# -*- coding: utf-8 -*-
# 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.
"""Utility functions for signurl command."""

import base64
from datetime import datetime
from datetime import timezone
import hashlib

from gslib.utils.constants import UTF8
import six
from six.moves import urllib

_CANONICAL_REQUEST_FORMAT = ('{method}\n{resource}\n{query_string}\n{headers}'
                             '\n{signed_headers}\n{hashed_payload}')
_SIGNING_ALGO = 'GOOG4-RSA-SHA256'
_STRING_TO_SIGN_FORMAT = ('{signing_algo}\n{request_time}\n{credential_scope}'
                          '\n{hashed_request}')
_SIGNED_URL_FORMAT = ('https://{host}/{path}?x-goog-signature={sig}&'
                      '{query_string}')
_UNSIGNED_PAYLOAD = 'UNSIGNED-PAYLOAD'


def _NowUTC():
  return datetime.now(tz=timezone.utc).replace(tzinfo=None)


def CreatePayload(client_id,
                  method,
                  duration,
                  path,
                  generation,
                  logger,
                  region,
                  signed_headers,
                  billing_project=None,
                  string_to_sign_debug=False):
  """Create a string that needs to be signed.

  Args:
    client_id: Client ID signing this URL.
    method: The HTTP method to be used with the signed URL.
    duration: timedelta for which the constructed signed URL should be valid.
    path: String path to the bucket of object for signing, in the form
        'bucket' or 'bucket/object'.
    generation: If not None, specifies a version of an object for signing.
    logger: logging.Logger for warning and debug output.
    region: Geographic region in which the requested resource resides.
    signed_headers: Dict containing the header  info like host
          content-type etc.
    billing_project: Specify a user project to be billed for the request.
    string_to_sign_debug: If true AND logger is enabled for debug level,
        print string to sign to debug. Used to differentiate user's
        signed URL from the probing permissions-check signed URL.

  Returns:
    A tuple where the 1st element is the string to sign.
    The second element is the query string.
  """
  signing_time = _NowUTC()

  canonical_day = signing_time.strftime('%Y%m%d')
  canonical_time = signing_time.strftime('%Y%m%dT%H%M%SZ')
  canonical_scope = '{date}/{region}/storage/goog4_request'.format(
      date=canonical_day, region=region)

  signed_query_params = {
      'x-goog-algorithm': _SIGNING_ALGO,
      'x-goog-credential': client_id + '/' + canonical_scope,
      'x-goog-date': canonical_time,
      'x-goog-signedheaders': ';'.join(sorted(signed_headers.keys())),
      'x-goog-expires': '%d' % duration.total_seconds()
  }

  if (billing_project is not None):
    signed_query_params['userProject'] = billing_project

  if generation is not None:
    signed_query_params['generation'] = generation

  canonical_resource = '/{}'.format(path)
  canonical_query_string = '&'.join([
      '{}={}'.format(param, urllib.parse.quote_plus(signed_query_params[param]))
      for param in sorted(signed_query_params.keys())
  ])
  canonical_headers = '\n'.join([
      '{}:{}'.format(header.lower(), signed_headers[header])
      for header in sorted(signed_headers.keys())
  ]) + '\n'
  canonical_signed_headers = ';'.join(sorted(signed_headers.keys()))

  canonical_request = _CANONICAL_REQUEST_FORMAT.format(
      method=method,
      resource=canonical_resource,
      query_string=canonical_query_string,
      headers=canonical_headers,
      signed_headers=canonical_signed_headers,
      hashed_payload=_UNSIGNED_PAYLOAD)

  if six.PY3:
    canonical_request = canonical_request.encode(UTF8)

  canonical_request_hasher = hashlib.sha256()
  canonical_request_hasher.update(canonical_request)
  hashed_canonical_request = base64.b16encode(
      canonical_request_hasher.digest()).lower().decode(UTF8)

  string_to_sign = _STRING_TO_SIGN_FORMAT.format(
      signing_algo=_SIGNING_ALGO,
      request_time=canonical_time,
      credential_scope=canonical_scope,
      hashed_request=hashed_canonical_request)

  if string_to_sign_debug and logger:
    logger.debug(
        'Canonical request (ignore opening/closing brackets): [[[%s]]]' %
        canonical_request)
    logger.debug('String to sign (ignore opening/closing brackets): [[[%s]]]' %
                 string_to_sign)

  return string_to_sign, canonical_query_string


def GetFinalUrl(raw_signature, host, path, canonical_query_string):
  """Get the final signed url."""
  signature = base64.b16encode(raw_signature).lower().decode()
  return _SIGNED_URL_FORMAT.format(host=host,
                                   path=path,
                                   sig=signature,
                                   query_string=canonical_query_string)

def to_bytes(value, encoding=UTF8):
  if value is None:
    return None
  if isinstance(value, bytes):
    return value
  return value.encode(encoding)
