feat(tui): Add CSV export format

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - All metrics include `module` and `topic` labels
   - Health check endpoints (`/health`, `/healthz`) for Kubernetes probes
   - Metrics: read/write counts, backlog, pending seconds, rates
+- **buswatch-tui**: CSV export format (press `E` for CSV, `e` for JSON)
 
 ## [0.1.0] - 2025-12-21
 

buswatch-tui/src/app.rs

@@ -533,4 +533,65 @@ impl App {
 
         Ok(())
     }
+
+    /// Export current state to a CSV file.
+    pub fn export_state_csv(&self, path: &std::path::Path) -> anyhow::Result<()> {
+        use crate::data::duration::format_duration;
+        use std::io::Write;
+
+        let Some(ref data) = self.data else {
+            anyhow::bail!("No data to export");
+        };
+
+        let mut output = String::new();
+
+        // CSV header
+        output.push_str("Module,Topic,Type,Count,Backlog,Pending,Health\n");
+
+        // Write rows for each module's topics
+        for module in &data.modules {
+            // Read topics
+            for read in &module.reads {
+                output.push_str(&format!(
+                    "{},{},{},{},{},{},{}\n",
+                    csv_escape(&module.name),
+                    csv_escape(&read.topic),
+                    "Read",
+                    read.read,
+                    read.unread.map(|u| u.to_string()).unwrap_or_default(),
+                    read.pending_for.map(format_duration).unwrap_or_default(),
+                    read.status.symbol()
+                ));
+            }
+
+            // Write topics
+            for write in &module.writes {
+                output.push_str(&format!(
+                    "{},{},{},{},{},{},{}\n",
+                    csv_escape(&module.name),
+                    csv_escape(&write.topic),
+                    "Write",
+                    write.written,
+                    "", // writes don't have backlog
+                    write.pending_for.map(format_duration).unwrap_or_default(),
+                    write.status.symbol()
+                ));
+            }
+        }
+
+        let mut file = std::fs::File::create(path)?;
+        file.write_all(output.as_bytes())?;
+
+        Ok(())
+    }
+}
+
+/// Escape a string for CSV format.
+/// Wraps in quotes if the string contains comma, quote, or newline.
+fn csv_escape(s: &str) -> String {
+    if s.contains(',') || s.contains('"') || s.contains('\n') {
+        format!("\"{}\"", s.replace('"', "\"\""))
+    } else {
+        s.to_string()
+    }
 }

buswatch-tui/src/events.rs

@@ -127,7 +127,7 @@ pub fn handle_key_event(app: &mut App, key: KeyEvent) {
             }
         }
 
-        // Export
+        // Export JSON
         KeyCode::Char('e') => {
             let export_path = std::path::PathBuf::from("monitor_export.json");
             match app.export_state(&export_path) {
@@ -140,6 +140,19 @@ pub fn handle_key_event(app: &mut App, key: KeyEvent) {
             }
         }
 
+        // Export CSV
+        KeyCode::Char('E') => {
+            let export_path = std::path::PathBuf::from("monitor_export.csv");
+            match app.export_state_csv(&export_path) {
+                Ok(()) => {
+                    app.set_status_message(format!("Exported to {}", export_path.display()));
+                }
+                Err(e) => {
+                    app.set_status_message(format!("Export failed: {}", e));
+                }
+            }
+        }
+
         _ => {}
     }
 }

buswatch-tui/src/ui/common.rs

@@ -225,6 +225,7 @@ pub fn render_help(frame: &mut Frame, app: &App, area: Rect) {
         )]),
         Line::from("  r         Reload data"),
         Line::from("  e         Export to JSON"),
+        Line::from("  E         Export to CSV"),
         Line::from("  q         Quit"),
         Line::from(""),
         Line::from(vec![Span::styled(