1 files changed, 191 insertions, 0 deletions
diff --git a/src/ui/scrollbar.rs b/src/ui/scrollbar.rs
new file mode 100644
index 00000000..34e739d0
--- /dev/null
+++ b/src/ui/scrollbar.rs
@@ -0,0 +1,191 @@
+use ratatui::{
+    layout::Rect,
+    style::{Color, Style},
+    Frame,
+};
+
+use crate::app::AppState;
+use crate::layout::PaneInfo;
+
+pub(crate) fn pane_scrollbar_rect(info: &PaneInfo) -> Option<Rect> {
+    info.scrollbar_rect
+}
+
+pub(crate) fn release_notes_scrollbar_rect(
+    body: Rect,
+    metrics: crate::pane::ScrollMetrics,
+) -> Option<Rect> {
+    (should_show_scrollbar(metrics) && body.width > 1).then_some(Rect::new(
+        body.x + body.width - 1,
+        body.y,
+        1,
+        body.height,
+    ))
+}
+
+pub(crate) fn should_show_scrollbar(metrics: crate::pane::ScrollMetrics) -> bool {
+    metrics.max_offset_from_bottom > 0
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct ScrollbarThumb {
+    pub top: u16,
+    pub len: u16,
+}
+
+pub(crate) fn scrollbar_thumb(
+    metrics: crate::pane::ScrollMetrics,
+    track: Rect,
+) -> Option<ScrollbarThumb> {
+    if metrics.max_offset_from_bottom == 0 || track.height == 0 {
+        return None;
+    }
+
+    let track_height = track.height as usize;
+    let total_rows = metrics.max_offset_from_bottom + metrics.viewport_rows;
+    if total_rows == 0 {
+        return None;
+    }
+
+    let thumb_len = ((metrics.viewport_rows * track_height) as f32 / total_rows as f32)
+        .round()
+        .max(1.0)
+        .min(track_height as f32) as usize;
+    let max_thumb_top = track_height.saturating_sub(thumb_len);
+    let scrolled_from_top = metrics
+        .max_offset_from_bottom
+        .saturating_sub(metrics.offset_from_bottom);
+    let thumb_top = if max_thumb_top == 0 || metrics.max_offset_from_bottom == 0 {
+        0
+    } else {
+        ((scrolled_from_top * max_thumb_top) as f32 / metrics.max_offset_from_bottom as f32)
+            .round()
+            .clamp(0.0, max_thumb_top as f32) as usize
+    };
+
+    Some(ScrollbarThumb {
+        top: track.y + thumb_top as u16,
+        len: thumb_len as u16,
+    })
+}
+
+pub(crate) fn scrollbar_thumb_grab_offset(
+    metrics: crate::pane::ScrollMetrics,
+    track: Rect,
+    row: u16,
+) -> Option<u16> {
+    let thumb = scrollbar_thumb(metrics, track)?;
+    (row >= thumb.top && row < thumb.top + thumb.len).then_some(row - thumb.top)
+}
+
+fn scrollbar_offset_from_thumb_top(
+    metrics: crate::pane::ScrollMetrics,
+    track: Rect,
+    thumb_top: usize,
+) -> usize {
+    if metrics.max_offset_from_bottom == 0 {
+        return 0;
+    }
+
+    let thumb_len = scrollbar_thumb(metrics, track)
+        .map(|thumb| thumb.len as usize)
+        .unwrap_or(1);
+    let max_thumb_top = track.height as usize - thumb_len.min(track.height as usize);
+    if max_thumb_top == 0 {
+        return 0;
+    }
+
+    let desired_top = thumb_top.min(max_thumb_top);
+    let scrolled_from_top = ((desired_top * metrics.max_offset_from_bottom) as f32
+        / max_thumb_top as f32)
+        .round() as usize;
+    metrics
+        .max_offset_from_bottom
+        .saturating_sub(scrolled_from_top)
+}
+
+pub(crate) fn scrollbar_offset_from_row(
+    metrics: crate::pane::ScrollMetrics,
+    track: Rect,
+    row: u16,
+) -> usize {
+    let thumb = match scrollbar_thumb(metrics, track) {
+        Some(thumb) => thumb,
+        None => return 0,
+    };
+    let clamped_row = row.clamp(track.y, track.y + track.height.saturating_sub(1));
+    let row_offset = clamped_row.saturating_sub(track.y) as usize;
+    let thumb_center = (thumb.len as usize) / 2;
+    let desired_top = row_offset.saturating_sub(thumb_center);
+    scrollbar_offset_from_thumb_top(metrics, track, desired_top)
+}
+
+pub(crate) fn scrollbar_offset_from_drag_row(
+    metrics: crate::pane::ScrollMetrics,
+    track: Rect,
+    row: u16,
+    grab_row_offset: u16,
+) -> usize {
+    let clamped_row = row.clamp(track.y, track.y + track.height.saturating_sub(1));
+    let row_offset = clamped_row.saturating_sub(track.y) as usize;
+    let desired_top = row_offset.saturating_sub(grab_row_offset as usize);
+    scrollbar_offset_from_thumb_top(metrics, track, desired_top)
+}
+
+pub(super) fn render_scrollbar(
+    frame: &mut Frame,
+    metrics: crate::pane::ScrollMetrics,
+    track: Rect,
+    track_color: Color,
+    thumb_color: Color,
+    thumb_symbol: &str,
+) {
+    if metrics.max_offset_from_bottom == 0 {
+        return;
+    }
+
+    let Some(thumb) = scrollbar_thumb(metrics, track) else {
+        return;
+    };
+
+    let buf = frame.buffer_mut();
+    for y in track.y..track.y + track.height {
+        let cell = &mut buf[(track.x, y)];
+        cell.set_symbol("▕");
+        cell.set_style(Style::default().fg(track_color));
+    }
+    for y in thumb.top..thumb.top + thumb.len {
+        let cell = &mut buf[(track.x, y)];
+        cell.set_symbol(thumb_symbol);
+        cell.set_style(Style::default().fg(thumb_color));
+    }
+}
+
+pub(super) fn render_pane_scrollbar(
+    app: &AppState,
+    frame: &mut Frame,
+    info: &PaneInfo,
+    rt: &crate::pane::PaneRuntime,
+) {
+    let Some(metrics) = rt.scroll_metrics() else {
+        return;
+    };
+    let Some(track) = pane_scrollbar_rect(info) else {
+        return;
+    };
+
+    let (track_color, thumb_color, thumb_symbol) = if info.is_focused {
+        (app.palette.overlay0, app.palette.overlay1, "▐")
+    } else {
+        (app.palette.surface_dim, app.palette.overlay0, "▕")
+    };
+
+    render_scrollbar(
+        frame,
+        metrics,
+        track,
+        track_color,
+        thumb_color,
+        thumb_symbol,
+    );
+}