"""
Module defining a simple Python shell Envisage tasks plugin.

This plugin provides a task with a simple Python shell.  This shouldn't be
confused with a more full-featured shell, such as those provided by IPython.
"""

# Standard library imports.
import logging

# Enthought library imports.
from traits.api import Str, List, Dict, Instance, Property
from pyface.tasks.contrib.python_shell import PythonShellTask
from envisage.api import Plugin, ExtensionPoint, IExtensionRegistry
from envisage.ui.tasks.api import TaskFactory

logger = logging.getLogger()

BINDINGS          = 'envisage.plugins.python_shell.bindings'
COMMANDS          = 'envisage.plugins.python_shell.commands'

class EnvisagePythonShellTask(PythonShellTask):
    """ Subclass of PythonShellTask that gets its bindings and commands from
    an Envisage ExtensionPoint
    """
    id='envisage.plugins.tasks.python_shell_task'
    
    # ExtensionPointUser interface
    extension_registry = Property(Instance(IExtensionRegistry))
    
    # The list of bindings for the shell
    bindings = ExtensionPoint(id=BINDINGS)
    
    # The list of commands to run on shell startup
    commands = ExtensionPoint(id=COMMANDS)
    
    # property getter/setters
    
    def _get_extension_registry(self):
        if self.window is not None:
            return self.window.application
        return None
        

class PythonShellPlugin(Plugin):
    """ A tasks plugin to display a simple Python shell to the user.
    """

    # Extension point IDs.
    BINDINGS          = BINDINGS
    COMMANDS          = COMMANDS
    TASKS             = 'envisage.ui.tasks.tasks'

    #### 'IPlugin' interface ##################################################

    # The plugin's unique identifier.
    id = 'envisage.plugins.tasks.python_shell_plugin'

    # The plugin's name (suitable for displaying to the user).
    name = 'Python Shell'
    
    #### Extension points exposed by this plugin ##############################

    bindings = ExtensionPoint(
        List(Dict), id=BINDINGS, desc="""
        This extension point allows you to contribute name/value pairs that
        will be bound when the interactive Python shell is started.

        e.g. Each item in the list is a dictionary of name/value pairs::

            {'x' : 10, 'y' : ['a', 'b', 'c']}
        """
    )

    commands = ExtensionPoint(
        List(Str), id=COMMANDS, desc="""
        This extension point allows you to contribute commands that are
        executed when the interactive Python shell is started.

        e.g. Each item in the list is a string of arbitrary Python code::

          'import os, sys'
          'from traits.api import *'

        Yes, I know this is insecure but it follows the usual Python rule of
        'we are all consenting adults'.
        """
    )
    
    #### Contributions to extension points made by this plugin ################

    # Bindings.
    contributed_bindings = List(contributes_to=BINDINGS)
    tasks = List(contributes_to=TASKS)

    ###########################################################################
    # Protected interface.
    ###########################################################################

    def start(self):
        logger.debug('started python shell plugin')

    def _contributed_bindings_default(self):
        """ By default we expose the Envisage application object to the namespace
        """
        return [{'application' : self.application}]

    def _tasks_default(self):
        return [
            TaskFactory(
                id='envisage.plugins.tasks.python_shell_task',
                name='Python Shell',
                factory=EnvisagePythonShellTask
            ),
        ]