#------------------------------------------------------------------------------
#
#  Copyright (c) 2005, Enthought, Inc.
#  All rights reserved.
#
#  This software is provided without warranty under the terms of the BSD
#  license included in enthought/LICENSE.txt and may be redistributed only
#  under the conditions described in the aforementioned license.  The license
#  is also available online at http://www.enthought.com/licenses/BSD.txt
#
#  Thanks for using Enthought open source!
#
#  Author: David C. Morrill
#  Date:   12/03/2004
#
#------------------------------------------------------------------------------

""" Defines the tree node descriptor used by the tree editor and tree editor
    factory classes.
"""

#-------------------------------------------------------------------------------
#  Imports:
#-------------------------------------------------------------------------------



from traits.api import (AdaptedTo, Adapter, Any, Bool, Callable, Either,
    HasPrivateTraits, Instance, Interface, isinterface, List, Property, Str,
    cached_property)

from traits.trait_base import SequenceTypes, get_resource_path, xgetattr, xsetattr

from .ui_traits import AView

#-------------------------------------------------------------------------------
#  'TreeNode' class:
#-------------------------------------------------------------------------------

class TreeNode ( HasPrivateTraits ):
    """ Represents a tree node. Used by the tree editor and tree editor factory
        classes.
    """

    #---------------------------------------------------------------------------
    #  Trait definitions:
    #---------------------------------------------------------------------------

    # Name of trait containing children (if '', the node is a leaf).
    children = Str

    # Either the name of a trait containing a label, or a constant label, if
    # the string starts with '='.
    label = Str

    # The name of a trait containing a list of labels for any columns.
    column_labels = Str

    # Either the name of a trait containing a tooltip, or constant tooltip, if
    # the string starts with '='.
    tooltip = Str

    # Name to use for a new instance
    name = Str

    # Can the object's children be renamed?
    rename = Bool( True )

    # Can the object be renamed?
    rename_me = Bool( True )

    # Can the object's children be copied?
    copy = Bool( True )

    # Can the object's children be deleted?
    delete = Bool( True )

    # Can the object be deleted (if its parent allows it)?
    delete_me = Bool( True )

    # Can children be inserted (vs. appended)?
    insert = Bool( True )

    # Should tree nodes be automatically opened (expanded)?
    auto_open = Bool( False )

    # Automatically close sibling tree nodes?
    auto_close = Bool( False )

    # List of object classes than can be added or copied
    add = List( Any )

    # List of object classes that can be moved
    move = List( Any )

    # List of object classes and/or interfaces that the node applies to
    node_for = List( Any )

    # Tuple of object classes that the node applies to
    node_for_class = Property( depends_on = 'node_for' )

    # List of object interfaces that the node applies to
    node_for_interface = Property( depends_on = 'node_for' )

    # Function for formatting the label
    formatter = Callable

    # Functions for formatting the other columns.
    column_formatters = List(Either(None, Callable))

    # Function for formatting the tooltip
    tooltip_formatter = Callable

    # Function for handling selecting an object
    on_select = Callable

    # Function for handling clicking an object
    on_click = Callable

    # Function for handling double-clicking an object
    on_dclick = Callable

    # Function for handling activation of an object
    # (double-click or Enter key press when node is in focus)
    on_activated = Callable

    # View to use for editing the object
    view = AView

    # Right-click context menu. The value can be one of:
    #
    # - Instance( Menu ): Use this menu as the context menu
    # - None: Use the default context menu
    # - False: Do not display a context menu
    menu = Any

    # Name of leaf item icon
    icon_item = Str( '<item>' )

    # Name of group item icon
    icon_group = Str( '<group>' )

    # Name of opened group item icon
    icon_open = Str( '<open>' )

    # Resource path used to locate the node icon
    icon_path = Str

    # Selector or name for background color
    background = Any

    # Selector or name for foreground color
    foreground = Any

    # fixme: The 'menu' trait should really be defined as:
    #        Instance( 'traitsui.menu.MenuBar' ), but it doesn't work
    #        right currently.

    #---------------------------------------------------------------------------
    #  Initializes the object:
    #---------------------------------------------------------------------------

    def __init__ ( self, **traits ):
        super( TreeNode, self ).__init__( **traits )
        if self.icon_path == '':
            self.icon_path = get_resource_path()

    #-- Property Implementations -----------------------------------------------

    @cached_property
    def _get_node_for_class ( self ):
        return tuple( [ klass for klass in self.node_for
                        if not isinterface(klass) ] )

    @cached_property
    def _get_node_for_interface ( self ):
        return [ klass for klass in self.node_for
                 if isinterface(klass) ]

    #-- Overridable Methods: ---------------------------------------------------

    #---------------------------------------------------------------------------
    #  Returns whether chidren of this object are allowed or not:
    #---------------------------------------------------------------------------

    def allows_children ( self, object ):
        """ Returns whether this object can have children.
        """
        return (self.children != '')

    #---------------------------------------------------------------------------
    #  Returns whether or not the object has children:
    #---------------------------------------------------------------------------

    def has_children ( self, object ):
        """ Returns whether the object has children.
        """
        return (len( self.get_children( object ) ) > 0)

    #---------------------------------------------------------------------------
    #  Gets the object's children:
    #---------------------------------------------------------------------------

    def get_children ( self, object ):
        """ Gets the object's children.
        """
        return getattr( object, self.children )

    #---------------------------------------------------------------------------
    #  Gets the object's children identifier:
    #---------------------------------------------------------------------------

    def get_children_id ( self, object ):
        """ Gets the object's children identifier.
        """
        return self.children

    #---------------------------------------------------------------------------
    #  Appends a child to the object's children:
    #---------------------------------------------------------------------------

    def append_child ( self, object, child ):
        """ Appends a child to the object's children.
        """
        getattr( object, self.children ).append( child )

    #---------------------------------------------------------------------------
    #  Inserts a child into the object's children:
    #---------------------------------------------------------------------------

    def insert_child ( self, object, index, child ):
        """ Inserts a child into the object's children.
        """
        getattr( object, self.children )[ index: index ] = [ child ]

    #---------------------------------------------------------------------------
    #  Confirms that a specified object can be deleted or not:
    #  Result = True:  Delete object with no further prompting
    #         = False: Do not delete object
    #         = other: Take default action (may prompt user to confirm delete)
    #---------------------------------------------------------------------------

    def confirm_delete ( self, object ):
        """ Checks whether a specified object can be deleted.

