"""
Module that provides a connection to the ModuleStore specified in the django settings.

Passes settings.MODULESTORE as kwargs to MongoModuleStore
"""

from __future__ import absolute_import

from importlib import import_module
import gettext
import logging
from pkg_resources import resource_filename
import re

from django.conf import settings

# This configuration must be executed BEFORE any additional Django imports. Otherwise, the imports may fail due to
# Django not being configured properly. This mostly applies to tests.
if not settings.configured:
    settings.configure()

from django.core.cache import caches, InvalidCacheBackendError
import django.dispatch
import django.utils
from django.utils.translation import get_language, to_locale

from pymongo import ReadPreference
from xmodule.contentstore.django import contentstore
from xmodule.modulestore.draft_and_published import BranchSettingMixin
from xmodule.modulestore.mixed import MixedModuleStore
from xmodule.util.django import get_current_request_hostname
import xblock.reference.plugins

try:
    # We may not always have the request_cache module available
    from request_cache.middleware import RequestCache

    HAS_REQUEST_CACHE = True
except ImportError:
    HAS_REQUEST_CACHE = False

# We also may not always have the current request user (crum) module available
try:
    from xblock_django.user_service import DjangoXBlockUserService
    from crum import get_current_user

    HAS_USER_SERVICE = True
except ImportError:
    HAS_USER_SERVICE = False

try:
    from xblock_django.api import disabled_xblocks
except ImportError:
    disabled_xblocks = None

log = logging.getLogger(__name__)
ASSET_IGNORE_REGEX = getattr(settings, "ASSET_IGNORE_REGEX", r"(^\._.*$)|(^\.DS_Store$)|(^.*~$)")


class SwitchedSignal(django.dispatch.Signal):
    """
    SwitchedSignal is like a normal Django signal, except that you can turn it
    on and off. This is especially useful for tests where we want to be able to
    isolate signals and disable expensive operations that are irrelevant to
    what's being tested (like everything that triggers off of a course publish).

    SwitchedSignals default to being on. You should be very careful if you ever
    turn one off -- the only instances of this class are shared class attributes
    of `SignalHandler`. You have to make sure that you re-enable the signal when
    you're done, or else you may permanently turn that signal off for that
    process. I can't think of any reason you'd want to disable signals outside
    of running tests.
    """
    def __init__(self, name, *args, **kwargs):
        """
        The `name` parameter exists only to make debugging more convenient.

        All other args are passed to the constructor for django.dispatch.Signal.
        """
        super(SwitchedSignal, self).__init__(*args, **kwargs)
        self.name = name
        self._allow_signals = True

    def disable(self):
        """
        Turn off signal sending.

        All calls to send/send_robust will no-op.
        """
        self._allow_signals = False

    def enable(self):
        """
        Turn on signal sending.

        Calls to send/send_robust will behave like normal Django Signals.
        """
        self._allow_signals = True

    def send(self, *args, **kwargs):
        """
        See `django.dispatch.Signal.send()`

        This method will no-op and return an empty list if the signal has been
        disabled.
        """
        log.debug(
            "SwitchedSignal %s's send() called with args %s, kwargs %s - %s",
            self.name,
            args,
            kwargs,
            "ALLOW" if self._allow_signals else "BLOCK"
        )
        if self._allow_signals:
            return super(SwitchedSignal, self).send(*args, **kwargs)
        return []

    def send_robust(self, *args, **kwargs):
        """
        See `django.dispatch.Signal.send_robust()`

        This method will no-op and return an empty list if the signal has been
        disabled.
        """
        log.debug(
            "SwitchedSignal %s's send_robust() called with args %s, kwargs %s - %s",
            self.name,
            args,
            kwargs,
            "ALLOW" if self._allow_signals else "BLOCK"
        )
        if self._allow_signals:
            return super(SwitchedSignal, self).send_robust(*args, **kwargs)
        return []

    def __repr__(self):
        return u"SwitchedSignal('{}')".format(self.name)


class SignalHandler(object):
    """
    This class is to allow the modulestores to emit signals that can be caught
    by other parts of the Django application. If your app needs to do something
    every time a course is published (e.g. search indexing), you can listen for
    that event and kick off a celery task when it happens.

    To listen for a signal, do the following::

        from django.dispatch import receiver
        from celery.task import task
        from xmodule.modulestore.django import modulestore, SignalHandler

        @receiver(SignalHandler.course_published)
        def listen_for_course_publish(sender, course_key, **kwargs):
            do_my_expensive_update.delay(course_key)

        @task()
        def do_my_expensive_update(course_key):
            # ...

