# vim: ft=python fileencoding=utf-8 sts=4 sw=4 et:

# Copyright 2014 Florian Bruhin (The Compiler) <mail@qutebrowser.org>
#
# This file is part of qutebrowser.
#
# qutebrowser is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# qutebrowser is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with qutebrowser.  If not, see <http://www.gnu.org/licenses/>.

"""The global object registry and related utility functions."""


import collections
import functools

from PyQt5.QtCore import QObject


class UnsetObject:

    """Class for an unset object.

    Only used (rather than object) so we can tell pylint to shut up about it.
    """

    __slots__ = ()


class RegistryUnavailableError(Exception):

    """Exception raised when a certain registry does not exist yet."""

    pass


_UNSET = UnsetObject()


class ObjectRegistry(collections.UserDict):

    """A registry of long-living objects in qutebrowser.

    Inspired by the eric IDE code (E5Gui/E5Application.py).
    """

    def __setitem__(self, name, obj):
        """Register an object in the object registry.

        Sets a slot to remove QObjects when they are destroyed.
        """
        if isinstance(obj, QObject):
            obj.destroyed.connect(functools.partial(self.on_destroyed, name))
        super().__setitem__(name, obj)

    def on_destroyed(self, name):
        """Remove a destroyed QObject."""
        try:
            del self[name]
        except KeyError:
            pass

    def dump_objects(self):
        """Dump all objects as a list of strings."""
        lines = []
        for name, obj in self.data.items():
            lines.append("{}: {}".format(name, repr(obj)))
        return lines


# The registry for global objects
global_registry = ObjectRegistry()
# The object registry of object registries.
meta_registry = ObjectRegistry()
meta_registry['global'] = global_registry


def _get_registry(scope):
    """Get the correct registry for a given scope."""
    if scope == 'global':
        return global_registry
    elif scope == 'tab':
        widget = get('tabbed-browser').currentWidget()
        if widget is None:
            raise RegistryUnavailableError(scope)
        return widget.registry
    else:
        raise ValueError("Invalid scope '{}'!".format(scope))



def get(name, default=_UNSET, scope='global'):
    """Helper function to get an object.

    Args:
        default: A default to return if the object does not exist.
    """
    reg = _get_registry(scope)
    try:
        return reg[name]
    except KeyError:
        if default is not _UNSET:
            return default
        else:
            raise


def register(name, obj, update=False, scope=None, registry=None):
    """Helper function to register an object.

    Args:
        name: The name the object will be registered as.
        obj: The object to register.
        update: If True, allows to update an already registered object.
    """
    if scope is not None and registry is not None:
        raise ValueError("scope ({}) and registry ({}) can't be given at the "
                         "same time!".format(scope, registry))
    if registry is not None:
        reg = registry
    else:
        if scope is None:
            scope = 'global'
        reg = _get_registry(scope)
    if not update and name in reg:
        raise KeyError("Object '{}' is already registered ({})!".format(
                       name, repr(reg[name])))
    reg[name] = obj


def delete(name, scope='global'):
    """Helper function to unregister an object."""
    reg = _get_registry(scope)
    del reg[name]