# Copyright (c) 2012-2013 Mitch Garnaat http://garnaat.org/
# Copyright 2012-2014 Amazon.com, Inc. or its affiliates. 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. A copy of
# the License is located at
#
# http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file 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.
import base64
import datetime
from hashlib import sha256
from hashlib import sha1
import hmac
import logging
from email.utils import formatdate
from operator import itemgetter
import functools
import time
import calendar
import json

from botocore.exceptions import NoCredentialsError
from botocore.utils import normalize_url_path, percent_encode_sequence
from botocore.compat import HTTPHeaders
from botocore.compat import quote, unquote, urlsplit, parse_qs
from botocore.compat import urlunsplit
from botocore.compat import encodebytes
from botocore.compat import six
from botocore.compat import json
from botocore.compat import MD5_AVAILABLE

logger = logging.getLogger(__name__)


EMPTY_SHA256_HASH = (
    'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855')
# This is the buffer size used when calculating sha256 checksums.
# Experimenting with various buffer sizes showed that this value generally
# gave the best result (in terms of performance).
PAYLOAD_BUFFER = 1024 * 1024
ISO8601 = '%Y-%m-%dT%H:%M:%SZ'
SIGV4_TIMESTAMP = '%Y%m%dT%H%M%SZ'
SIGNED_HEADERS_BLACKLIST = [
    'expect',
    'user-agent',
    'x-amzn-trace-id',
]


class BaseSigner(object):
    REQUIRES_REGION = False

    def add_auth(self, request):
        raise NotImplementedError("add_auth")


class SigV2Auth(BaseSigner):
    """
    Sign a request with Signature V2.
    """

    def __init__(self, credentials):
        self.credentials = credentials

    def calc_signature(self, request, params):
        logger.debug("Calculating signature using v2 auth.")
        split = urlsplit(request.url)
        path = split.path
        if len(path) == 0:
            path = '/'
        string_to_sign = '%s\n%s\n%s\n' % (request.method,
                                           split.netloc,
                                           path)
        lhmac = hmac.new(self.credentials.secret_key.encode('utf-8'),
                         digestmod=sha256)
        pairs = []
        for key in sorted(params):
            # Any previous signature should not be a part of this
            # one, so we skip that particular key. This prevents
            # issues during retries.
            if key == 'Signature':
                continue
            value = six.text_type(params[key])
            pairs.append(quote(key.encode('utf-8'), safe='') + '=' +
                         quote(value.encode('utf-8'), safe='-_~'))
        qs = '&'.join(pairs)
        string_to_sign += qs
        logger.debug('String to sign: %s', string_to_sign)
        lhmac.update(string_to_sign.encode('utf-8'))
        b64 = base64.b64encode(lhmac.digest()).strip().decode('utf-8')
        return (qs, b64)

    def add_auth(self, request):
        # The auth handler is the last thing called in the
        # preparation phase of a prepared request.
        # Because of this we have to parse the query params
        # from the request body so we can update them with
        # the sigv2 auth params.
        if self.credentials is None:
            raise NoCredentialsError
        if request.data:
            # POST
            params = request.data
        else:
            # GET
            params = request.param
        params['AWSAccessKeyId'] = self.credentials.access_key
        params['SignatureVersion'] = '2'
        params['SignatureMethod'] = 'HmacSHA256'
        params['Timestamp'] = time.strftime(ISO8601, time.gmtime())
        if self.credentials.token:
            params['SecurityToken'] = self.credentials.token
        qs, signature = self.calc_signature(request, params)
        params['Signature'] = signature
        return request


class SigV3Auth(BaseSigner):
    def __init__(self, credentials):
        self.credentials = credentials

