"""
Definition of function to connect to database
using environment variables.
"""
from __future__ import annotations

import logging
import os

from dotenv import load_dotenv
from pymongo import MongoClient


def connect():
    """Connect to MongoDB using env vars."""
    # load env vars
    load_dotenv()
    necessary_env_vars = [
        'MONGO_HOST',
        'MONGO_DB',
        'MONGO_COLLECTION',
    ]
    for env_var in necessary_env_vars:
        assert env_var in os.environ, f"{env_var} not found"
    # connect to database
    client = MongoClient(os.getenv('MONGO_HOST'))
    db = client[os.getenv('MONGO_DB')]
    # extract collection
    collection = db[os.getenv('MONGO_COLLECTION')]
    # set unique index on "name"
    collection.create_index('name', unique=True)
    logging.debug('finished')
    return collection, db, client