Gracefully handle missing tarball in Gradio UI

app.py

@@ -1,7 +1,7 @@
 import os
 from pathlib import Path
 from threading import Event
-from typing import Dict, Tuple
+from typing import Dict, Optional, Tuple
 
 import gradio as gr
 
@@ -19,7 +19,7 @@ def ensure_refresh() -> None:
         manager.trigger_refresh()
 
 
-def format_status(status: Dict) -> Tuple[Dict, str]:
+def format_status(status: Dict, notice: Optional[str] = None) -> Tuple[Dict, str]:
     """Return status JSON and a markdown summary."""
     latest = status.get("latest_state", {})
     lines = [
@@ -40,32 +40,47 @@ def format_status(status: Dict) -> Tuple[Dict, str]:
     else:
         lines.append("- No cycle downloaded yet.")
     lines.append("\nUse **Trigger Refresh** to fetch a newer cycle when available.")
+    if notice:
+        lines.append(f"\n⚠️ {notice}")
     return status, "\n".join(lines)
 
 
-def get_status() -> Tuple[Dict, str]:
+def get_status() -> Tuple[Dict, str, Optional[str]]:
     ensure_refresh()
     status = manager.status()
-    return format_status(status)
+    status_dict, status_text = format_status(status)
+    return status_dict, status_text, None
 
 
-def trigger_refresh() -> Tuple[Dict, str]:
+def trigger_refresh() -> Tuple[Dict, str, Optional[str]]:
     ensure_refresh()
     manager.trigger_refresh()
     status = manager.status()
-    return format_status(status)
+    status_dict, status_text = format_status(status)
+    return status_dict, status_text, None
 
 
-def download_tarball() -> str:
+def download_tarball() -> Tuple[Dict, str, Optional[str]]:
     ensure_refresh()
-    state = manager.downloader.current_state()
-    if not state or "tarball" not in state:
-        raise gr.Error("Wave dataset not available yet. Try triggering a refresh.")
+    status = manager.status()
+    state = status.get("latest_state", {})
+
+    tarball_rel = state.get("tarball")
+    if not tarball_rel:
+        status_dict, status_text = format_status(
+            status, "Wave dataset not available yet. Trigger a refresh and try again."
+        )
+        return status_dict, status_text, None
 
-    tarball_path = DATA_ROOT / state["tarball"]
+    tarball_path = DATA_ROOT / tarball_rel
     if not tarball_path.exists():
-        raise gr.Error("Tarball missing on disk. Trigger a refresh and try again.")
-    return str(tarball_path)
+        status_dict, status_text = format_status(
+            status, "Tarball missing on disk. Trigger a refresh and try again."
+        )
+        return status_dict, status_text, None
+
+    status_dict, status_text = format_status(status)
+    return status_dict, status_text, str(tarball_path)
 
 
 with gr.Blocks(title="GFES Wave 0 Downloader") as demo:
@@ -86,9 +101,9 @@ with gr.Blocks(title="GFES Wave 0 Downloader") as demo:
         refresh_button = gr.Button("Trigger Refresh", variant="secondary")
         download_button = gr.DownloadButton("Download Latest Tarball", variant="primary")
 
-    demo.load(get_status, outputs=[status_json, status_md])
-    refresh_button.click(trigger_refresh, outputs=[status_json, status_md])
-    download_button.click(download_tarball, outputs=download_button)
+    demo.load(get_status, outputs=[status_json, status_md, download_button])
+    refresh_button.click(trigger_refresh, outputs=[status_json, status_md, download_button])
+    download_button.click(download_tarball, outputs=[status_json, status_md, download_button])
 
 demo.queue()