import logging

from base64 import b64decode
from flask import request

from app import authentication
from auth.oauth import validate_oauth_token
from auth.validateresult import ValidateResult, AuthKind
from data import model
from util.names import parse_robot_username

logger = logging.getLogger(__name__)

ACCESS_TOKEN_USERNAME = '$token'
OAUTH_TOKEN_USERNAME = '$oauthtoken'


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_user and result.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.
  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

  # Check for access tokens.
  if auth_username == ACCESS_TOKEN_USERNAME:
    logger.debug('Found basic auth header for access token')
    try:
      token = model.token.load_token_data(auth_password_or_token)
      logger.debug('Successfully validated basic auth for access token %s', token.id)
      return ValidateResult(AuthKind.basic, token=token)
    except model.DataModelException:
      logger.warning('Failed to validate basic auth for access token %s', auth_password_or_token)
      return ValidateResult(AuthKind.basic, error_message='Invalid access token')

  # Check for OAuth tokens.
  if auth_username == OAUTH_TOKEN_USERNAME:
    return validate_oauth_token(auth_password_or_token)

  # Check for robots and users.
  is_robot = parse_robot_username(auth_username)
  if is_robot:
    logger.debug('Found basic auth header for robot %s', auth_username)
    try:
      robot = model.user.verify_robot(auth_username, auth_password_or_token)

      logger.debug('Successfully validated basic auth for robot %s', auth_username)
      return ValidateResult(AuthKind.basic, robot=robot)
    except model.InvalidRobotException as ire:
      logger.warning('Failed to validate basic auth for robot %s: %s', auth_username, ire.message)
      return ValidateResult(AuthKind.basic, error_message=ire.message)

  # Otherwise, treat as a standard user.
  (authenticated, err) = authentication.verify_and_link_user(auth_username, auth_password_or_token,
                                                             basic_auth=True)
  if authenticated:
    logger.debug('Successfully validated basic auth for user %s', authenticated.username)
    return ValidateResult(AuthKind.basic, user=authenticated)
  else:
    logger.warning('Failed to validate basic auth for user %s: %s', auth_username, err)
    return ValidateResult(AuthKind.basic, error_message=err)


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:
    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