# Copyright (c) 2010 OpenStack, LLC.
#
# 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.

import os
import re

from webob.exc import HTTPBadRequest, HTTPLengthRequired, \
    HTTPRequestEntityTooLarge


#: Max file size allowed for objects
MAX_FILE_SIZE = 5 * 1024 * 1024 * 1024 + 2
#: Max length of the name of a key for metadata
MAX_META_NAME_LENGTH = 128
#: Max length of the value of a key for metadata
MAX_META_VALUE_LENGTH = 256
#: Max number of metadata items
MAX_META_COUNT = 90
#: Max overall size of metadata
MAX_META_OVERALL_SIZE = 4096
#: Max object name length
MAX_OBJECT_NAME_LENGTH = 1024


def check_metadata(req):
    """
    Check metadata sent for objects in the request headers.

    :param req: request object
    :raises HTTPBadRequest: bad metadata
    """
    meta_count = 0
    meta_size = 0
    for key, value in req.headers.iteritems():
        if not key.lower().startswith('x-object-meta-'):
            continue
        key = key[len('x-object-meta-'):]
        if not key:
            return HTTPBadRequest(body='Metadata name cannot be empty',
                    request=req, content_type='text/plain')
        meta_count += 1
        meta_size += len(key) + len(value)
        if len(key) > MAX_META_NAME_LENGTH:
            return HTTPBadRequest(
                    body='Metadata name too long; max %d'
                        % MAX_META_NAME_LENGTH,
                    request=req, content_type='text/plain')
        elif len(value) > MAX_META_VALUE_LENGTH:
            return HTTPBadRequest(
                    body='Metadata value too long; max %d'
                        % MAX_META_VALUE_LENGTH,
                    request=req, content_type='text/plain')
        elif meta_count > MAX_META_COUNT:
            return HTTPBadRequest(
                    body='Too many metadata items; max %d' % MAX_META_COUNT,
                    request=req, content_type='text/plain')
        elif meta_size > MAX_META_OVERALL_SIZE:
            return HTTPBadRequest(
                    body='Total metadata too large; max %d'
                        % MAX_META_OVERALL_SIZE,
                    request=req, content_type='text/plain')
    return None


def check_object_creation(req, object_name):
    """
    Check to ensure that everything is alright about an object to be created.

    :param req: HTTP request object
    :param object_name: name of object to be created
    :raises HTTPRequestEntityTooLarge: the object is too large
    :raises HTTPLengthRequered: missing content-length header and not
                                a chunked request
    :raises HTTPBadRequest: missing or bad content-type header, or
                            bad metadata
    """
    if req.content_length and req.content_length > MAX_FILE_SIZE:
        return HTTPRequestEntityTooLarge(body='Your request is too large.',
                request=req, content_type='text/plain')
    if req.content_length is None and \
            req.headers.get('transfer-encoding') != 'chunked':
        return HTTPLengthRequired(request=req)
    if len(object_name) > MAX_OBJECT_NAME_LENGTH:
        return HTTPBadRequest(body='Object name length of %d longer than %d' %
                (len(object_name), MAX_OBJECT_NAME_LENGTH), request=req,
                content_type='text/plain')
    if 'Content-Type' not in req.headers:
        return HTTPBadRequest(request=req, content_type='text/plain',
                    body='No content type')
    if not check_xml_encodable(req.headers['Content-Type']):
        return HTTPBadRequest(request=req, body='Invalid Content-Type',
                    content_type='text/plain')
    return check_metadata(req)


def check_mount(root, drive):
    """
    Verify that the path to the device is a mount point and mounted.  This
    allows us to fast fail on drives that have been unmounted because of
    issues, and also prevents us for accidently filling up the root partition.

    :param root:  base path where the devices are mounted
    :param drive: drive name to be checked
    :returns: True if it is a valid mounted device, False otherwise
    """
    if not drive.isalnum():
        return False
    path = os.path.join(root, drive)
    return os.path.exists(path) and os.path.ismount(path)


def check_float(string):
    """
    Helper function for checking if a string can be converted to a float.

    :param string: string to be verified as a float
    :returns: True if the string can be converted to a float, False otherwise
    """
    try:
        float(string)
        return True
    except ValueError:
        return False


_invalid_xml = re.compile(ur'[^\x09\x0a\x0d\x20-\uD7FF\uE000-\uFFFD%s-%s]' %
                        (unichr(0x10000), unichr(0x10FFFF)))


def check_xml_encodable(string):
    """
    Validate if a string can be encoded in xml.

    :param string: string to be validated
    :returns: True if the string can be encoded in xml, False otherwise
    """
    try:
        return not _invalid_xml.search(string.decode('UTF-8'))
    except UnicodeDecodeError:
        return False
