import json
import time
import warnings
from collections import defaultdict
from typing import Any, Dict, Generator, Iterable, List, Tuple, Union

from channels import Channel, Group
from channels.asgi import get_channel_layer
from channels.auth import channel_session_user, channel_session_user_from_http
from django.apps import apps
from django.core.exceptions import ObjectDoesNotExist
from django.db import transaction
from django.db.models import Model

from ..core.config import config
from ..core.models import Projector
from .auth import anonymous_is_enabled, has_perm, user_to_collection_user
from .cache import restricted_data_cache, websocket_user_cache
from .collection import AutoupdateFormat  # noqa
from .collection import (
    ChannelMessageFormat,
    Collection,
    CollectionElement,
    format_for_autoupdate,
    from_channel_message,
    to_channel_message,
)


def send_or_wait(send_func: Any, *args: Any, **kwargs: Any) -> None:
    """
    Wrapper for channels' send() method.

    If the method send() raises ChannelFull exception the worker waits for 20
    milliseconds and tries again. After 5 secondes it gives up, drops the
    channel message and writes a warning to stderr.

    Django channels' consumer atomicity feature is disabled.
    """
    kwargs['immediately'] = True
    for i in range(250):
        try:
            send_func(*args, **kwargs)
        except get_channel_layer().ChannelFull:
            time.sleep(0.02)
        else:
            break
    else:
        warnings.warn(
            'Channel layer is full. Channel message dropped.',
            RuntimeWarning
        )


@channel_session_user_from_http
def ws_add_site(message: Any) -> None:
    """
    Adds the websocket connection to a group specific to the connecting user.

    The group with the name 'user-None' stands for all anonymous users.

    Send all "startup-data" through the connection.
    """
    if not anonymous_is_enabled() and not message.user.id:
        send_or_wait(message.reply_channel.send, {'accept': False})
        return

    Group('site').add(message.reply_channel)
    message.channel_session['user_id'] = message.user.id
    # Saves the reply channel to the user. Uses 0 for anonymous users.
    websocket_user_cache.add(message.user.id or 0, message.reply_channel.name)

    # Open the websocket connection.
    send_or_wait(message.reply_channel.send, {'accept': True})

    # Collect all elements that shoud be send to the client when the websocket
    # connection is established.
    user = user_to_collection_user(message.user.id)
    user_id = user.id if user is not None else 0
    if restricted_data_cache.exists_for_user(user_id):
        output = restricted_data_cache.get_data(user_id)
    else:
        output = []
        for collection in get_startup_collections():
            access_permissions = collection.get_access_permissions()
            restricted_data = access_permissions.get_restricted_data(collection.get_full_data(), user)

            for data in restricted_data:
                if data is None:
                    # We do not want to send 'deleted' objects on startup.
                    # That's why we skip such data.
                    continue

                formatted_data = format_for_autoupdate(
                    collection_string=collection.collection_string,
                    id=data['id'],
                    action='changed',
                    data=data)

                output.append(formatted_data)
                # Cache restricted data for user
                restricted_data_cache.add_element(
                    user_id,
                    collection.collection_string,
                    data['id'],
                    formatted_data)

    # Send all data.
    if output:
        send_or_wait(message.reply_channel.send, {'text': json.dumps(output)})


@channel_session_user
def ws_disconnect_site(message: Any) -> None:
    """
    This function is called, when a client on the site disconnects.
    """
    Group('site').discard(message.reply_channel)
    websocket_user_cache.remove(message.user.id or 0, message.reply_channel.name)


@channel_session_user
def ws_receive_site(message: Any) -> None:
    """
    This function is called if a message from a client comes in. The message
    should be a list. Every item is broadcasted to the given users (or all
    users if no user list is given) if it is a notify element.

