platypush/platypush/context/__init__.py

import asyncio
import importlib
import logging

from threading import RLock
from typing import Optional, Callable, Any

from ..bus import Bus
from ..config import Config
from ..utils import get_enabled_plugins

logger = logging.getLogger('platypush:context')

# Map: backend_name -> backend_instance
backends = {}

# Map: plugin_name -> plugin_instance
plugins = {}

# Map: plugin_name -> init_lock to make sure that a plugin isn't initialized
# multiple times
plugins_init_locks = {}

# Reference to the main application bus
main_bus = None


def register_backends(bus=None, global_scope=False, **kwargs):
    """ Initialize the backend objects based on the configuration and returns
        a name -> backend_instance map.
    Params:
        bus -- If specific (it usually should), the messages processed by the
            backends will be posted on this bus.

        kwargs -- Any additional key-value parameters required to initialize the backends
        """

    global main_bus
    if bus:
        main_bus = bus

    if global_scope:
        global backends
    else:
        backends = {}

    for (name, cfg) in Config.get_backends().items():
        module = importlib.import_module('platypush.backend.' + name)

        # e.g. backend.pushbullet main class: PushbulletBackend
        cls_name = ''
        for token in module.__name__.title().split('.')[2:]:
            cls_name += token.title()
        cls_name += 'Backend'

        try:
            b = getattr(module, cls_name)(bus=bus, **cfg, **kwargs)
            backends[name] = b
        except AttributeError as e:
            logger.warning('No such class in {}: {}'.format(
                module.__name__, cls_name))
            raise RuntimeError(e)

    return backends


def register_plugins(bus=None):
    from ..plugins import RunnablePlugin

    for plugin in get_enabled_plugins().values():
        if isinstance(plugin, RunnablePlugin):
            plugin.bus = bus
            plugin.start()


def get_backend(name):
    """ Returns the backend instance identified by name if it exists """

    global backends
    return backends.get(name)


def get_plugin(plugin_name, reload=False):
    """ Registers a plugin instance by name if not registered already, or
        returns the registered plugin instance"""
    global plugins
    global plugins_init_locks

    if plugin_name not in plugins_init_locks:
        plugins_init_locks[plugin_name] = RLock()

    if plugin_name in plugins and not reload:
        return plugins[plugin_name]

    try:
        plugin = importlib.import_module('platypush.plugins.' + plugin_name)
    except ImportError as e:
        logger.warning('No such plugin: {}'.format(plugin_name))
        raise RuntimeError(e)

    # e.g. plugins.music.mpd main class: MusicMpdPlugin
    cls_name = ''
    for token in plugin_name.split('.'):
        cls_name += token.title()
    cls_name += 'Plugin'

    plugin_conf = Config.get_plugins()[plugin_name] \
        if plugin_name in Config.get_plugins() else {}

    if 'disabled' in plugin_conf:
        if plugin_conf['disabled'] is True:
            return None
        del plugin_conf['disabled']

    if 'enabled' in plugin_conf:
        if plugin_conf['enabled'] is False:
            return None
        del plugin_conf['enabled']

    try:
        plugin_class = getattr(plugin, cls_name)
    except AttributeError as e:
        logger.warning('No such class in {}: {} [error: {}]'.format(plugin_name, cls_name, str(e)))
        raise RuntimeError(e)

    with plugins_init_locks[plugin_name]:
        if plugins.get(plugin_name) and not reload:
            return plugins[plugin_name]
        plugins[plugin_name] = plugin_class(**plugin_conf)

    return plugins[plugin_name]


def get_bus() -> Bus:
    global main_bus
    assert main_bus, 'The bus is not registered'
    return main_bus


def get_or_create_event_loop():
    try:
        loop = asyncio.get_event_loop()
    except RuntimeError:
        loop = asyncio.new_event_loop()
        asyncio.set_event_loop(loop)

    return loop


class Variable:
    """
    Utility class to wrap platform variables in your custom scripts.
    Usage:

        .. code-block:: python

            # Pass `persisted=False` to get/set an in-memory variable
            # on the Redis instance (default: the variable is
            # persisted on the internal database)
            var = Variable('myvar')
            value = var.get()
            var.set('new value')

    """

    def __init__(self, name: str, persisted: bool = True):
        self.name = name
        plugin = get_plugin('variable')
        self._get_action = getattr(plugin, 'get' if persisted else 'mget')
        self._set_action = getattr(plugin, 'set' if persisted else 'mset')

    def get(self) -> Optional[Any]:
        return self._get_action(self.name).output.get(self.name)

    def set(self, value: Any):
        self._set_action(**{self.name: value})


# vim:sw=4:ts=4:et: