import logging
import yaml

from abc import ABCMeta, abstractmethod
from six import add_metaclass

from jsonschema import validate, ValidationError

from util.config.schema import CONFIG_SCHEMA

logger = logging.getLogger(__name__)


class CannotWriteConfigException(Exception):
  """ Exception raised when the config cannot be written. """
  pass


class SetupIncompleteException(Exception):
  """ Exception raised when attempting to verify config that has not yet been setup. """
  pass


def import_yaml(config_obj, config_file):
  with open(config_file) as f:
    c = yaml.safe_load(f)
    if not c:
      logger.debug('Empty YAML config file')
      return

    if isinstance(c, str):
      raise Exception('Invalid YAML config file: ' + str(c))

    for key in c.iterkeys():
      if key.isupper():
        config_obj[key] = c[key]

  if config_obj.get('SETUP_COMPLETE', True):
    try:
      validate(config_obj, CONFIG_SCHEMA)
    except ValidationError:
      # TODO: Change this into a real error
      logger.exception('Could not validate config schema')
  else:
    logger.debug('Skipping config schema validation because setup is not complete')

  return config_obj


def get_yaml(config_obj):
  return yaml.safe_dump(config_obj, encoding='utf-8', allow_unicode=True)


def export_yaml(config_obj, config_file):
  try:
    with open(config_file, 'w') as f:
      f.write(get_yaml(config_obj))
  except IOError as ioe:
    raise CannotWriteConfigException(str(ioe))


@add_metaclass(ABCMeta)
class BaseProvider(object):
  """ A configuration provider helps to load, save, and handle config override in the application.
  """

  @property
  def provider_id(self):
    raise NotImplementedError

  @abstractmethod
  def update_app_config(self, app_config):
    """ Updates the given application config object with the loaded override config. """

  @abstractmethod
  def get_config(self):
    """ Returns the contents of the config override file, or None if none. """

  @abstractmethod
  def save_config(self, config_object):
    """ Updates the contents of the config override file to those given. """

  @abstractmethod
  def config_exists(self):
    """ Returns true if a config override file exists in the config volume. """

  @abstractmethod
  def volume_exists(self):
    """ Returns whether the config override volume exists. """

  @abstractmethod
  def volume_file_exists(self, relative_file_path):
    """ Returns whether the file with the given relative path exists under the config override
        volume. """

  @abstractmethod
  def get_volume_file(self, relative_file_path, mode='r'):
    """ Returns a Python file referring to the given path under the config override volume. """

  @abstractmethod
  def remove_volume_file(self, relative_file_path):
    """ Removes the config override volume file with the given path. """

  @abstractmethod
  def list_volume_directory(self, path):
    """ Returns a list of strings representing the names of the files found in the config override
        directory under the given path. If the path doesn't exist, returns None.
    """

  @abstractmethod
  def save_volume_file(self, flask_file, relative_file_path):
    """ Saves the given flask file to the config override volume, with the given
        relative path.
    """

  @abstractmethod
  def get_volume_path(self, directory, filename):
    """ Helper for constructing relative file paths, which may differ between providers.
        For example, kubernetes can't have subfolders in configmaps """

  @abstractmethod
  def get_config_root(self):
    """ Returns the config root directory. """