Update app.py

app.py

@@ -1,11 +1,10 @@
 """
-Radar Data Downloader with Full Station Selector via Gradio
-============================================================
+Radar Data Downloader with Two-Step Workflow via Gradio Blocks
+===============================================================
 
-This script downloads the latest radar data file from public AWS S3 buckets.
-It now dynamically fetches the complete list of radar sites via an API (here,
-we use NOAA’s public radar stations endpoint as an example) so you can select from
-all available radar sites.
+Step 1: Click "Fetch Stations" to dynamically retrieve the full list of radar sites.
+Step 2: In the "Download Data" tab, select a radar type, choose a station (from the updated list),
+        enter a date (YYYY-MM-DD), and click "Download Data" to fetch the latest radar file.
 
 Required packages:
     pip install gradio boto3 requests
@@ -13,7 +12,6 @@ Required packages:
 
 import datetime
 import io
-import json
 
 import boto3
 from botocore import UNSIGNED
@@ -25,11 +23,8 @@ import requests
 def get_full_station_list():
     """
     Fetches a full list of radar stations from a public API endpoint.
-    
-    For example, NOAA's NWS API offers radar station data at:
-      https://api.weather.gov/radar/stations
-      
-    Note: This endpoint and its structure may change. Adjust the code accordingly.
+    For example, we use NOAA’s public radar station API endpoint as an example.
+    (If the API fails, falls back to fetching the static JSON file from GitHub.)
     Returns a sorted list of station identifiers.
     """
     api_url = "https://api.weather.gov/radar/stations"
@@ -37,28 +32,20 @@ def get_full_station_list():
         response = requests.get(api_url, timeout=10)
         response.raise_for_status()
         data = response.json()
-    except Exception as e:
-        print(f"Error fetching station list from API: {e}")
-        # Fallback to the static file from GitHub if API fails.
-        return get_station_list_from_github()
-    
-    # The API returns a JSON object with a "features" key,
-    # where each feature is a station. We assume that the station identifier is in properties["stationIdentifier"]
-    stations = []
-    try:
         features = data.get("features", [])
+        stations = []
         for feature in features:
             props = feature.get("properties", {})
             station_id = props.get("stationIdentifier")
             if station_id:
                 stations.append(station_id.upper())
+        stations = sorted(list(set(stations)))
+        if stations:
+            return stations
     except Exception as e:
-        print(f"Error processing API data: {e}")
-        return get_station_list_from_github()
-    
-    # Remove duplicates and sort.
-    stations = sorted(list(set(stations)))
-    return stations
+        print(f"Error fetching station list from API: {e}")
+    # Fallback to static JSON from GitHub
+    return get_station_list_from_github()
 
 
 def get_station_list_from_github():
@@ -85,25 +72,40 @@ def get_station_list_from_github():
     return stations
 
 
+def update_station_list():
+    """
+    Retrieves the full station list and returns an update for the dropdown component.
+    """
+    stations = get_full_station_list()
+    if stations:
+        # Update with the full list and set the default to the first station.
+        return gr.Dropdown.update(choices=stations, value=stations[0])
+    else:
+        return gr.Dropdown.update(choices=[], value=None)
+
+
 def fetch_latest_radar_data(radar_type, station, date_str):
     """
     Downloads the latest radar data file from the appropriate AWS S3 bucket.
     
     Parameters:
         radar_type (str): Either "Level 2" or "Level 3".
-        station (str): Radar station identifier (e.g. "KTLX").
+        station (str): Radar station identifier (e.g. "KTLX"). Must be non-empty.
         date_str (str): Date string in "YYYY-MM-DD" format. If blank, uses current UTC date.
     
     Returns:
         str: A summary of the downloaded file (S3 key, size, last modified, and hex preview).
     """
-    if not date_str.strip():
-        date_obj = datetime.datetime.utcnow()
-    else:
-        try:
+    if not station:
+        return "Error: No station selected. Please fetch stations first."
+    
+    try:
+        if not date_str.strip():
+            date_obj = datetime.datetime.utcnow()
+        else:
             date_obj = datetime.datetime.strptime(date_str, "%Y-%m-%d")
-        except ValueError:
-            return "Error: Date must be in YYYY-MM-DD format."
+    except ValueError:
+        return "Error: Date must be in YYYY-MM-DD format."
     
     year = date_obj.strftime("%Y")
     month = date_obj.strftime("%m")
@@ -154,26 +156,44 @@ def fetch_latest_radar_data(radar_type, station, date_str):
     return summary
 
 
-# Get full station list dynamically.
-# Try API first, fall back to GitHub file if needed.
-station_list = get_full_station_list()
-
-# Create the Gradio interface.
-interface = gr.Interface(
-    fn=fetch_latest_radar_data,
-    inputs=[
-        gr.Radio(choices=["Level 2", "Level 3"], label="Radar Data Type"),
-        gr.Dropdown(choices=station_list, label="Select Radar Station"),
-        gr.Textbox(value=datetime.datetime.utcnow().strftime("%Y-%m-%d"), label="Date (YYYY-MM-DD)")
-    ],
-    outputs="text",
-    title="Radar Data Downloader",
-    description=(
-        "This tool downloads the latest radar data file from public AWS S3 buckets "
-        "used by Supercell Wx. Choose a radar data type (Level 2 or Level 3), select a "
-        "radar station from the full list, and enter a date (UTC)."
+# Build the Gradio Blocks interface.
+with gr.Blocks() as demo:
+    gr.Markdown("# Radar Data Downloader")
+    gr.Markdown(
+        "Step 1: **Fetch Stations** to retrieve the full list of radar sites.<br>"
+        "Step 2: **Download Data** by selecting a radar type, station, and date."
+    )
+    
+    with gr.Tab("Fetch Stations"):
+        with gr.Row():
+            fetch_btn = gr.Button("Fetch Stations")
+            # This dropdown will show the fetched station list.
+            station_dropdown_fetch = gr.Dropdown(choices=[], label="Available Radar Stations")
+        # Clicking fetch_btn will update the dropdown.
+        fetch_btn.click(fn=update_station_list, inputs=[], outputs=station_dropdown_fetch)
+    
+    with gr.Tab("Download Data"):
+        with gr.Row():
+            radar_type = gr.Radio(choices=["Level 2", "Level 3"], label="Radar Data Type")
+            # The download dropdown; initially empty. It can be updated by a separate sync button.
+            station_dropdown_download = gr.Dropdown(choices=[], label="Select Radar Station")
+        date_input = gr.Textbox(value=datetime.datetime.utcnow().strftime("%Y-%m-%d"),
+                                  label="Date (YYYY-MM-DD)")
+        download_btn = gr.Button("Download Data")
+        download_output = gr.Textbox(label="Download Output", interactive=False)
+        # When download_btn is clicked, call fetch_latest_radar_data.
+        download_btn.click(fn=fetch_latest_radar_data,
+                           inputs=[radar_type, station_dropdown_download, date_input],
+                           outputs=download_output)
+        
+        # Optional: a button to sync the station list to the download dropdown.
+        sync_btn = gr.Button("Sync Station List to Download Tab")
+        sync_btn.click(fn=update_station_list, inputs=[], outputs=station_dropdown_download)
+    
+    gr.Markdown(
+        "Note: First click **Fetch Stations** (or **Sync Station List to Download Tab**) to populate the radar site list before downloading data."
     )
-)
 
 if __name__ == "__main__":
-    interface.launch()
+    # For Spaces you might want to use share=True
+    demo.launch()