use std::io::Result;
use std::sync::Arc;
use std::time::Duration;

use crate::history_cell::HistoryCell;
use crate::history_cell::UserHistoryCell;
use crate::key_hint;
use crate::key_hint::KeyBinding;
use crate::render::Insets;
use crate::render::renderable::InsetRenderable;
use crate::render::renderable::Renderable;
use crate::style::user_message_style;
use crate::tui;
use crate::tui::TuiEvent;
use crossterm::event::KeyCode;
use crossterm::event::KeyEvent;
use ratatui::buffer::Buffer;
use ratatui::buffer::Cell;
use ratatui::layout::Rect;
use ratatui::style::Style;
use ratatui::style::Stylize;
use ratatui::text::Line;
use ratatui::text::Span;
use ratatui::text::Text;
use ratatui::widgets::Clear;
use ratatui::widgets::Paragraph;
use ratatui::widgets::Widget;
use ratatui::widgets::WidgetRef;
use ratatui::widgets::Wrap;

pub(crate) enum Overlay {
    Transcript(TranscriptOverlay),
    Static(StaticOverlay),
}

impl Overlay {
    pub(crate) fn new_transcript(cells: Vec<Arc<dyn HistoryCell>>) -> Self {
        Self::Transcript(TranscriptOverlay::new(cells))
    }

    pub(crate) fn new_static_with_lines(lines: Vec<Line<'static>>, title: String) -> Self {
        Self::Static(StaticOverlay::with_title(lines, title))
    }

    pub(crate) fn new_static_with_renderables(
        renderables: Vec<Box<dyn Renderable>>,
        title: String,
    ) -> Self {
        Self::Static(StaticOverlay::with_renderables(renderables, title))
    }

    pub(crate) fn handle_event(&mut self, tui: &mut tui::Tui, event: TuiEvent) -> Result<()> {
        match self {
            Overlay::Transcript(o) => o.handle_event(tui, event),
            Overlay::Static(o) => o.handle_event(tui, event),
        }
    }

    pub(crate) fn is_done(&self) -> bool {
        match self {
            Overlay::Transcript(o) => o.is_done(),
            Overlay::Static(o) => o.is_done(),
        }
    }
}

const KEY_UP: KeyBinding = key_hint::plain(KeyCode::Up);
const KEY_DOWN: KeyBinding = key_hint::plain(KeyCode::Down);
const KEY_PAGE_UP: KeyBinding = key_hint::plain(KeyCode::PageUp);
const KEY_PAGE_DOWN: KeyBinding = key_hint::plain(KeyCode::PageDown);
const KEY_SPACE: KeyBinding = key_hint::plain(KeyCode::Char(' '));
const KEY_HOME: KeyBinding = key_hint::plain(KeyCode::Home);
const KEY_END: KeyBinding = key_hint::plain(KeyCode::End);
const KEY_Q: KeyBinding = key_hint::plain(KeyCode::Char('q'));
const KEY_ESC: KeyBinding = key_hint::plain(KeyCode::Esc);
const KEY_ENTER: KeyBinding = key_hint::plain(KeyCode::Enter);
const KEY_CTRL_T: KeyBinding = key_hint::ctrl(KeyCode::Char('t'));
const KEY_CTRL_C: KeyBinding = key_hint::ctrl(KeyCode::Char('c'));

// Common pager navigation hints rendered on the first line
const PAGER_KEY_HINTS: &[(&[KeyBinding], &str)] = &[
    (&[KEY_UP, KEY_DOWN], "to scroll"),
    (&[KEY_PAGE_UP, KEY_PAGE_DOWN], "to page"),
    (&[KEY_HOME, KEY_END], "to jump"),
];

// Render a single line of key hints from (key(s), description) pairs.
fn render_key_hints(area: Rect, buf: &mut Buffer, pairs: &[(&[KeyBinding], &str)]) {
    let mut spans: Vec<Span<'static>> = vec![" ".into()];
    let mut first = true;
    for (keys, desc) in pairs {
        if !first {
            spans.push("   ".into());
        }
        for (i, key) in keys.iter().enumerate() {
            if i > 0 {
                spans.push("/".into());
            }
            spans.push(Span::from(key));
        }
        spans.push(" ".into());
        spans.push(Span::from(desc.to_string()));
        first = false;
    }
    Paragraph::new(vec![Line::from(spans).dim()]).render_ref(area, buf);
}

