vamp/src/tui.rs

use std::{
    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},
    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},
    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);
    }
}

/// 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 top, mut left) = (0, 0);
        while !session.editor().should_quit() {
            terminal.draw(|frame| draw(frame, session.editor(), &mut top, &mut left))?;
            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),
        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 [viewport, status_area, prompt_area] = Layout::vertical([
        Constraint::Fill(1),
        Constraint::Length(u16::from(area.height >= 3)),
        Constraint::Length(u16::from(area.height >= 2 || prompting)),
    ])
    .areas(area);
    let height = usize::from(viewport.height);
    let width = usize::from(viewport.width);
    let cursor = editor.cursor();
    if height > 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;
        }
        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 status = format!(
        " {}  {}{}  {}:{}{}",
        editor.mode(),
        path,
        if editor.dirty() { " [+]" } else { "" },
        cursor.row + 1,
        cursor.column + 1,
        if editor.selection_count() > 1 {
            format!("  {} selections", editor.selection_count())
        } else {
            String::new()
        }
    );
    frame.render_widget(
        Paragraph::new(status).style(Style::default().fg(Color::Black).bg(Color::Cyan)),
        status_area,
    );
    if prompting && prompt_area.height > 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 - 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 {
            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(palette) = editor.palette() {
        draw_palette(frame, palette, editor.mode());
    }
}

fn draw_palette(frame: &mut Frame, palette: &Palette, mode: Mode) {
    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} · ↑↓/Ctrl+k/n select · Enter accept · Esc/Ctrl+p cancel"
        )),
        help_area,
    );
}

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

    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 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::Down);
        }
        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 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))
                .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))
                .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[(0, 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(0, (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 = 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(
                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(10, 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[(x, 0)].bg, Color::Blue);
        }
        assert_eq!(buffer[(4, 0)].symbol(), "界");
        assert_eq!(buffer[(6, 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[(8, 0)].symbol(), " ");
        assert_eq!(buffer[(8, 0)].bg, Color::Blue);
        assert_eq!(buffer[(0, 1)].bg, Color::Blue);
        assert_eq!(buffer[(0, 2)].bg, Color::Blue);
        assert_ne!(buffer[(1, 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(5, 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[(0, 0)].symbol(), "界");
        assert_eq!(buffer[(2, 0)].symbol(), "e\u{301}");
        assert_eq!(buffer[(4, 0)].symbol(), " ");
        for x in [0, 2, 3, 4] {
            assert_eq!(buffer[(x, 0)].bg, Color::Blue);
        }
        assert_ne!(buffer[(0, 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[(0, 0)].bg, Color::Yellow);
        assert_eq!(buffer[(2, 0)].bg, Color::Yellow);
        assert_ne!(buffer[(3, 0)].bg, Color::Blue);
        assert_ne!(buffer[(4, 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(5, 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[(0, 0)].symbol(), "界");
        assert_eq!(buffer[(2, 0)].symbol(), "e\u{301}");
        for x in [0, 2] {
            assert_eq!(buffer[(x, 0)].bg, Color::Yellow);
        }
        for x in 3..5 {
            assert_ne!(buffer[(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[(0, 4)].symbol(), "界");
        assert_eq!(buffer[(2, 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() {
        const CHILD: &str = "VAMP_TERMINAL_HOOK_PROBE";
        if let Ok(mode) = std::env::var(CHILD) {
            std::panic::set_hook(Box::new(|_| {
                assert!(!crossterm::terminal::is_raw_mode_enabled().unwrap());
                println!("CALLER_HOOK");
            }));
            if mode == "entry" {
                let mut editor = EditorSession::open(None, vec![], None).unwrap();
                assert!(run(&mut editor).is_err());
            } else {
                let result = panic::catch_unwind(|| {
                    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),
                            _ => unreachable!(),
                        }
                    })
                });
                match mode.as_str() {
                    "normal" => 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| {
            assert!(output.status.success(), "{output:?}");
            let stdout = String::from_utf8(output.stdout).unwrap();
            let after = stdout.split_once("AFTER_TERMINAL_RETURN").unwrap().1;
            assert!(after.contains("CALLER_HOOK"), "{after:?}");
            assert!(
                !after.contains('\u{1b}'),
                "terminal hook outlived its session: {after:?}"
            );
        };
        check(command.output().unwrap());

        // 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"] {
            let output =
                Command::new(std::env::var_os("VAMP_RUBY").unwrap_or_else(|| "ruby".into()))
                    .args([
                        "-rpty",
                        "-e",
                        r#"
PTY.spawn(*ARGV) do |output, input, pid|
  input.close
  begin
    loop { STDOUT.write(output.readpartial(4096)) }
  rescue EOFError, Errno::EIO
  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);
        }
    }
}