# Base image: matches Python 3.12. Change this if you tested locally on a
# different version — a mismatch can cause subtle bugs that don't show up
# until production (e.g. dependency wheels built for the wrong version).
FROM python:3.12-slim

# All subsequent commands run from here inside the container.
WORKDIR /app

# Copy ONLY requirements.txt first, not the whole app. Docker caches each
# layer — as long as requirements.txt hasn't changed, this layer (and the
# slow pip install below) gets reused on every rebuild, even if you've
# edited your Python files. Copying everything first would bust that cache
# on every single code change.
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Now copy the rest of the application code.
COPY . .

# Documents which port the app listens on. This does NOT actually publish
# the port anywhere — that happens in compose.yaml via `expose`.
EXPOSE 5000

# Production entrypoint. Never use `flask run` or `app.run()` in production —
# that's Flask's single-threaded development server, not meant to handle
# real traffic or run unattended. gunicorn is a proper WSGI server.
# "wsgi:app" means: import the `app` object from wsgi.py.
CMD ["gunicorn", "--bind", "0.0.0.0:5000", "wsgi:app"]