/// Generic widget for rendering a pager view.
struct PagerView {
    renderables: Vec<Box<dyn Renderable>>,
    scroll_offset: usize,
    title: String,
    last_content_height: Option<usize>,
    last_rendered_height: Option<usize>,
    /// If set, on next render ensure this chunk is visible.
    pending_scroll_chunk: Option<usize>,
}

impl PagerView {
    fn new(renderables: Vec<Box<dyn Renderable>>, title: String, scroll_offset: usize) -> Self {
        Self {
            renderables,
            scroll_offset,
            title,
            last_content_height: None,
            last_rendered_height: None,
            pending_scroll_chunk: None,
        }
    }

    fn content_height(&self, width: u16) -> usize {
        self.renderables
            .iter()
            .map(|c| c.desired_height(width) as usize)
            .sum()
    }

    fn render(&mut self, area: Rect, buf: &mut Buffer) {
        Clear.render(area, buf);
        self.render_header(area, buf);
        let content_area = self.content_area(area);
        self.update_last_content_height(content_area.height);
        let content_height = self.content_height(content_area.width);
        self.last_rendered_height = Some(content_height);
        // If there is a pending request to scroll a specific chunk into view,
        // satisfy it now that wrapping is up to date for this width.
        if let Some(idx) = self.pending_scroll_chunk.take() {
            self.ensure_chunk_visible(idx, content_area);
        }
        self.scroll_offset = self
            .scroll_offset
            .min(content_height.saturating_sub(content_area.height as usize));

        self.render_content(content_area, buf);

        self.render_bottom_bar(area, content_area, buf, content_height);
    }

    fn render_header(&self, area: Rect, buf: &mut Buffer) {
        Span::from("/ ".repeat(area.width as usize / 2))
            .dim()
            .render_ref(area, buf);
        let header = format!("/ {}", self.title);
        header.dim().render_ref(area, buf);
    }

    fn render_content(&self, area: Rect, buf: &mut Buffer) {
        let mut y = -(self.scroll_offset as isize);
        let mut drawn_bottom = area.y;
        for renderable in &self.renderables {
            let top = y;
            let height = renderable.desired_height(area.width) as isize;
            y += height;
            let bottom = y;
            if bottom < area.y as isize {
                continue;
            }
            if top > area.y as isize + area.height as isize {
                break;
            }
            if top < 0 {
                let drawn = render_offset_content(area, buf, &**renderable, (-top) as u16);
                drawn_bottom = drawn_bottom.max(area.y + drawn);
            } else {
                let draw_height = (height as u16).min(area.height.saturating_sub(top as u16));
                let draw_area = Rect::new(area.x, area.y + top as u16, area.width, draw_height);
                renderable.render(draw_area, buf);
                drawn_bottom = drawn_bottom.max(draw_area.y.saturating_add(draw_area.height));
            }
        }

        for y in drawn_bottom..area.bottom() {
            if area.width == 0 {
                break;
            }
            buf[(area.x, y)] = Cell::from('~');
            for x in area.x + 1..area.right() {
                buf[(x, y)] = Cell::from(' ');
            }
        }
    }

    fn render_bottom_bar(
        &self,
        full_area: Rect,
        content_area: Rect,
        buf: &mut Buffer,
        total_len: usize,
    ) {
        let sep_y = content_area.bottom();
        let sep_rect = Rect::new(full_area.x, sep_y, full_area.width, 1);

        Span::from("─".repeat(sep_rect.width as usize))
            .dim()
            .render_ref(sep_rect, buf);
        let percent = if total_len == 0 {
            100
        } else {
            let max_scroll = total_len.saturating_sub(content_area.height as usize);
            if max_scroll == 0 {
                100
            } else {
                (((self.scroll_offset.min(max_scroll)) as f32 / max_scroll as f32) * 100.0).round()
                    as u8
            }
        };
        let pct_text = format!(" {percent}% ");
        let pct_w = pct_text.chars().count() as u16;
        let pct_x = sep_rect.x + sep_rect.width - pct_w - 1;
        Span::from(pct_text)
            .dim()
            .render_ref(Rect::new(pct_x, sep_rect.y, pct_w, 1), buf);
    }