    Things to note:

    1. We receive using the Django Signals mechanism.
    2. The sender is going to be the class of the modulestore sending it.
    3. The names of your handler function's parameters *must* be "sender" and "course_key".
    4. Always have **kwargs in your signal handler, as new things may be added.
    5. The thing that listens for the signal lives in process, but should do
       almost no work. Its main job is to kick off the celery task that will
       do the actual work.
    """

    # If you add a new signal, please don't forget to add it to the _mapping
    # as well.
    pre_publish = SwitchedSignal("pre_publish", providing_args=["course_key"])
    course_published = SwitchedSignal("course_published", providing_args=["course_key"])
    course_deleted = SwitchedSignal("course_deleted", providing_args=["course_key"])
    library_updated = SwitchedSignal("library_updated", providing_args=["library_key"])
    item_deleted = SwitchedSignal("item_deleted", providing_args=["usage_key", "user_id"])

    _mapping = {
        signal.name: signal
        for signal
        in [pre_publish, course_published, course_deleted, library_updated, item_deleted]
    }

    def __init__(self, modulestore_class):
        self.modulestore_class = modulestore_class

    @classmethod
    def all_signals(cls):
        """Return a list with all our signals in it."""
        return cls._mapping.values()

    @classmethod
    def signal_by_name(cls, signal_name):
        """Given a signal name, return the appropriate signal."""
        return cls._mapping[signal_name]

    def send(self, signal_name, **kwargs):
        """
        Send the signal to the receivers.
        """
        signal = self._mapping[signal_name]
        responses = signal.send_robust(sender=self.modulestore_class, **kwargs)

        for receiver, response in responses:
            log.info('Sent %s signal to %s with kwargs %s. Response was: %s', signal_name, receiver, kwargs, response)


def load_function(path):
    """
    Load a function by name.

    Arguments:
        path: String of the form 'path.to.module.function'. Strings of the form
            'path.to.module:Class.function' are also valid.

    Returns:
        The imported object 'function'.
    """
    if ':' in path:
        module_path, _, method_path = path.rpartition(':')
        module = import_module(module_path)

        class_name, method_name = method_path.split('.')
        _class = getattr(module, class_name)
        function = getattr(_class, method_name)
    else:
        module_path, _, name = path.rpartition('.')
        function = getattr(import_module(module_path), name)

    return function


def create_modulestore_instance(
        engine,
        content_store,
        doc_store_config,
        options,
        i18n_service=None,
        fs_service=None,
        user_service=None,
        signal_handler=None,
):
    """
    This will return a new instance of a modulestore given an engine and options
    """
    class_ = load_function(engine)

    _options = {}
    _options.update(options)

    FUNCTION_KEYS = ['render_template']
    for key in FUNCTION_KEYS:
        if key in _options and isinstance(_options[key], basestring):
            _options[key] = load_function(_options[key])

    if HAS_REQUEST_CACHE:
        request_cache = RequestCache.get_request_cache()
    else:
        request_cache = None

    try:
        metadata_inheritance_cache = caches['mongo_metadata_inheritance']
    except InvalidCacheBackendError:
        metadata_inheritance_cache = caches['default']

    if issubclass(class_, MixedModuleStore):
        _options['create_modulestore_instance'] = create_modulestore_instance

    if issubclass(class_, BranchSettingMixin):
        _options['branch_setting_func'] = _get_modulestore_branch_setting

    if HAS_USER_SERVICE and not user_service:
        xb_user_service = DjangoXBlockUserService(get_current_user())
    else:
        xb_user_service = None

    if 'read_preference' in doc_store_config:
        doc_store_config['read_preference'] = getattr(ReadPreference, doc_store_config['read_preference'])

    xblock_field_data_wrappers = [load_function(path) for path in settings.XBLOCK_FIELD_DATA_WRAPPERS]

    def fetch_disabled_xblock_types():
        """
        Get the disabled xblock names, using the request_cache if possible to avoid hitting
        a database every time the list is needed.
        """
        # If the import could not be loaded, return an empty list.
        if disabled_xblocks is None:
            return []

        if request_cache:
            if 'disabled_xblock_types' not in request_cache.data:
                request_cache.data['disabled_xblock_types'] = [block.name for block in disabled_xblocks()]
            return request_cache.data['disabled_xblock_types']
        else:
            disabled_xblock_types = [block.name for block in disabled_xblocks()]

        return disabled_xblock_types

    return class_(
        contentstore=content_store,
        metadata_inheritance_cache_subsystem=metadata_inheritance_cache,
        request_cache=request_cache,
        xblock_mixins=getattr(settings, 'XBLOCK_MIXINS', ()),
        xblock_select=getattr(settings, 'XBLOCK_SELECT_FUNCTION', None),
        xblock_field_data_wrappers=xblock_field_data_wrappers,
        disabled_xblock_types=fetch_disabled_xblock_types,
        doc_store_config=doc_store_config,
        i18n_service=i18n_service or ModuleI18nService,
        fs_service=fs_service or xblock.reference.plugins.FSService(),
        user_service=user_service or xb_user_service,
        signal_handler=signal_handler or SignalHandler(class_),
        **_options
    )


