"""
Adds support for first class plugins that can be added to the edX platform.
"""
from __future__ import absolute_import
from collections import OrderedDict

from stevedore.extension import ExtensionManager
from openedx.core.lib.cache_utils import process_cached


class PluginError(Exception):
    """
    Base Exception for when an error was found regarding plugins.
    """
    pass


class PluginManager(object):
    """
    Base class that manages plugins for the edX platform.
    """
    @classmethod
    @process_cached
    def get_available_plugins(cls, namespace=None):
        """
        Returns a dict of all the plugins that have been made available through the platform.
        """
        # Note: we're creating the extension manager lazily to ensure that the Python path
        # has been correctly set up. Trying to create this statically will fail, unfortunately.
        plugins = OrderedDict()
        extension_manager = ExtensionManager(namespace=namespace or cls.NAMESPACE)  # pylint: disable=no-member
        for plugin_name in extension_manager.names():
            plugins[plugin_name] = extension_manager[plugin_name].plugin
        return plugins

    @classmethod
    def get_plugin(cls, name, namespace=None):
        """
        Returns the plugin with the given name.
        """
        plugins = cls.get_available_plugins(namespace)
        if name not in plugins:
            raise PluginError(u"No such plugin {name} for entry point {namespace}".format(
                name=name,
                namespace=namespace or cls.NAMESPACE,  # pylint: disable=no-member
            ))
        return plugins[name]