    The server adds the sender's user id (0 for anonymous) and reply
    channel name so that a receiver client may reply to the sender or to all
    sender's instances.
    """
    try:
        incomming = json.loads(message.content['text'])
    except ValueError:
        # Message content is invalid. Just do nothing.
        pass
    else:
        if isinstance(incomming, list):
            # Parse all items
            receivers_users = defaultdict(list)  # type: Dict[int, List[Any]]
            receivers_reply_channels = defaultdict(list)  # type: Dict[str, List[Any]]
            items_for_all = []
            for item in incomming:
                if item.get('collection') == 'notify':
                    use_receivers_dict = False
                    item['senderReplyChannelName'] = message.reply_channel.name
                    item['senderUserId'] = message.user.id or 0

                    # Force the params to be a dict
                    if not isinstance(item.get('params'), dict):
                        item['params'] = {}

                    users = item.get('users')
                    if isinstance(users, list):
                        # Send this item only to all reply channels of some site users.
                        for user_id in users:
                            receivers_users[user_id].append(item)
                        use_receivers_dict = True

                    reply_channels = item.get('replyChannels')
                    if isinstance(reply_channels, list):
                        # Send this item only to some reply channels.
                        for reply_channel_name in reply_channels:
                            receivers_reply_channels[reply_channel_name].append(item)
                        use_receivers_dict = True

                    if not use_receivers_dict:
                        # Send this item to all reply channels.
                        items_for_all.append(item)

            # Send all items
            for user_id, channel_names in websocket_user_cache.get_all().items():
                output = receivers_users[user_id]
                if len(output) > 0:
                    for channel_name in channel_names:
                        send_or_wait(Channel(channel_name).send, {'text': json.dumps(output)})

            for channel_name, output in receivers_reply_channels.items():
                if len(output) > 0:
                    send_or_wait(Channel(channel_name).send, {'text': json.dumps(output)})

            if len(items_for_all) > 0:
                send_or_wait(Group('site').send, {'text': json.dumps(items_for_all)})


@channel_session_user_from_http
def ws_add_projector(message: Any, projector_id: int) -> None:
    """
    Adds the websocket connection to a group specific to the projector with the given id.
    Also sends all data that are shown on the projector.
    """
    user = user_to_collection_user(message.user.id)

    if not has_perm(user, 'core.can_see_projector'):
        send_or_wait(message.reply_channel.send, {'text': 'No permissions to see this projector.'})
    else:
        try:
            projector = Projector.objects.get(pk=projector_id)
        except Projector.DoesNotExist:
            send_or_wait(message.reply_channel.send, {'text': 'The projector {} does not exist.'.format(projector_id)})
        else:
            # At first, the client is added to the projector group, so it is
            # informed if the data change.
            Group('projector-{}'.format(projector_id)).add(message.reply_channel)

            # Then it is also added to the global projector group which is
            # used for broadcasting data.
            Group('projector-all').add(message.reply_channel)

            # Now check whether broadcast is active at the moment. If yes,
            # change the local projector variable.
            if config['projector_broadcast'] > 0:
                projector = Projector.objects.get(pk=config['projector_broadcast'])

            # Collect all elements that are on the projector.
            output = []  # type: List[AutoupdateFormat]
            for requirement in projector.get_all_requirements():
                required_collection_element = CollectionElement.from_instance(requirement)
                output.append(required_collection_element.as_autoupdate_for_projector())

            # Collect all config elements.
            config_collection = Collection(config.get_collection_string())
            projector_data = (config_collection.get_access_permissions()
                              .get_projector_data(config_collection.get_full_data()))
            for data in projector_data:
                output.append(format_for_autoupdate(
                    config_collection.collection_string,
                    data['id'],
                    'changed',
                    data))

            # Collect the projector instance.
            collection_element = CollectionElement.from_instance(projector)
            output.append(collection_element.as_autoupdate_for_projector())

            # Send all the data that were only collected before.
            send_or_wait(message.reply_channel.send, {'text': json.dumps(output)})


def ws_disconnect_projector(message: Any, projector_id: int) -> None:
    """
    This function is called, when a client on the projector disconnects.
    """
    Group('projector-{}'.format(projector_id)).discard(message.reply_channel)


def send_data(message: ChannelMessageFormat) -> None:
    """
    Informs all site users and projector clients about changed data.
    """
    collection_elements = from_channel_message(message)

    # Send data to site users.
    for user_id, channel_names in websocket_user_cache.get_all().items():
        if not user_id:
            # Anonymous user
            user = None
        else:
            try:
                user = user_to_collection_user(user_id)
            except ObjectDoesNotExist:
                # The user does not exist. Skip him/her.
                continue

        output = []
        for collection_element in collection_elements:
            formatted_data = collection_element.as_autoupdate_for_user(user)
            if formatted_data['action'] == 'changed':
                restricted_data_cache.add_element(
                    user_id or 0,
                    collection_element.collection_string,
                    collection_element.id,
                    formatted_data)
            else:
                restricted_data_cache.del_element(
                    user_id or 0,
                    collection_element.collection_string,
                    collection_element.id)
            output.append(formatted_data)

        for channel_name in channel_names:
            send_or_wait(Channel(channel_name).send, {'text': json.dumps(output)})

