backend/utils/model_fetcher.py

import os
import urllib.request
import sys

def download_if_missing():
    """
    Checks if the model weights exist locally. 
    If not, attempts to download them from the URL provided in environment variables.
    """
    model_url = os.getenv("MODEL_URL")
    # Default local path relative to backend directory
    model_path = os.path.join(os.path.dirname(__file__), "../../model/saved_models/oil_spill_unet_best.keras")
    
    # Ensure directory exists
    os.makedirs(os.path.dirname(model_path), exist_ok=True)

    if not os.path.exists(model_path):
        if not model_url or model_url == "https://your-r2-public-url/oil_spill_unet_best.keras":
            print("⚠️ MODEL_URL not configured. Skipping download.")
            print("💡 Please provide a valid URL in your docker-compose.yml to enable automated fetching.")
            return

        print(f"🚀 Model weights missing. Initializing download from: {model_url}")
        try:
            # Using urllib as it's built-in and sufficient for this simple GET
            urllib.request.urlretrieve(model_url, model_path)
            print("✅ Model weights downloaded successfully.")
        except Exception as e:
            print(f"❌ Failed to download model: {e}")
            print("💡 Fallback: The system will use an untrained stub model for now.")
    else:
        print("📦 Production model weights detected locally. Skipping download.")

if __name__ == "__main__":
    # Test run
    download_if_missing()