"""
Classes used to model the roles used in the courseware. Each role is responsible for checking membership,
adding users, removing users, and listing members
"""

from __future__ import absolute_import

import logging
from abc import ABCMeta, abstractmethod
from collections import defaultdict

import six
from django.contrib.auth.models import User
from opaque_keys.edx.django.models import CourseKeyField

from openedx.core.lib.cache_utils import get_cache
from student.models import CourseAccessRole

log = logging.getLogger(__name__)

# A list of registered access roles.
REGISTERED_ACCESS_ROLES = {}


def register_access_role(cls):
    """
    Decorator that allows access roles to be registered within the roles module and referenced by their
    string values.

    Assumes that the decorated class has a "ROLE" attribute, defining its type.

    """
    try:
        role_name = cls.ROLE
        REGISTERED_ACCESS_ROLES[role_name] = cls
    except AttributeError:
        log.exception(u"Unable to register Access Role with attribute 'ROLE'.")
    return cls


class BulkRoleCache(object):
    CACHE_NAMESPACE = u"student.roles.BulkRoleCache"
    CACHE_KEY = u'roles_by_user'

    @classmethod
    def prefetch(cls, users):
        roles_by_user = defaultdict(set)
        get_cache(cls.CACHE_NAMESPACE)[cls.CACHE_KEY] = roles_by_user

        for role in CourseAccessRole.objects.filter(user__in=users).select_related('user'):
            roles_by_user[role.user.id].add(role)

        users_without_roles = [u for u in users if u.id not in roles_by_user]
        for user in users_without_roles:
            roles_by_user[user.id] = set()

    @classmethod
    def get_user_roles(cls, user):
        return get_cache(cls.CACHE_NAMESPACE)[cls.CACHE_KEY][user.id]


class RoleCache(object):
    """
    A cache of the CourseAccessRoles held by a particular user
    """
    def __init__(self, user):
        try:
            self._roles = BulkRoleCache.get_user_roles(user)
        except KeyError:
            self._roles = set(
                CourseAccessRole.objects.filter(user=user).all()
            )

    def has_role(self, role, course_id, org):
        """
        Return whether this RoleCache contains a role with the specified role, course_id, and org
        """
        return any(
            access_role.role == role and
            access_role.course_id == course_id and
            access_role.org == org
            for access_role in self._roles
        )


class AccessRole(six.with_metaclass(ABCMeta, object)):
    """
    Object representing a role with particular access to a resource
    """

    @abstractmethod
    def has_user(self, user):
        """
        Return whether the supplied django user has access to this role.
        """
        return False

    @abstractmethod
    def add_users(self, *users):
        """
        Add the role to the supplied django users.
        """
        pass

    @abstractmethod
    def remove_users(self, *users):
        """
        Remove the role from the supplied django users.
        """
        pass

    @abstractmethod
    def users_with_role(self):
        """
        Return a django QuerySet for all of the users with this role
        """
        return User.objects.none()


class GlobalStaff(AccessRole):
    """
    The global staff role
    """
    def has_user(self, user):
        return bool(user and user.is_staff)

    def add_users(self, *users):
        for user in users:
            if user.is_authenticated and user.is_active:
                user.is_staff = True
                user.save()

    def remove_users(self, *users):
        for user in users:
            # don't check is_authenticated nor is_active on purpose
            user.is_staff = False
            user.save()

    def users_with_role(self):
        raise Exception("This operation is un-indexed, and shouldn't be used")


class RoleBase(AccessRole):
    """
    Roles by type (e.g., instructor, beta_user) and optionally org, course_key
    """
    def __init__(self, role_name, org='', course_key=None):
        """
        Create role from required role_name w/ optional org and course_key. You may just provide a role
        name if it's a global role (not constrained to an org or course). Provide org if constrained to
        an org. Provide org and course if constrained to a course. Although, you should use the subclasses
        for all of these.
        """
        super(RoleBase, self).__init__()

        self.org = org
        self.course_key = course_key
        self._role_name = role_name

    # pylint: disable=arguments-differ
    def has_user(self, user, check_user_activation=True):
        """
        Check if the supplied django user has access to this role.

