refactor email viewer app

maildir_gtd/actions/show_message.py

@@ -0,0 +1,22 @@
+from textual.widgets import Static
+import subprocess
+
+def show_message(app, message_id: int) -> None:
+    """Fetch and display the email message by ID."""
+    app.query_one("#main_content", Static).loading = True
+    try:
+        result = subprocess.run(
+            ["himalaya", "message", "read", str(message_id)],
+            capture_output=True,
+            text=True
+        )
+        if result.returncode == 0:
+            # Render the email content as Markdown
+            from rich.markdown import Markdown
+            markdown_content = Markdown(result.stdout, justify=True)
+            app.query_one("#main_content", Static).loading = False
+            app.query_one("#main_content", Static).update(markdown_content)
+        else:
+            app.query_one("#main_content", Static).update(f"Failed to fetch message {message_id}.")
+    except Exception as e:
+        app.query_one("#main_content", Static).update(f"Error: {e}")