from __future__ import unicode_literals

from collections import OrderedDict

from django import forms
from django.core.mail import EmailMultiAlternatives
from django.forms.utils import flatatt
from django.template import loader
from django.utils.encoding import force_bytes
from django.utils.html import format_html, format_html_join
from django.utils.http import urlsafe_base64_encode
from django.utils.safestring import mark_safe
from django.utils.text import capfirst
from django.utils.translation import ugettext, ugettext_lazy as _

from django.contrib.auth import authenticate, get_user_model
from django.contrib.auth.models import User
from django.contrib.auth.hashers import UNUSABLE_PASSWORD_PREFIX, identify_hasher
from django.contrib.auth.tokens import default_token_generator
from django.contrib.sites.shortcuts import get_current_site


UNMASKED_DIGITS_TO_SHOW = 6


def mask_password(password):
    shown = password[:UNMASKED_DIGITS_TO_SHOW]
    masked = "*" * max(len(password) - UNMASKED_DIGITS_TO_SHOW, 0)
    return shown + masked


class ReadOnlyPasswordHashWidget(forms.Widget):
    def render(self, name, value, attrs):
        encoded = value
        final_attrs = self.build_attrs(attrs)

        if not encoded or encoded.startswith(UNUSABLE_PASSWORD_PREFIX):
            summary = mark_safe("<strong>%s</strong>" % ugettext("No password set."))
        else:
            try:
                hasher = identify_hasher(encoded)
            except ValueError:
                summary = mark_safe("<strong>%s</strong>" % ugettext(
                    "Invalid password format or unknown hashing algorithm."))
            else:
                summary = format_html_join('',
                                           "<strong>{}</strong>: {} ",
                                           ((ugettext(key), value)
                                            for key, value in hasher.safe_summary(encoded).items())
                                           )

        return format_html("<div{}>{}</div>", flatatt(final_attrs), summary)


class ReadOnlyPasswordHashField(forms.Field):
    widget = ReadOnlyPasswordHashWidget

    def __init__(self, *args, **kwargs):
        kwargs.setdefault("required", False)
        super(ReadOnlyPasswordHashField, self).__init__(*args, **kwargs)

    def bound_data(self, data, initial):
        # Always return initial because the widget doesn't
        # render an input field.
        return initial

    def has_changed(self, initial, data):
        return False


class UserCreationForm(forms.ModelForm):
    """
    A form that creates a user, with no privileges, from the given username and
    password.
    """
    error_messages = {
        'password_mismatch': _("The two password fields didn't match."),
    }
    password1 = forms.CharField(label=_("Password"),
        widget=forms.PasswordInput)
    password2 = forms.CharField(label=_("Password confirmation"),
        widget=forms.PasswordInput,
        help_text=_("Enter the same password as above, for verification."))

    class Meta:
        model = User
        fields = ("username",)

    def clean_password2(self):
        password1 = self.cleaned_data.get("password1")
        password2 = self.cleaned_data.get("password2")
        if password1 and password2 and password1 != password2:
            raise forms.ValidationError(
                self.error_messages['password_mismatch'],
                code='password_mismatch',
            )
        return password2

    def save(self, commit=True):
        user = super(UserCreationForm, self).save(commit=False)
        user.set_password(self.cleaned_data["password1"])
        if commit:
            user.save()
        return user


class UserChangeForm(forms.ModelForm):
    password = ReadOnlyPasswordHashField(label=_("Password"),
        help_text=_("Raw passwords are not stored, so there is no way to see "
                    "this user's password, but you can change the password "
                    "using <a href=\"password/\">this form</a>."))

    class Meta:
        model = User
        fields = '__all__'

    def __init__(self, *args, **kwargs):
        super(UserChangeForm, self).__init__(*args, **kwargs)
        f = self.fields.get('user_permissions', None)
        if f is not None:
            f.queryset = f.queryset.select_related('content_type')

    def clean_password(self):
        # Regardless of what the user provides, return the initial value.
        # This is done here, rather than on the field, because the
        # field does not have access to the initial value
        return self.initial["password"]


class AuthenticationForm(forms.Form):
    """
    Base class for authenticating users. Extend this to get a form that accepts
    username/password logins.
    """
    username = forms.CharField(max_length=254)
    password = forms.CharField(label=_("Password"), widget=forms.PasswordInput)

    error_messages = {
        'invalid_login': _("Please enter a correct %(username)s and password. "
                           "Note that both fields may be case-sensitive."),
        'inactive': _("This account is inactive."),
    }

    def __init__(self, request=None, *args, **kwargs):
        """
        The 'request' parameter is set for custom auth use by subclasses.
        The form data comes in via the standard 'data' kwarg.
        """
        self.request = request
        self.user_cache = None
        super(AuthenticationForm, self).__init__(*args, **kwargs)

        # Set the label for the "username" field.
        UserModel = get_user_model()
        self.username_field = UserModel._meta.get_field(UserModel.USERNAME_FIELD)
        if self.fields['username'].label is None:
            self.fields['username'].label = capfirst(self.username_field.verbose_name)

    def clean(self):
        username = self.cleaned_data.get('username')
        password = self.cleaned_data.get('password')

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

        return self.cleaned_data

    def confirm_login_allowed(self, user):
        """
        Controls whether the given User may log in. This is a policy setting,
        independent of end-user authentication. This default behavior is to
        allow login by active users, and reject login by inactive users.

        If the given user cannot log in, this method should raise a
        ``forms.ValidationError``.