# A singleton instance of the Mixed Modulestore
_MIXED_MODULESTORE = None


def modulestore():
    """
    Returns the Mixed modulestore
    """
    global _MIXED_MODULESTORE  # pylint: disable=global-statement
    if _MIXED_MODULESTORE is None:
        _MIXED_MODULESTORE = create_modulestore_instance(
            settings.MODULESTORE['default']['ENGINE'],
            contentstore(),
            settings.MODULESTORE['default'].get('DOC_STORE_CONFIG', {}),
            settings.MODULESTORE['default'].get('OPTIONS', {})
        )

        if settings.FEATURES.get('CUSTOM_COURSES_EDX'):
            # TODO: This import prevents a circular import issue, but is
            # symptomatic of a lib having a dependency on code in lms.  This
            # should be updated to have a setting that enumerates modulestore
            # wrappers and then uses that setting to wrap the modulestore in
            # appropriate wrappers depending on enabled features.
            from lms.djangoapps.ccx.modulestore import CCXModulestoreWrapper
            _MIXED_MODULESTORE = CCXModulestoreWrapper(_MIXED_MODULESTORE)

    return _MIXED_MODULESTORE


def clear_existing_modulestores():
    """
    Clear the existing modulestore instances, causing
    them to be re-created when accessed again.

    This is useful for flushing state between unit tests.
    """
    global _MIXED_MODULESTORE  # pylint: disable=global-statement
    _MIXED_MODULESTORE = None


class ModuleI18nService(object):
    """
    Implement the XBlock runtime "i18n" service.

    Mostly a pass-through to Django's translation module.
    django.utils.translation implements the gettext.Translations interface (it
    has ugettext, ungettext, etc), so we can use it directly as the runtime
    i18n service.

    """
    def __init__(self, block=None):
        """
        Attempt to load an XBlock-specific GNU gettext translator using the XBlock's own domain
        translation catalog, currently expected to be found at:
            <xblock_root>/conf/locale/<language>/LC_MESSAGES/<domain>.po|mo
        If we can't locate the domain translation catalog then we fall-back onto
        django.utils.translation, which will point to the system's own domain translation catalog
        This effectively achieves translations by coincidence for an XBlock which does not provide
        its own dedicated translation catalog along with its implementation.
        """
        self.translator = django.utils.translation
        if block:
            xblock_class = getattr(block, 'unmixed_class', block.__class__)
            xblock_resource = xblock_class.__module__
            xblock_locale_dir = '/translations'
            xblock_locale_path = resource_filename(xblock_resource, xblock_locale_dir)
            xblock_domain = 'text'
            selected_language = get_language()
            try:
                self.translator = gettext.translation(
                    xblock_domain,
                    xblock_locale_path,
                    [to_locale(selected_language if selected_language else settings.LANGUAGE_CODE)]
                )
            except IOError:
                # Fall back to the default Django translator if the XBlock translator is not found.
                pass

    def __getattr__(self, name):
        return getattr(self.translator, name)

    def strftime(self, *args, **kwargs):
        """
        A locale-aware implementation of strftime.
        """
        # This is the wrong place to import this function.  I'm putting it here
        # because the xmodule test suite can't import this module, because
        # Django is not available in that suite.  This function isn't called in
        # that suite, so this hides the import so the test won't fail.
        #
        # As I said, this is wrong.  But Cale says this code will soon be
        # refactored to a place that will be right, and the code can be made
        # right there.  If you are reading this comment after April 1, 2014,
        # then Cale was a liar.
        from util.date_utils import strftime_localized

        return strftime_localized(*args, **kwargs)


def _get_modulestore_branch_setting():
    """
    Returns the branch setting for the module store from the current Django request if configured,
    else returns the branch value from the configuration settings if set,
    else returns None

    The value of the branch setting is cached in a thread-local variable so it is not repeatedly recomputed
    """

    def get_branch_setting():
        """
        Finds and returns the branch setting based on the Django request and the configuration settings
        """
        branch = None
        hostname = get_current_request_hostname()
        if hostname:
            # get mapping information which is defined in configurations
            mappings = getattr(settings, 'HOSTNAME_MODULESTORE_DEFAULT_MAPPINGS', None)

            # compare hostname against the regex expressions set of mappings which will tell us which branch to use
            if mappings:
                for key in mappings.iterkeys():
                    if re.match(key, hostname):
                        return mappings[key]
        if branch is None:
            branch = getattr(settings, 'MODULESTORE_BRANCH', None)
        return branch

    # leaving this in code structured in closure-friendly format b/c we might eventually cache this (again)
    # using request_cache
    return get_branch_setting()