        Arguments:
            user: user to check against access to role
            check_user_activation: Indicating whether or not we need to check
                user activation while checking user roles
        Return:
            bool identifying if user has that particular role or not
        """
        if check_user_activation and not (user.is_authenticated and user.is_active):
            return False

        # pylint: disable=protected-access
        if not hasattr(user, '_roles'):
            # Cache a list of tuples identifying the particular roles that a user has
            # Stored as tuples, rather than django models, to make it cheaper to construct objects for comparison
            user._roles = RoleCache(user)

        return user._roles.has_role(self._role_name, self.course_key, self.org)

    def add_users(self, *users):
        """
        Add the supplied django users to this role.
        """
        # silently ignores anonymous and inactive users so that any that are
        # legit get updated.
        from student.models import CourseAccessRole
        for user in users:
            if user.is_authenticated and user.is_active and not self.has_user(user):
                entry = CourseAccessRole(user=user, role=self._role_name, course_id=self.course_key, org=self.org)
                entry.save()
                if hasattr(user, '_roles'):
                    del user._roles

    def remove_users(self, *users):
        """
        Remove the supplied django users from this role.
        """
        entries = CourseAccessRole.objects.filter(
            user__in=users, role=self._role_name, org=self.org, course_id=self.course_key
        )
        entries.delete()
        for user in users:
            if hasattr(user, '_roles'):
                del user._roles

    def users_with_role(self):
        """
        Return a django QuerySet for all of the users with this role
        """
        # Org roles don't query by CourseKey, so use CourseKeyField.Empty for that query
        if self.course_key is None:
            self.course_key = CourseKeyField.Empty
        entries = User.objects.filter(
            courseaccessrole__role=self._role_name,
            courseaccessrole__org=self.org,
            courseaccessrole__course_id=self.course_key
        )
        return entries


class CourseRole(RoleBase):
    """
    A named role in a particular course
    """
    def __init__(self, role, course_key):
        """
        Args:
            course_key (CourseKey)
        """
        super(CourseRole, self).__init__(role, course_key.org, course_key)

    @classmethod
    def course_group_already_exists(self, course_key):
        return CourseAccessRole.objects.filter(org=course_key.org, course_id=course_key).exists()

    def __repr__(self):
        return '<{}: course_key={}>'.format(self.__class__.__name__, self.course_key)


class OrgRole(RoleBase):
    """
    A named role in a particular org independent of course
    """
    def __repr__(self):
        return '<{}>'.format(self.__class__.__name__)


@register_access_role
class CourseStaffRole(CourseRole):
    """A Staff member of a course"""
    ROLE = 'staff'

    def __init__(self, *args, **kwargs):
        super(CourseStaffRole, self).__init__(self.ROLE, *args, **kwargs)


@register_access_role
class CourseInstructorRole(CourseRole):
    """A course Instructor"""
    ROLE = 'instructor'

    def __init__(self, *args, **kwargs):
        super(CourseInstructorRole, self).__init__(self.ROLE, *args, **kwargs)


@register_access_role
class CourseFinanceAdminRole(CourseRole):
    """A course staff member with privileges to review financial data."""
    ROLE = 'finance_admin'

    def __init__(self, *args, **kwargs):
        super(CourseFinanceAdminRole, self).__init__(self.ROLE, *args, **kwargs)


@register_access_role
class CourseSalesAdminRole(CourseRole):
    """A course staff member with privileges to perform sales operations. """
    ROLE = 'sales_admin'

    def __init__(self, *args, **kwargs):
        super(CourseSalesAdminRole, self).__init__(self.ROLE, *args, **kwargs)


