re2o/re2o/acl.py

# -*- mode: python; coding: utf-8 -*-
# Re2o est un logiciel d'administration développé initiallement au Rézo Metz. Il
# se veut agnostique au réseau considéré, de manière à être installable en
# quelques clics.
#
# Copyright © 2017  Gabriel Détraz
# Copyright © 2017  Lara Kermarec
# Copyright © 2017  Augustin Lemesle
#
# This program 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 2 of the License, or
# (at your option) any later version.
#
# This program 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 this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

"""Handles ACL for re2o.

Here are defined some decorators that can be used in views to handle ACL.
"""
from __future__ import unicode_literals

import sys
from itertools import chain

from django.db.models import Model
from django.contrib import messages
from django.shortcuts import redirect
from django.urls import reverse
from django.utils.translation import ugettext as _
from rest_framework.response import Response

from re2o.utils import get_group_having_permission


def acl_error_message(msg, permissions):
    """Create an error message for msg and permissions."""
    if permissions is None:
        return msg
    groups = ", ".join([g.name for g in get_group_having_permission(*permissions)])
    message = msg or _("You don't have the right to edit this option.")
    if groups:
        return (
            message + _("You need to be a member of one of these groups: %s.") % groups
        )
    else:
        return message + _("No group has the %s permission(s)!") % " or ".join(
            [",".join(permissions[:-1]), permissions[-1]]
            if len(permissions) > 2
            else permissions
        )


# This is the function of main interest of this file. Almost all the decorators
# use it, and it is a fairly complicated piece of code. Let me guide you through
# this ! 🌈😸
def acl_base_decorator(method_name, *targets, on_instance=True, api=False):
    """Base decorator for acl. It checks if the `request.user` has the
    permission by calling model.method_name. If the flag on_instance is True,
    tries to get an instance of the model by calling
    `model.get_instance(obj_id, *args, **kwargs)` and runs `instance.mehod_name`
    rather than model.method_name.

    It is not intended to be used as is. It is a base for others ACL
    decorators. Beware, if you redefine the `get_instance` method for your 
    model, give it a signature such as 
    `def get_instance(cls, object_id, *_args, **_kwargs)`, because you will
    likely have an url with a named parameter "userid" if *e.g.* your model
    is an user. Otherwise, if the parameter name in `get_instance` was also
    `userid`, then `get_instance` would end up having two identical parameter
    passed on, and this would result in a `TypeError` exception.

    Args:
        method_name: The name of the method which is to to be used for ACL.
            (ex: 'can_edit') WARNING: if no method called 'method_name' exists,
            then no error will be triggered, the decorator will act as if
            permission was granted. This is to allow you to run ACL tests on
            fields only. If the method exists, it has to return a 2-tuple
            `(can, reason, permissions)` with `can` being a boolean stating
            whether the access is granted, `reason` an arror message to be
            displayed if `can` equals `False` (can be `None`) and `permissions`
            a list of permissions needed for access (can be `None`). If can is
            True and permission is not `None`, a warning message will be
            displayed.
        *targets: The targets. Targets are specified like a sequence of models
            and fields names. As an example
            ```
                acl_base_decorator('can_edit', ModelA, 'field1', 'field2', \
ModelB, ModelC, 'field3', on_instance=False)
            ```
            will make the following calls (where `user` is the current user,
            `*args` and `**kwargs` are the arguments initially passed to the
            view):
                - `ModelA.can_edit(user, *args, **kwargs)`
                - `ModelA.can_change_field1(user, *args, **kwargs)`
                - `ModelA.can_change_field2(user, *args, **kwargs)`
                - `ModelB.can_edit(user, *args, **kwargs)`
                - `ModelC.can_edit(user, *args, **kwargs)`
                - `ModelC.can_change_field3(user, *args, **kwargs)`

            Note that
            ```
                acl_base_decorator('can_edit', 'field1', ModelA, 'field2', \
on_instance=False)
            ```
            would have the same effect that
            ```
                acl_base_decorator('can_edit', ModelA, 'field1', 'field2', \
on_instance=False)
            ```
            But don't do that, it's silly.
        on_instance: When `on_instance` equals `False`, the decorator runs the
            ACL method on the model class rather than on an instance. If an
            instance need to fetched, it is done calling the assumed existing
            method `get_instance` of the model, with the arguments originally
            passed to the view.

        api: when set to True, errors will no longer trigger redirection and
            messages but will send a 403 with errors in JSON

