import logging

from base64 import b64decode
from flask import request

from auth.credentials import validate_credentials
from auth.validateresult import ValidateResult, AuthKind

logger = logging.getLogger(__name__)

def has_basic_auth(username):
  """ Returns true if a basic auth header exists with a username and password pair that validates
      against the internal authentication system. Returns True on full success and False on any
      failure (missing header, invalid header, invalid credentials, etc).
  """
  auth_header = request.headers.get('authorization', '')
  result = validate_basic_auth(auth_header)
  return result.has_nonrobot_user and result.context.user.username == username


def validate_basic_auth(auth_header):
  """ Validates the specified basic auth header, returning whether its credentials point
      to a valid user or token.
  """
  if not auth_header:
    return ValidateResult(AuthKind.basic, missing=True)

  logger.debug('Attempt to process basic auth header')

  # Parse the basic auth header.
  assert isinstance(auth_header, basestring)
  credentials, err = _parse_basic_auth_header(auth_header)
  if err is not None:
    logger.debug('Got invalid basic auth header: %s', auth_header)
    return ValidateResult(AuthKind.basic, missing=True)

  auth_username, auth_password_or_token = credentials
  result, _ = validate_credentials(auth_username, auth_password_or_token)
  return result.with_kind(AuthKind.basic)


def _parse_basic_auth_header(auth):
  """ Parses the given basic auth header, returning the credentials found inside.
  """
  normalized = [part.strip() for part in auth.split(' ') if part]
  if normalized[0].lower() != 'basic' or len(normalized) != 2:
    return None, 'Invalid basic auth header'

  try:
    credentials = [part.decode('utf-8') for part in b64decode(normalized[1]).split(':', 1)]
  except (TypeError, UnicodeDecodeError, ValueError):
    logger.exception('Exception when parsing basic auth header: %s', auth)
    return None, 'Could not parse basic auth header'

  if len(credentials) != 2:
    return None, 'Unexpected number of credentials found in basic auth header'

  return credentials, None