# -*- coding: utf-8 -*-
# Copyright 2014-2016 OpenMarket Ltd
# Copyright 2020 The Matrix.org Foundation C.I.C.
#
# 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 itertools
import random
import re
import string
from collections import Iterable

import six
from six import PY2, PY3
from six.moves import range

from synapse.api.errors import Codes, SynapseError

_string_with_symbols = string.digits + string.ascii_letters + ".,;:^&*-_+=#~@"

# https://matrix.org/docs/spec/client_server/r0.6.0#post-matrix-client-r0-register-email-requesttoken
# Note: The : character is allowed here for older clients, but will be removed in a
# future release. Context: https://github.com/matrix-org/synapse/issues/6766
client_secret_regex = re.compile(r"^[0-9a-zA-Z\.\=\_\-\:]+$")

# random_string and random_string_with_symbols are used for a range of things,
# some cryptographically important, some less so. We use SystemRandom to make sure
# we get cryptographically-secure randoms.
rand = random.SystemRandom()


def random_string(length):
    return "".join(rand.choice(string.ascii_letters) for _ in range(length))


def random_string_with_symbols(length):
    return "".join(rand.choice(_string_with_symbols) for _ in range(length))


def is_ascii(s):

    if PY3:
        if isinstance(s, bytes):
            try:
                s.decode("ascii").encode("ascii")
            except UnicodeDecodeError:
                return False
            except UnicodeEncodeError:
                return False
            return True

    try:
        s.encode("ascii")
    except UnicodeEncodeError:
        return False
    except UnicodeDecodeError:
        return False
    else:
        return True


def to_ascii(s):
    """Converts a string to ascii if it is ascii, otherwise leave it alone.

    If given None then will return None.
    """
    if PY3:
        return s

    if s is None:
        return None

    try:
        return s.encode("ascii")
    except UnicodeEncodeError:
        return s


def assert_valid_client_secret(client_secret):
    """Validate that a given string matches the client_secret regex defined by the spec"""
    if client_secret_regex.match(client_secret) is None:
        raise SynapseError(
            400, "Invalid client_secret parameter", errcode=Codes.INVALID_PARAM
        )


def shortstr(iterable: Iterable, maxitems: int = 5) -> str:
    """If iterable has maxitems or fewer, return the stringification of a list
    containing those items.

    Otherwise, return the stringification of a a list with the first maxitems items,
    followed by "...".

    Args:
        iterable: iterable to truncate
        maxitems: number of items to return before truncating
    """

    items = list(itertools.islice(iterable, maxitems + 1))
    if len(items) <= maxitems:
        return str(items)
    return "[" + ", ".join(repr(r) for r in items[:maxitems]) + ", ...]"