# (C) Copyright 2007-2020 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in 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!

""" An IPython kernel plugin. """

import logging
import warnings

# Enthought library imports.
from envisage.api import (
    bind_extension_point,
    ExtensionPoint,
    Plugin,
    ServiceOffer,
)
from traits.api import Bool, Instance, List

# Constants kept around for backwards compatibility.
# These will be removed in a future release.
# Extension point IDs.
SERVICE_OFFERS = "envisage.service_offers"
IPYTHON_NAMESPACE = "ipython_plugin.namespace"

# Protocol for the contributed service offer.
IPYTHON_KERNEL_PROTOCOL = (
    "envisage.plugins.ipython_kernel.internal_ipkernel.InternalIPKernel")

logger = logging.getLogger(__name__)


class IPythonKernelPlugin(Plugin):
    """ An IPython kernel plugin. """

    #: The plugin unique identifier.
    id = "envisage.plugins.ipython_kernel"

    #: The plugin name (suitable for displaying to the user).
    name = "IPython embedded kernel plugin"

    #: Extension point for objects contributed to the IPython kernel namespace.
    IPYTHON_NAMESPACE = 'ipython_plugin.namespace'

    #: Ipython kernel namespace ExtensionPoint
    kernel_namespace = ExtensionPoint(
        List,
        id=IPYTHON_NAMESPACE,
        desc="""

        Variables to add to the IPython kernel namespace.
        This is a list of tuples (name, value).

        """,
    )

    #: Service offers contributed by this plugin.
    service_offers = List(contributes_to=SERVICE_OFFERS)

    # Protocol for the contributed service offer.
    IPYTHON_KERNEL_PROTOCOL = 'envisage.plugins.ipython_kernel.internal_ipkernel.InternalIPKernel'  # noqa: E501

    #: Whether to initialize the kernel when the service is created.
    #: The default is ``False```, for backwards compatibility. It will change
    #: to ``True`` in a future version of Envisage. External users wanting
    #: to use the future behaviour now should pass ``init_ipkernel=True``
    #: when creating the plugin.
    init_ipkernel = Bool(False)

    def stop(self):
        """ Stop the plugin. """
        self._destroy_kernel()

    # Private traits and methods

    #: The InternalIPKernel instance provided by the service.
    _kernel = Instance(IPYTHON_KERNEL_PROTOCOL)

    def _create_kernel(self):
        from .internal_ipkernel import InternalIPKernel

        # This shouldn't happen with a normal lifecycle, but add a warning
        # just in case.
        if self._kernel is not None:
            warnings.warn(
                "A kernel already exists. " "No new kernel will be created.",
                RuntimeWarning,
            )
            return

        logger.debug("Creating the embedded IPython kernel")
        kernel = self._kernel = InternalIPKernel()
        bind_extension_point(
            kernel, "initial_namespace", IPYTHON_NAMESPACE, self.application
        )
        if self.init_ipkernel:
            kernel.init_ipkernel()
        else:
            warnings.warn(
                (
                    "In the future, the IPython kernel will be initialized "
                    "automatically at creation time. To enable this "
                    "future behaviour now, create the plugin using "
                    "IPythonKernelPlugin(init_ipkernel=True)"
                ),
                DeprecationWarning,
            )

        return kernel

    def _destroy_kernel(self):
        """
        Destroy any existing kernel.
        """
        if self._kernel is None:
            return

        logger.debug("Shutting down the embedded IPython kernel")
        self._kernel.shutdown()
        self._kernel = None

    def _service_offers_default(self):
        ipython_kernel_service_offer = ServiceOffer(
            protocol=IPYTHON_KERNEL_PROTOCOL, factory=self._create_kernel,
        )
        return [ipython_kernel_service_offer]
