tmpl-fastapi/app/common.py

import secrets
from pathlib import Path
from typing import Literal

from fastapi.templating import Jinja2Templates
from pydantic import BaseSettings


# Directories
file_dir = Path(__file__).parent
templates_dir = str(file_dir.parent / 'templates')
static_dir = str(file_dir.parent / 'static')


# Main configuration
class Settings(BaseSettings):
    debug: bool = False
    session_key: str = 'secret'
    csrf_key: str = 'secret'
    app_host: str = '127.0.0.1'
    app_port: int = 8000


# Type alias for secret keys settings fields
SecretKey = Literal['session_key', 'csrf_key']

# Settings class instantiating
settings = Settings()

# Jinja templates handler
templates = Jinja2Templates(
    directory=templates_dir,
)


def secret_key_check(name: SecretKey) -> None:
    """Generates a secret key automatically
    if an environment variable is not set
    or contains text `secret`"""

    settings_dict = settings.dict()
    if settings_dict.get(name) != 'secret':
        return

    key_file = Path(f'/tmp/{name}')

    if key_file.exists():
        with key_file.open('rt') as f:
            key = f.read()

    else:
        key = secrets.token_hex(32)
        with key_file.open('wt') as f:
            f.write(key)

    settings_dict[name] = key


# Calling the function
# for session and CSRF keys
secret_key_check('session_key')
secret_key_check('csrf_key')