    fn handle_key_event(&mut self, tui: &mut tui::Tui, key_event: KeyEvent) -> Result<()> {
        match key_event {
            e if KEY_UP.is_press(e) => {
                self.scroll_offset = self.scroll_offset.saturating_sub(1);
            }
            e if KEY_DOWN.is_press(e) => {
                self.scroll_offset = self.scroll_offset.saturating_add(1);
            }
            e if KEY_PAGE_UP.is_press(e) => {
                let area = self.content_area(tui.terminal.viewport_area);
                self.scroll_offset = self.scroll_offset.saturating_sub(area.height as usize);
            }
            e if KEY_PAGE_DOWN.is_press(e) || KEY_SPACE.is_press(e) => {
                let area = self.content_area(tui.terminal.viewport_area);
                self.scroll_offset = self.scroll_offset.saturating_add(area.height as usize);
            }
            e if KEY_HOME.is_press(e) => {
                self.scroll_offset = 0;
            }
            e if KEY_END.is_press(e) => {
                self.scroll_offset = usize::MAX;
            }
            _ => {
                return Ok(());
            }
        }
        tui.frame_requester()
            .schedule_frame_in(Duration::from_millis(16));
        Ok(())
    }

    fn update_last_content_height(&mut self, height: u16) {
        self.last_content_height = Some(height as usize);
    }

    fn content_area(&self, area: Rect) -> Rect {
        let mut area = area;
        area.y = area.y.saturating_add(1);
        area.height = area.height.saturating_sub(2);
        area
    }
}

impl PagerView {
    fn is_scrolled_to_bottom(&self) -> bool {
        if self.scroll_offset == usize::MAX {
            return true;
        }
        let Some(height) = self.last_content_height else {
            return false;
        };
        if self.renderables.is_empty() {
            return true;
        }
        let Some(total_height) = self.last_rendered_height else {
            return false;
        };
        if total_height <= height {
            return true;
        }
        let max_scroll = total_height.saturating_sub(height);
        self.scroll_offset >= max_scroll
    }

    /// Request that the given text chunk index be scrolled into view on next render.
    fn scroll_chunk_into_view(&mut self, chunk_index: usize) {
        self.pending_scroll_chunk = Some(chunk_index);
    }

    fn ensure_chunk_visible(&mut self, idx: usize, area: Rect) {
        if area.height == 0 || idx >= self.renderables.len() {
            return;
        }
        let first = self
            .renderables
            .iter()
            .take(idx)
            .map(|r| r.desired_height(area.width) as usize)
            .sum();
        let last = first + self.renderables[idx].desired_height(area.width) as usize;
        let current_top = self.scroll_offset;
        let current_bottom = current_top.saturating_add(area.height.saturating_sub(1) as usize);
        if first < current_top {
            self.scroll_offset = first;
        } else if last > current_bottom {
            self.scroll_offset = last.saturating_sub(area.height.saturating_sub(1) as usize);
        }
    }
}

/// A renderable that caches its desired height.
struct CachedRenderable {
    renderable: Box<dyn Renderable>,
    height: std::cell::Cell<Option<u16>>,
    last_width: std::cell::Cell<Option<u16>>,
}

impl CachedRenderable {
    fn new(renderable: impl Into<Box<dyn Renderable>>) -> Self {
        Self {
            renderable: renderable.into(),
            height: std::cell::Cell::new(None),
            last_width: std::cell::Cell::new(None),
        }
    }
}

impl Renderable for CachedRenderable {
    fn render(&self, area: Rect, buf: &mut Buffer) {
        self.renderable.render(area, buf);
    }
    fn desired_height(&self, width: u16) -> u16 {
        if self.last_width.get() != Some(width) {
            let height = self.renderable.desired_height(width);
            self.height.set(Some(height));
            self.last_width.set(Some(width));
        }
        self.height.get().unwrap_or(0)
    }
}

struct CellRenderable {
    cell: Arc<dyn HistoryCell>,
    style: Style,
}

impl Renderable for CellRenderable {
    fn render(&self, area: Rect, buf: &mut Buffer) {
        let p =
            Paragraph::new(Text::from(self.cell.transcript_lines(area.width))).style(self.style);
        p.render(area, buf);
    }

    fn desired_height(&self, width: u16) -> u16 {
        self.cell.desired_transcript_height(width)
    }
}

pub(crate) struct TranscriptOverlay {
    view: PagerView,
    cells: Vec<Arc<dyn HistoryCell>>,
    highlight_cell: Option<usize>,
    is_done: bool,
}

