import asyncio
import fnmatch
import random
import re
import string
import time
from copy import deepcopy

from django.conf import settings
from django.core.signals import setting_changed
from django.utils.module_loading import import_string

from channels import DEFAULT_CHANNEL_LAYER

from .exceptions import ChannelFull, InvalidChannelLayerError


class ChannelLayerManager:
    """
    Takes a settings dictionary of backends and initialises them on request.
    """

    def __init__(self):
        self.backends = {}
        setting_changed.connect(self._reset_backends)

    def _reset_backends(self, setting, **kwargs):
        """
        Removes cached channel layers when the CHANNEL_LAYERS setting changes.
        """
        if setting == "CHANNEL_LAYERS":
            self.backends = {}

    @property
    def configs(self):
        # Lazy load settings so we can be imported
        return getattr(settings, "CHANNEL_LAYERS", {})

    def make_backend(self, name):
        """
        Instantiate channel layer.
        """
        config = self.configs[name].get("CONFIG", {})
        return self._make_backend(name, config)

    def make_test_backend(self, name):
        """
        Instantiate channel layer using its test config.
        """
        try:
            config = self.configs[name]["TEST_CONFIG"]
        except KeyError:
            raise InvalidChannelLayerError("No TEST_CONFIG specified for %s" % name)
        return self._make_backend(name, config)

    def _make_backend(self, name, config):
        # Check for old format config
        if "ROUTING" in self.configs[name]:
            raise InvalidChannelLayerError(
                "ROUTING key found for %s - this is no longer needed in Channels 2."
                % name
            )
        # Load the backend class
        try:
            backend_class = import_string(self.configs[name]["BACKEND"])
        except KeyError:
            raise InvalidChannelLayerError("No BACKEND specified for %s" % name)
        except ImportError:
            raise InvalidChannelLayerError(
                "Cannot import BACKEND %r specified for %s"
                % (self.configs[name]["BACKEND"], name)
            )
        # Initialise and pass config
        return backend_class(**config)

    def __getitem__(self, key):
        if key not in self.backends:
            self.backends[key] = self.make_backend(key)
        return self.backends[key]

    def __contains__(self, key):
        return key in self.configs

    def set(self, key, layer):
        """
        Sets an alias to point to a new ChannelLayerWrapper instance, and
        returns the old one that it replaced. Useful for swapping out the
        backend during tests.
        """
        old = self.backends.get(key, None)
        self.backends[key] = layer
        return old


class BaseChannelLayer:
    """
    Base channel layer class that others can inherit from, with useful
    common functionality.
    """

    MAX_NAME_LENGTH = 100

    def __init__(self, expiry=60, capacity=100, channel_capacity=None):
        self.expiry = expiry
        self.capacity = capacity
        self.channel_capacity = channel_capacity or {}

    def compile_capacities(self, channel_capacity):
        """
        Takes an input channel_capacity dict and returns the compiled list
        of regexes that get_capacity will look for as self.channel_capacity
        """
        result = []
        for pattern, value in channel_capacity.items():
            # If they passed in a precompiled regex, leave it, else interpret
            # it as a glob.
            if hasattr(pattern, "match"):
                result.append((pattern, value))
            else:
                result.append((re.compile(fnmatch.translate(pattern)), value))
        return result

    def get_capacity(self, channel):
        """
        Gets the correct capacity for the given channel; either the default,
        or a matching result from channel_capacity. Returns the first matching
        result; if you want to control the order of matches, use an ordered dict
        as input.
        """
        for pattern, capacity in self.channel_capacity:
            if pattern.match(channel):
                return capacity
        return self.capacity

    def match_type_and_length(self, name):
        if isinstance(name, str) and (len(name) < self.MAX_NAME_LENGTH):
            return True
        return False