    def add_auth(self, request):
        if self.credentials is None:
            raise NoCredentialsError
        if 'Date' in request.headers:
            del request.headers['Date']
        request.headers['Date'] = formatdate(usegmt=True)
        if self.credentials.token:
            if 'X-Amz-Security-Token' in request.headers:
                del request.headers['X-Amz-Security-Token']
            request.headers['X-Amz-Security-Token'] = self.credentials.token
        new_hmac = hmac.new(self.credentials.secret_key.encode('utf-8'),
                            digestmod=sha256)
        new_hmac.update(request.headers['Date'].encode('utf-8'))
        encoded_signature = encodebytes(new_hmac.digest()).strip()
        signature = ('AWS3-HTTPS AWSAccessKeyId=%s,Algorithm=%s,Signature=%s' %
                     (self.credentials.access_key, 'HmacSHA256',
                      encoded_signature.decode('utf-8')))
        if 'X-Amzn-Authorization' in request.headers:
            del request.headers['X-Amzn-Authorization']
        request.headers['X-Amzn-Authorization'] = signature


class SigV4Auth(BaseSigner):
    """
    Sign a request with Signature V4.
    """
    REQUIRES_REGION = True

    def __init__(self, credentials, service_name, region_name):
        self.credentials = credentials
        # We initialize these value here so the unit tests can have
        # valid values.  But these will get overriden in ``add_auth``
        # later for real requests.
        self._region_name = region_name
        self._service_name = service_name

    def _sign(self, key, msg, hex=False):
        if hex:
            sig = hmac.new(key, msg.encode('utf-8'), sha256).hexdigest()
        else:
            sig = hmac.new(key, msg.encode('utf-8'), sha256).digest()
        return sig

    def headers_to_sign(self, request):
        """
        Select the headers from the request that need to be included
        in the StringToSign.
        """
        header_map = HTTPHeaders()
        split = urlsplit(request.url)
        for name, value in request.headers.items():
            lname = name.lower()
            if lname not in SIGNED_HEADERS_BLACKLIST:
                header_map[lname] = value
        if 'host' not in header_map:
            header_map['host'] = split.netloc
        return header_map

    def canonical_query_string(self, request):
        # The query string can come from two parts.  One is the
        # params attribute of the request.  The other is from the request
        # url (in which case we have to re-split the url into its components
        # and parse out the query string component).
        if request.params:
            return self._canonical_query_string_params(request.params)
        else:
            return self._canonical_query_string_url(urlsplit(request.url))

    def _canonical_query_string_params(self, params):
        l = []
        for param in sorted(params):
            value = str(params[param])
            l.append('%s=%s' % (quote(param, safe='-_.~'),
                                quote(value, safe='-_.~')))
        cqs = '&'.join(l)
        return cqs

    def _canonical_query_string_url(self, parts):
        canonical_query_string = ''
        if parts.query:
            # [(key, value), (key2, value2)]
            key_val_pairs = []
            for pair in parts.query.split('&'):
                key, _, value = pair.partition('=')
                key_val_pairs.append((key, value))
            sorted_key_vals = []
            # Sort by the key names, and in the case of
            # repeated keys, then sort by the value.
            for key, value in sorted(key_val_pairs):
                sorted_key_vals.append('%s=%s' % (key, value))
            canonical_query_string = '&'.join(sorted_key_vals)
        return canonical_query_string

    def canonical_headers(self, headers_to_sign):
        """
        Return the headers that need to be included in the StringToSign
        in their canonical form by converting all header keys to lower
        case, sorting them in alphabetical order and then joining
        them into a string, separated by newlines.
        """
        headers = []
        sorted_header_names = sorted(set(headers_to_sign))
        for key in sorted_header_names:
            value = ','.join(v.strip() for v in
                             sorted(headers_to_sign.get_all(key)))
            headers.append('%s:%s' % (key, value))
        return '\n'.join(headers)

    def signed_headers(self, headers_to_sign):
        l = ['%s' % n.lower().strip() for n in set(headers_to_sign)]
        l = sorted(l)
        return ';'.join(l)