@register_access_role
class CourseBetaTesterRole(CourseRole):
    """A course Beta Tester"""
    ROLE = 'beta_testers'

    def __init__(self, *args, **kwargs):
        super(CourseBetaTesterRole, self).__init__(self.ROLE, *args, **kwargs)


@register_access_role
class LibraryUserRole(CourseRole):
    """
    A user who can view a library and import content from it, but not edit it.
    Used in Studio only.
    """
    ROLE = 'library_user'

    def __init__(self, *args, **kwargs):
        super(LibraryUserRole, self).__init__(self.ROLE, *args, **kwargs)


class CourseCcxCoachRole(CourseRole):
    """A CCX Coach"""
    ROLE = 'ccx_coach'

    def __init__(self, *args, **kwargs):
        super(CourseCcxCoachRole, self).__init__(self.ROLE, *args, **kwargs)


class OrgStaffRole(OrgRole):
    """An organization staff member"""
    def __init__(self, *args, **kwargs):
        super(OrgStaffRole, self).__init__('staff', *args, **kwargs)


class OrgInstructorRole(OrgRole):
    """An organization instructor"""
    def __init__(self, *args, **kwargs):
        super(OrgInstructorRole, self).__init__('instructor', *args, **kwargs)


class OrgLibraryUserRole(OrgRole):
    """
    A user who can view any libraries in an org and import content from them, but not edit them.
    Used in Studio only.
    """
    ROLE = LibraryUserRole.ROLE

    def __init__(self, *args, **kwargs):
        super(OrgLibraryUserRole, self).__init__(self.ROLE, *args, **kwargs)


@register_access_role
class CourseCreatorRole(RoleBase):
    """
    This is the group of people who have permission to create new courses (we may want to eventually
    make this an org based role).
    """
    ROLE = "course_creator_group"

    def __init__(self, *args, **kwargs):
        super(CourseCreatorRole, self).__init__(self.ROLE, *args, **kwargs)


@register_access_role
class SupportStaffRole(RoleBase):
    """
    Student support team members.
    """
    ROLE = "support"

    def __init__(self, *args, **kwargs):
        super(SupportStaffRole, self).__init__(self.ROLE, *args, **kwargs)


class UserBasedRole(object):
    """
    Backward mapping: given a user, manipulate the courses and roles
    """
    def __init__(self, user, role):
        """
        Create a UserBasedRole accessor: for a given user and role (e.g., "instructor")
        """
        self.user = user
        self.role = role

    def has_course(self, course_key):
        """
        Return whether the role's user has the configured role access to the passed course
        """
        if not (self.user.is_authenticated and self.user.is_active):
            return False

        # pylint: disable=protected-access
        if not hasattr(self.user, '_roles'):
            self.user._roles = RoleCache(self.user)

        return self.user._roles.has_role(self.role, course_key, course_key.org)

    def add_course(self, *course_keys):
        """
        Grant this object's user the object's role for the supplied courses
        """
        if self.user.is_authenticated and self.user.is_active:
            for course_key in course_keys:
                entry = CourseAccessRole(user=self.user, role=self.role, course_id=course_key, org=course_key.org)
                entry.save()
            if hasattr(self.user, '_roles'):
                del self.user._roles
        else:
            raise ValueError("user is not active. Cannot grant access to courses")

    def remove_courses(self, *course_keys):
        """
        Remove the supplied courses from this user's configured role.
        """
        entries = CourseAccessRole.objects.filter(user=self.user, role=self.role, course_id__in=course_keys)
        entries.delete()
        if hasattr(self.user, '_roles'):
            del self.user._roles

    def courses_with_role(self):
        """
        Return a django QuerySet for all of the courses with this user x role. You can access
        any of these properties on each result record:
        * user (will be self.user--thus uninteresting)
        * org
        * course_id
        * role (will be self.role--thus uninteresting)
        """
        return CourseAccessRole.objects.filter(role=self.role, user=self.user)