        Returns
        -------
        * **True** if the object should be deleted with no further prompting.
        * **False** if the object should not be deleted.
        * Anything else: Caller should take its default action (which might
          include prompting the user to confirm deletion).
        """
        return None

    #---------------------------------------------------------------------------
    #  Deletes a child at a specified index from the object's children:
    #---------------------------------------------------------------------------

    def delete_child ( self, object, index ):
        """ Deletes a child at a specified index from the object's children.
        """
        del getattr( object, self.children )[ index ]

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'children replaced' on a specified
    #  object:
    #---------------------------------------------------------------------------

    def when_children_replaced ( self, object, listener, remove ):
        """ Sets up or removes a listener for children being replaced on a
        specified object.
        """
        object.on_trait_change( listener, self.children, remove = remove,
                                dispatch = 'fast_ui' )

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'children changed' on a specified
    #  object:
    #---------------------------------------------------------------------------

    def when_children_changed ( self, object, listener, remove ):
        """ Sets up or removes a listener for children being changed on a
        specified object.
        """
        object.on_trait_change( listener, self.children + '_items',
                                remove = remove, dispatch = 'fast_ui' )

    #---------------------------------------------------------------------------
    #  Gets the label to display for a specified object:
    #---------------------------------------------------------------------------

    def get_label ( self, object ):
        """ Gets the label to display for a specified object.
        """
        label = self.label
        if label[:1] == '=':
            return label[1:]

        label = xgetattr( object, label, '' )

        if self.formatter is None:
            return label

        return self.formatter( object, label )

    #---------------------------------------------------------------------------
    #  Sets the label for a specified object:
    #---------------------------------------------------------------------------

    def set_label ( self, object, label ):
        """ Sets the label for a specified object.
        """
        label_name = self.label
        if label_name[:1] != '=':
            xsetattr( object, label_name, label )

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'label changed' on a specified object:
    #---------------------------------------------------------------------------

    def when_label_changed ( self, object, listener, remove ):
        """ Sets up or removes a listener for the label being changed on a
        specified object.
        """
        label = self.label
        if label[:1] != '=':
            object.on_trait_change( listener, label, remove = remove,
                                    dispatch = 'ui' )

    def get_column_labels(self, object):
        """ Get the labels for any columns that have been defined.
        """
        trait = self.column_labels
        labels = xgetattr(object, trait, [])
        formatted = []
        for formatter, label in map(None, self.column_formatters, labels):
            # If the list of column formatters is shorter than the list of
            # labels, then map(None) will extend it with Nones. Just pass the label
            # as preformatted. Similarly, explicitly using None in the list will
            # pass through the item.
            if formatter is None:
                formatted.append(label)
            else:
                formatted.append(formatter(label))
        return formatted

    def when_column_labels_change(self, object, listener, remove):
        """ Sets up or removes a listener for the column labels being changed on
        a specified object.

        This will fire when either the list is reassigned or when it is
        modified. I.e., it listens both to the trait change event and the
        trait_items change event. Implement the listener appropriately to handle
        either case.
        """
        trait = self.column_labels
        if trait != '':
            object.on_trait_change(listener, trait, remove=remove, dispatch='ui')
            object.on_trait_change(listener, trait+'_items', remove=remove, dispatch='ui')

    #---------------------------------------------------------------------------
    #  Gets the tooltip to display for a specified object:
    #---------------------------------------------------------------------------

    def get_tooltip ( self, object ):
        """ Gets the tooltip to display for a specified object.
        """
        tooltip = self.tooltip
        if tooltip == '':
            return tooltip

        if tooltip[:1] == '=':
            return tooltip[1:]

        tooltip = xgetattr( object, tooltip, '' )

        if self.tooltip_formatter is None:
            return tooltip

        return self.tooltip_formatter( object, tooltip )

    #---------------------------------------------------------------------------
    #  Returns the icon for a specified object:
    #---------------------------------------------------------------------------

    def get_icon ( self, object, is_expanded ):
        """ Returns the icon for a specified object.
        """
        if not self.allows_children( object ):
            return self.icon_item

        if is_expanded:
            return self.icon_open

        return self.icon_group

    #---------------------------------------------------------------------------
    #  Returns the path used to locate an object's icon:
    #---------------------------------------------------------------------------

    def get_icon_path ( self, object ):
        """ Returns the path used to locate an object's icon.
        """
        return self.icon_path

    #---------------------------------------------------------------------------
    #  Returns the name to use when adding a new object instance (displayed in
    #  the 'New' submenu):
    #---------------------------------------------------------------------------

    def get_name ( self, object ):
        """ Returns the name to use when adding a new object instance
            (displayed in the "New" submenu).
        """
        return self.name

    #---------------------------------------------------------------------------
    #  Gets the View to use when editing an object:
    #---------------------------------------------------------------------------

    def get_view ( self, object ):
        """ Gets the view to use when editing an object.
        """
        return self.view

    #---------------------------------------------------------------------------
    #  Returns the right-click context menu for an object:
    #---------------------------------------------------------------------------

    def get_menu ( self, object ):
        """ Returns the right-click context menu for an object.
        """
        return self.menu

    def get_background(self, object) :
        background = self.background
        if isinstance(background, str) :
            background = getattr(object, background, background)
        return background

    def get_foreground(self, object) :
        foreground = self.foreground
        if isinstance(foreground, str) :
            foreground = getattr(object, foreground, foreground)
        return foreground

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be renamed:
    #---------------------------------------------------------------------------

    def can_rename ( self, object ):
        """ Returns whether the object's children can be renamed.
        """
        return self.rename

    #---------------------------------------------------------------------------
    #  Returns whether or not the object can be renamed:
    #---------------------------------------------------------------------------

    def can_rename_me ( self, object ):
        """ Returns whether the object can be renamed.
        """
        return self.rename_me

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be copied:
    #---------------------------------------------------------------------------

    def can_copy ( self, object ):
        """ Returns whether the object's children can be copied.
        """
        return self.copy

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be deleted:
    #---------------------------------------------------------------------------

    def can_delete ( self, object ):
        """ Returns whether the object's children can be deleted.
        """
        return self.delete

    #---------------------------------------------------------------------------
    #  Returns whether or not the object can be deleted:
    #---------------------------------------------------------------------------

    def can_delete_me ( self, object ):
        """ Returns whether the object can be deleted.
        """
        return self.delete_me

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be inserted (or just
    #  appended):
    #---------------------------------------------------------------------------

    def can_insert ( self, object ):
        """ Returns whether the object's children can be inserted (vs.
        appended).
        """
        return self.insert

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children should be auto-opened:
    #---------------------------------------------------------------------------

    def can_auto_open ( self, object ):
        """ Returns whether the object's children should be automatically
        opened.
        """
        return self.auto_open

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children should be auto-closed:
    #---------------------------------------------------------------------------

    def can_auto_close ( self, object ):
        """ Returns whether the object's children should be automatically
        closed.
        """
        return self.auto_close

    #---------------------------------------------------------------------------
    #  Returns whether or not this is the node that should handle a specified
    #  object:
    #---------------------------------------------------------------------------

    def is_node_for ( self, object ):
        """ Returns whether this is the node that handles a specified object.
        """
        return (isinstance( object, self.node_for_class ) or
                object.has_traits_interface( *self.node_for_interface ))

    #---------------------------------------------------------------------------
    #  Returns whether a given 'add_object' can be added to an object:
    #---------------------------------------------------------------------------

    def can_add ( self, object, add_object ):
        """ Returns whether a given object is droppable on the node.
        """
        klass = self._class_for( add_object )
        if self.is_addable( klass ):
            return True

        for item in self.move:
            if type( item ) in SequenceTypes:
                item = item[0]
            if issubclass( klass, item ):
                return True

        return False

    #---------------------------------------------------------------------------
    #  Returns the list of classes that can be added to the object:
    #---------------------------------------------------------------------------

    def get_add ( self, object ):
        """ Returns the list of classes that can be added to the object.
        """
        return self.add

    #---------------------------------------------------------------------------
    #  Returns the 'draggable' version of a specified object:
    #---------------------------------------------------------------------------

    def get_drag_object ( self, object ):
        """ Returns a draggable version of a specified object.
        """
        return object

