Enhance TUI scrolling: add viewport dimension tracking, autoscroll logic, and message line calculation. Refactor related components for dynamic rendering.

crates/owlen-tui/src/chat_app.rs

@@ -64,6 +64,8 @@ pub struct ChatApp {
     pub selected_provider_index: usize,   // Index into the available_providers list
     pub selected_model: Option<usize>,    // Index into the *filtered* models list
     scroll: usize,
+    viewport_height: usize, // Track the height of the messages viewport
+    content_width: usize,   // Track the content width for line wrapping calculations
     session_tx: mpsc::UnboundedSender<SessionEvent>,
     streaming: HashSet<Uuid>,
     textarea: TextArea<'static>, // Advanced text input widget
@@ -86,6 +88,8 @@ impl ChatApp {
             selected_provider_index: 0,
             selected_model: None,
             scroll: 0,
+            viewport_height: 10, // Default viewport height, will be updated during rendering
+            content_width: 80,   // Default content width, will be updated during rendering
             session_tx,
             streaming: std::collections::HashSet::new(),
             textarea,
@@ -396,9 +400,9 @@ impl ChatApp {
                 message_id,
                 response,
             } => {
-                let at_bottom = self.scroll == 0;
+                let was_at_bottom = self.is_at_bottom();
                 self.controller.apply_stream_chunk(message_id, &response)?;
-                if at_bottom {
+                if was_at_bottom {
                     self.scroll_to_bottom();
                 }
                 if response.is_final {
@@ -559,8 +563,52 @@ impl ChatApp {
         }
     }
 
+    pub fn set_viewport_dimensions(&mut self, height: usize, content_width: usize) {
+        self.viewport_height = height;
+        self.content_width = content_width;
+    }
+
+    fn is_at_bottom(&self) -> bool {
+        let total_lines = self.calculate_total_content_lines();
+        let max_scroll = total_lines.saturating_sub(self.viewport_height);
+
+        // We're at bottom if scroll is at or near the maximum scroll position
+        self.scroll >= max_scroll || total_lines <= self.viewport_height
+    }
+
+    fn calculate_total_content_lines(&self) -> usize {
+        let conversation = self.controller.conversation();
+        let mut formatter = self.controller.formatter().clone();
+
+        // Set the wrap width to match the current display
+        formatter.set_wrap_width(self.content_width);
+
+        let mut total_lines = 0;
+        for (message_index, message) in conversation.messages.iter().enumerate() {
+            let formatted = formatter.format_message(message);
+            let show_role_labels = formatter.show_role_labels();
+
+            // Add role label line if enabled
+            if show_role_labels {
+                total_lines += 1;
+            }
+
+            // Add message content lines
+            total_lines += formatted.len();
+
+            // Add empty line after each message, except the last one
+            if message_index < conversation.messages.len() - 1 {
+                total_lines += 1;
+            }
+        }
+
+        // Minimum 1 line for empty state
+        total_lines.max(1)
+    }
+
     fn scroll_to_bottom(&mut self) {
-        self.scroll = 0;
+        let total_lines = self.calculate_total_content_lines();
+        self.scroll = total_lines.saturating_sub(self.viewport_height);
     }
 
     fn spawn_stream(&mut self, message_id: Uuid, mut stream: owlen_core::provider::ChatStream) {

crates/owlen-tui/src/ui.rs

@@ -10,7 +10,7 @@ use unicode_width::UnicodeWidthStr;
 use crate::chat_app::{ChatApp, InputMode};
 use owlen_core::types::Role;
 
-pub fn render_chat(frame: &mut Frame<'_>, app: &ChatApp) {
+pub fn render_chat(frame: &mut Frame<'_>, app: &mut ChatApp) {
     // Calculate dynamic input height based on textarea content
     let available_width = frame.area().width;
     let input_height = if matches!(app.mode(), InputMode::Editing) {
@@ -345,12 +345,16 @@ fn render_header(frame: &mut Frame<'_>, area: Rect, app: &ChatApp) {
     frame.render_widget(paragraph, inner_area);
 }
 
-fn render_messages(frame: &mut Frame<'_>, area: Rect, app: &ChatApp) {
+fn render_messages(frame: &mut Frame<'_>, area: Rect, app: &mut ChatApp) {
+    // Calculate viewport dimensions for autoscroll calculations
+    let viewport_height = area.height.saturating_sub(2) as usize; // subtract borders
+    let content_width = area.width.saturating_sub(4).max(20);
+    app.set_viewport_dimensions(viewport_height, usize::from(content_width));
+
     let conversation = app.conversation();
     let mut formatter = app.formatter().clone();
 
     // Reserve space for borders and the message indent so text fits within the block
-    let content_width = area.width.saturating_sub(4).max(20);
     formatter.set_wrap_width(usize::from(content_width));
 
     let mut lines: Vec<Line> = Vec::new();