        If the given user may log in, this method should return None.
        """
        if not user.is_active:
            raise forms.ValidationError(
                self.error_messages['inactive'],
                code='inactive',
            )

    def get_user_id(self):
        if self.user_cache:
            return self.user_cache.id
        return None

    def get_user(self):
        return self.user_cache


class PasswordResetForm(forms.Form):
    email = forms.EmailField(label=_("Email"), max_length=254)

    def send_mail(self, subject_template_name, email_template_name,
                  context, from_email, to_email, html_email_template_name=None):
        """
        Sends a django.core.mail.EmailMultiAlternatives to `to_email`.
        """
        subject = loader.render_to_string(subject_template_name, context)
        # Email subject *must not* contain newlines
        subject = ''.join(subject.splitlines())
        body = loader.render_to_string(email_template_name, context)

        email_message = EmailMultiAlternatives(subject, body, from_email, [to_email])
        if html_email_template_name is not None:
            html_email = loader.render_to_string(html_email_template_name, context)
            email_message.attach_alternative(html_email, 'text/html')

        email_message.send()

    def get_users(self, email):
        """Given an email, return matching user(s) who should receive a reset.

        This allows subclasses to more easily customize the default policies
        that prevent inactive users and users with unusable passwords from
        resetting their password.

        """
        active_users = get_user_model()._default_manager.filter(
            email__iexact=email, is_active=True)
        return (u for u in active_users if u.has_usable_password())

    def save(self, domain_override=None,
             subject_template_name='registration/password_reset_subject.txt',
             email_template_name='registration/password_reset_email.html',
             use_https=False, token_generator=default_token_generator,
             from_email=None, request=None, html_email_template_name=None):
        """
        Generates a one-use only link for resetting password and sends to the
        user.
        """
        email = self.cleaned_data["email"]
        for user in self.get_users(email):
            if not domain_override:
                current_site = get_current_site(request)
                site_name = current_site.name
                domain = current_site.domain
            else:
                site_name = domain = domain_override
            context = {
                'email': user.email,
                'domain': domain,
                'site_name': site_name,
                'uid': urlsafe_base64_encode(force_bytes(user.pk)),
                'user': user,
                'token': token_generator.make_token(user),
                'protocol': 'https' if use_https else 'http',
            }

            self.send_mail(subject_template_name, email_template_name,
                           context, from_email, user.email,
                           html_email_template_name=html_email_template_name)


class SetPasswordForm(forms.Form):
    """
    A form that lets a user change set their password without entering the old
    password
    """
    error_messages = {
        'password_mismatch': _("The two password fields didn't match."),
    }
    new_password1 = forms.CharField(label=_("New password"),
                                    widget=forms.PasswordInput)
    new_password2 = forms.CharField(label=_("New password confirmation"),
                                    widget=forms.PasswordInput)

    def __init__(self, user, *args, **kwargs):
        self.user = user
        super(SetPasswordForm, self).__init__(*args, **kwargs)

    def clean_new_password2(self):
        password1 = self.cleaned_data.get('new_password1')
        password2 = self.cleaned_data.get('new_password2')
        if password1 and password2:
            if password1 != password2:
                raise forms.ValidationError(
                    self.error_messages['password_mismatch'],
                    code='password_mismatch',
                )
        return password2

    def save(self, commit=True):
        self.user.set_password(self.cleaned_data['new_password1'])
        if commit:
            self.user.save()
        return self.user


class PasswordChangeForm(SetPasswordForm):
    """
    A form that lets a user change their password by entering their old
    password.
    """
    error_messages = dict(SetPasswordForm.error_messages, **{
        'password_incorrect': _("Your old password was entered incorrectly. "
                                "Please enter it again."),
    })
    old_password = forms.CharField(label=_("Old password"),
                                   widget=forms.PasswordInput)

    def clean_old_password(self):
        """
        Validates that the old_password field is correct.
        """
        old_password = self.cleaned_data["old_password"]
        if not self.user.check_password(old_password):
            raise forms.ValidationError(
                self.error_messages['password_incorrect'],
                code='password_incorrect',
            )
        return old_password

PasswordChangeForm.base_fields = OrderedDict(
    (k, PasswordChangeForm.base_fields[k])
    for k in ['old_password', 'new_password1', 'new_password2']
)


class AdminPasswordChangeForm(forms.Form):
    """
    A form used to change the password of a user in the admin interface.
    """
    error_messages = {
        'password_mismatch': _("The two password fields didn't match."),
    }
    required_css_class = 'required'
    password1 = forms.CharField(label=_("Password"),
                                widget=forms.PasswordInput)
    password2 = forms.CharField(label=_("Password (again)"),
                                widget=forms.PasswordInput)

    def __init__(self, user, *args, **kwargs):
        self.user = user
        super(AdminPasswordChangeForm, self).__init__(*args, **kwargs)

    def clean_password2(self):
        password1 = self.cleaned_data.get('password1')
        password2 = self.cleaned_data.get('password2')
        if password1 and password2:
            if password1 != password2:
                raise forms.ValidationError(
                    self.error_messages['password_mismatch'],
                    code='password_mismatch',
                )
        return password2

    def save(self, commit=True):
        """
        Saves the new password.
        """
        self.user.set_password(self.cleaned_data["password1"])
        if commit:
            self.user.save()
        return self.user

    def _get_changed_data(self):
        data = super(AdminPasswordChangeForm, self).changed_data
        for name in self.fields.keys():
            if name not in data:
                return []
        return ['password']
    changed_data = property(_get_changed_data)