    #---------------------------------------------------------------------------
    #  Returns a droppable version of a specified object:
    #---------------------------------------------------------------------------

    def drop_object ( self, object, dropped_object ):
        """ Returns a droppable version of a specified object.
        """
        klass = self._class_for( dropped_object )
        if self.is_addable( klass ):
            return dropped_object

        for item in self.move:
            if type( item ) in SequenceTypes:
                if issubclass( klass, item[0] ):
                    return item[1]( object, dropped_object )
            elif issubclass( klass, item ):
                return dropped_object

        return dropped_object

    #---------------------------------------------------------------------------
    #  Handles an object being selected:
    #---------------------------------------------------------------------------

    def select ( self, object ):
        """ Handles an object being selected.
        """
        if self.on_select is not None:
            self.on_select( object )
            return None

        return True

    #---------------------------------------------------------------------------
    #  Handles an object being clicked:
    #---------------------------------------------------------------------------

    def click ( self, object ):
        """ Handles an object being clicked.
        """
        if self.on_click is not None:
            self.on_click( object )
            return None

        return True

    #---------------------------------------------------------------------------
    #  Handles an object being double-clicked:
    #---------------------------------------------------------------------------

    def dclick ( self, object ):
        """ Handles an object being double-clicked.
        """
        if self.on_dclick is not None:
            self.on_dclick( object )
            return None

        return True

    #---------------------------------------------------------------------------
    #  Handles an object being activated:
    #---------------------------------------------------------------------------

    def activated ( self, object ):
        """ Handles an object being activated.
        """
        if self.on_activated is not None:
            self.on_activated( object )
            return None

        return True

    #---------------------------------------------------------------------------
    #  Returns whether or not a specified object class can be added to the node:
    #---------------------------------------------------------------------------

    def is_addable ( self, klass ):
        """ Returns whether a specified object class can be added to the node.
        """
        for item in self.add:
            if type( item ) in SequenceTypes:
                item = item[0]

            if issubclass( klass, item ):
                return True

        return False

    #---------------------------------------------------------------------------
    #  Returns the class of an object:
    #---------------------------------------------------------------------------

    def _class_for ( self, object ):
        """ Returns the class of an object.
        """
        if isinstance( object, type ):
            return object

        return object.__class__

#-------------------------------------------------------------------------------
#  'ITreeNode' class
#-------------------------------------------------------------------------------

class ITreeNode ( Interface ):

    def allows_children ( self ):
        """ Returns whether this object can have children.
        """

    def has_children ( self ):
        """ Returns whether the object has children.
        """

    def get_children ( self ):
        """ Gets the object's children.
        """

    def get_children_id ( self ):
        """ Gets the object's children identifier.
        """

    def append_child ( self, child ):
        """ Appends a child to the object's children.
        """

    def insert_child ( self, index, child ):
        """ Inserts a child into the object's children.
        """

    def confirm_delete ( self ):
        """ Checks whether a specified object can be deleted.

        Returns
        -------
        * **True** if the object should be deleted with no further prompting.
        * **False** if the object should not be deleted.
        * Anything else: Caller should take its default action (which might
          include prompting the user to confirm deletion).
        """

    def delete_child ( self, index ):
        """ Deletes a child at a specified index from the object's children.
        """

    def when_children_replaced ( self, listener, remove ):
        """ Sets up or removes a listener for children being replaced on a
            specified object.
        """

    def when_children_changed ( self, listener, remove ):
        """ Sets up or removes a listener for children being changed on a
            specified object.
        """

    def get_label ( self ):
        """ Gets the label to display for a specified object.
        """

    def set_label ( self, label ):
        """ Sets the label for a specified object.
        """

    def when_label_changed ( self, listener, remove ):
        """ Sets up or removes a listener for the label being changed on a
            specified object.
        """

    def get_column_labels(self, object):
        """ Get the labels for any columns that have been defined.
        """

    def when_column_labels_change(self, object, listener, remove):
        """ Sets up or removes a listener for the column labels being changed on
        a specified object.

        This will fire when either the list is reassigned or when it is
        modified. I.e., it listens both to the trait change event and the
        trait_items change event. Implement the listener appropriately to handle
        either case.
        """

    def get_tooltip ( self ):
        """ Gets the tooltip to display for a specified object.
        """

    def get_icon ( self, is_expanded ):
        """ Returns the icon for a specified object.
        """

    def get_icon_path ( self ):
        """ Returns the path used to locate an object's icon.
        """

    def get_name ( self ):
        """ Returns the name to use when adding a new object instance
            (displayed in the "New" submenu).
        """

    def get_view ( self ):
        """ Gets the view to use when editing an object.
        """

    def get_menu ( self ):
        """ Returns the right-click context menu for an object.
        """

    def can_rename ( self ):
        """ Returns whether the object's children can be renamed.
        """

    def can_rename_me ( self ):
        """ Returns whether the object can be renamed.
        """

    def can_copy ( self ):
        """ Returns whether the object's children can be copied.
        """

    def can_delete ( self ):
        """ Returns whether the object's children can be deleted.
        """

    def can_delete_me ( self ):
        """ Returns whether the object can be deleted.
        """

    def can_insert ( self ):
        """ Returns whether the object's children can be inserted (vs.
            appended).
        """

    def can_auto_open ( self ):
        """ Returns whether the object's children should be automatically
            opened.
        """

    def can_auto_close ( self ):
        """ Returns whether the object's children should be automatically
            closed.
        """

    def can_add ( self, add_object ):
        """ Returns whether a given object is droppable on the node.
        """

    def get_add ( self ):
        """ Returns the list of classes that can be added to the object.
        """

    def get_drag_object ( self ):
        """ Returns a draggable version of a specified object.
        """

    def drop_object ( self, dropped_object ):
        """ Returns a droppable version of a specified object.
        """

    def select ( self ):
        """ Handles an object being selected.
        """

    def click ( self ):
        """ Handles an object being clicked.
        """

    def dclick ( self ):
        """ Handles an object being double-clicked.
        """

    def activated ( self ):
        """ Handles an object being activated.
        """

#-------------------------------------------------------------------------------
#  'ITreeNodeAdapter' class
#-------------------------------------------------------------------------------

class ITreeNodeAdapter ( Adapter ):
    """ Abstract base class for an adapter that implements the ITreeNode
        interface.

        Usage:

        1. Create a subclass of ITreeNodeAdapter.
        2. Add an 'adapts( xxx_class, ITreeNode )' declaration (usually placed
           right after the 'class' statement) to define what class (or classes)
           this is an ITreeNode adapter for.
        3. Override any of the following methods as necessary, using the
           'self.adaptee' trait to access the adapted object if needed.

       Note: This base class implements all of the ITreeNode interface methods,
       but does not necessarily provide useful implementations for all of the
       methods. It allows you to get a new adapter class up and running quickly,
       but you should carefully review your final adapter implementation class
       to make sure it behaves correctly in your application.
    """

    def allows_children ( self ):
        """ Returns whether this object can have children.
        """
        return False

    def has_children ( self ):
        """ Returns whether the object has children.
        """
        return False

    def get_children ( self ):
        """ Gets the object's children.
        """
        return []

    def get_children_id ( self ):
        """ Gets the object's children identifier.
        """
        return ''

    def append_child ( self, child ):
        """ Appends a child to the object's children.
        """
        pass

    def insert_child ( self, index, child ):
        """ Inserts a child into the object's children.
        """
        pass

    def confirm_delete ( self ):
        """ Checks whether a specified object can be deleted.