    Returns:
        The user is either redirected to their own page with an explanation
        message if at least one access is not granted, or to the view. In order
        to avoid duplicate DB calls, when the `on_instance` flag equals `True`,
        the instances are passed to the view. Example, with this decorator:
        ```
            acl_base_decorator('can_edit', ModelA, 'field1', 'field2', ModelB,\
ModelC)
        ```
        The view will be called like this:
        ```
             view(request, instance_of_A, instance_of_b, *args, **kwargs)
        ```
        where `*args` and `**kwargs` are the original view arguments.
    """

    # First we define a utilitary functions. This is what parses the input of
    #  the decorator. It will group a target (i.e. a model class) with a list
    # of associated fields (possibly empty).

    def group_targets():
        """This generator parses the targets of the decorator, yielding
        2-tuples of (model, [fields]).
        """
        current_target = None
        current_fields = []
        # We iterate over all the possible target passed in argument of the
        # decorator. Let's call the `target` variable a target candidate.
        # We basically want to discriminate the valid targets over the field
        # names.
        for target in targets:
            # We enter this conditional block if the current target is not
            # a string, i.e. if it is not a field name, i.e. it is a model
            # name.
            if not isinstance(target, str):
                # if the current target is defined, this means we already
                # encountered a valid target and we have been storing field
                # names ever since. This group is ready and we can `yield` it.
                if current_target:
                    yield (current_target, current_fields)
                # Then we define the current target and reset its fields.
                current_target = target
                current_fields = []
            else:
                # When we encounter a string, this is not valid target and is
                # thus a field name. We store it for later.
                current_fields.append(target)
        # We need to yield the last pair of target and fields.
        yield (current_target, current_fields)

    # Now to the main topic ! if you are not sure why we need to use a function
    # `wrapper` inside the `decorator` function, you need to read some
    #  documentation on decorators !
    def decorator(view):
        """The decorator to use on a specific view"""

        def wrapper(request, *args, **kwargs):
            """The wrapper used for a specific request"""
            instances = []

            def process_target(target, fields, target_id=None):
                """This function calls the methods on the target and checks for
                the can_change_`field` method with the given fields. It also
                stores the instances of models in order to avoid duplicate DB
                calls for the view.
                """
                # When working on instances, retrieve the associated instance
                # and store it to pass it to the view.
                if on_instance:
                    try:
                        target = target.get_instance(target_id, *args, **kwargs)
                        instances.append(target)
                    except target.DoesNotExist:
                        # A non existing instance is a valid reason to deny
                        # access to the view.
                        yield False, _("Nonexistent entry."), []
                        return
                # Now we can actually make the ACL test, using the right ACL
                # method.
                if hasattr(target, method_name):
                    can_fct = getattr(target, method_name)
                    yield can_fct(request.user, *args, **kwargs)

                # If working on fields, iterate through the concerned ones
                # and check that the user can change this field. (this is
                # the only available ACL for fields)
                for field in fields:
                    can_change_fct = getattr(target, "can_change_" + field)
                    yield can_change_fct(request.user, *args, **kwargs)

            # Now to the main loop. We are going iterate through the targets
            # pairs (remember the `group_targets` function) and the keyword
            # arguments of the view to retrieve the associated model instances
            # and check that the user making the request is authorized to do it
            # as well as storing the the associated error and warning messages.
            error_messages = []
            warning_messages = []

            if on_instance:
                iterator = zip(kwargs.keys(), group_targets())
            else:
                iterator = group_targets()

            for it in iterator:
                # If the decorator must work on instances, retrieve the
                # associated instance.
                if on_instance:
                    arg_key, (target, fields) = it
                    target_id = int(kwargs[arg_key])
                else:
                    target, fields = it
                    target_id = None

                # Store the messages at the right place.
                for can, msg, permissions in process_target(target, fields, target_id):
                    if not can:
                        error_messages.append(acl_error_message(msg, permissions))
                    elif msg:
                        warning_messages.append(acl_error_message(msg, permissions))

            # Display the warning messages
            if not api:
                if warning_messages:
                    for msg in warning_messages:
                        messages.warning(request, msg)

