Kigi-CLI/crates/codegen/kigi-tui/src/views/overlay_list.rs

//! Shared prompt-area list overlay: accent bar, bold title, and a
//! scrollable single-line row list with a cursor.
//!
//! One source of truth for the row geometry shared by `/rewind`'s picker
//! phase and `/jump` across their render, hit-test, and height paths. Row
//! *content* stays with the caller (a closure); this owns chrome, cursor
//! styling, and the scroll window.

use ratatui::buffer::Buffer;
use ratatui::layout::Rect;
use ratatui::style::{Color, Modifier, Style};
use ratatui::text::{Line, Span};

use crate::theme::Theme;

/// Rows shown before the list scrolls (matches the historical picker cap).
const MAX_ROWS: usize = 15;

/// List geometry: row count + cursor position. Construct per call; all
/// methods derive the same scroll window from these two fields, so the
/// render, hit-test, and height paths cannot drift.
pub struct ListOverlay {
    pub len: usize,
    pub selected: usize,
}

/// Per-row style context handed to the row-content closure.
pub struct RowCtx {
    pub is_cursor: bool,
    /// Resolved row background (cursor rows get the visual-selection bg).
    pub row_bg: Color,
    pub content_width: u16,
}

impl ListOverlay {
    /// Overlay height: title + rows (≤ [`MAX_ROWS`]), capped at 60% of the
    /// screen, plus one padding row.
    pub fn height(&self, screen_h: u16) -> u16 {
        let rows = self.len.min(MAX_ROWS) as u16;
        let h = 2 + rows;
        let cap = (screen_h as u32 * 60 / 100).max(6) as u16;
        h.min(cap) + 1
    }

    /// Rows that fit in `area` (title + padding excluded).
    fn visible_rows(area: Rect) -> usize {
        area.height.saturating_sub(3) as usize
    }

    /// First visible row index (keeps the cursor inside the window).
    fn scroll_offset(&self, visible_rows: usize) -> usize {
        if visible_rows > 0 && self.selected >= visible_rows {
            self.selected - visible_rows + 1
        } else {
            0
        }
    }

    /// Row index under a screen position, or `None` off the rows.
    pub fn row_at(&self, area: Rect, col: u16, row: u16) -> Option<usize> {
        if area.height == 0 || area.width < 10 {
            return None;
        }
        if col < area.x || col >= area.x + area.width {
            return None;
        }
        if row < area.y || row >= area.y + area.height {
            return None;
        }
        let first = area.y + 2;
        if row < first {
            return None;
        }
        let visible_rows = Self::visible_rows(area);
        let rel = (row - first) as usize;
        if rel >= visible_rows {
            return None;
        }
        let idx = self.scroll_offset(visible_rows) + rel;
        (idx < self.len).then_some(idx)
    }

    /// Render the overlay: bg fill, accent bar, title, then the visible
    /// window of rows. `row_line(idx, ctx)` produces each row's content;
    /// cursor/row backgrounds are painted here. Applies the standard
    /// unfocus dim, so callers must not blend again.
    pub fn render(
        &self,
        buf: &mut Buffer,
        area: Rect,
        title: &str,
        focused: bool,
        mut row_line: impl FnMut(usize, &RowCtx) -> Line<'static>,
    ) {
        if area.height == 0 || area.width < 10 {
            return;
        }

        let theme = Theme::current();
        let bg = theme.bg_light;
        buf.set_style(area, Style::default().bg(bg));

        let accent_style = Style::default().fg(theme.accent_user);
        for row in area.y..area.y + area.height {
            if let Some(cell) = buf.cell_mut((area.x, row)) {
                cell.set_symbol(crate::glyphs::accent_bar());
                cell.set_style(accent_style);
            }
        }

        let content_x = area.x + 3;
        let content_w = area.width.saturating_sub(5);

        let title_style = Style::default()
            .fg(theme.accent_user)
            .add_modifier(Modifier::BOLD);
        let mut y = area.y + 1;
        buf.set_line(
            content_x,
            y,
            &Line::from(Span::styled(title.to_string(), title_style)),
            content_w,
        );
        y += 1;

        let visible_rows = Self::visible_rows(area);
        let scroll_offset = self.scroll_offset(visible_rows);

        for i in (scroll_offset..self.len).take(visible_rows) {
            if y >= area.y + area.height {
                break;
            }
            let is_cursor = i == self.selected;
            let row_bg = if is_cursor && focused {
                theme.bg_visual
            } else {
                bg
            };
            let row_rect = Rect {
                x: content_x.saturating_sub(1),
                y,
                width: content_w + 2,
                height: 1,
            };
            buf.set_style(row_rect, Style::default().bg(row_bg));

            let ctx = RowCtx {
                is_cursor,
                row_bg,
                content_width: content_w,
            };
            let line = row_line(i, &ctx);
            buf.set_line(content_x, y, &line, content_w);
            y += 1;
        }

        // Unfocus dim: blend foregrounds toward the panel bg so the overlay
        // recedes when the prompt area is unfocused (prompt_widget pattern).
        if !focused {
            crate::render::color::blend_area(buf, area, Some((bg, 0.66)), None);
        }
    }
}

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

    fn area() -> Rect {
        Rect {
            x: 0,
            y: 0,
            width: 40,
            height: 10,
        }
    }

    #[test]
    fn row_at_maps_rows_and_rejects_chrome() {
        let list = ListOverlay {
            len: 3,
            selected: 0,
        };
        // Title at y+1; rows start at y+2.
        assert_eq!(list.row_at(area(), 5, 1), None);
        assert_eq!(list.row_at(area(), 5, 2), Some(0));
        assert_eq!(list.row_at(area(), 5, 4), Some(2));
        // Past the last row.
        assert_eq!(list.row_at(area(), 5, 5), None);
        // Outside horizontally.
        assert_eq!(list.row_at(area(), 99, 2), None);
    }

    #[test]
    fn row_at_respects_scroll_window() {
        // 20 rows, 7 visible (height 10 - 3), cursor at the end: the window
        // starts at 13 so the cursor stays visible.
        let list = ListOverlay {
            len: 20,
            selected: 19,
        };
        assert_eq!(list.row_at(area(), 5, 2), Some(13));
        assert_eq!(list.row_at(area(), 5, 8), Some(19));
    }

    #[test]
    fn height_caps_at_max_rows_and_screen_fraction() {
        let two = ListOverlay {
            len: 2,
            selected: 0,
        };
        // title + 2 rows + padding
        assert_eq!(two.height(40), 5);
        let many = ListOverlay {
            len: 30,
            selected: 0,
        };
        // 15-row cap
        assert_eq!(many.height(40), 18);
        // 60% screen cap
        assert_eq!(many.height(12), 8);
    }
}