# -*- coding: utf-8; -*-
################################################################################
#
#  Rattail -- Retail Software Framework
#  Copyright © 2010-2020 Lance Edgar
#
#  This file is part of Rattail.
#
#  Rattail is free software: you can redistribute it and/or modify it under the
#  terms of the GNU General Public License as published by the Free Software
#  Foundation, either version 3 of the License, or (at your option) any later
#  version.
#
#  Rattail is distributed in the hope that it will be useful, but WITHOUT ANY
#  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
#  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
#  details.
#
#  You should have received a copy of the GNU General Public License along with
#  Rattail.  If not, see <http://www.gnu.org/licenses/>.
#
################################################################################
"""
Authentication & Authorization
"""

from __future__ import unicode_literals, absolute_import

from passlib.context import CryptContext
from sqlalchemy.orm.exc import NoResultFound

from rattail.db import model


password_context = CryptContext(schemes=['bcrypt'])


def authenticate_user(session, userobj, password):
    """
    Attempt to authenticate a user.

    :param userobj: May be a :class:`model.User` instance, or a username as
       string.  If the latter, it will be used to look up the User instance.

    :returns: The User instance, if found and the password was correct;
       otherwise ``None``.
    """
    if isinstance(userobj, model.User):
        user = userobj
    else:
        try:
            user = session.query(model.User)\
                          .filter_by(username=userobj)\
                          .one()
        except NoResultFound:
            user = None
    if user and user.active and user.password is not None:
        if password_context.verify(password, user.password):
            return user


def set_user_password(user, password):
    """
    Set a user's password.
    """
    user.password = password_context.hash(password)


def special_role(session, uuid, name):
    """
    Fetches, or creates, a "special" role.
    """

    role = session.query(model.Role).get(uuid)
    if not role:
        role = model.Role(uuid=uuid, name=name)
        session.add(role)
    return role


def administrator_role(session):
    """
    Returns the "Administrator" role.
    """

    return special_role(session, 'd937fa8a965611dfa0dd001143047286', 'Administrator')


def guest_role(session):
    """
    Returns the "Guest" role.
    """

    return special_role(session, 'f8a27c98965a11dfaff7001143047286', 'Guest')


def authenticated_role(session):
    """
    Returns the "Authenticated" role.
    """
    return special_role(session, 'b765a9cc331a11e6ac2a3ca9f40bc550', "Authenticated")


def grant_permission(role, permission):
    """
    Grant a permission to a role.
    """

    # TODO: Make this a `Role` method (or make `Role.permissions` a `set` so we
    # can do `role.permissions.add('some.perm')` ?).
    if permission not in role.permissions:
        role.permissions.append(permission)


def revoke_permission(role, permission):
    """
    Revoke the given permission for the given role.  This first checks to see
    if the role currently has the permission; if not then no change is made.
    """
    if permission in role.permissions:
        role.permissions.remove(permission)


def has_permission(session, principal, permission, include_guest=True, include_authenticated=True):
    """
    Determine if a principal has been granted a permission.

    :param session: A SQLAlchemy session instance.

    :param principal: May be either a :class:`.model.User` or
       :class:`.model.Role` instance.  It is also expected that this may
       sometimes be ``None``, in which case the "Guest" role will typically be
       assumed.

    :param permission: The full internal name of a permission,
       e.g. ``'users.create'``.

    :param include_guest: Whether or not the "Guest" role should be included
       when checking permissions.  If ``False``, then Guest's permissions will
       *not* be consulted.

    :param include_authenticated: Whether or not the "Authenticated" role
       should be included when checking permissions.

    Note that if no ``principal`` is provided, and ``include_guest`` is set to
    ``False``, then no checks will actually be done, and the return value will
    be ``False``.
    """

    if hasattr(principal, 'roles'):
        roles = list(principal.roles)
        if include_authenticated:
            roles.append(authenticated_role(session))
    elif principal is not None:
        roles = [principal]
    else:
        roles = []

    if include_guest:
        roles.append(guest_role(session))
    for role in roles:
        for perm in role.permissions:
            if perm == permission:
                return True
    return False


def cache_permissions(session, principal, include_guest=True, include_authenticated=True):
    """
    Return a set of permission names, which represents all permissions
    effectively granted to the given principal.

    :param session: A SQLAlchemy session instance.

    :param principal: May be either a :class:`.model.User` or
       :class:`.model.Role` instance.  It is also expected that this may
       sometimes be ``None``, in which case the "Guest" role will typically be
       assumed.

    :param include_guest: Whether or not the "Guest" role should be included
       when checking permissions.  If ``False``, then Guest's permissions will
       *not* be consulted.

    :param include_authenticated: Whether or not the "Authenticated" role
       should be included when checking permissions.

    Note that if no ``principal`` is provided, and ``include_guest`` is set to
    ``False``, then no checks will actually be done, and the return value will
    be ``False``.
    """
    # we will use any `roles` attribute which may be present.  in practice we
    # would be assuming a User in this case
    if hasattr(principal, 'roles'):
        roles = list(principal.roles)

        # here our User assumption gets a little more explicit
        if include_authenticated:
            roles.append(authenticated_role(session))

    # otherwise a non-null principal is assumed to be a Role
    elif principal is not None:
        roles = [principal]

    # fallback assumption is "no roles"
    else:
        roles = []

    # maybe include guest roles
    if include_guest:
        roles.append(guest_role(session))

    # build the permissions cache
    cache = set()
    for role in roles:
        cache.update(role.permissions)

    return cache
