from __future__ import unicode_literals

from django.core.exceptions import PermissionDenied
from django.core.mail import send_mail
from django.core import validators
from django.db import models
from django.db.models.manager import EmptyManager
from django.utils.crypto import get_random_string, salted_hmac
from django.utils import six
from django.utils.translation import ugettext_lazy as _
from django.utils import timezone

from django.contrib import auth
from django.contrib.auth.hashers import (
    check_password, make_password, is_password_usable)
from django.contrib.auth.signals import user_logged_in
from django.contrib.contenttypes.models import ContentType
from django.utils.encoding import python_2_unicode_compatible


def update_last_login(sender, user, **kwargs):
    """
    A signal receiver which updates the last_login date for
    the user logging in.
    """
    user.last_login = timezone.now()
    user.save(update_fields=['last_login'])
user_logged_in.connect(update_last_login)


class PermissionManager(models.Manager):
    def get_by_natural_key(self, codename, app_label, model):
        return self.get(
            codename=codename,
            content_type=ContentType.objects.get_by_natural_key(app_label,
                                                                model),
        )


@python_2_unicode_compatible
class Permission(models.Model):
    """
    The permissions system provides a way to assign permissions to specific
    users and groups of users.

    The permission system is used by the Django admin site, but may also be
    useful in your own code. The Django admin site uses permissions as follows:

        - The "add" permission limits the user's ability to view the "add" form
          and add an object.
        - The "change" permission limits a user's ability to view the change
          list, view the "change" form and change an object.
        - The "delete" permission limits the ability to delete an object.

    Permissions are set globally per type of object, not per specific object
    instance. It is possible to say "Mary may change news stories," but it's
    not currently possible to say "Mary may change news stories, but only the
    ones she created herself" or "Mary may only change news stories that have a
    certain status or publication date."

    Three basic permissions -- add, change and delete -- are automatically
    created for each Django model.
    """
    name = models.CharField(_('name'), max_length=255)
    content_type = models.ForeignKey(ContentType)
    codename = models.CharField(_('codename'), max_length=100)
    objects = PermissionManager()

    class Meta:
        verbose_name = _('permission')
        verbose_name_plural = _('permissions')
        unique_together = (('content_type', 'codename'),)
        ordering = ('content_type__app_label', 'content_type__model',
                    'codename')

    def __str__(self):
        return "%s | %s | %s" % (
            six.text_type(self.content_type.app_label),
            six.text_type(self.content_type),
            six.text_type(self.name))

    def natural_key(self):
        return (self.codename,) + self.content_type.natural_key()
    natural_key.dependencies = ['contenttypes.contenttype']


class GroupManager(models.Manager):
    """
    The manager for the auth's Group model.
    """
    def get_by_natural_key(self, name):
        return self.get(name=name)


@python_2_unicode_compatible
class Group(models.Model):
    """
    Groups are a generic way of categorizing users to apply permissions, or
    some other label, to those users. A user can belong to any number of
    groups.

    A user in a group automatically has all the permissions granted to that
    group. For example, if the group Site editors has the permission
    can_edit_home_page, any user in that group will have that permission.

    Beyond permissions, groups are a convenient way to categorize users to
    apply some label, or extended functionality, to them. For example, you
    could create a group 'Special users', and you could write code that would
    do special things to those users -- such as giving them access to a
    members-only portion of your site, or sending them members-only email
    messages.
    """
    name = models.CharField(_('name'), max_length=80, unique=True)
    permissions = models.ManyToManyField(Permission,
        verbose_name=_('permissions'), blank=True)

    objects = GroupManager()

    class Meta:
        verbose_name = _('group')
        verbose_name_plural = _('groups')

    def __str__(self):
        return self.name

    def natural_key(self):
        return (self.name,)


class BaseUserManager(models.Manager):

    @classmethod
    def normalize_email(cls, email):
        """
        Normalize the address by lowercasing the domain part of the email
        address.
        """
        email = email or ''
        try:
            email_name, domain_part = email.strip().rsplit('@', 1)
        except ValueError:
            pass
        else:
            email = '@'.join([email_name, domain_part.lower()])
        return email

    def make_random_password(self, length=10,
                             allowed_chars='abcdefghjkmnpqrstuvwxyz'
                                           'ABCDEFGHJKLMNPQRSTUVWXYZ'
                                           '23456789'):
        """
        Generates a random password with the given length and given
        allowed_chars. Note that the default value of allowed_chars does not
        have "I" or "O" or letters and digits that look similar -- just to
        avoid confusion.
        """
        return get_random_string(length, allowed_chars)

    def get_by_natural_key(self, username):
        return self.get(**{self.model.USERNAME_FIELD: username})


class UserManager(BaseUserManager):

