""" Context holding multiple subcontexts.

"""

from itertools import chain

from UserDict import DictMixin

from traits.api import (Instance, List, Str, Undefined, implements,

on_trait_change)

from traits.protocols.api import adapt

from data_context import DataContext, ListenableMixin, PersistableMixin

from i_context import (ICheckpointable, IListenableContext,

IPersistableContext, IRestrictedContext)

from utils import safe_repr

class MultiContext(ListenableMixin, PersistableMixin, DictMixin):

""" Wrap several subcontexts.

"""

implements(ICheckpointable, IListenableContext, IPersistableContext, IRestrictedContext)

# The name of the context.

name = Str("multidummy")

# The underlying dictionary.

subcontexts = List(Instance(IRestrictedContext, factory=DataContext,

adapt='yes'))

def __init__(self, *subcontexts, **traits):

subcontexts = list(subcontexts)

super(MultiContext, self).__init__(subcontexts=subcontexts, **traits)

#### IContext interface ####################################################

def __contains__(self, key):

for c in self.subcontexts:

if key in c:

return True

return False

def __delitem__(self, key):

""" Remove the given key with [] access.

Only deletes the first instance of the key.

Parameters

----------

key : str

Raises

------

KeyError if the kew is not available in the context.

"""

for c in self.subcontexts:

try:

del c[key]

return

except KeyError:

continue

raise KeyError(key)

def __getitem__(self, key):

for c in self.subcontexts:

try:

return c[key]

except KeyError:

continue

raise KeyError(key)

def __setitem__(self, key, value):

""" Set item with [] access.

The first subcontext which allows the key/value pair will get it. If an

earlier subcontext has the key, but does not allow the assignment, then

that key will be deleted. Later contexts with the key will be untouched.

If the key/value pair cannot be assigned to anything, no deletion will

take place.

Parameters

----------

key : str

value : object

Raises

------

ValueError if the key is not permitted to be assigned that value.

"""

# Let subtypes dictate compatibility independently of contained contexts

if not self.allows(value, key):

raise ValueError('Disallowed mapping: %s = %s' % (key, safe_repr(value)))

set = False

blocking_contexts = []

for c in self.subcontexts:

if not set:

if c.allows(value, key):

if key in c:

added = []

current_value = c[key]

try:

is_modified = bool(current_value != value)

except Exception:

is_modified = current_value is not value

if is_modified:

modified = [key]

c[key] = value

else:

modified = []

else:

added = [key]

modified = []

c[key] = value

set = True

break

elif key in c:

# Record this context as blocking access to the final

# location of the value.

blocking_contexts.append(c)

# Remove all blocking instances.

for c in blocking_contexts:

del c[key]

if not set:

raise ValueError('Disallowed mapping: %s = %s' % (key, safe_repr(value)))

def keys(self):

return list(set(chain(*[c.keys() for c in self.subcontexts])))

# Expose DictMixin's get method over HasTraits'.

get = DictMixin.get

def __str__(self):

# Maybe a good default string

subcontext_str = '[%s]' % ', '.join([str(x) for x in self.subcontexts])

return '%s(name=%r, subcontexts=%s)' % (type(self).__name__, self.name,

subcontext_str)

def __repr__(self):

# Maybe a good default representation

return '%s(name=%r)' % (type(self).__name__, self.name)

#### IRestrictedContext interface ##########################################

def allows(self, value, name=None):

for c in self.subcontexts:

if c.allows(value, name=name):

return True

return False

#### Trait Event Handlers ##################################################

@on_trait_change('subcontexts:items_modified')

def subcontexts_items_modified(self, event):

""" Pass events up.

"""

if event is Undefined:

# Nothing to do.

return

event.veto = True

self._fire_event(added=event.added, removed=event.removed,

modified=event.modified, context=event.context)

def _subcontexts_items_changed(self, event):

""" Trait listener for items of subcontexts list.

"""

added = []

removed = []

# Add to the list of items added

if len(event.added):

for context in event.added:

added.extend(context.keys())

# Add to the list of items removed

if len(event.removed):

for context in event.removed:

removed.extend(context.keys())

self._fire_event(added=added, removed=removed)

#### ICheckpointable interface ############################################

def checkpoint(self):

""" Make a shallow copy of the context.

Technically, this is actually a fairly deep copy. All of the object

structure should be replicated, but the actual dictionary storage will

be shallowly copied::

copy = context.shallow_copy()

copy[key] is context[key] for key in context.keys()

These semantics are useful for saving out checkpointed versions of the

context for implementing an undo/redo stack. They may not be useful for

other purposes.

Returns

-------

copy : IContext

"""

copy = self.clone_traits()

new_subcontexts = []

for context in self.subcontexts:

checkpointable_subcontext = adapt(context, ICheckpointable)

new_subcontexts.append(checkpointable_subcontext.checkpoint())

copy.subcontexts = new_subcontexts

return copy