"""Simple wrapper module for fetching and storing access tokens for VAPI.

Currently only stores and returns the access token, ignoring the other
values returned by the Oauth client (e.g. refresh_token, expires_at, etc.)
because VAPI does not expire access tokens. If we do need those values in
the future, this code can be updated to store and expose them as well.
"""

import hashlib


def get_access_token(oauth_client, cache, cache_timeout=None):
    """Retrieve the access token, looking in cache first.

    If no token is found in cache, fetch a token from the client
    and store it in the cache for posterity.

    Args:
        oauth_client (OauthClient): Client for fetching new access tokens.
        cache (werkzeug.contrib.cache.BaseCache): Cache implementation for
            persisting an access token after fetching it from the client.
        cache_timeout (None|int): timeout
    Returns:
        string: Access token
    """
    key = cache_key(oauth_client)
    access_token = cache.get(key)
    if not access_token:
        token_data = oauth_client.fetch_token()
        access_token = token_data.get("access_token")
        cache.set(key, access_token, cache_timeout)
    return access_token


def cache_key(oauth_client):
    """Calculate cache key based on values in the Oauth client object.

    Args:
        oauth_client (OauthClient) Client which holds relevant config data.
    """
    properties = ("client_id", "client_secret", "base_url", "user_id", "user_type")
    param_values = []
    for prop in properties:
        param_values.append(str(getattr(oauth_client, prop)))
    # Construct a unique string from these values. Delimiter is arbitrary.
    cache_suffix = ",".join(param_values)
    h = hashlib.sha256(cache_suffix.encode())
    return "access-token-" + h.hexdigest()