    def _create_user(self, username, email, password,
                     is_staff, is_superuser, **extra_fields):
        """
        Creates and saves a User with the given username, email and password.
        """
        now = timezone.now()
        if not username:
            raise ValueError('The given username must be set')
        email = self.normalize_email(email)
        user = self.model(username=username, email=email,
                          is_staff=is_staff, is_active=True,
                          is_superuser=is_superuser, last_login=now,
                          date_joined=now, **extra_fields)
        user.set_password(password)
        user.save(using=self._db)
        return user

    def create_user(self, username, email=None, password=None, **extra_fields):
        return self._create_user(username, email, password, False, False,
                                 **extra_fields)

    def create_superuser(self, username, email, password, **extra_fields):
        return self._create_user(username, email, password, True, True,
                                 **extra_fields)


@python_2_unicode_compatible
class AbstractBaseUser(models.Model):
    password = models.CharField(_('password'), max_length=128)
    last_login = models.DateTimeField(_('last login'), default=timezone.now)

    is_active = True

    REQUIRED_FIELDS = []

    class Meta:
        abstract = True

    def get_username(self):
        "Return the identifying username for this User"
        return getattr(self, self.USERNAME_FIELD)

    def __str__(self):
        return self.get_username()

    def natural_key(self):
        return (self.get_username(),)

    def is_anonymous(self):
        """
        Always returns False. This is a way of comparing User objects to
        anonymous users.
        """
        return False

    def is_authenticated(self):
        """
        Always return True. This is a way to tell if the user has been
        authenticated in templates.
        """
        return True

    def set_password(self, raw_password):
        self.password = make_password(raw_password)

    def check_password(self, raw_password):
        """
        Returns a boolean of whether the raw_password was correct. Handles
        hashing formats behind the scenes.
        """
        def setter(raw_password):
            self.set_password(raw_password)
            self.save(update_fields=["password"])
        return check_password(raw_password, self.password, setter)

    def set_unusable_password(self):
        # Sets a value that will never be a valid hash
        self.password = make_password(None)

    def has_usable_password(self):
        return is_password_usable(self.password)

    def get_full_name(self):
        raise NotImplementedError('subclasses of AbstractBaseUser must provide a get_full_name() method')

    def get_short_name(self):
        raise NotImplementedError('subclasses of AbstractBaseUser must provide a get_short_name() method.')

    def get_session_auth_hash(self):
        """
        Returns an HMAC of the password field.
        """
        key_salt = "django.contrib.auth.models.AbstractBaseUser.get_session_auth_hash"
        return salted_hmac(key_salt, self.password).hexdigest()


# A few helper functions for common logic between User and AnonymousUser.
def _user_get_all_permissions(user, obj):
    permissions = set()
    for backend in auth.get_backends():
        if hasattr(backend, "get_all_permissions"):
            permissions.update(backend.get_all_permissions(user, obj))
    return permissions


def _user_has_perm(user, perm, obj):
    """
    A backend can raise `PermissionDenied` to short-circuit permission checking.
    """
    for backend in auth.get_backends():
        if not hasattr(backend, 'has_perm'):
            continue
        try:
            if backend.has_perm(user, perm, obj):
                return True
        except PermissionDenied:
            return False
    return False


def _user_has_module_perms(user, app_label):
    """
    A backend can raise `PermissionDenied` to short-circuit permission checking.
    """
    for backend in auth.get_backends():
        if not hasattr(backend, 'has_module_perms'):
            continue
        try:
            if backend.has_module_perms(user, app_label):
                return True
        except PermissionDenied:
            return False
    return False


class PermissionsMixin(models.Model):
    """
    A mixin class that adds the fields and methods necessary to support
    Django's Group and Permission model using the ModelBackend.
    """
    is_superuser = models.BooleanField(_('superuser status'), default=False,
        help_text=_('Designates that this user has all permissions without '
                    'explicitly assigning them.'))
    groups = models.ManyToManyField(Group, verbose_name=_('groups'),
        blank=True, help_text=_('The groups this user belongs to. A user will '
                                'get all permissions granted to each of '
                                'his/her group.'),
        related_name="user_set", related_query_name="user")
    user_permissions = models.ManyToManyField(Permission,
        verbose_name=_('user permissions'), blank=True,
        help_text=_('Specific permissions for this user.'),
        related_name="user_set", related_query_name="user")

    class Meta:
        abstract = True

    def get_group_permissions(self, obj=None):
        """
        Returns a list of permission strings that this user has through his/her
        groups. This method queries all available auth backends. If an object
        is passed in, only permissions matching this object are returned.
        """
        permissions = set()
        for backend in auth.get_backends():
            if hasattr(backend, "get_group_permissions"):
                permissions.update(backend.get_group_permissions(self, obj))
        return permissions

    def get_all_permissions(self, obj=None):
        return _user_get_all_permissions(self, obj)

    def has_perm(self, perm, obj=None):
        """
        Returns True if the user has the specified permission. This method
        queries all available auth backends, but returns immediately if any
        backend returns True. Thus, a user who has permission from a single
        auth backend is assumed to have permission in general. If an object is
        provided, permissions for this specific object are checked.
        """

