"""
This file enables email-based authentication for Django. The only steps required are
1. Add 'EmailAuthenticationBackend' to your settings' AUTHENTICATION_BACKENDS file
2. Add the {'authentication_form': EmailAuthenticationForm} to your login view (if using 'django.contrib.auth.views.login')
3. When saving a User instance, generate the username from the email using the 'generate_hash_from_email' function
"""

import hashlib

from django import forms
from django.contrib.auth.models import User, check_password
from django.contrib.auth import authenticate
from django.core.exceptions import MultipleObjectsReturned
from django.core.validators import email_re

def generate_hash_from_email(email_string):
    """
    Make a hash of the email to store as a username (no longer than 30 characters)
    This ensures that the emails stay unique as only the username field in the User model is required to be unique.
    """
    m = hashlib.md5()
    m.update(email_string.lower())
    return m.hexdigest()[:30]

class BasicBackend:
    """Basic backend: used by EmailAuthenticationBackend"""
    def get_user(self, user_id):
        try:
            return User.objects.get(pk=user_id)
        except User.DoesNotExist:
            return None


class EmailAuthenticationBackend(BasicBackend):
    """Backend used by django authentication: set in base.py"""

    def authenticate(self, email=None, password=None):
        if email_re.search(email):
            try:
                user = User.objects.get(email=email)
            except User.DoesNotExist:
                user = None
            except MultipleObjectsReturned:
                user = None
            else:
                if not user.check_password(password):
                   user = None
            finally:
                return user
        return None


class EmailAuthenticationForm(forms.Form):
    """Email login form: passed to django.contrib.auth.login"""

    email = forms.CharField(label="Email", max_length=75)
    password = forms.CharField(label="Password", widget=forms.PasswordInput)

    def __init__(self, request=None, *args, **kwargs):
        self.request = request
        self.user_cache = None
        super(EmailAuthenticationForm, self).__init__(*args, **kwargs)

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

        if email and password:
            self.user_cache = authenticate(email=email, password=password)
            if not email_re.search(email):
                raise forms.ValidationError("Please enter a valid email")
            if self.user_cache is None:
                raise forms.ValidationError("Please enter a correct email and password.")
            elif not self.user_cache.is_active:
                raise forms.ValidationError("This account is inactive.")

        if self.request:
            if not self.request.session.test_cookie_worked():
                raise forms.ValidationError("Your Web browser doesn't appear to have cookies enabled. Cookies are required for logging in.")

        return self.cleaned_data

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

    def get_user(self):
        return self.user_cache