impl TranscriptOverlay {
    pub(crate) fn new(transcript_cells: Vec<Arc<dyn HistoryCell>>) -> Self {
        Self {
            view: PagerView::new(
                Self::render_cells(&transcript_cells, None),
                "T R A N S C R I P T".to_string(),
                usize::MAX,
            ),
            cells: transcript_cells,
            highlight_cell: None,
            is_done: false,
        }
    }

    fn render_cells(
        cells: &[Arc<dyn HistoryCell>],
        highlight_cell: Option<usize>,
    ) -> Vec<Box<dyn Renderable>> {
        cells
            .iter()
            .enumerate()
            .flat_map(|(i, c)| {
                let mut v: Vec<Box<dyn Renderable>> = Vec::new();
                let mut cell_renderable = if c.as_any().is::<UserHistoryCell>() {
                    Box::new(CachedRenderable::new(CellRenderable {
                        cell: c.clone(),
                        style: if highlight_cell == Some(i) {
                            user_message_style().reversed()
                        } else {
                            user_message_style()
                        },
                    })) as Box<dyn Renderable>
                } else {
                    Box::new(CachedRenderable::new(CellRenderable {
                        cell: c.clone(),
                        style: Style::default(),
                    })) as Box<dyn Renderable>
                };
                if !c.is_stream_continuation() && i > 0 {
                    cell_renderable = Box::new(InsetRenderable::new(
                        cell_renderable,
                        Insets::tlbr(1, 0, 0, 0),
                    ));
                }
                v.push(cell_renderable);
                v
            })
            .collect()
    }

    pub(crate) fn insert_cell(&mut self, cell: Arc<dyn HistoryCell>) {
        let follow_bottom = self.view.is_scrolled_to_bottom();
        self.cells.push(cell);
        self.view.renderables = Self::render_cells(&self.cells, self.highlight_cell);
        if follow_bottom {
            self.view.scroll_offset = usize::MAX;
        }
    }

    pub(crate) fn set_highlight_cell(&mut self, cell: Option<usize>) {
        self.highlight_cell = cell;
        self.view.renderables = Self::render_cells(&self.cells, self.highlight_cell);
        if let Some(idx) = self.highlight_cell {
            self.view.scroll_chunk_into_view(idx);
        }
    }

    fn render_hints(&self, area: Rect, buf: &mut Buffer) {
        let line1 = Rect::new(area.x, area.y, area.width, 1);
        let line2 = Rect::new(area.x, area.y.saturating_add(1), area.width, 1);
        render_key_hints(line1, buf, PAGER_KEY_HINTS);

        let mut pairs: Vec<(&[KeyBinding], &str)> =
            vec![(&[KEY_Q], "to quit"), (&[KEY_ESC], "to edit prev")];
        if self.highlight_cell.is_some() {
            pairs.push((&[KEY_ENTER], "to edit message"));
        }
        render_key_hints(line2, buf, &pairs);
    }

    pub(crate) fn render(&mut self, area: Rect, buf: &mut Buffer) {
        let top_h = area.height.saturating_sub(3);
        let top = Rect::new(area.x, area.y, area.width, top_h);
        let bottom = Rect::new(area.x, area.y + top_h, area.width, 3);
        self.view.render(top, buf);
        self.render_hints(bottom, buf);
    }
}

impl TranscriptOverlay {
    pub(crate) fn handle_event(&mut self, tui: &mut tui::Tui, event: TuiEvent) -> Result<()> {
        match event {
            TuiEvent::Key(key_event) => match key_event {
                e if KEY_Q.is_press(e) || KEY_CTRL_C.is_press(e) || KEY_CTRL_T.is_press(e) => {
                    self.is_done = true;
                    Ok(())
                }
                other => self.view.handle_key_event(tui, other),
            },
            TuiEvent::Draw => {
                tui.draw(u16::MAX, |frame| {
                    self.render(frame.area(), frame.buffer);
                })?;
                Ok(())
            }
            _ => Ok(()),
        }
    }
    pub(crate) fn is_done(&self) -> bool {
        self.is_done
    }
}

pub(crate) struct StaticOverlay {
    view: PagerView,
    is_done: bool,
}

impl StaticOverlay {
    pub(crate) fn with_title(lines: Vec<Line<'static>>, title: String) -> Self {
        let paragraph = Paragraph::new(Text::from(lines)).wrap(Wrap { trim: false });
        Self::with_renderables(vec![Box::new(CachedRenderable::new(paragraph))], title)
    }

