from __future__ import annotations

import os
from pathlib import Path

from google_auth_oauthlib.flow import InstalledAppFlow
from google.auth.transport.requests import Request
from google.oauth2.credentials import Credentials

# REQUIRED scopes based on your plan:
# - read messages, move labels, mark read => modify
# - send mail => send
SCOPES = [
    "https://www.googleapis.com/auth/gmail.modify",
    "https://www.googleapis.com/auth/gmail.send",
]

ROOT = Path(__file__).resolve().parent
CREDS_PATH = Path("backend/credentials.json")
TOKEN_PATH = Path("backend/token.json")

def main() -> None:
    if not CREDS_PATH.exists():
        raise FileNotFoundError(
            f"Missing {CREDS_PATH}. Download OAuth client JSON from Google Cloud and save as credentials.json in this folder."
        )

    creds: Credentials | None = None

    # Load existing token if present
    if TOKEN_PATH.exists():
        creds = Credentials.from_authorized_user_file(str(TOKEN_PATH), SCOPES)

    # Refresh or re-authenticate
    if not creds or not creds.valid:
        if creds and creds.expired and creds.refresh_token:
            creds.refresh(Request())
        else:
            flow = InstalledAppFlow.from_client_secrets_file(str(CREDS_PATH), SCOPES)
            # Local loopback server OAuth (Desktop app)
            creds = flow.run_local_server(port=0)

        # Save token
        TOKEN_PATH.write_text(creds.to_json(), encoding="utf-8")

    print("✅ OAuth complete.")
    print(f"Saved token: {TOKEN_PATH}")
    print("Scopes granted:", creds.scopes)

if __name__ == "__main__":
    main()