            # If there is any error message, then the request must be denied.
            if error_messages:
                # We display the message
                if not api:
                    for msg in error_messages:
                        messages.error(
                            request,
                            msg or _("You don't have the right to access this menu."),
                        )
                # And redirect the user to the right place.
                if request.user.id is not None:
                    if not api:
                        return redirect(
                            reverse(
                                "users:profil", kwargs={"userid": str(request.user.id)}
                            )
                        )
                    else:
                        return Response(
                            data={
                                "errors": error_messages,
                                "warning": warning_messages,
                            },
                            status=403,
                        )
                else:
                    return redirect(reverse("index"))
            return view(request, *chain(instances, args), **kwargs)

        return wrapper

    return decorator


def can_create(*models):
    """Decorator to check if an user can create the given models. It runs
    `acl_base_decorator` with the flag `on_instance=False` and the method
    'can_create'. See `acl_base_decorator` documentation for further details.
    """
    return acl_base_decorator("can_create", *models, on_instance=False)


def can_edit(*targets):
    """Decorator to check if an user can edit the models.
    It runs `acl_base_decorator` with the flag `on_instance=True` and the
    method 'can_edit'. See `acl_base_decorator` documentation for further
    details.
    """
    return acl_base_decorator("can_edit", *targets)


def can_change(*targets):
    """Decorator to check if an user can edit a field of a model class.
    Difference with can_edit : takes a class and not an instance
    It runs `acl_base_decorator` with the flag `on_instance=False` and the
    method 'can_change'. See `acl_base_decorator` documentation for further
    details.
    """
    return acl_base_decorator("can_change", *targets, on_instance=False)


def can_delete(*targets):
    """Decorator to check if an user can delete a model.
    It runs `acl_base_decorator` with the flag `on_instance=True` and the
    method 'can_edit'. See `acl_base_decorator` documentation for further
    details.
    """
    return acl_base_decorator("can_delete", *targets)


def can_delete_set(model):
    """Decorator which returns a list of detable models by request user.
    If none of them, return an error"""

    def decorator(view):
        """The decorator to use on a specific view"""

        def wrapper(request, *args, **kwargs):
            """The wrapper used for a specific request"""
            all_objects = model.objects.all()
            instances_id = []
            for instance in all_objects:
                can, _msg, _reason = instance.can_delete(request.user)
                if can:
                    instances_id.append(instance.id)
            instances = model.objects.filter(id__in=instances_id)
            if not instances:
                messages.error(
                    request, _("You don't have the right to access this menu.")
                )
                return redirect(
                    reverse("users:profil", kwargs={"userid": str(request.user.id)})
                )
            return view(request, instances, *args, **kwargs)

        return wrapper

    return decorator


def can_view(*targets):
    """Decorator to check if an user can view a model.
    It runs `acl_base_decorator` with the flag `on_instance=True` and the
    method 'can_view'. See `acl_base_decorator` documentation for further
    details.
    """
    return acl_base_decorator("can_view", *targets)


def can_view_all(*targets):
    """Decorator to check if an user can view a class of model.
    It runs `acl_base_decorator` with the flag `on_instance=False` and the
    method 'can_view_all'. See `acl_base_decorator` documentation for further
    details.
    """
    return acl_base_decorator("can_view_all", *targets, on_instance=False)


def can_view_app(*apps_name):
    """Decorator to check if an user can view the applications."""
    for app_name in apps_name:
        assert app_name in sys.modules.keys()
    return acl_base_decorator(
        "can_view",
        *chain(sys.modules[app_name] for app_name in apps_name),
        on_instance=False
    )


def can_edit_history(view):
    """Decorator to check if an user can edit history."""

    def wrapper(request, *args, **kwargs):
        """The wrapper used for a specific request"""
        if request.user.has_perm("admin.change_logentry"):
            return view(request, *args, **kwargs)
        messages.error(request, _("You don't have the right to edit the history."))
        return redirect(
            reverse("users:profil", kwargs={"userid": str(request.user.id)})
        )

    return wrapper


def can_view_all_api(*models):
    """Decorator to check if an user can see an api page
    Only used on functionnal api views (class-based api views ACL are checked
    in api/permissions.py)
    """
    return acl_base_decorator("can_view_all", *models, on_instance=False, api=True)


def can_edit_all_api(*models):
    """Decorator to check if an user can edit via the api
    We do not always know which instances will be edited, so we may need to know
    if the user can edit any instance.
    Only used on functionnal api views (class-based api views ACL are checked
    in api/permissions.py)
    """
    return acl_base_decorator("can_edit_all", *models, on_instance=False, api=True)


def can_create_api(*models):
    """Decorator to check if an user can create the given models. via the api
    Only used on functionnal api views (class-based api views ACL are checked
    in api/permissions.py)
    """
    return acl_base_decorator("can_create", *models, on_instance=False, api=True)