    pub(crate) fn with_renderables(renderables: Vec<Box<dyn Renderable>>, title: String) -> Self {
        Self {
            view: PagerView::new(renderables, title, 0),
            is_done: false,
        }
    }

    fn render_hints(&self, area: Rect, buf: &mut Buffer) {
        let line1 = Rect::new(area.x, area.y, area.width, 1);
        let line2 = Rect::new(area.x, area.y.saturating_add(1), area.width, 1);
        render_key_hints(line1, buf, PAGER_KEY_HINTS);
        let pairs: Vec<(&[KeyBinding], &str)> = vec![(&[KEY_Q], "to quit")];
        render_key_hints(line2, buf, &pairs);
    }

    pub(crate) fn render(&mut self, area: Rect, buf: &mut Buffer) {
        let top_h = area.height.saturating_sub(3);
        let top = Rect::new(area.x, area.y, area.width, top_h);
        let bottom = Rect::new(area.x, area.y + top_h, area.width, 3);
        self.view.render(top, buf);
        self.render_hints(bottom, buf);
    }
}

impl StaticOverlay {
    pub(crate) fn handle_event(&mut self, tui: &mut tui::Tui, event: TuiEvent) -> Result<()> {
        match event {
            TuiEvent::Key(key_event) => match key_event {
                e if KEY_Q.is_press(e) || KEY_CTRL_C.is_press(e) => {
                    self.is_done = true;
                    Ok(())
                }
                other => self.view.handle_key_event(tui, other),
            },
            TuiEvent::Draw => {
                tui.draw(u16::MAX, |frame| {
                    self.render(frame.area(), frame.buffer);
                })?;
                Ok(())
            }
            _ => Ok(()),
        }
    }
    pub(crate) fn is_done(&self) -> bool {
        self.is_done
    }
}

fn render_offset_content(
    area: Rect,
    buf: &mut Buffer,
    renderable: &dyn Renderable,
    scroll_offset: u16,
) -> u16 {
    let height = renderable.desired_height(area.width);
    let mut tall_buf = Buffer::empty(Rect::new(
        0,
        0,
        area.width,
        height.min(area.height + scroll_offset),
    ));
    renderable.render(*tall_buf.area(), &mut tall_buf);
    let copy_height = area
        .height
        .min(tall_buf.area().height.saturating_sub(scroll_offset));
    for y in 0..copy_height {
        let src_y = y + scroll_offset;
        for x in 0..area.width {
            buf[(area.x + x, area.y + y)] = tall_buf[(x, src_y)].clone();
        }
    }

    copy_height
}

#[cfg(test)]
mod tests {
    use super::*;
    use codex_core::protocol::ReviewDecision;
    use insta::assert_snapshot;
    use std::collections::HashMap;
    use std::path::PathBuf;
    use std::sync::Arc;
    use std::time::Duration;

    use crate::exec_cell::CommandOutput;
    use crate::history_cell;
    use crate::history_cell::HistoryCell;
    use crate::history_cell::new_patch_event;
    use codex_core::protocol::FileChange;
    use codex_protocol::parse_command::ParsedCommand;
    use ratatui::Terminal;
    use ratatui::backend::TestBackend;
    use ratatui::text::Text;

    #[derive(Debug)]
    struct TestCell {
        lines: Vec<Line<'static>>,
    }

    impl crate::history_cell::HistoryCell for TestCell {
        fn display_lines(&self, _width: u16) -> Vec<Line<'static>> {
            self.lines.clone()
        }

        fn transcript_lines(&self, _width: u16) -> Vec<Line<'static>> {
            self.lines.clone()
        }
    }

    fn paragraph_block(label: &str, lines: usize) -> Box<dyn Renderable> {
        let text = Text::from(
            (0..lines)
                .map(|i| Line::from(format!("{label}{i}")))
                .collect::<Vec<_>>(),
        );
        Box::new(Paragraph::new(text)) as Box<dyn Renderable>
    }

    #[test]
    fn edit_prev_hint_is_visible() {
        let mut overlay = TranscriptOverlay::new(vec![Arc::new(TestCell {
            lines: vec![Line::from("hello")],
        })]);

        // Render into a small buffer and assert the backtrack hint is present
        let area = Rect::new(0, 0, 40, 10);
        let mut buf = Buffer::empty(area);
        overlay.render(area, &mut buf);

