auth.py

"""Gmail API authentication"""
import os
import pickle
from google.auth.transport.requests import Request
from google_auth_oauthlib.flow import InstalledAppFlow
from googleapiclient.discovery import build

from config import SCOPES


def authenticate_gmail():
    """Authenticate with Gmail API using OAuth"""
    creds = None
    
    if os.path.exists('token.pickle'):
        with open('token.pickle', 'rb') as token:
            creds = pickle.load(token)
    
    if not creds or not creds.valid:
        if creds and creds.expired and creds.refresh_token:
            creds.refresh(Request())
        else:
            if not os.path.exists('credentials.json'):
                raise FileNotFoundError(
                    "credentials.json not found. Please download OAuth credentials from Google Cloud Console."
                )
            flow = InstalledAppFlow.from_client_secrets_file(
                'credentials.json', SCOPES)
            creds = flow.run_local_server(port=0)
        
        with open('token.pickle', 'wb') as token:
            pickle.dump(creds, token)
    
    service = build('gmail', 'v1', credentials=creds)
    return service