io::Error::last_os_error())
                } else {
                    Ok(())
                }
            });
        }
        let check = |output: std::process::Output, mode: &str| {
            assert!(output.status.success(), "{mode}: {output:?}");
            let stdout = String::from_utf8(output.stdout).unwrap();
            let (before, after) = stdout.split_once("AFTER_TERMINAL_RETURN").unwrap();
            let entered = usize::from(mode != "entry");
            assert_eq!(
                before.matches("\x1b[?1049h").count(),
                entered,
                "{mode}: {before:?}"
            );
            assert_eq!(
                before.matches("\x1b[?1049l").count(),
                entered,
                "{mode}: {before:?}"
            );
            if mode == "panic" {
                assert!(
                    before.find("\x1b[?1049l").unwrap() < before.find("CALLER_HOOK").unwrap(),
                    "{before:?}",
                );
            }
            assert!(after.contains("CALLER_HOOK"), "{after:?}");
            assert!(
                !after.contains('\u{1b}'),
                "terminal hook outlived its session: {after:?}"
            );
        };
        check(command.output().unwrap(), "entry");

        // Ruby's standard-library PTY gives each positive-entry scenario a real
        // terminal, keeping process-global hooks isolated from the test runner.
        for mode in ["normal", "error", "panic", "keys"] {
            let output =
                Command::new(std::env::var_os("VAMP_RUBY").unwrap_or_else(|| "ruby".into()))
                    .args([
                        "-rpty",
                        "-rtimeout",
                        "-e",
                        r#"
PTY.spawn(*ARGV) do |output, input, pid|
  sent_keys = false
  captured = +""
  begin
    Timeout.timeout(10) do
      loop do
        chunk = output.readpartial(4096)
        STDOUT.write(chunk)
        captured << chunk
        if !sent_keys && captured.include?("READING_KEYS")
          input.write("\e[106;5u\e[107;5u\n\v\e[13u\r")
          input.flush
          sent_keys = true
        end
      end
    end
  rescue EOFError, Errno::EIO
  rescue Timeout::Error
    Process.kill("TERM", pid)
    Process.wait(pid)
    abort "terminal lifecycle probe timed out"
  ensure
    input.close
  end
  Process.wait(pid)
  exit($?.exitstatus || 1)
end
"#,
                        "--",
                    ])
                    .arg(std::env::current_exe().unwrap())
                    .args([
                        "--exact",
                        "tui::tests::terminal_session_scopes_the_callers_panic_hook",
                        "--nocapture",
                        "--color",
                        "never",
                    ])
                    .env(CHILD, mode)
                    .output()
                    .unwrap();
            check(output, mode);
        }
    }
}