import json
import os
import logging
from typing import Optional

import google.auth
import google.auth.credentials
from google.oauth2 import service_account

logger = logging.getLogger(__name__)

_SCOPES = ["https://www.googleapis.com/auth/cloud-platform"]


def get_google_credentials() -> google.auth.credentials.Credentials:
    """
    Resolution order:
    1. GOOGLE_CREDENTIALS_JSON env var (raw JSON string) → service account info
    2. GOOGLE_APPLICATION_CREDENTIALS env var set & file exists → service account file
    3. Fallback → ADC (gcloud auth application-default login)
    """
    creds_json: Optional[str] = os.environ.get("GOOGLE_CREDENTIALS_JSON")
    if creds_json:
        logger.info("Google auth: service account dari GOOGLE_CREDENTIALS_JSON")
        # Value may be raw JSON or base64-encoded JSON
        try:
            import base64
            decoded = base64.b64decode(creds_json).decode("utf-8")
            info = json.loads(decoded)
        except Exception:
            info = json.loads(creds_json)
        return service_account.Credentials.from_service_account_info(info, scopes=_SCOPES)

    creds_path: Optional[str] = os.environ.get("GOOGLE_APPLICATION_CREDENTIALS")
    if creds_path:
        if not os.path.isfile(creds_path):
            raise FileNotFoundError(
                f"GOOGLE_APPLICATION_CREDENTIALS='{creds_path}' tapi file tidak ditemukan."
            )
        logger.info("Google auth: service account dari %s", creds_path)
        return service_account.Credentials.from_service_account_file(creds_path, scopes=_SCOPES)

    logger.info("Google auth: menggunakan ADC (gcloud login)")
    credentials, _ = google.auth.default(scopes=_SCOPES)
    return credentials