        # Active superusers have all permissions.
        if self.is_active and self.is_superuser:
            return True

        # Otherwise we need to check the backends.
        return _user_has_perm(self, perm, obj)

    def has_perms(self, perm_list, obj=None):
        """
        Returns True if the user has each of the specified permissions. If
        object is passed, it checks if the user has all required perms for this
        object.
        """
        for perm in perm_list:
            if not self.has_perm(perm, obj):
                return False
        return True

    def has_module_perms(self, app_label):
        """
        Returns True if the user has any permissions in the given app label.
        Uses pretty much the same logic as has_perm, above.
        """
        # Active superusers have all permissions.
        if self.is_active and self.is_superuser:
            return True

        return _user_has_module_perms(self, app_label)


class AbstractUser(AbstractBaseUser, PermissionsMixin):
    """
    An abstract base class implementing a fully featured User model with
    admin-compliant permissions.

    Username, password and email are required. Other fields are optional.
    """
    username = models.CharField(_('username'), max_length=30, unique=True,
        help_text=_('Required. 30 characters or fewer. Letters, digits and '
                    '@/./+/-/_ only.'),
        validators=[
            validators.RegexValidator(r'^[\w.@+-]+$', _('Enter a valid username.'), 'invalid')
        ])
    first_name = models.CharField(_('first name'), max_length=30, blank=True)
    last_name = models.CharField(_('last name'), max_length=30, blank=True)
    email = models.EmailField(_('email address'), blank=True)
    is_staff = models.BooleanField(_('staff status'), default=False,
        help_text=_('Designates whether the user can log into this admin '
                    'site.'))
    is_active = models.BooleanField(_('active'), default=True,
        help_text=_('Designates whether this user should be treated as '
                    'active. Unselect this instead of deleting accounts.'))
    date_joined = models.DateTimeField(_('date joined'), default=timezone.now)

    objects = UserManager()

    USERNAME_FIELD = 'username'
    REQUIRED_FIELDS = ['email']

    class Meta:
        verbose_name = _('user')
        verbose_name_plural = _('users')
        abstract = True

    def get_full_name(self):
        """
        Returns the first_name plus the last_name, with a space in between.
        """
        full_name = '%s %s' % (self.first_name, self.last_name)
        return full_name.strip()

    def get_short_name(self):
        "Returns the short name for the user."
        return self.first_name

    def email_user(self, subject, message, from_email=None, **kwargs):
        """
        Sends an email to this User.
        """
        send_mail(subject, message, from_email, [self.email], **kwargs)


class User(AbstractUser):
    """
    Users within the Django authentication system are represented by this
    model.

    Username, password and email are required. Other fields are optional.
    """
    class Meta(AbstractUser.Meta):
        swappable = 'AUTH_USER_MODEL'


@python_2_unicode_compatible
class AnonymousUser(object):
    id = None
    pk = None
    username = ''
    is_staff = False
    is_active = False
    is_superuser = False
    _groups = EmptyManager(Group)
    _user_permissions = EmptyManager(Permission)

    def __init__(self):
        pass

    def __str__(self):
        return 'AnonymousUser'

    def __eq__(self, other):
        return isinstance(other, self.__class__)

    def __ne__(self, other):
        return not self.__eq__(other)

    def __hash__(self):
        return 1  # instances always return the same hash value

    def save(self):
        raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")

    def delete(self):
        raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")

    def set_password(self, raw_password):
        raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")

    def check_password(self, raw_password):
        raise NotImplementedError("Django doesn't provide a DB representation for AnonymousUser.")

    def _get_groups(self):
        return self._groups
    groups = property(_get_groups)

    def _get_user_permissions(self):
        return self._user_permissions
    user_permissions = property(_get_user_permissions)

    def get_group_permissions(self, obj=None):
        return set()

    def get_all_permissions(self, obj=None):
        return _user_get_all_permissions(self, obj=obj)

    def has_perm(self, perm, obj=None):
        return _user_has_perm(self, perm, obj=obj)

    def has_perms(self, perm_list, obj=None):
        for perm in perm_list:
            if not self.has_perm(perm, obj):
                return False
        return True

    def has_module_perms(self, module):
        return _user_has_module_perms(self, module)

    def is_anonymous(self):
        return True

    def is_authenticated(self):
        return False