        Returns
        -------
        * **True** if the object should be deleted with no further prompting.
        * **False** if the object should not be deleted.
        * Anything else: Caller should take its default action (which might
          include prompting the user to confirm deletion).
        """
        return False

    def delete_child ( self, index ):
        """ Deletes a child at a specified index from the object's children.
        """
        pass

    def when_children_replaced ( self, listener, remove ):
        """ Sets up or removes a listener for children being replaced on a
            specified object.
        """
        pass

    def when_children_changed ( self, listener, remove ):
        """ Sets up or removes a listener for children being changed on a
            specified object.
        """
        pass

    def get_label ( self ):
        """ Gets the label to display for a specified object.
        """
        return 'No label specified'

    def set_label ( self, label ):
        """ Sets the label for a specified object.
        """
        pass

    def when_label_changed ( self, listener, remove ):
        """ Sets up or removes a listener for the label being changed on a
            specified object.
        """
        pass

    def get_column_labels(self):
        """ Get the labels for any columns that have been defined.
        """
        return []

    def when_column_labels_change(self, listener, remove):
        """ Sets up or removes a listener for the column labels being changed on
        a specified object.

        This will fire when either the list is reassigned or when it is
        modified. I.e., it listens both to the trait change event and the
        trait_items change event. Implement the listener appropriately to handle
        either case.
        """
        pass

    def get_tooltip ( self ):
        """ Gets the tooltip to display for a specified object.
        """
        return ''

    def get_icon ( self, is_expanded ):
        """ Returns the icon for a specified object.
        """
        return '<item>'

    def get_icon_path ( self ):
        """ Returns the path used to locate an object's icon.
        """
        return ''

    def get_name ( self ):
        """ Returns the name to use when adding a new object instance
            (displayed in the "New" submenu).
        """
        return ''

    def get_view ( self ):
        """ Gets the view to use when editing an object.
        """
        return None

    def get_menu ( self ):
        """ Returns the right-click context menu for an object.
        """
        return None

    def get_background ( self ):
        """ Returns the background for object
        """
        return None

    def get_foreground ( self ):
        """ Returns the foreground for object
        """
        return None

    def can_rename ( self ):
        """ Returns whether the object's children can be renamed.
        """
        return False

    def can_rename_me ( self ):
        """ Returns whether the object can be renamed.
        """
        return False

    def can_copy ( self ):
        """ Returns whether the object's children can be copied.
        """
        return False

    def can_delete ( self ):
        """ Returns whether the object's children can be deleted.
        """
        return False

    def can_delete_me ( self ):
        """ Returns whether the object can be deleted.
        """
        return False

    def can_insert ( self ):
        """ Returns whether the object's children can be inserted (vs.
            appended).
        """
        return False

    def can_auto_open ( self ):
        """ Returns whether the object's children should be automatically
            opened.
        """
        return False

    def can_auto_close ( self ):
        """ Returns whether the object's children should be automatically
            closed.
        """
        return False

    def can_add ( self, add_object ):
        """ Returns whether a given object is droppable on the node.
        """
        return False

    def get_add ( self ):
        """ Returns the list of classes that can be added to the object.
        """
        return []

    def get_drag_object ( self ):
        """ Returns a draggable version of a specified object.
        """
        return self.adaptee

    def drop_object ( self, dropped_object ):
        """ Returns a droppable version of a specified object.
        """
        return dropped_object

    def select ( self ):
        """ Handles an object being selected.
        """
        pass

    def click ( self ):
        """ Handles an object being clicked.
        """
        pass

    def dclick ( self ):
        """ Handles an object being double-clicked.
        """
        pass

    def activated ( self ):
        """ Handles an object being activated.
        """
        pass

#-------------------------------------------------------------------------------
#  'ITreeNodeAdapterBridge' class
#-------------------------------------------------------------------------------

class ITreeNodeAdapterBridge ( HasPrivateTraits ):
    """ Private class for use by a toolkit-specific implementation of the
        TreeEditor to allow bridging the TreeNode interface used by the editor
        to the ITreeNode interface used by object adapters.
    """

    # The ITreeNode adapter being bridged:
    adapter = AdaptedTo( ITreeNode )

    #-- TreeNode implementation ------------------------------------------------

    def allows_children ( self, object ):
        """ Returns whether this object can have children.
        """
        return self.adapter.allows_children()

    def has_children ( self, object ):
        """ Returns whether the object has children.
        """
        return self.adapter.has_children()

    def get_children ( self, object ):
        """ Gets the object's children.
        """
        return self.adapter.get_children()

    def get_children_id ( self, object ):
        """ Gets the object's children identifier.
        """
        return self.adapter.get_children_id()

    def append_child ( self, object, child ):
        """ Appends a child to the object's children.
        """
        return self.adapter.append_child( child )

    def insert_child ( self, object, index, child ):
        """ Inserts a child into the object's children.
        """
        return self.adapter.insert_child( index, child )

    def confirm_delete ( self, object ):
        """ Checks whether a specified object can be deleted.

        Returns
        -------
        * **True** if the object should be deleted with no further prompting.
        * **False** if the object should not be deleted.
        * Anything else: Caller should take its default action (which might
          include prompting the user to confirm deletion).
        """
        return self.adapter.confirm_delete()

    def delete_child ( self, object, index ):
        """ Deletes a child at a specified index from the object's children.
        """
        return self.adapter.delete_child( index )

    def when_children_replaced ( self, object, listener, remove ):
        """ Sets up or removes a listener for children being replaced on a
            specified object.
        """
        return self.adapter.when_children_replaced( listener, remove )

    def when_children_changed ( self, object, listener, remove ):
        """ Sets up or removes a listener for children being changed on a
            specified object.
        """
        return self.adapter.when_children_changed( listener, remove )

    def get_label ( self, object ):
        """ Gets the label to display for a specified object.
        """
        return self.adapter.get_label()

    def set_label ( self, object, label ):
        """ Sets the label for a specified object.
        """
        return self.adapter.set_label( label )

    def when_label_changed ( self, object, listener, remove ):
        """ Sets up or removes a listener for the label being changed on a
            specified object.
        """
        return self.adapter.when_label_changed( listener, remove )

    def get_column_labels(self, object):
        """ Get the labels for any columns that have been defined.
        """
        return self.adapter.get_column_labels()

    def when_column_labels_change(self, object, listener, remove):
        """ Sets up or removes a listener for the column labels being changed on
        a specified object.

        This will fire when either the list is reassigned or when it is
        modified. I.e., it listens both to the trait change event and the
        trait_items change event. Implement the listener appropriately to handle
        either case.
        """
        return self.adapter.when_column_labels_change(listener, remove)

    def get_tooltip ( self, object ):
        """ Gets the tooltip to display for a specified object.
        """
        return self.adapter.get_tooltip()

    def get_icon ( self, object, is_expanded ):
        """ Returns the icon for a specified object.
        """
        return self.adapter.get_icon( is_expanded )

    def get_icon_path ( self, object ):
        """ Returns the path used to locate an object's icon.
        """
        return self.adapter.get_icon_path()

    def get_name ( self, object ):
        """ Returns the name to use when adding a new object instance
            (displayed in the "New" submenu).
        """
        return self.adapter.get_name()

    def get_view ( self, object ):
        """ Gets the view to use when editing an object.
        """
        return self.adapter.get_view()

    def get_menu ( self, object ):
        """ Returns the right-click context menu for an object.
        """
        return self.adapter.get_menu()

    def get_background ( self, object ):
        """ Returns the background for object
        """
        return self.adapter.get_background()