        // Flatten buffer to a string and check for the hint text
        let mut s = String::new();
        for y in area.y..area.bottom() {
            for x in area.x..area.right() {
                s.push(buf[(x, y)].symbol().chars().next().unwrap_or(' '));
            }
            s.push('\n');
        }
        assert!(
            s.contains("edit prev"),
            "expected 'edit prev' hint in overlay footer, got: {s:?}"
        );
    }

    #[test]
    fn transcript_overlay_snapshot_basic() {
        // Prepare a transcript overlay with a few lines
        let mut overlay = TranscriptOverlay::new(vec![
            Arc::new(TestCell {
                lines: vec![Line::from("alpha")],
            }),
            Arc::new(TestCell {
                lines: vec![Line::from("beta")],
            }),
            Arc::new(TestCell {
                lines: vec![Line::from("gamma")],
            }),
        ]);
        let mut term = Terminal::new(TestBackend::new(40, 10)).expect("term");
        term.draw(|f| overlay.render(f.area(), f.buffer_mut()))
            .expect("draw");
        assert_snapshot!(term.backend());
    }

    fn buffer_to_text(buf: &Buffer, area: Rect) -> String {
        let mut out = String::new();
        for y in area.y..area.bottom() {
            for x in area.x..area.right() {
                let symbol = buf[(x, y)].symbol();
                if symbol.is_empty() {
                    out.push(' ');
                } else {
                    out.push(symbol.chars().next().unwrap_or(' '));
                }
            }
            // Trim trailing spaces for stability.
            while out.ends_with(' ') {
                out.pop();
            }
            out.push('\n');
        }
        out
    }

    #[test]
    fn transcript_overlay_apply_patch_scroll_vt100_clears_previous_page() {
        let cwd = PathBuf::from("/repo");
        let mut cells: Vec<Arc<dyn HistoryCell>> = Vec::new();

        let mut approval_changes = HashMap::new();
        approval_changes.insert(
            PathBuf::from("foo.txt"),
            FileChange::Add {
                content: "hello\nworld\n".to_string(),
            },
        );
        let approval_cell: Arc<dyn HistoryCell> = Arc::new(new_patch_event(approval_changes, &cwd));
        cells.push(approval_cell);

        let mut apply_changes = HashMap::new();
        apply_changes.insert(
            PathBuf::from("foo.txt"),
            FileChange::Add {
                content: "hello\nworld\n".to_string(),
            },
        );
        let apply_begin_cell: Arc<dyn HistoryCell> = Arc::new(new_patch_event(apply_changes, &cwd));
        cells.push(apply_begin_cell);

        let apply_end_cell: Arc<dyn HistoryCell> =
            history_cell::new_approval_decision_cell(vec!["ls".into()], ReviewDecision::Approved)
                .into();
        cells.push(apply_end_cell);

        let mut exec_cell = crate::exec_cell::new_active_exec_command(
            "exec-1".into(),
            vec!["bash".into(), "-lc".into(), "ls".into()],
            vec![ParsedCommand::Unknown { cmd: "ls".into() }],
        );
        exec_cell.complete_call(
            "exec-1",
            CommandOutput {
                exit_code: 0,
                aggregated_output: "src\nREADME.md\n".into(),
                formatted_output: "src\nREADME.md\n".into(),
            },
            Duration::from_millis(420),
        );
        let exec_cell: Arc<dyn HistoryCell> = Arc::new(exec_cell);
        cells.push(exec_cell);

        let mut overlay = TranscriptOverlay::new(cells);
        let area = Rect::new(0, 0, 80, 12);
        let mut buf = Buffer::empty(area);

        overlay.render(area, &mut buf);
        overlay.view.scroll_offset = 0;
        overlay.render(area, &mut buf);

        let snapshot = buffer_to_text(&buf, area);
        assert_snapshot!("transcript_overlay_apply_patch_scroll_vt100", snapshot);
    }