    def payload(self, request):
        if request.body and hasattr(request.body, 'seek'):
            position = request.body.tell()
            read_chunksize = functools.partial(request.body.read,
                                               PAYLOAD_BUFFER)
            checksum = sha256()
            for chunk in iter(read_chunksize, b''):
                checksum.update(chunk)
            hex_checksum = checksum.hexdigest()
            request.body.seek(position)
            return hex_checksum
        elif request.body:
            # The request serialization has ensured that
            # request.body is a bytes() type.
            return sha256(request.body).hexdigest()
        else:
            return EMPTY_SHA256_HASH

    def canonical_request(self, request):
        cr = [request.method.upper()]
        path = self._normalize_url_path(urlsplit(request.url).path)
        cr.append(path)
        cr.append(self.canonical_query_string(request))
        headers_to_sign = self.headers_to_sign(request)
        cr.append(self.canonical_headers(headers_to_sign) + '\n')
        cr.append(self.signed_headers(headers_to_sign))
        if 'X-Amz-Content-SHA256' in request.headers:
            body_checksum = request.headers['X-Amz-Content-SHA256']
        else:
            body_checksum = self.payload(request)
        cr.append(body_checksum)
        return '\n'.join(cr)

    def _normalize_url_path(self, path):
        normalized_path = quote(normalize_url_path(path), safe='/~')
        return normalized_path

    def scope(self, request):
        scope = [self.credentials.access_key]
        scope.append(request.context['timestamp'][0:8])
        scope.append(self._region_name)
        scope.append(self._service_name)
        scope.append('aws4_request')
        return '/'.join(scope)

    def credential_scope(self, request):
        scope = []
        scope.append(request.context['timestamp'][0:8])
        scope.append(self._region_name)
        scope.append(self._service_name)
        scope.append('aws4_request')
        return '/'.join(scope)

    def string_to_sign(self, request, canonical_request):
        """
        Return the canonical StringToSign as well as a dict
        containing the original version of all headers that
        were included in the StringToSign.
        """
        sts = ['AWS4-HMAC-SHA256']
        sts.append(request.context['timestamp'])
        sts.append(self.credential_scope(request))
        sts.append(sha256(canonical_request.encode('utf-8')).hexdigest())
        return '\n'.join(sts)

    def signature(self, string_to_sign, request):
        key = self.credentials.secret_key
        k_date = self._sign(('AWS4' + key).encode('utf-8'),
                            request.context['timestamp'][0:8])
        k_region = self._sign(k_date, self._region_name)
        k_service = self._sign(k_region, self._service_name)
        k_signing = self._sign(k_service, 'aws4_request')
        return self._sign(k_signing, string_to_sign, hex=True)

    def add_auth(self, request):
        if self.credentials is None:
            raise NoCredentialsError
        datetime_now = datetime.datetime.utcnow()
        request.context['timestamp'] = datetime_now.strftime(SIGV4_TIMESTAMP)
        # This could be a retry.  Make sure the previous
        # authorization header is removed first.
        self._modify_request_before_signing(request)
        canonical_request = self.canonical_request(request)
        logger.debug("Calculating signature using v4 auth.")
        logger.debug('CanonicalRequest:\n%s', canonical_request)
        string_to_sign = self.string_to_sign(request, canonical_request)
        logger.debug('StringToSign:\n%s', string_to_sign)
        signature = self.signature(string_to_sign, request)
        logger.debug('Signature:\n%s', signature)

        self._inject_signature_to_request(request, signature)

    def _inject_signature_to_request(self, request, signature):
        l = ['AWS4-HMAC-SHA256 Credential=%s' % self.scope(request)]
        headers_to_sign = self.headers_to_sign(request)
        l.append('SignedHeaders=%s' % self.signed_headers(headers_to_sign))
        l.append('Signature=%s' % signature)
        request.headers['Authorization'] = ', '.join(l)
        return request

    def _modify_request_before_signing(self, request):
        if 'Authorization' in request.headers:
            del request.headers['Authorization']
        self._set_necessary_date_headers(request)
        if self.credentials.token:
            if 'X-Amz-Security-Token' in request.headers: