refactor email viewer app

maildir_gtd/actions/previous.py

@@ -0,0 +1,26 @@
+from textual.widgets import Static
+import subprocess
+
+def action_previous(app) -> None:
+    """Show the previous email message by finding the next lower ID from the list of envelope IDs."""
+    try:
+        result = subprocess.run(
+            ["himalaya", "envelope", "list", "-o", "json"],
+            capture_output=True,
+            text=True
+        )
+        if result.returncode == 0:
+            import json
+            envelopes = json.loads(result.stdout)
+            ids = sorted((int(envelope['id']) for envelope in envelopes), reverse=True)
+            for envelope_id in ids:
+                if envelope_id < app.current_message_id:
+                    app.current_message_id = envelope_id
+                    app.show_message(app.current_message_id)
+                    app.show_status(f"Showing previous message: {app.current_message_id}")
+                    return
+            app.show_status("No older messages found.", severity="warning")
+        else:
+            app.show_status("Failed to fetch envelope list.", severity="error")
+    except Exception as e:
+        app.show_status(f"Error: {e}", severity="error")