    #[test]
    fn transcript_overlay_keeps_scroll_pinned_at_bottom() {
        let mut overlay = TranscriptOverlay::new(
            (0..20)
                .map(|i| {
                    Arc::new(TestCell {
                        lines: vec![Line::from(format!("line{i}"))],
                    }) as Arc<dyn HistoryCell>
                })
                .collect(),
        );
        let mut term = Terminal::new(TestBackend::new(40, 12)).expect("term");
        term.draw(|f| overlay.render(f.area(), f.buffer_mut()))
            .expect("draw");

        assert!(
            overlay.view.is_scrolled_to_bottom(),
            "expected initial render to leave view at bottom"
        );

        overlay.insert_cell(Arc::new(TestCell {
            lines: vec!["tail".into()],
        }));

        assert_eq!(overlay.view.scroll_offset, usize::MAX);
    }

    #[test]
    fn transcript_overlay_preserves_manual_scroll_position() {
        let mut overlay = TranscriptOverlay::new(
            (0..20)
                .map(|i| {
                    Arc::new(TestCell {
                        lines: vec![Line::from(format!("line{i}"))],
                    }) as Arc<dyn HistoryCell>
                })
                .collect(),
        );
        let mut term = Terminal::new(TestBackend::new(40, 12)).expect("term");
        term.draw(|f| overlay.render(f.area(), f.buffer_mut()))
            .expect("draw");

        overlay.view.scroll_offset = 0;

        overlay.insert_cell(Arc::new(TestCell {
            lines: vec!["tail".into()],
        }));

        assert_eq!(overlay.view.scroll_offset, 0);
    }

    #[test]
    fn static_overlay_snapshot_basic() {
        // Prepare a static overlay with a few lines and a title
        let mut overlay = StaticOverlay::with_title(
            vec!["one".into(), "two".into(), "three".into()],
            "S T A T I C".to_string(),
        );
        let mut term = Terminal::new(TestBackend::new(40, 10)).expect("term");
        term.draw(|f| overlay.render(f.area(), f.buffer_mut()))
            .expect("draw");
        assert_snapshot!(term.backend());
    }

    #[test]
    fn static_overlay_wraps_long_lines() {
        let mut overlay = StaticOverlay::with_title(
            vec!["a very long line that should wrap when rendered within a narrow pager overlay width".into()],
            "S T A T I C".to_string(),
        );
        let mut term = Terminal::new(TestBackend::new(24, 8)).expect("term");
        term.draw(|f| overlay.render(f.area(), f.buffer_mut()))
            .expect("draw");
        assert_snapshot!(term.backend());
    }

    #[test]
    fn pager_view_content_height_counts_renderables() {
        let pv = PagerView::new(
            vec![paragraph_block("a", 2), paragraph_block("b", 3)],
            "T".to_string(),
            0,
        );

        assert_eq!(pv.content_height(80), 5);
    }

    #[test]
    fn pager_view_ensure_chunk_visible_scrolls_down_when_needed() {
        let mut pv = PagerView::new(
            vec![
                paragraph_block("a", 1),
                paragraph_block("b", 3),
                paragraph_block("c", 3),
            ],
            "T".to_string(),
            0,
        );
        let area = Rect::new(0, 0, 20, 8);

        pv.scroll_offset = 0;
        let content_area = pv.content_area(area);
        pv.ensure_chunk_visible(2, content_area);

        let mut buf = Buffer::empty(area);
        pv.render(area, &mut buf);
        let rendered = buffer_to_text(&buf, area);

        assert!(
            rendered.contains("c0"),
            "expected chunk top in view: {rendered:?}"
        );
        assert!(
            rendered.contains("c1"),
            "expected chunk middle in view: {rendered:?}"
        );
        assert!(
            rendered.contains("c2"),
            "expected chunk bottom in view: {rendered:?}"
        );
    }

    #[test]
    fn pager_view_ensure_chunk_visible_scrolls_up_when_needed() {
        let mut pv = PagerView::new(
            vec![
                paragraph_block("a", 2),
                paragraph_block("b", 3),
                paragraph_block("c", 3),
            ],
            "T".to_string(),
            0,
        );
        let area = Rect::new(0, 0, 20, 3);

        pv.scroll_offset = 6;
        pv.ensure_chunk_visible(0, area);

        assert_eq!(pv.scroll_offset, 0);
    }

    #[test]
    fn pager_view_is_scrolled_to_bottom_accounts_for_wrapped_height() {
        let mut pv = PagerView::new(vec![paragraph_block("a", 10)], "T".to_string(), 0);
        let area = Rect::new(0, 0, 20, 8);
        let mut buf = Buffer::empty(area);

        pv.render(area, &mut buf);

        assert!(
            !pv.is_scrolled_to_bottom(),
            "expected view to report not at bottom when offset < max"
        );

        pv.scroll_offset = usize::MAX;
        pv.render(area, &mut buf);

        assert!(
            pv.is_scrolled_to_bottom(),
            "expected view to report at bottom after scrolling to end"
        );
    }
}