# Copyright 2014 Google Inc. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Utilities for OAuth.

Utilities for making it easier to work with OAuth 2.0
credentials.
"""

__author__ = 'jcgregorio@google.com (Joe Gregorio)'

import os
import threading

from oauth2client.client import Credentials
from oauth2client.client import Storage as BaseStorage


class CredentialsFileSymbolicLinkError(Exception):
  """Credentials files must not be symbolic links."""


class Storage(BaseStorage):
  """Store and retrieve a single credential to and from a file."""

  def __init__(self, filename):
    self._filename = filename
    self._lock = threading.Lock()

  def _validate_file(self):
    if os.path.islink(self._filename):
      raise CredentialsFileSymbolicLinkError(
          'File: %s is a symbolic link.' % self._filename)

  def acquire_lock(self):
    """Acquires any lock necessary to access this Storage.

    This lock is not reentrant."""
    self._lock.acquire()

  def release_lock(self):
    """Release the Storage lock.

    Trying to release a lock that isn't held will result in a
    RuntimeError.
    """
    self._lock.release()

  def locked_get(self):
    """Retrieve Credential from file.

    Returns:
      oauth2client.client.Credentials

    Raises:
      CredentialsFileSymbolicLinkError if the file is a symbolic link.
    """
    credentials = None
    self._validate_file()
    try:
      f = open(self._filename, 'rb')
      content = f.read()
      f.close()
    except IOError:
      return credentials

    try:
      credentials = Credentials.new_from_json(content)
      credentials.set_store(self)
    except ValueError:
      pass

    return credentials

  def _create_file_if_needed(self):
    """Create an empty file if necessary.

    This method will not initialize the file. Instead it implements a
    simple version of "touch" to ensure the file has been created.
    """
    if not os.path.exists(self._filename):
      old_umask = os.umask(0o177)
      try:
        open(self._filename, 'a+b').close()
      finally:
        os.umask(old_umask)

  def locked_put(self, credentials):
    """Write Credentials to file.

    Args:
      credentials: Credentials, the credentials to store.

    Raises:
      CredentialsFileSymbolicLinkError if the file is a symbolic link.
    """

    self._create_file_if_needed()
    self._validate_file()
    f = open(self._filename, 'w')
    f.write(credentials.to_json())
    f.close()

  def locked_delete(self):
    """Delete Credentials file.

    Args:
      credentials: Credentials, the credentials to store.
    """

    os.unlink(self._filename)