    def get_foreground ( self, object ):
        """ Returns the foreground for object
        """
        return self.adapter.get_foreground()

    def can_rename ( self, object ):
        """ Returns whether the object's children can be renamed.
        """
        return self.adapter.can_rename()

    def can_rename_me ( self, object ):
        """ Returns whether the object can be renamed.
        """
        return self.adapter.can_rename_me()

    def can_copy ( self, object ):
        """ Returns whether the object's children can be copied.
        """
        return self.adapter.can_copy()

    def can_delete ( self, object ):
        """ Returns whether the object's children can be deleted.
        """
        return self.adapter.can_delete()

    def can_delete_me ( self, object ):
        """ Returns whether the object can be deleted.
        """
        return self.adapter.can_delete_me()

    def can_insert ( self, object ):
        """ Returns whether the object's children can be inserted (vs.
            appended).
        """
        return self.adapter.can_insert()

    def can_auto_open ( self, object ):
        """ Returns whether the object's children should be automatically
            opened.
        """
        return self.adapter.can_auto_open()

    def can_auto_close ( self, object ):
        """ Returns whether the object's children should be automatically
            closed.
        """
        return self.adapter.can_auto_close()

    def can_add ( self, object, add_object ):
        """ Returns whether a given object is droppable on the node.
        """
        return self.adapter.can_add( add_object )

    def get_add ( self, object ):
        """ Returns the list of classes that can be added to the object.
        """
        return self.adapter.get_add()

    def get_drag_object ( self, object ):
        """ Returns a draggable version of a specified object.
        """
        return self.adapter.get_drag_object()

    def drop_object ( self, object, dropped_object ):
        """ Returns a droppable version of a specified object.
        """
        return self.adapter.drop_object( dropped_object )

    def select ( self, object ):
        """ Handles an object being selected.
        """
        return self.adapter.select()

    def click ( self, object ):
        """ Handles an object being clicked.
        """
        return self.adapter.click()

    def dclick ( self, object ):
        """ Handles an object being double-clicked.
        """
        return self.adapter.dclick()

    def activated ( self, object ):
        """ Handles an object being activated.
        """
        return self.adapter.activated()


# FIXME RTK: add the column_labels API to the following TreeNodes, too.


#-------------------------------------------------------------------------------
#  'ObjectTreeNode' class
#-------------------------------------------------------------------------------

class ObjectTreeNode ( TreeNode ):

    #---------------------------------------------------------------------------
    #  Returns whether chidren of this object are allowed or not:
    #---------------------------------------------------------------------------

    def allows_children ( self, object ):
        """ Returns whether this object can have children.
        """
        return object.tno_allows_children( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object has children:
    #---------------------------------------------------------------------------

    def has_children ( self, object ):
        """ Returns whether the object has children.
        """
        return object.tno_has_children( self )

    #---------------------------------------------------------------------------
    #  Gets the object's children:
    #---------------------------------------------------------------------------

    def get_children ( self, object ):
        """ Gets the object's children.
        """
        return object.tno_get_children( self )

    #---------------------------------------------------------------------------
    #  Gets the object's children identifier:
    #---------------------------------------------------------------------------

    def get_children_id ( self, object ):
        """ Gets the object's children identifier.
        """
        return object.tno_get_children_id( self )

    #---------------------------------------------------------------------------
    #  Appends a child to the object's children:
    #---------------------------------------------------------------------------

    def append_child ( self, object, child ):
        """ Appends a child to the object's children.
        """
        return object.tno_append_child( self, child )

    #---------------------------------------------------------------------------
    #  Inserts a child into the object's children:
    #---------------------------------------------------------------------------

    def insert_child ( self, object, index, child ):
        """ Inserts a child into the object's children.
        """
        return object.tno_insert_child( self, index, child )

    #---------------------------------------------------------------------------
    #  Confirms that a specified object can be deleted or not:
    #  Result = True:  Delete object with no further prompting
    #         = False: Do not delete object
    #         = other: Take default action (may prompt user to confirm delete)
    #---------------------------------------------------------------------------

    def confirm_delete ( self, object ):
        """ Checks whether a specified object can be deleted.

        Returns
        -------
        * **True** if the object should be deleted with no further prompting.
        * **False** if the object should not be deleted.
        * Anything else: Caller should take its default action (which might
          include prompting the user to confirm deletion).
        """
        return object.tno_confirm_delete( self )

    #---------------------------------------------------------------------------
    #  Deletes a child at a specified index from the object's children:
    #---------------------------------------------------------------------------

    def delete_child ( self, object, index ):
        """ Deletes a child at a specified index from the object's children.
        """
        return object.tno_delete_child( self, index )

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'children replaced' on a specified
    #  object:
    #---------------------------------------------------------------------------

    def when_children_replaced ( self, object, listener, remove ):
        """ Sets up or removes a listener for children being replaced on a
            specified object.
        """
        return object.tno_when_children_replaced( self, listener, remove )

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'children changed' on a specified
    #  object:
    #---------------------------------------------------------------------------

    def when_children_changed ( self, object, listener, remove ):
        """ Sets up or removes a listener for children being changed on a
            specified object.
        """
        return object.tno_when_children_changed( self, listener, remove )

    #---------------------------------------------------------------------------
    #  Gets the label to display for a specified object:
    #---------------------------------------------------------------------------

    def get_label ( self, object ):
        """ Gets the label to display for a specified object.
        """
        return object.tno_get_label( self )

    #---------------------------------------------------------------------------
    #  Sets the label for a specified object:
    #---------------------------------------------------------------------------

    def set_label ( self, object, label ):
        """ Sets the label for a specified object.
        """
        return object.tno_set_label( self, label )

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'label changed' on a specified object:
    #---------------------------------------------------------------------------

    def when_label_changed ( self, object, listener, remove ):
        """ Sets up or removes a listener for the label being changed on a
            specified object.
        """
        return object.tno_when_label_changed( self, listener, remove )

    #---------------------------------------------------------------------------
    #  Gets the tooltip to display for a specified object:
    #---------------------------------------------------------------------------

    def get_tooltip ( self, object ):
        """ Gets the tooltip to display for a specified object.
        """
        return object.tno_get_tooltip( self )

    #---------------------------------------------------------------------------
    #  Returns the icon for a specified object:
    #---------------------------------------------------------------------------

    def get_icon ( self, object, is_expanded ):
        """ Returns the icon for a specified object.
        """
        return object.tno_get_icon( self, is_expanded )

    #---------------------------------------------------------------------------
    #  Returns the path used to locate an object's icon:
    #---------------------------------------------------------------------------

    def get_icon_path ( self, object ):
        """ Returns the path used to locate an object's icon.
        """
        return object.tno_get_icon_path( self )

    #---------------------------------------------------------------------------
    #  Returns the name to use when adding a new object instance (displayed in
    #  the 'New' submenu):
    #---------------------------------------------------------------------------

    def get_name ( self, object ):
        """ Returns the name to use when adding a new object instance
            (displayed in the "New" submenu).
        """
        return object.tno_get_name( self )

    #---------------------------------------------------------------------------
    #  Gets the View to use when editing an object:
    #---------------------------------------------------------------------------

    def get_view ( self, object ):
        """ Gets the view to use when editing an object.
        """
        return object.tno_get_view( self )

