tuskar-ui/horizon/workflows/base.py
Gabriel Hurley d8affa596c Adds initial workflow support to Horizon.
Implements blueprint workflows.

Adds a reusable workflow component to Horizon, and puts it
to use for the Launch Instance user interface. Contains
tests with roughly 90% coverage and full documentation.

Change-Id: I7325ef9db2ba2496d3fc1e2767cfeda50c71cbca
2012-05-22 17:13:39 -07:00

720 lines
27 KiB
Python

# vim: tabstop=4 shiftwidth=4 softtabstop=4
# Copyright 2012 Nebula, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
import copy
import inspect
from django import forms
from django import template
from django.core import urlresolvers
from django.template.defaultfilters import slugify
from django.utils.encoding import force_unicode
from django.utils.importlib import import_module
from django.utils.translation import ugettext as _
from django.template.defaultfilters import linebreaks, safe
from horizon import base
from horizon import exceptions
from horizon.templatetags.horizon import can_haz
from horizon.utils import html
class WorkflowContext(dict):
def __init__(self, workflow, *args, **kwargs):
super(WorkflowContext, self).__init__(*args, **kwargs)
self.__workflow = workflow
def __setitem__(self, key, val):
super(WorkflowContext, self).__setitem__(key, val)
return self.__workflow._trigger_handlers(key)
def __delitem__(self, key):
return self.__setitem__(key, None)
def set(self, key, val):
return self.__setitem__(key, val)
def unset(self, key):
return self.__delitem__(key)
class ActionMetaclass(forms.forms.DeclarativeFieldsMetaclass):
def __new__(mcs, name, bases, attrs):
super(ActionMetaclass, mcs).__new__(mcs, name, bases, attrs)
# Process options from Meta
opts = attrs.pop("Meta", None)
attrs['name'] = getattr(opts, "name", name)
attrs['slug'] = getattr(opts, "slug", slugify(name))
attrs['roles'] = getattr(opts, "roles", ())
attrs['progress_message'] = getattr(opts,
"progress_message",
_("Processing..."))
attrs['help_text'] = getattr(opts, "help_text", "")
attrs['help_text_template'] = getattr(opts, "help_text_template", None)
# Create our new class!
return type.__new__(mcs, name, bases, attrs)
class Action(forms.Form):
"""
An ``Action`` represents an atomic logical interaction you can have with
the system. This is easier to understand with a conceptual example: in the
context of a "launch instance" workflow, actions would include "naming
the instance", "selecting an image", and ultimately "launching the
instance".
Because ``Actions`` are always interactive, they always provide form
controls, and thus inherit from Django's ``Form`` class. However, they
have some additional intelligence added to them:
* ``Actions`` are aware of the roles required to complete them.
* ``Actions`` have a meta-level concept of "help text" which is meant to be
displayed in such a way as to give context to the action regardless of
where the action is presented in a site or workflow.
* ``Actions`` understand how to handle their inputs and produce outputs,
much like :class:`~horizon.forms.SelfHandlingForm` does now.
``Action`` classes may define the following attributes in a ``Meta``
class within them:
.. attribute:: name
The verbose name for this action. Defaults to the name of the class.
.. attribute:: slug
A semi-unique slug for this action. Defaults to the "slugified" name
of the class.
.. attribute:: roles
A list of role names which this action requires in order to be
completed. Defaults to an empty list (``[]``).
.. attribute:: help_text
A string of simple help text to be displayed alongside the Action's
fields.
.. attribute:: help_text_template
A path to a template which contains more complex help text to be
displayed alongside the Action's fields. In conjunction with
:meth:`~horizon.workflows.Action.get_help_text` method you can
customize your help text template to display practically anything.
"""
__metaclass__ = ActionMetaclass
def __init__(self, request, context, *args, **kwargs):
if request.method == "POST":
super(Action, self).__init__(request.POST)
else:
super(Action, self).__init__(initial=context)
if not hasattr(self, "handle"):
raise AttributeError("The action %s must define a handle method."