    # Check whether broadcast is active at the moment and set the local
    # projector queryset.
    if config['projector_broadcast'] > 0:
        queryset = Projector.objects.filter(pk=config['projector_broadcast'])
    else:
        queryset = Projector.objects.all()

    # Loop over all projectors and send data that they need.
    for projector in queryset:
        output = []
        for collection_element in collection_elements:
            if collection_element.is_deleted():
                output.append(collection_element.as_autoupdate_for_projector())
            else:
                for element in projector.get_collection_elements_required_for_this(collection_element):
                    output.append(element.as_autoupdate_for_projector())
        if output:
            if config['projector_broadcast'] > 0:
                send_or_wait(
                    Group('projector-all').send,
                    {'text': json.dumps(output)})
            else:
                send_or_wait(
                    Group('projector-{}'.format(projector.pk)).send,
                    {'text': json.dumps(output)})


def inform_changed_data(instances: Union[Iterable[Model], Model], information: Dict[str, Any]=None) -> None:
    """
    Informs the autoupdate system and the caching system about the creation or
    update of an element.

    The argument instances can be one instance or an interable over instances.
    """
    root_instances = set()
    if not isinstance(instances, Iterable):
        instances = (instances, )

    for instance in instances:
        try:
            root_instances.add(instance.get_root_rest_element())
        except AttributeError:
            # Instance has no method get_root_rest_element. Just ignore it.
            pass

    # Generates an collection element list for the root_instances.
    collection_elements = []  # type: List[CollectionElement]
    for root_instance in root_instances:
        collection_elements.append(
            CollectionElement.from_instance(
                root_instance,
                information=information))
    # If currently there is an open database transaction, then the
    # send_autoupdate function is only called, when the transaction is
    # commited. If there is currently no transaction, then the function
    # is called immediately.
    transaction.on_commit(lambda: send_autoupdate(collection_elements))


def inform_deleted_data(elements: Iterable[Tuple[str, int]], information: Dict[str, Any]=None) -> None:
    """
    Informs the autoupdate system and the caching system about the deletion of
    elements.

    The argument information is added to each collection element.
    """
    # Go through each pair of collection_string and id and generate a collection
    # element from it.
    collection_elements = []  # type: List[CollectionElement]
    for element in elements:
        collection_elements.append(CollectionElement.from_values(
            collection_string=element[0],
            id=element[1],
            deleted=True,
            information=information))
    # If currently there is an open database transaction, then the
    # send_autoupdate function is only called, when the transaction is
    # commited. If there is currently no transaction, then the function
    # is called immediately.
    transaction.on_commit(lambda: send_autoupdate(collection_elements))


def inform_data_collection_element_list(collection_elements: List[CollectionElement],
                                        information: Dict[str, Any]=None) -> None:
    """
    Informs the autoupdate system about some collection elements. This is
    used just to send some data to all users.
    """
    # If currently there is an open database transaction, then the
    # send_autoupdate function is only called, when the transaction is
    # commited. If there is currently no transaction, then the function
    # is called immediately.
    transaction.on_commit(lambda: send_autoupdate(collection_elements))


def send_autoupdate(collection_elements: List[CollectionElement]) -> None:
    """
    Helper function, that sends collection_elements through a channel to the
    autoupdate system.

    Does nothing if collection_elements is empty.
    """
    if collection_elements:
        send_or_wait(
            Channel('autoupdate.send_data').send,
            to_channel_message(collection_elements))


def get_startup_collections() -> Generator[Collection, None, None]:
    """
    Returns all Collections that should be send to the user at startup
    """
    for app in apps.get_app_configs():
        try:
            # Get the method get_startup_elements() from an app.
            # This method has to return an iterable of Collection objects.
            get_startup_elements = app.get_startup_elements
        except AttributeError:
            # Skip apps that do not implement get_startup_elements.
            continue

        yield from get_startup_elements()