    #---------------------------------------------------------------------------
    #  Returns the right-click context menu for an object:
    #---------------------------------------------------------------------------

    def get_menu ( self, object ):
        """ Returns the right-click context menu for an object.
        """
        return object.tno_get_menu( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be renamed:
    #---------------------------------------------------------------------------

    def can_rename ( self, object ):
        """ Returns whether the object's children can be renamed.
        """
        return object.tno_can_rename( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object can be renamed:
    #---------------------------------------------------------------------------

    def can_rename_me ( self, object ):
        """ Returns whether the object can be renamed.
        """
        return object.tno_can_rename_me( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be copied:
    #---------------------------------------------------------------------------

    def can_copy ( self, object ):
        """ Returns whether the object's children can be copied.
        """
        return object.tno_can_copy( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be deleted:
    #---------------------------------------------------------------------------

    def can_delete ( self, object ):
        """ Returns whether the object's children can be deleted.
        """
        return object.tno_can_delete( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object can be deleted:
    #---------------------------------------------------------------------------

    def can_delete_me ( self, object ):
        """ Returns whether the object can be deleted.
        """
        return object.tno_can_delete_me( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be inserted (or just
    #  appended):
    #---------------------------------------------------------------------------

    def can_insert ( self, object ):
        """ Returns whether the object's children can be inserted (vs.
        appended).
        """
        return object.tno_can_insert( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children should be auto-opened:
    #---------------------------------------------------------------------------

    def can_auto_open ( self, object ):
        """ Returns whether the object's children should be automatically
            opened.
        """
        return object.tno_can_auto_open( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children should be auto-closed:
    #---------------------------------------------------------------------------

    def can_auto_close ( self, object ):
        """ Returns whether the object's children should be automatically
            closed.
        """
        return object.tno_can_auto_close( self )

    #---------------------------------------------------------------------------
    #  Returns whether or not this is the node that should handle a specified
    #  object:
    #---------------------------------------------------------------------------

    def is_node_for ( self, object ):
        """ Returns whether this is the node that should handle a
            specified object.
        """
        if isinstance( object, TreeNodeObject ):
            return object.tno_is_node_for( self )

        return False

    #---------------------------------------------------------------------------
    #  Returns whether a given 'add_object' can be added to an object:
    #---------------------------------------------------------------------------

    def can_add ( self, object, add_object ):
        """ Returns whether a given object is droppable on the node.
        """
        return object.tno_can_add( self, add_object )

    #---------------------------------------------------------------------------
    #  Returns the list of classes that can be added to the object:
    #---------------------------------------------------------------------------

    def get_add ( self, object ):
        """ Returns the list of classes that can be added to the object.
        """
        return object.tno_get_add( self )

    #---------------------------------------------------------------------------
    #  Returns the 'draggable' version of a specified object:
    #---------------------------------------------------------------------------

    def get_drag_object ( self, object ):
        """ Returns a draggable version of a specified object.
        """
        return object.tno_get_drag_object( self )

    #---------------------------------------------------------------------------
    #  Returns a droppable version of a specified object:
    #---------------------------------------------------------------------------

    def drop_object ( self, object, dropped_object ):
        """ Returns a droppable version of a specified object.
        """
        return object.tno_drop_object( self, dropped_object )

    #---------------------------------------------------------------------------
    #  Handles an object being selected:
    #---------------------------------------------------------------------------

    def select ( self, object ):
        """ Handles an object being selected.
        """
        return object.tno_select( self )

    #---------------------------------------------------------------------------
    #  Handles an object being clicked:
    #---------------------------------------------------------------------------

    def click ( self, object ):
        """ Handles an object being clicked.
        """
        return object.tno_click( self )

    #---------------------------------------------------------------------------
    #  Handles an object being double-clicked:
    #---------------------------------------------------------------------------

    def dclick ( self, object ):
        """ Handles an object being double-clicked.
        """
        return object.tno_dclick( self )

    #---------------------------------------------------------------------------
    #  Handles an object being activated:
    #---------------------------------------------------------------------------

    def activated ( self, object ):
        """ Handles an object being activated.
        """
        return object.tno_activated( self )

#-------------------------------------------------------------------------------
#  'TreeNodeObject' class:
#-------------------------------------------------------------------------------

class TreeNodeObject ( HasPrivateTraits ):
    """ Represents the object that corresponds to a tree node.
    """

    #---------------------------------------------------------------------------
    #  Returns whether chidren of this object are allowed or not:
    #---------------------------------------------------------------------------

    def tno_allows_children ( self, node ):
        """ Returns whether this object allows children.
        """
        return (node.children != '')

    #---------------------------------------------------------------------------
    #  Returns whether or not the object has children:
    #---------------------------------------------------------------------------

    def tno_has_children ( self, node ):
        """ Returns whether this object has children.
        """
        return (len( self.tno_get_children( node ) ) > 0)

    #---------------------------------------------------------------------------
    #  Gets the object's children:
    #---------------------------------------------------------------------------

    def tno_get_children ( self, node ):
        """ Gets the object's children.
        """
        return getattr( self, node.children )

    #---------------------------------------------------------------------------
    #  Gets the object's children identifier:
    #---------------------------------------------------------------------------

    def tno_get_children_id ( self, node ):
        """ Gets the object's children identifier.
        """
        return node.children

    #---------------------------------------------------------------------------
    #  Appends a child to the object's children:
    #---------------------------------------------------------------------------

    def tno_append_child ( self, node, child ):
        """ Appends a child to the object's children.
        """
        getattr( self, node.children ).append( child )

    #---------------------------------------------------------------------------
    #  Inserts a child into the object's children:
    #---------------------------------------------------------------------------

    def tno_insert_child ( self, node, index, child ):
        """ Inserts a child into the object's children.
        """
        getattr( self, node.children )[ index: index ] = [ child ]

    #---------------------------------------------------------------------------
    #  Confirms that a specified object can be deleted or not:
    #  Result = True:  Delete object with no further prompting
    #         = False: Do not delete object
    #         = other: Take default action (may prompt user to confirm delete)
    #---------------------------------------------------------------------------

    def tno_confirm_delete ( self, node ):
        """ Checks whether a specified object can be deleted.

        Returns
        -------
        * **True** if the object should be deleted with no further prompting.
        * **False** if the object should not be deleted.
        * Anything else: Caller should take its default action (which might
          include prompting the user to confirm deletion).
        """
        return None

    #---------------------------------------------------------------------------
    #  Deletes a child at a specified index from the object's children:
    #---------------------------------------------------------------------------

    def tno_delete_child ( self, node, index ):
        """ Deletes a child at a specified index from the object's children.
        """
        del getattr( self, node.children )[ index ]

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'children replaced' on a specified
    #  object:
    #---------------------------------------------------------------------------

    def tno_when_children_replaced ( self, node, listener, remove ):
        """ Sets up or removes a listener for children being replaced on a
        specified object.
        """
        self.on_trait_change( listener, node.children, remove = remove,
                              dispatch = 'fast_ui' )

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'children changed' on a specified
    #  object:
    #---------------------------------------------------------------------------

    def tno_when_children_changed ( self, node, listener, remove ):
        """ Sets up or removes a listener for children being changed on a
        specified object.
        """
        self.on_trait_change( listener, node.children + '_items',
                              remove = remove, dispatch = 'fast_ui' )

    #---------------------------------------------------------------------------
    #  Gets the label to display for a specified object:
    #---------------------------------------------------------------------------

    def tno_get_label ( self, node ):
        """ Gets the label to display for a specified object.
        """
        label = node.label
        if label[:1] == '=':
            return label[1:]

        label = xgetattr( self, label )

        if node.formatter is None:
            return label

        return node.formatter( self, label )

