import functools
import gzip
import re
from difflib import SequenceMatcher
from pathlib import Path

from django.conf import settings
from django.core.exceptions import (
    FieldDoesNotExist, ImproperlyConfigured, ValidationError,
)
from django.utils.functional import lazy
from django.utils.html import format_html, format_html_join
from django.utils.module_loading import import_string
from django.utils.translation import gettext as _, ngettext


@functools.lru_cache(maxsize=None)
def get_default_password_validators():
    return get_password_validators(settings.AUTH_PASSWORD_VALIDATORS)


def get_password_validators(validator_config):
    validators = []
    for validator in validator_config:
        try:
            klass = import_string(validator['NAME'])
        except ImportError:
            msg = "The module in NAME could not be imported: %s. Check your AUTH_PASSWORD_VALIDATORS setting."
            raise ImproperlyConfigured(msg % validator['NAME'])
        validators.append(klass(**validator.get('OPTIONS', {})))

    return validators


def validate_password(password, user=None, password_validators=None):
    """
    Validate whether the password meets all validator requirements.

    If the password is valid, return ``None``.
    If the password is invalid, raise ValidationError with all error messages.
    """
    errors = []
    if password_validators is None:
        password_validators = get_default_password_validators()
    for validator in password_validators:
        try:
            validator.validate(password, user)
        except ValidationError as error:
            errors.append(error)
    if errors:
        raise ValidationError(errors)


def password_changed(password, user=None, password_validators=None):
    """
    Inform all validators that have implemented a password_changed() method
    that the password has been changed.
    """
    if password_validators is None:
        password_validators = get_default_password_validators()
    for validator in password_validators:
        password_changed = getattr(validator, 'password_changed', lambda *a: None)
        password_changed(password, user)


def password_validators_help_texts(password_validators=None):
    """
    Return a list of all help texts of all configured validators.
    """
    help_texts = []
    if password_validators is None:
        password_validators = get_default_password_validators()
    for validator in password_validators:
        help_texts.append(validator.get_help_text())
    return help_texts


def _password_validators_help_text_html(password_validators=None):
    """
    Return an HTML string with all help texts of all configured validators
    in an <ul>.
    """
    help_texts = password_validators_help_texts(password_validators)
    help_items = format_html_join('', '<li>{}</li>', ((help_text,) for help_text in help_texts))
    return format_html('<ul>{}</ul>', help_items) if help_items else ''


password_validators_help_text_html = lazy(_password_validators_help_text_html, str)


class MinimumLengthValidator:
    """
    Validate whether the password is of a minimum length.
    """
    def __init__(self, min_length=8):
        self.min_length = min_length

    def validate(self, password, user=None):
        if len(password) < self.min_length:
            raise ValidationError(
                ngettext(
                    "This password is too short. It must contain at least %(min_length)d character.",
                    "This password is too short. It must contain at least %(min_length)d characters.",
                    self.min_length
                ),
                code='password_too_short',
                params={'min_length': self.min_length},
            )

    def get_help_text(self):
        return ngettext(
            "Your password must contain at least %(min_length)d character.",
            "Your password must contain at least %(min_length)d characters.",
            self.min_length
        ) % {'min_length': self.min_length}


def exceeds_maximum_length_ratio(password, max_similarity, value):
    """
    Test that value is within a reasonable range of password.

    The following ratio calculations are based on testing SequenceMatcher like
    this:

    for i in range(0,6):
      print(10**i, SequenceMatcher(a='A', b='A'*(10**i)).quick_ratio())

    which yields:

    1 1.0
    10 0.18181818181818182
    100 0.019801980198019802
    1000 0.001998001998001998
    10000 0.00019998000199980003
    100000 1.999980000199998e-05

    This means a length_ratio of 10 should never yield a similarity higher than
    0.2, for 100 this is down to 0.02 and for 1000 it is 0.002. This can be
    calculated via 2 / length_ratio. As a result we avoid the potentially
    expensive sequence matching.
    """
    pwd_len = len(password)
    length_bound_similarity = max_similarity / 2 * pwd_len
    value_len = len(value)
    return pwd_len >= 10 * value_len and value_len < length_bound_similarity


class UserAttributeSimilarityValidator:
    """
    Validate whether the password is sufficiently different from the user's
    attributes.

    If no specific attributes are provided, look at a sensible list of
    defaults. Attributes that don't exist are ignored. Comparison is made to
    not only the full attribute value, but also its components, so that, for
    example, a password is validated against either part of an email address,
    as well as the full address.
    """
    DEFAULT_USER_ATTRIBUTES = ('username', 'first_name', 'last_name', 'email')

    def __init__(self, user_attributes=DEFAULT_USER_ATTRIBUTES, max_similarity=0.7):
        self.user_attributes = user_attributes
        if max_similarity < 0.1:
            raise ValueError('max_similarity must be at least 0.1')
        self.max_similarity = max_similarity

    def validate(self, password, user=None):
        if not user:
            return

        password = password.lower()
        for attribute_name in self.user_attributes:
            value = getattr(user, attribute_name, None)
            if not value or not isinstance(value, str):
                continue
            value_lower = value.lower()
            value_parts = re.split(r'\W+', value_lower) + [value_lower]
            for value_part in value_parts:
                if exceeds_maximum_length_ratio(password, self.max_similarity, value_part):
                    continue
                if SequenceMatcher(a=password, b=value_part).quick_ratio() >= self.max_similarity:
                    try:
                        verbose_name = str(user._meta.get_field(attribute_name).verbose_name)
                    except FieldDoesNotExist:
                        verbose_name = attribute_name
                    raise ValidationError(
                        _("The password is too similar to the %(verbose_name)s."),
                        code='password_too_similar',
                        params={'verbose_name': verbose_name},
                    )

    def get_help_text(self):
        return _('Your password can’t be too similar to your other personal information.')


class CommonPasswordValidator:
    """
    Validate whether the password is a common password.

    The password is rejected if it occurs in a provided list of passwords,
    which may be gzipped. The list Django ships with contains 20000 common
    passwords (lowercased and deduplicated), created by Royce Williams:
    https://gist.github.com/roycewilliams/281ce539915a947a23db17137d91aeb7
    The password list must be lowercased to match the comparison in validate().
    """
    DEFAULT_PASSWORD_LIST_PATH = Path(__file__).resolve().parent / 'common-passwords.txt.gz'

    def __init__(self, password_list_path=DEFAULT_PASSWORD_LIST_PATH):
        try:
            with gzip.open(password_list_path, 'rt', encoding='utf-8') as f:
                self.passwords = {x.strip() for x in f}
        except OSError:
            with open(password_list_path) as f:
                self.passwords = {x.strip() for x in f}

    def validate(self, password, user=None):
        if password.lower().strip() in self.passwords:
            raise ValidationError(
                _("This password is too common."),
                code='password_too_common',
            )

    def get_help_text(self):
        return _('Your password can’t be a commonly used password.')


class NumericPasswordValidator:
    """
    Validate whether the password is alphanumeric.
    """
    def validate(self, password, user=None):
        if password.isdigit():
            raise ValidationError(
                _("This password is entirely numeric."),
                code='password_entirely_numeric',
            )

    def get_help_text(self):
        return _('Your password can’t be entirely numeric.')
