# Use a Python base image
FROM python:3.9-slim

# Set the working directory
WORKDIR /app

# Copy the requirements file and install dependencies
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Copy the application script
COPY app.py .

# Expose the port Streamlit runs on
EXPOSE 8501

# CRITICAL FIX: Use CMD to combine the execution command and filename
# This ensures 'streamlit run app.py' is executed upon container start.
CMD ["streamlit", "run", "app.py"]