    #---------------------------------------------------------------------------
    #  Sets the label for a specified node:
    #---------------------------------------------------------------------------

    def tno_set_label ( self, node, label ):
        """ Sets the label for a specified object.
        """
        label_name = node.label
        if label_name[:1] != '=':
            xsetattr( self, label_name, label )

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'label changed' on a specified object:
    #---------------------------------------------------------------------------

    def tno_when_label_changed ( self, node, listener, remove ):
        """ Sets up or removes a listener for  the label being changed on a
        specified object.
        """
        label = node.label
        if label[:1] != '=':
            self.on_trait_change( listener, label, remove = remove,
                                  dispatch = 'ui' )

    #---------------------------------------------------------------------------
    #  Gets the tooltip to display for a specified object:
    #---------------------------------------------------------------------------

    def tno_get_tooltip ( self, node ):
        """ Gets the tooltip to display for a specified object.
        """
        tooltip = node.tooltip
        if tooltip == '':
            return tooltip

        if tooltip[:1] == '=':
            return tooltip[1:]

        tooltip = xgetattr( self, tooltip )

        if node.tooltip_formatter is None:
            return tooltip

        return node.tooltip_formatter( self, tooltip )

    #---------------------------------------------------------------------------
    #  Returns the icon for a specified object:
    #---------------------------------------------------------------------------

    def tno_get_icon ( self, node, is_expanded ):
        """ Returns the icon for a specified object.
        """
        if not self.tno_allows_children( node ):
            return node.icon_item

        if is_expanded:
            return node.icon_open

        return node.icon_group

    #---------------------------------------------------------------------------
    #  Returns the path used to locate an object's icon:
    #---------------------------------------------------------------------------

    def tno_get_icon_path ( self, node ):
        """ Returns the path used to locate an object's icon.
        """
        return node.icon_path

    #---------------------------------------------------------------------------
    #  Returns the name to use when adding a new object instance (displayed in
    #  the 'New' submenu):
    #---------------------------------------------------------------------------

    def tno_get_name ( self, node ):
        """ Returns the name to use when adding a new object instance
            (displayed in the "New" submenu).
        """
        return node.name

    #---------------------------------------------------------------------------
    #  Gets the View to use when editing an object:
    #---------------------------------------------------------------------------

    def tno_get_view ( self, node ):
        """ Gets the view to use when editing an object.
        """
        return node.view

    #---------------------------------------------------------------------------
    #  Returns the right-click context menu for an object:
    #---------------------------------------------------------------------------

    def tno_get_menu ( self, node ):
        """ Returns the right-click context menu for an object.
        """
        return node.menu

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be renamed:
    #---------------------------------------------------------------------------

    def tno_can_rename ( self, node ):
        """ Returns whether the object's children can be renamed.
        """
        return node.rename

    #---------------------------------------------------------------------------
    #  Returns whether or not the object can be renamed:
    #---------------------------------------------------------------------------

    def tno_can_rename_me ( self, node ):
        """ Returns whether the object can be renamed.
        """
        return node.rename_me

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be copied:
    #---------------------------------------------------------------------------

    def tno_can_copy ( self, node ):
        """ Returns whether the object's children can be copied.
        """
        return node.copy

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be deleted:
    #---------------------------------------------------------------------------

    def tno_can_delete ( self, node ):
        """ Returns whether the object's children can be deleted.
        """
        return node.delete

    #---------------------------------------------------------------------------
    #  Returns whether or not the object can be deleted:
    #---------------------------------------------------------------------------

    def tno_can_delete_me ( self, node ):
        """ Returns whether the object can be deleted.
        """
        return node.delete_me

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be inserted (or just
    #  appended):
    #---------------------------------------------------------------------------

    def tno_can_insert ( self, node ):
        """ Returns whether the object's children can be inserted (vs.
        appended).
        """
        return node.insert

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children should be auto-opened:
    #---------------------------------------------------------------------------

    def tno_can_auto_open ( self, node ):
        """ Returns whether the object's children should be automatically
        opened.
        """
        return node.auto_open

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children should be auto-closed:
    #---------------------------------------------------------------------------

    def tno_can_auto_close ( self, node ):
        """ Returns whether the object's children should be automatically
        closed.
        """
        return node.auto_close

    #---------------------------------------------------------------------------
    #  Returns whether or not this is the node that should handle a specified
    #  object:
    #---------------------------------------------------------------------------

    def tno_is_node_for ( self, node ):
        """ Returns whether this is the node that should handle a
            specified object.
        """
        return (isinstance( self, node.node_for_class ) or
                self.has_traits_interface( *node.node_for_interface ))

    #---------------------------------------------------------------------------
    #  Returns whether a given 'add_object' can be added to an object:
    #---------------------------------------------------------------------------

    def tno_can_add ( self, node, add_object ):
        """ Returns whether a given object is droppable on the node.
        """
        klass = node._class_for( add_object )
        if node.is_addable( klass ):
            return True

        for item in node.move:
            if type( item ) in SequenceTypes:
                item = item[0]
            if issubclass( klass, item ):
                return True

        return False

    #---------------------------------------------------------------------------
    #  Returns the list of classes that can be added to the object:
    #---------------------------------------------------------------------------

    def tno_get_add ( self, node ):
        """ Returns the list of classes that can be added to the object.
        """
        return node.add

    #---------------------------------------------------------------------------
    #  Returns the 'draggable' version of a specified object:
    #---------------------------------------------------------------------------

    def tno_get_drag_object ( self, node ):
        """ Returns a draggable version of a specified object.
        """
        return self

    #---------------------------------------------------------------------------
    #  Returns a droppable version of a specified object:
    #---------------------------------------------------------------------------

    def tno_drop_object ( self, node, dropped_object ):
        """ Returns a droppable version of a specified object.
        """
        if node.is_addable( dropped_object ):
            return dropped_object

        for item in node.move:
            if type( item ) in SequenceTypes:
                if isinstance( dropped_object, item[0] ):
                    return item[1]( self, dropped_object )
            else:
                if isinstance( dropped_object, item ):
                    return dropped_object

    #---------------------------------------------------------------------------
    #  Handles an object being selected:
    #---------------------------------------------------------------------------

    def tno_select ( self, node ):
        """ Handles an object being selected.
        """
        if node.on_select is not None:
            node.on_select( self )
            return None

        return True

    #---------------------------------------------------------------------------
    #  Handles an object being clicked:
    #---------------------------------------------------------------------------

    def tno_click ( self, node ):
        """ Handles an object being clicked.
        """
        if node.on_click is not None:
            node.on_click( self )
            return None

        return True

    #---------------------------------------------------------------------------
    #  Handles an object being double-clicked:
    #---------------------------------------------------------------------------

    def tno_dclick ( self, node ):
        """ Handles an object being double-clicked.
        """
        if node.on_dclick is not None:
            node.on_dclick( self )
            return None

        return True

    #---------------------------------------------------------------------------
    #  Handles an object being activated:
    #---------------------------------------------------------------------------

    def tno_activated ( self, node ):
        """ Handles an object being activated.
        """
        if node.on_activated is not None:
            node.on_activated( self )
            return None

        return True

#-------------------------------------------------------------------------------
#  'MultiTreeNode' object:
#-------------------------------------------------------------------------------

class MultiTreeNode ( TreeNode ):