% self.__class__.__name__)
self.request = request
self._populate_choices(request, context)
def __unicode__(self):
return force_unicode(self.name)
def __repr__(self):
return "<%s: %s>" % (self.__class__.__name__, self.slug)
def _populate_choices(self, request, context):
for field_name, bound_field in self.fields.items():
meth = getattr(self, "populate_%s_choices" % field_name, None)
if meth is not None and callable(meth):
bound_field.choices = meth(request, context)
def get_help_text(self, extra_context=None):
""" Returns the help text for this step. """
text = ""
extra_context = extra_context or {}
if self.help_text_template:
tmpl = template.loader.get_template(self.help_text_template)
context = template.RequestContext(self.request, extra_context)
text += tmpl.render(context)
else:
text += linebreaks(self.help_text)
return safe(text)
def handle(self, request, context):
"""
Handles any requisite processing for this action. The method should
return either ``None`` or a dictionary of data to be passed to
:meth:`~horizon.workflows.Step.contribute`.
Returns ``None`` by default, effectively making it a no-op.
"""
return None
class Step(object):
"""
A step is a wrapper around an action which defines it's context in a
workflow. It knows about details such as:
* The workflow's context data (data passed from step to step).
* The data which must be present in the context to begin this step (the
step's dependencies).
* The keys which will be added to the context data upon completion of the
step.
* The connections between this step's fields and changes in the context
data (e.g. if that piece of data changes, what needs to be updated in
this step).
A ``Step`` class has the following attributes:
.. attribute:: action
The :class:`~horizon.workflows.Action` class which this step wraps.
.. attribute:: depends_on
A list of context data keys which this step requires in order to
begin interaction.
.. attribute:: contributes
A list of keys which this step will contribute to the workflow's
context data. Optional keys should still be listed, even if their
values may be set to ``None``.
.. attribute:: connections
A dictionary which maps context data key names to lists of callbacks.
The callbacks may be functions, dotted python paths to functions
which may be imported, or dotted strings beginning with ``"self"``
to indicate methods on the current ``Step`` instance.
.. attribute:: before
Another ``Step`` class. This optional attribute is used to provide
control over workflow ordering when steps are dynamically added to
workflows. The workflow mechanism will attempt to place the current
step before the step specified in the attribute.
.. attribute:: after
Another ``Step`` class. This attribute has the same purpose as
:meth:`~horizon.workflows.Step.before` except that it will instead
attempt to place the current step after the given step.
.. attribute:: help_text
A string of simple help text which will be prepended to the ``Action``
class' help text if desired.
.. attribute:: template_name
A path to a template which will be used to render this step. In
general the default common template should be used. Default:
``"horizon/common/_workflow_step.html"``.
.. attribute:: has_errors
A boolean value which indicates whether or not this step has any
errors on the action within it or in the scope of the workflow. This
attribute will only accurately reflect this status after validation
has occurred.
.. attribute:: slug
Inherited from the ``Action`` class.
.. attribute:: name
Inherited from the ``Action`` class.
.. attribute:: roles
Inherited from the ``Action`` class.
"""
action = None
depends_on = ()
contributes = ()
connections = None
before = None
after = None
help_text = ""
template_name = "horizon/common/_workflow_step.html"
def __repr__(self):
return "<%s: %s>" % (self.__class__.__name__, self.slug)
def __unicode__(self):
return force_unicode(self.name)
def __init__(self, workflow):
super(Step, self).__init__()
self.workflow = workflow
cls = self.__class__.__name__
if not (self.action and issubclass(self.action, Action)):
raise AttributeError("You must specify an action for %s." % cls)
self._action = None
self.slug = self.action.slug
self.name = self.action.name
self.roles = self.action.roles
self.has_errors = False
self._handlers = {}
if self.connections is None:
# We want a dict, but don't want to declare a mutable type on the
# class directly.
self.connections = {}
# Gather our connection handlers and make sure they exist.
for key, handlers in self.connections.items():
self._handlers[key] = []
# TODO(gabriel): This is a poor substitute for broader handling
if not isinstance(handlers, (list, tuple)):
raise TypeError("The connection handlers for %s must be a "
"list or tuple." % cls)
for possible_handler in handlers:
if callable(possible_handler):
# If it's callable we know the function exists and is valid
self._handlers[key].append(possible_handler)
continue
elif not isinstance(possible_handler, basestring):
return TypeError("Connection handlers must be either "
"callables or strings.")
bits = possible_handler.split(".")
if bits[0] == "self":
root = self
for bit in bits[1:]:
try:
root = getattr(root, bit)
except AttributeError:
raise AttributeError("The connection handler %s "
"could not be found on %s."
% (possible_handler, cls))
handler = root
elif len(bits) == 1:
# Import by name from local module not supported
raise ValueError("Importing a local function as a string "
"is not supported for the connection "
"handler %s on %s."
% (possible_handler, cls))
else:
# Try a general import
module_name = ".".join(bits[:-1])
try:
mod = import_module(module_name)
handler = getattr(mod, bits[-1])
except ImportError:
raise ImportError("Could not import %s from the "
"module %s as a connection "
"handler on %s."
% (bits[-1], module_name, cls))
except AttributeError:
raise AttributeError("Could not import %s from the "
"module %s as a connection "
"handler on %s."
% (bits[-1], module_name, cls))
self._handlers[key].append(handler)
def _init_action(self, request, data):
self._action = self.action(request, data)
def get_id(self):
""" Returns the ID for this step. Suitable for use in HTML markup. """
return "%s__%s" % (self.workflow.slug, self.slug)
def _verify_contributions(self, context):
for key in self.contributes:
# Make sure we don't skip steps based on weird behavior of
# POST query dicts.
field = self._action.fields.get(key, None)
if field and field.required and not context.get(key):
context.pop(key, None)
failed_to_contribute = set(self.contributes)
failed_to_contribute -= set(context.keys())
if failed_to_contribute:
raise exceptions.WorkflowError("The following expected data was "
"not added to the workflow context "
"by the step %s: %s."
% (self.__class__,
failed_to_contribute))
return True
def contribute(self, data, context):
"""
Adds the data listed in ``contributes`` to the workflow's shared
context. By default, the context is simply updated with all the data
returned by the action.
Note that even if the value of one of the ``contributes`` keys is
not present (e.g. optional) the key should still be added to the
context with a value of ``None``.
"""
if data:
for key in self.contributes:
context[key] = data.get(key, None)
return context
def render(self):
""" Renders the step. """
step_template = template.loader.get_template(self.template_name)
extra_context = {"form": self._action,
"step": self}
context = template.RequestContext(self.workflow.request, extra_context)
return step_template.render(context)
def get_help_text(self):
""" Returns the help text for this step. """
text = linebreaks(self.help_text)
text += self._action.get_help_text()
return safe(text)
class WorkflowMetaclass(type):
def __new__(mcs, name, bases, attrs):
super(WorkflowMetaclass, mcs).__new__(mcs, name, bases, attrs)
attrs["_cls_registry"] = set([])
return type.__new__(mcs, name, bases, attrs)
class Workflow(html.HTMLElement):
"""
A Workflow is a collection of Steps. It's interface is very
straightforward, but it is responsible for handling some very
important tasks such as:
* Handling the injection, removal, and ordering of arbitrary steps.
* Determining if the workflow can be completed by a given user at runtime
based on all available information.
* Dispatching connections between steps to ensure that when context data
changes all the applicable callback functions are executed.
* Verifying/validating the overall data integrity and subsequently
triggering the final method to complete the workflow.
The ``Workflow`` class has the following attributes:
.. attribute:: name
The verbose name for this workflow which will be displayed to the user.
