from django import forms
from django.conf import settings
from django.contrib.auth import authenticate
from django.contrib.auth.forms import SetPasswordForm, AuthenticationForm, \
    PasswordResetForm
from django.core.exceptions import ValidationError
from django.urls import reverse
from django.core.validators import validate_email
from django.utils.translation import ugettext as _
from django.contrib.auth.tokens import default_token_generator
from django.utils.http import urlsafe_base64_encode
from django.utils.encoding import force_bytes
from django.contrib.auth.tokens import PasswordResetTokenGenerator
from django.http import HttpRequest
from jinja2 import Markup as mark_safe

from zerver.lib.actions import do_change_password, email_not_system_bot
from zerver.lib.email_validation import email_allowed_for_realm, \
    validate_email_not_already_in_realm
from zerver.lib.name_restrictions import is_reserved_subdomain, is_disposable_domain
from zerver.lib.rate_limiter import RateLimited, RateLimitedObject
from zerver.lib.request import JsonableError
from zerver.lib.send_email import send_email, FromAddress
from zerver.lib.subdomains import get_subdomain, is_root_domain_available
from zerver.lib.users import check_full_name
from zerver.models import Realm, get_user_by_delivery_email, UserProfile, get_realm, \
    email_to_domain, \
    DisposableEmailError, DomainNotAllowedForRealmError, \
    EmailContainsPlusError
from zproject.backends import email_auth_enabled, email_belongs_to_ldap, check_password_strength

import logging
import re
import DNS

from typing import Any, List, Optional, Dict, Tuple
from two_factor.forms import AuthenticationTokenForm as TwoFactorAuthenticationTokenForm
from two_factor.utils import totp_digits

MIT_VALIDATION_ERROR = 'That user does not exist at MIT or is a ' + \
                       '<a href="https://ist.mit.edu/email-lists">mailing list</a>. ' + \
                       'If you want to sign up an alias for Zulip, ' + \
                       '<a href="mailto:support@zulipchat.com">contact us</a>.'
WRONG_SUBDOMAIN_ERROR = "Your Zulip account is not a member of the " + \
                        "organization associated with this subdomain.  " + \
                        "Please contact your organization administrator with any questions."
DEACTIVATED_ACCOUNT_ERROR = "Your account is no longer active. " + \
                            "Please contact your organization administrator to reactivate it."
PASSWORD_TOO_WEAK_ERROR = "The password is too weak."
AUTHENTICATION_RATE_LIMITED_ERROR = "You're making too many attempts to sign in. " + \
                                    "Try again in %s seconds or contact your organization administrator " + \
                                    "for help."

def email_is_not_mit_mailing_list(email: str) -> None:
    """Prevent MIT mailing lists from signing up for Zulip"""
    if "@mit.edu" in email:
        username = email.rsplit("@", 1)[0]
        # Check whether the user exists and can get mail.
        try:
            DNS.dnslookup("%s.pobox.ns.athena.mit.edu" % (username,), DNS.Type.TXT)
        except DNS.Base.ServerError as e:
            if e.rcode == DNS.Status.NXDOMAIN:
                raise ValidationError(mark_safe(MIT_VALIDATION_ERROR))
            else:
                raise AssertionError("Unexpected DNS error")

def check_subdomain_available(subdomain: str, from_management_command: bool=False) -> None:
    error_strings = {
        'too short': _("Subdomain needs to have length 3 or greater."),
        'extremal dash': _("Subdomain cannot start or end with a '-'."),
        'bad character': _("Subdomain can only have lowercase letters, numbers, and '-'s."),
        'unavailable': _("Subdomain unavailable. Please choose a different one.")}

    if subdomain == Realm.SUBDOMAIN_FOR_ROOT_DOMAIN:
        if is_root_domain_available():
            return
        raise ValidationError(error_strings['unavailable'])
    if subdomain[0] == '-' or subdomain[-1] == '-':
        raise ValidationError(error_strings['extremal dash'])
    if not re.match('^[a-z0-9-]*$', subdomain):
        raise ValidationError(error_strings['bad character'])
    if from_management_command:
        return
    if len(subdomain) < 3:
        raise ValidationError(error_strings['too short'])
    if is_reserved_subdomain(subdomain) or \
       Realm.objects.filter(string_id=subdomain).exists():
        raise ValidationError(error_strings['unavailable'])