    #---------------------------------------------------------------------------
    #  Trait definitions:
    #---------------------------------------------------------------------------

    # TreeNode that applies to the base object itself
    root_node = Instance( TreeNode )

    # List of TreeNodes (one for each sub-item list)
    nodes = List( TreeNode )

    #---------------------------------------------------------------------------
    #  Returns whether chidren of this object are allowed or not:
    #---------------------------------------------------------------------------

    def allows_children ( self, object ):
        """ Returns whether this object can have children (True for this
        class).
        """
        return True

    #---------------------------------------------------------------------------
    #  Returns whether or not the object has children:
    #---------------------------------------------------------------------------

    def has_children ( self, object ):
        """ Returns whether this object has children (True for this class).
        """
        return True

    #---------------------------------------------------------------------------
    #  Gets the object's children:
    #---------------------------------------------------------------------------

    def get_children ( self, object ):
        """ Gets the object's children.
        """
        return [ ( object, node ) for node in self.nodes ]

    #---------------------------------------------------------------------------
    #  Gets the object's children identifier:
    #---------------------------------------------------------------------------

    def get_children_id ( self, object ):
        """ Gets the object's children identifier.
        """
        return ''

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'children replaced' on a specified
    #  object:
    #---------------------------------------------------------------------------

    def when_children_replaced ( self, object, listener, remove ):
        """ Sets up or removes a listener for children being replaced on a
        specified object.
        """
        pass

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'children changed' on a specified
    #  object:
    #---------------------------------------------------------------------------

    def when_children_changed ( self, object, listener, remove ):
        """ Sets up or removes a listener for children being changed on a
        specified object.
        """
        pass

    #---------------------------------------------------------------------------
    #  Gets the label to display for a specified object:
    #---------------------------------------------------------------------------

    def get_label ( self, object ):
        """ Gets the label to display for a specified object.
        """
        return self.root_node.get_label( object )

    #---------------------------------------------------------------------------
    #  Sets the label for a specified object:
    #---------------------------------------------------------------------------

    def set_label ( self, object, label ):
        """ Sets the label for a specified object.
        """
        return self.root_node.set_label( object, label )

    #---------------------------------------------------------------------------
    #  Sets up/Tears down a listener for 'label changed' on a specified object:
    #---------------------------------------------------------------------------

    def when_label_changed ( self, object, listener, remove ):
        """ Sets up or removes a listener for the label being changed on a
        specified object.
        """
        return self.root_node.when_label_changed( object, listener, remove )

    #---------------------------------------------------------------------------
    #  Returns the icon for a specified object:
    #---------------------------------------------------------------------------

    def get_icon ( self, object, is_expanded ):
        """ Returns the icon for a specified object.
        """
        return self.root_node.get_icon( object, is_expanded )

    #---------------------------------------------------------------------------
    #  Returns the path used to locate an object's icon:
    #---------------------------------------------------------------------------

    def get_icon_path ( self, object ):
        """ Returns the path used to locate an object's icon.
        """
        return self.root_node.get_icon_path( object )

    #---------------------------------------------------------------------------
    #  Returns the name to use when adding a new object instance (displayed in
    #  the 'New' submenu):
    #---------------------------------------------------------------------------

    def get_name ( self, object ):
        """ Returns the name to use when adding a new object instance
            (displayed in the "New" submenu).
        """
        return self.root_node.get_name( object )

    #---------------------------------------------------------------------------
    #  Gets the View to use when editing an object:
    #---------------------------------------------------------------------------

    def get_view ( self, object ):
        """ Gets the view to use when editing an object.
        """
        return self.root_node.get_view( object )

    #---------------------------------------------------------------------------
    #  Returns the right-click context menu for an object:
    #---------------------------------------------------------------------------

    def get_menu ( self, object ):
        """ Returns the right-click context menu for an object.
        """
        return self.root_node.get_menu( object )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be renamed:
    #---------------------------------------------------------------------------

    def can_rename ( self, object ):
        """ Returns whether the object's children can be renamed (False for
        this class).
        """
        return False

    #---------------------------------------------------------------------------
    #  Returns whether or not the object can be renamed:
    #---------------------------------------------------------------------------

    def can_rename_me ( self, object ):
        """ Returns whether the object can be renamed (False for this class).
        """
        return False

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be copied:
    #---------------------------------------------------------------------------

    def can_copy ( self, object ):
        """ Returns whether the object's children can be copied.
        """
        return self.root_node.can_copy( object )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be deleted:
    #---------------------------------------------------------------------------

    def can_delete ( self, object ):
        """ Returns whether the object's children can be deleted (False for
        this class).
        """
        return False

    #---------------------------------------------------------------------------
    #  Returns whether or not the object can be deleted:
    #---------------------------------------------------------------------------

    def can_delete_me ( self, object ):
        """ Returns whether the object can be deleted (True for this class).
        """
        return True

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children can be inserted (or just
    #  appended):
    #---------------------------------------------------------------------------

    def can_insert ( self, object ):
        """ Returns whether the object's children can be inserted (False,
        meaning that children are appended, for this class).
        """
        return False

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children should be auto-opened:
    #---------------------------------------------------------------------------

    def can_auto_open ( self, object ):
        """ Returns whether the object's children should be automatically
        opened.
        """
        return self.root_node.can_auto_open( object )

    #---------------------------------------------------------------------------
    #  Returns whether or not the object's children should be auto-closed:
    #---------------------------------------------------------------------------

    def can_auto_close ( self, object ):
        """ Returns whether the object's children should be automatically
        closed.
        """
        return self.root_node.can_auto_close( object )

    #---------------------------------------------------------------------------
    #  Returns whether a given 'add_object' can be added to an object:
    #---------------------------------------------------------------------------

    def can_add ( self, object, add_object ):
        """ Returns whether a given object is droppable on the node (False for
        this class).
        """
        return False

    #---------------------------------------------------------------------------
    #  Returns the list of classes that can be added to the object:
    #---------------------------------------------------------------------------

    def get_add ( self, object ):
        """ Returns the list of classes that can be added to the object.
        """
        return []

    #-------------------------------------------------------------------------------
    #  Returns the 'draggable' version of a specified object:
    #-------------------------------------------------------------------------------

    def get_drag_object ( self, object ):
        """ Returns a draggable version of a specified object.
        """
        return self.root_node.get_drag_object( object )

    #---------------------------------------------------------------------------
    #  Returns a droppable version of a specified object:
    #---------------------------------------------------------------------------

    def drop_object ( self, object, dropped_object ):
        """ Returns a droppable version of a specified object.
        """
        return self.root_node.drop_object( object, dropped_object )

    #---------------------------------------------------------------------------
    #  Handles an object being selected:
    #---------------------------------------------------------------------------

    def select ( self, object ):
        """ Handles an object being selected.
        """
        return self.root_node.select( object )

    #---------------------------------------------------------------------------
    #  Handles an object being clicked:
    #---------------------------------------------------------------------------

    def click ( self, object ):
        """ Handles an object being clicked.
        """
        return self.root_node.click( object )

    #---------------------------------------------------------------------------
    #  Handles an object being double-clicked:
    #---------------------------------------------------------------------------

    def dclick ( self, object ):
        """ Handles an object being double-clicked.
        """
        return self.root_node.dclick( object )

    #---------------------------------------------------------------------------
    #  Handles an object being activated:
    #---------------------------------------------------------------------------

    def activated ( self, object ):
        """ Handles an object being activated.
        """
        return self.root_node.activated( object )

