# -*- coding: utf-8 -*-
#
# Copyright (C) 2003-2011 Edgewall Software
# Copyright (C) 2003-2004 Jonas Borgström <jonas@edgewall.com>
# Copyright (C) 2004-2005 Christopher Lenz <cmlenz@gmx.de>
# All rights reserved.
#
# This software is licensed as described in the file COPYING, which
# you should have received as part of this distribution. The terms
# are also available at http://trac.edgewall.org/wiki/TracLicense.
#
# This software consists of voluntary contributions made by many
# individuals. For the exact contribution history, see the revision
# history and logs, available at http://trac.edgewall.org/log/.
#
# Author: Jonas Borgström <jonas@edgewall.com>
#         Christopher Lenz <cmlenz@gmx.de>

__all__ = ['Component', 'ExtensionPoint', 'implements', 'Interface', ]


class Interface(object):
    """Marker base class for extension point interfaces."""


class ExtensionPoint(property):
    """Marker class for extension points in components."""

    def __init__(self, interface):
        """Create the extension point.

        :param interface: the `Interface` subclass that defines the
                          protocol for the extension point
        """
        property.__init__(self, self.extensions)
        self.interface = interface
        self.__doc__ = ("List of components that implement `~%s.%s`" %
                        (self.interface.__module__, self.interface.__name__))

    def extensions(self, component):
        """Return a list of components that declare to implement the
        extension point interface.
        """
        classes = ComponentMeta._registry.get(self.interface, ())
        components = [component.compmgr[cls] for cls in classes]
        return [c for c in components if c]

    def __repr__(self):
        """Return a textual representation of the extension point."""
        return '<ExtensionPoint %s>' % self.interface.__name__


class ComponentMeta(type):
    """Meta class for components.

    Takes care of component and extension point registration.
    """
    _components = []
    _registry = {}

    def __new__(mcs, name, bases, d):
        """Create the component class."""

        new_class = type.__new__(mcs, name, bases, d)
        if name == 'Component':
            # Don't put the Component base class in the registry
            return new_class

        if d.get('abstract'):
            # Don't put abstract component classes in the registry
            return new_class

        ComponentMeta._components.append(new_class)
        registry = ComponentMeta._registry
        for cls in new_class.__mro__:
            for interface in cls.__dict__.get('_implements', ()):
                classes = registry.setdefault(interface, [])
                if new_class not in classes:
                    classes.append(new_class)

        return new_class

    def __call__(cls, *args, **kwargs):
        """Return an existing instance of the component if it has
        already been activated, otherwise create a new instance.
        """
        # If this component is also the component manager, just invoke that
        if issubclass(cls, ComponentManager):
            self = cls.__new__(cls)
            self.compmgr = self
            self.__init__(*args, **kwargs)
            return self

        # The normal case where the component is not also the component manager
        compmgr = args[0]
        self = compmgr.components.get(cls)
        # Note that this check is racy, we intentionally don't use a
        # lock in order to keep things simple and avoid the risk of
        # deadlocks, as the impact of having temporarily two (or more)
        # instances for a given `cls` is negligible.
        if self is None:
            self = cls.__new__(cls)
            self.compmgr = compmgr
            compmgr.componentActivated(self)
            self.__init__()
            # Only register the instance once it is fully initialized (#9418)
            compmgr.components[cls] = self
        return self


class Component(object):
    """Base class for components.

    Every component can declare what extension points it provides, as
    well as what extension points of other components it extends.
    """
    __metaclass__ = ComponentMeta

    @staticmethod
    def implements(*interfaces):
        """Can be used in the class definition of `Component`
        subclasses to declare the extension points that are extended.
        """
        import sys

        frame = sys._getframe(1)
        locals_ = frame.f_locals

        # Some sanity checks
        assert locals_ is not frame.f_globals and '__module__' in locals_, \
           'implements() can only be used in a class definition'

        locals_.setdefault('_implements', []).extend(interfaces)


implements = Component.implements


class ComponentManager(object):
    """The component manager keeps a pool of active components."""

    def __init__(self):
        """Initialize the component manager."""
        self.components = {}
        self.enabled = {}
        if isinstance(self, Component):
            self.components[self.__class__] = self

    def __contains__(self, cls):
        """Return wether the given class is in the list of active
        components."""
        return cls in self.components

    def __getitem__(self, cls):
        """Activate the component instance for the given class, or
        return the existing instance if the component has already been
        activated.
        """
        if not self.isEnabled(cls):
            return None
        component = self.components.get(cls)
        if not component:
            if cls not in ComponentMeta._components:
                raise NameError('Component "%s" not registered' % cls.__name__)
            try:
                component = cls(self)
            except TypeError, e:
                raise TypeError('Unable to instantiate component %r (%s)' %
                                (cls, e))
        return component

    def isEnabled(self, cls):
        """Return whether the given component class is enabled."""
        if cls not in self.enabled:
            self.enabled[cls] = self.isComponentEnabled(cls)
        return self.enabled[cls]

    def disableComponent(self, component):
        """Force a component to be disabled.

        :param component: can be a class or an instance.
        """
        if not isinstance(component, type):
            component = component.__class__
        self.enabled[component] = False
        self.components[component] = None

    def componentActivated(self, component):
        """Can be overridden by sub-classes so that special
        initialization for components can be provided.
        """

    def isComponentEnabled(self, cls):
        """Can be overridden by sub-classes to veto the activation of
        a component.

        If this method returns `False`, the component was disabled
        explicitly.  If it returns `None`, the component was neither
        enabled nor disabled explicitly. In both cases, the component
        with the given class will not be available.
        """
        return True