class RegistrationForm(forms.Form):
    MAX_PASSWORD_LENGTH = 100
    full_name = forms.CharField(max_length=UserProfile.MAX_NAME_LENGTH)
    # The required-ness of the password field gets overridden if it isn't
    # actually required for a realm
    password = forms.CharField(widget=forms.PasswordInput, max_length=MAX_PASSWORD_LENGTH)
    realm_subdomain = forms.CharField(max_length=Realm.MAX_REALM_SUBDOMAIN_LENGTH, required=False)

    def __init__(self, *args: Any, **kwargs: Any) -> None:
        # Since the superclass doesn't except random extra kwargs, we
        # remove it from the kwargs dict before initializing.
        self.realm_creation = kwargs['realm_creation']
        del kwargs['realm_creation']

        super().__init__(*args, **kwargs)
        if settings.TERMS_OF_SERVICE:
            self.fields['terms'] = forms.BooleanField(required=True)
        self.fields['realm_name'] = forms.CharField(
            max_length=Realm.MAX_REALM_NAME_LENGTH,
            required=self.realm_creation)

    def clean_full_name(self) -> str:
        try:
            return check_full_name(self.cleaned_data['full_name'])
        except JsonableError as e:
            raise ValidationError(e.msg)

    def clean_password(self) -> str:
        password = self.cleaned_data['password']
        if self.fields['password'].required and not check_password_strength(password):
            # The frontend code tries to stop the user from submitting the form with a weak password,
            # but if the user bypasses that protection, this error code path will run.
            raise ValidationError(mark_safe(PASSWORD_TOO_WEAK_ERROR))

        return password

    def clean_realm_subdomain(self) -> str:
        if not self.realm_creation:
            # This field is only used if realm_creation
            return ""

        subdomain = self.cleaned_data['realm_subdomain']
        if 'realm_in_root_domain' in self.data:
            subdomain = Realm.SUBDOMAIN_FOR_ROOT_DOMAIN

        check_subdomain_available(subdomain)
        return subdomain

class ToSForm(forms.Form):
    terms = forms.BooleanField(required=True)

class HomepageForm(forms.Form):
    email = forms.EmailField()

    def __init__(self, *args: Any, **kwargs: Any) -> None:
        self.realm = kwargs.pop('realm', None)
        self.from_multiuse_invite = kwargs.pop('from_multiuse_invite', False)
        super().__init__(*args, **kwargs)

    def clean_email(self) -> str:
        """Returns the email if and only if the user's email address is
        allowed to join the realm they are trying to join."""
        email = self.cleaned_data['email']

        # Otherwise, the user is trying to join a specific realm.
        realm = self.realm
        from_multiuse_invite = self.from_multiuse_invite

        if realm is None:
            raise ValidationError(_("The organization you are trying to "
                                    "join using {email} does not "
                                    "exist.").format(email=email))

        if not from_multiuse_invite and realm.invite_required:
            raise ValidationError(_("Please request an invite for {email} "
                                    "from the organization "
                                    "administrator.").format(email=email))

        try:
            email_allowed_for_realm(email, realm)
        except DomainNotAllowedForRealmError:
            raise ValidationError(
                _("Your email address, {email}, is not in one of the domains "
                  "that are allowed to register for accounts in this organization.").format(
                      string_id=realm.string_id, email=email))
        except DisposableEmailError:
            raise ValidationError(_("Please use your real email address."))
        except EmailContainsPlusError:
            raise ValidationError(_("Email addresses containing + are not allowed in this organization."))

        validate_email_not_already_in_realm(realm, email)

        if realm.is_zephyr_mirror_realm:
            email_is_not_mit_mailing_list(email)

        return email

def email_is_not_disposable(email: str) -> None:
    if is_disposable_domain(email_to_domain(email)):
        raise ValidationError(_("Please use your real email address."))