Defaults to the class name.
.. attribute:: slug
The unique slug for this workflow. Required.
.. attribute:: steps
Read-only access to the final ordered set of step instances for
this workflow.
.. attribute:: default_steps
A list of :class:`~horizon.workflows.Step` classes which serve as the
starting point for this workflow's ordered steps. Defaults to an empty
list (``[]``).
.. attribute:: finalize_button_name
The name which will appear on the submit button for the workflow's
form. Defaults to ``"Save"``.
.. attribute:: success_message
A string which will be displayed to the user upon successful completion
of the workflow. Defaults to
``"{{ workflow.name }} completed successfully."``
.. attribute:: failure_message
A string which will be displayed to the user upon failure to complete
the workflow. Defaults to ``"{{ workflow.name }} did not complete."``
.. attribute:: depends_on
A roll-up list of all the ``depends_on`` values compiled from the
workflow's steps.
.. attribute:: contributions
A roll-up list of all the ``contributes`` values compiled from the
workflow's steps.
.. attribute:: template_name
Path to the template which should be used to render this workflow.
In general the default common template should be used. Default:
``"horizon/common/_workflow.html"``.
"""
__metaclass__ = WorkflowMetaclass
slug = None
default_steps = ()
template_name = "horizon/common/_workflow.html"
finalize_button_name = _("Save")
success_message = _("%s completed successfully.")
failure_message = _("%s did not complete.")
_registerable_class = Step
def __unicode__(self):
return self.name
def __repr__(self):
return "<%s: %s>" % (self.__class__.__name__, self.slug)
def __init__(self, request=None, context_seed=None, *args, **kwargs):
super(Workflow, self).__init__(*args, **kwargs)
if self.slug is None:
raise AttributeError("The workflow %s must have a slug."
% self.__class__.__name__)
self.name = getattr(self, "name", self.__class__.__name__)
self.request = request
self.depends_on = set([])
self.contributions = set([])
# Put together our steps in order. Note that we pre-register
# non-default steps so that we can identify them and subsequently
# insert them in order correctly.
self._registry = dict([(step_class, step_class(self)) for step_class
in self.__class__._cls_registry
if step_class not in self.default_steps])
self._gather_steps()
# Determine all the context data we need to end up with.
for step in self.steps:
self.depends_on = self.depends_on | set(step.depends_on)
self.contributions = self.contributions | set(step.contributes)
# Initialize our context. For ease we can preseed it with a
# regular dictionary. This should happen after steps have been
# registered and ordered.
self.context = WorkflowContext(self)
context_seed = context_seed or {}
clean_seed = dict([(key, val)
for key, val in context_seed.items()
if key in self.contributions | self.depends_on])
self.context.update(clean_seed)
for step in self.steps:
self.context = step.contribute(request.POST, self.context)
step._init_action(request, self.context)
@property
def steps(self):
if getattr(self, "_ordered_steps", None) is None:
self._gather_steps()
return self._ordered_steps
def _gather_steps(self):
ordered_step_classes = self._order_steps()
for default_step in self.default_steps:
self.register(default_step)
self._registry[default_step] = default_step(self)
self._ordered_steps = [self._registry[step_class]
for step_class in ordered_step_classes
if can_haz(self.request.user,
self._registry[step_class])]
def _order_steps(self):
steps = list(copy.copy(self.default_steps))
additional = self._registry.keys()
for step in additional:
try:
min_pos = steps.index(step.after)
except ValueError:
min_pos = 0
try:
max_pos = steps.index(step.before)
except ValueError:
max_pos = len(steps)
if min_pos > max_pos:
raise exceptions.WorkflowError("The step %(new)s can't be "
"placed between the steps "
"%(after)s and %(before)s; the "
"step %(before)s comes before "
"%(after)s."
% {"new": additional,
"after": step.after,
"before": step.before})
steps.insert(max_pos, step)
return steps
def get_entry_point(self):
"""
Returns the slug of the step which the workflow should begin on.
