ced/src/ui/central_panel/line_numbers.rs

use eframe::egui;

thread_local! {
    static VISUAL_LINE_MAPPING_CACHE: std::cell::RefCell<Option<(String, f32, Vec<Option<usize>>)>> = std::cell::RefCell::new(None);
}

pub(super) fn get_visual_line_mapping(
    ui: &egui::Ui,
    content: &str,
    available_width: f32,
    font_size: f32,
) -> Vec<Option<usize>> {
    let should_recalculate = VISUAL_LINE_MAPPING_CACHE.with(|cache| {
        if let Some((cached_content, cached_width, _)) = cache.borrow().as_ref() {
            content != cached_content || available_width != *cached_width
        } else {
            true
        }
    });

    if should_recalculate {
        let visual_lines = calculate_visual_line_mapping(ui, content, available_width, font_size);
        VISUAL_LINE_MAPPING_CACHE.with(|cache| {
            *cache.borrow_mut() = Some((content.to_owned(), available_width, visual_lines));
        });
    }

    VISUAL_LINE_MAPPING_CACHE.with(|cache| {
        cache
            .borrow()
            .as_ref()
            .map(|(_, _, mapping)| mapping.clone())
            .unwrap_or_default()
    })
}

fn calculate_visual_line_mapping(
    ui: &egui::Ui,
    content: &str,
    available_width: f32,
    font_size: f32,
) -> Vec<Option<usize>> {
    let mut visual_lines = Vec::new();
    let font_id = egui::FontId::monospace(font_size);

    for (line_num, line) in content.lines().enumerate() {
        if line.is_empty() {
            visual_lines.push(Some(line_num + 1));
            continue;
        }

        let galley = ui.fonts(|fonts| {
            fonts.layout(
                line.to_string(),
                font_id.clone(),
                egui::Color32::WHITE,
                available_width,
            )
        });

        let wrapped_line_count = galley.rows.len().max(1);

        visual_lines.push(Some(line_num + 1));

        for _ in 1..wrapped_line_count {
            visual_lines.push(None);
        }
    }

    visual_lines
}

pub(super) fn render_line_numbers(
    ui: &mut egui::Ui,
    line_count: usize,
    visual_line_mapping: &[Option<usize>],
    line_number_width: f32,
    word_wrap: bool,
    font_size: f32,
) {
    ui.vertical(|ui| {
        ui.set_width(line_number_width);
        ui.spacing_mut().item_spacing.y = 0.0;

        let text_color = ui.visuals().weak_text_color();
        let bg_color = ui.visuals().extreme_bg_color;

        let line_numbers_rect = ui.available_rect_before_wrap();
        ui.painter().rect_filled(line_numbers_rect, 0.0, bg_color);

        let font_id = egui::FontId::monospace(font_size);
        let line_count_width = line_count.to_string().len();

        if word_wrap {
            for line_number_opt in visual_line_mapping {
                let text = if let Some(line_number) = line_number_opt {
                    format!("{:>width$}", line_number, width = line_count_width)
                } else {
                    " ".repeat(line_count_width)
                };
                ui.label(
                    egui::RichText::new(text)
                        .font(font_id.clone())
                        .color(text_color),
                );
            }
        } else {
            for i in 1..=line_count {
                let text = format!("{:>width$}", i, width = line_count_width);
                ui.label(
                    egui::RichText::new(text)
                        .font(font_id.clone())
                        .color(text_color),
                );
            }
        }
    });
}