class RealmCreationForm(forms.Form):
    # This form determines whether users can create a new realm.
    email = forms.EmailField(validators=[email_not_system_bot,
                                         email_is_not_disposable])

class LoggingSetPasswordForm(SetPasswordForm):
    def clean_new_password1(self) -> str:
        new_password = self.cleaned_data['new_password1']
        if not check_password_strength(new_password):
            # The frontend code tries to stop the user from submitting the form with a weak password,
            # but if the user bypasses that protection, this error code path will run.
            raise ValidationError(PASSWORD_TOO_WEAK_ERROR)

        return new_password

    def save(self, commit: bool=True) -> UserProfile:
        do_change_password(self.user, self.cleaned_data['new_password1'],
                           commit=commit)
        return self.user

def generate_password_reset_url(user_profile: UserProfile,
                                token_generator: PasswordResetTokenGenerator) -> str:
    token = token_generator.make_token(user_profile)
    uid = urlsafe_base64_encode(force_bytes(user_profile.id))
    endpoint = reverse('django.contrib.auth.views.password_reset_confirm',
                       kwargs=dict(uidb64=uid, token=token))
    return "{}{}".format(user_profile.realm.uri, endpoint)

class ZulipPasswordResetForm(PasswordResetForm):
    def save(self,
             domain_override: Optional[bool]=None,
             subject_template_name: str='registration/password_reset_subject.txt',
             email_template_name: str='registration/password_reset_email.html',
             use_https: bool=False,
             token_generator: PasswordResetTokenGenerator=default_token_generator,
             from_email: Optional[str]=None,
             request: HttpRequest=None,
             html_email_template_name: Optional[str]=None,
             extra_email_context: Optional[Dict[str, Any]]=None
             ) -> None:
        """
        If the email address has an account in the target realm,
        generates a one-use only link for resetting password and sends
        to the user.

        We send a different email if an associated account does not exist in the
        database, or an account does exist, but not in the realm.

        Note: We ignore protocol and the various email template arguments (those
        are an artifact of using Django's password reset framework).
        """
        email = self.cleaned_data["email"]

        realm = get_realm(get_subdomain(request))

        if not email_auth_enabled(realm):
            logging.info("Password reset attempted for %s even though password auth is disabled.", email)
            return
        if email_belongs_to_ldap(realm, email):
            # TODO: Ideally, we'd provide a user-facing error here
            # about the fact that they aren't allowed to have a
            # password in the Zulip server and should change it in LDAP.
            logging.info("Password reset not allowed for user in LDAP domain")
            return
        if realm.deactivated:
            logging.info("Realm is deactivated")
            return

        if settings.RATE_LIMITING:
            try:
                rate_limit_password_reset_form_by_email(email)
            except RateLimited:
                # TODO: Show an informative, user-facing error message.
                logging.info("Too many password reset attempts for email %s", email)
                return

        user: Optional[UserProfile] = None
        try:
            user = get_user_by_delivery_email(email, realm)
        except UserProfile.DoesNotExist:
            pass

        context = {
            'email': email,
            'realm_uri': realm.uri,
            'realm_name': realm.name,
        }

        if user is not None and not user.is_active:
            context['user_deactivated'] = True
            user = None

        if user is not None:
            context['active_account_in_realm'] = True
            context['reset_url'] = generate_password_reset_url(user, token_generator)
            send_email('zerver/emails/password_reset', to_user_ids=[user.id],
                       from_name=FromAddress.security_email_from_name(user_profile=user),
                       from_address=FromAddress.tokenized_no_reply_address(),
                       context=context)
        else:
            context['active_account_in_realm'] = False
            active_accounts_in_other_realms = UserProfile.objects.filter(
                delivery_email__iexact=email, is_active=True)
            if active_accounts_in_other_realms:
                context['active_accounts_in_other_realms'] = active_accounts_in_other_realms
            language = request.LANGUAGE_CODE
            send_email('zerver/emails/password_reset', to_emails=[email],
                       from_name=FromAddress.security_email_from_name(language=language),
                       from_address=FromAddress.tokenized_no_reply_address(),
                       language=language, context=context)

class RateLimitedPasswordResetByEmail(RateLimitedObject):
    def __init__(self, email: str) -> None:
        self.email = email
        super().__init__()