This method takes into account both already-available data and errors
within the steps.
"""
for step in self.steps:
if step.has_errors:
return step.slug
try:
step._verify_contributions(self.context)
except exceptions.WorkflowError:
return step.slug
def _trigger_handlers(self, key):
responses = []
handlers = [(step.slug, f) for step in self.steps
for f in step._handlers.get(key, [])]
for slug, handler in handlers:
responses.append((slug, handler(self.request, self.context)))
return responses
@classmethod
def register(cls, step_class):
""" Registers a :class:`~horizon.workflows.Step` with the workflow. """
if not inspect.isclass(step_class):
raise ValueError('Only classes may be registered.')
elif not issubclass(step_class, cls._registerable_class):
raise ValueError('Only %s classes or subclasses may be registered.'
% cls._registerable_class.__name__)
if step_class in cls._cls_registry:
return False
else:
cls._cls_registry.add(step_class)
return True
@classmethod
def unregister(cls, step_class):
"""
Unregisters a :class:`~horizon.workflows.Step` from the workflow.
"""
try:
cls._cls_registry.remove(step_class)
except KeyError:
raise base.NotRegistered('%s is not registered' % cls)
return cls._unregister(step_class)
def validate(self, context):
"""
Hook for custom context data validation. Should return a boolean
value or raise :class:`~horizon.exceptions.WorkflowValidationError`.
"""
return True
def is_valid(self):
"""
Verified that all required data is present in the context and
calls the ``validate`` method to allow for finer-grained checks
on the context data.
"""
missing = self.depends_on - set(self.context.keys())
if missing:
raise exceptions.WorkflowValidationError(
"Unable to complete the workflow. The values %s are "
"required but not present." % ", ".join(missing))
# Validate each step. Cycle through all of them to catch all errors
# in one pass before returning.
steps_valid = True
for step in self.steps:
if not step._action.is_valid():
steps_valid = False
step.has_errors = True
if not steps_valid:
return steps_valid
return self.validate(self.context)
def finalize(self):
"""
Finalizes a workflow by running through all the actions in order
and calling their ``handle`` methods. Returns ``True`` on full success,
or ``False`` for a partial success, e.g. there were non-critical
errors. (If it failed completely the function wouldn't return.)
"""
partial = False
for step in self.steps:
try:
data = step._action.handle(self.request, self.context)
if data is True or data is None:
continue
elif data is False:
partial = True
else:
self.context = step.contribute(data or {}, self.context)
except:
partial = True
exceptions.handle(self.request)
if not self.handle(self.request, self.context):
partial = True
return not partial
def handle(self, request, context):
"""
Handles any final processing for this workflow. Should return a boolean
value indicating success.
"""
return True
def get_success_url(self):
"""
Returns a URL to redirect the user to upon completion. By default it
will attempt to parse a ``success_url`` attribute on the workflow,
which can take the form of a reversible URL pattern name, or a
standard HTTP URL.
"""
try:
return urlresolvers.reverse(self.success_url)
except urlresolvers.NoReverseMatch:
return self.success_url
def format_status_message(self, message):
"""
Hook to allow customization of the message returned to the user
upon successful or unsuccessful completion of the workflow.
By default it simply inserts the workflow's name into the message
string.
"""
if "%s" in message:
return message % self.name
else:
return message
def render(self):
""" Renders the workflow. """
workflow_template = template.loader.get_template(self.template_name)
extra_context = {"workflow": self}
if self.request.is_ajax():
extra_context['modal'] = True
context = template.RequestContext(self.request, extra_context)
return workflow_template.render(context)
def get_absolute_url(self):
""" Returns the canonical URL for this workflow.
This is used for the POST action attribute on the form element
wrapping the workflow.
For convenience it defaults to the value of
``request.get_full_path()`` with any query string stripped off,
e.g. the path at which the workflow was requested.
"""
return self.request.get_full_path().partition('?')[0]