    def key(self) -> str:
        return "{}:{}".format(type(self).__name__, self.email)

    def rules(self) -> List[Tuple[int, int]]:
        return settings.RATE_LIMITING_RULES['password_reset_form_by_email']

def rate_limit_password_reset_form_by_email(email: str) -> None:
    ratelimited, _ = RateLimitedPasswordResetByEmail(email).rate_limit()
    if ratelimited:
        raise RateLimited

class CreateUserForm(forms.Form):
    full_name = forms.CharField(max_length=100)
    email = forms.EmailField()

class OurAuthenticationForm(AuthenticationForm):
    def clean(self) -> Dict[str, Any]:
        username = self.cleaned_data.get('username')
        password = self.cleaned_data.get('password')

        if username is not None and password:
            subdomain = get_subdomain(self.request)
            try:
                realm = get_realm(subdomain)
            except Realm.DoesNotExist:
                logging.warning("User %s attempted to password login to nonexistent subdomain %s",
                                username, subdomain)
                raise ValidationError("Realm does not exist")

            return_data: Dict[str, Any] = {}
            try:
                self.user_cache = authenticate(request=self.request, username=username, password=password,
                                               realm=realm, return_data=return_data)
            except RateLimited as e:
                secs_to_freedom = int(float(str(e)))
                raise ValidationError(AUTHENTICATION_RATE_LIMITED_ERROR % (secs_to_freedom,))

            if return_data.get("inactive_realm"):
                raise AssertionError("Programming error: inactive realm in authentication form")

            if return_data.get("inactive_user") and not return_data.get("is_mirror_dummy"):
                # We exclude mirror dummy accounts here. They should be treated as the
                # user never having had an account, so we let them fall through to the
                # normal invalid_login case below.
                raise ValidationError(mark_safe(DEACTIVATED_ACCOUNT_ERROR))

            if return_data.get("invalid_subdomain"):
                logging.warning("User %s attempted to password login to wrong subdomain %s",
                                username, subdomain)
                raise ValidationError(mark_safe(WRONG_SUBDOMAIN_ERROR))

            if self.user_cache is None:
                raise forms.ValidationError(
                    self.error_messages['invalid_login'],
                    code='invalid_login',
                    params={'username': self.username_field.verbose_name},
                )

            self.confirm_login_allowed(self.user_cache)

        return self.cleaned_data

    def add_prefix(self, field_name: str) -> str:
        """Disable prefix, since Zulip doesn't use this Django forms feature
        (and django-two-factor does use it), and we'd like both to be
        happy with this form.
        """
        return field_name

class AuthenticationTokenForm(TwoFactorAuthenticationTokenForm):
    """
    We add this form to update the widget of otp_token. The default
    widget is an input element whose type is a number, which doesn't
    stylistically match our theme.
    """
    otp_token = forms.IntegerField(label=_("Token"), min_value=1,
                                   max_value=int('9' * totp_digits()),
                                   widget=forms.TextInput)

class MultiEmailField(forms.Field):
    def to_python(self, emails: str) -> List[str]:
        """Normalize data to a list of strings."""
        if not emails:
            return []

        return [email.strip() for email in emails.split(',')]

    def validate(self, emails: List[str]) -> None:
        """Check if value consists only of valid emails."""
        super().validate(emails)
        for email in emails:
            validate_email(email)

class FindMyTeamForm(forms.Form):
    emails = MultiEmailField(
        help_text=_("Add up to 10 comma-separated email addresses."))

    def clean_emails(self) -> List[str]:
        emails = self.cleaned_data['emails']
        if len(emails) > 10:
            raise forms.ValidationError(_("Please enter at most 10 emails."))

        return emails

class RealmRedirectForm(forms.Form):
    subdomain = forms.CharField(max_length=Realm.MAX_REALM_SUBDOMAIN_LENGTH, required=True)

    def clean_subdomain(self) -> str:
        subdomain = self.cleaned_data['subdomain']
        try:
            get_realm(subdomain)
        except Realm.DoesNotExist:
            raise ValidationError(_("We couldn't find that Zulip organization."))
        return subdomain