    # Name validation functions

    channel_name_regex = re.compile(r"^[a-zA-Z\d\-_.]+(\![\d\w\-_.]*)?$")
    group_name_regex = re.compile(r"^[a-zA-Z\d\-_.]+$")
    invalid_name_error = (
        "{} name must be a valid unicode string "
        + "with length < {} ".format(MAX_NAME_LENGTH)
        + "containing only ASCII alphanumerics, hyphens, underscores, or periods, "
        + "not {}"
    )

    def valid_channel_name(self, name, receive=False):
        if self.match_type_and_length(name):
            if bool(self.channel_name_regex.match(name)):
                # Check cases for special channels
                if "!" in name and not name.endswith("!") and receive:
                    raise TypeError(
                        "Specific channel names in receive() must end at the !"
                    )
                return True
        raise TypeError(self.invalid_name_error.format("Channel", name))

    def valid_group_name(self, name):
        if self.match_type_and_length(name):
            if bool(self.group_name_regex.match(name)):
                return True
        raise TypeError(self.invalid_name_error.format("Group", name))

    def valid_channel_names(self, names, receive=False):
        _non_empty_list = True if names else False
        _names_type = isinstance(names, list)
        assert _non_empty_list and _names_type, "names must be a non-empty list"

        assert all(
            self.valid_channel_name(channel, receive=receive) for channel in names
        )
        return True

    def non_local_name(self, name):
        """
        Given a channel name, returns the "non-local" part. If the channel name
        is a process-specific channel (contains !) this means the part up to
        and including the !; if it is anything else, this means the full name.
        """
        if "!" in name:
            return name[: name.find("!") + 1]
        else:
            return name


class InMemoryChannelLayer(BaseChannelLayer):
    """
    In-memory channel layer implementation
    """

    def __init__(
        self,
        expiry=60,
        group_expiry=86400,
        capacity=100,
        channel_capacity=None,
        **kwargs
    ):
        super().__init__(
            expiry=expiry,
            capacity=capacity,
            channel_capacity=channel_capacity,
            **kwargs
        )
        self.channels = {}
        self.groups = {}
        self.group_expiry = group_expiry

    # Channel layer API

    extensions = ["groups", "flush"]

    async def send(self, channel, message):
        """
        Send a message onto a (general or specific) channel.
        """
        # Typecheck
        assert isinstance(message, dict), "message is not a dict"
        assert self.valid_channel_name(channel), "Channel name not valid"
        # If it's a process-local channel, strip off local part and stick full
        # name in message
        assert "__asgi_channel__" not in message

        queue = self.channels.setdefault(channel, asyncio.Queue())
        # Are we full
        if queue.qsize() >= self.capacity:
            raise ChannelFull(channel)

        # Add message
        await queue.put((time.time() + self.expiry, deepcopy(message)))

    async def receive(self, channel):
        """
        Receive the first message that arrives on the channel.
        If more than one coroutine waits on the same channel, a random one
        of the waiting coroutines will get the result.
        """
        assert self.valid_channel_name(channel)
        self._clean_expired()

        queue = self.channels.setdefault(channel, asyncio.Queue())

        # Do a plain direct receive
        try:
            _, message = await queue.get()
        finally:
            if queue.empty():
                del self.channels[channel]

        return message

    async def new_channel(self, prefix="specific."):
        """
        Returns a new channel name that can be used by something in our
        process as a specific channel.
        """
        return "%s.inmemory!%s" % (
            prefix,
            "".join(random.choice(string.ascii_letters) for i in range(12)),
        )

    # Expire cleanup

    def _clean_expired(self):
        """
        Goes through all messages and groups and removes those that are expired.
        Any channel with an expired message is removed from all groups.
        """
        # Channel cleanup
        for channel, queue in list(self.channels.items()):
            # See if it's expired
            while not queue.empty() and queue._queue[0][0] < time.time():
                queue.get_nowait()
                # Any removal prompts group discard
                self._remove_from_groups(channel)
                # Is the channel now empty and needs deleting?
                if queue.empty():
                    del self.channels[channel]

        # Group Expiration
        timeout = int(time.time()) - self.group_expiry
        for group in self.groups:
            for channel in list(self.groups.get(group, set())):
                # If join time is older than group_expiry end the group membership
                if (
                    self.groups[group][channel]
                    and int(self.groups[group][channel]) < timeout
                ):
                    # Delete from group
                    del self.groups[group][channel]

    # Flush extension

    async def flush(self):
        self.channels = {}
        self.groups = {}

    async def close(self):
        # Nothing to go
        pass

    def _remove_from_groups(self, channel):
        """
        Removes a channel from all groups. Used when a message on it expires.
        """
        for channels in self.groups.values():
            if channel in channels:
                del channels[channel]

    # Groups extension

    async def group_add(self, group, channel):
        """
        Adds the channel name to a group.
        """
        # Check the inputs
        assert self.valid_group_name(group), "Group name not valid"
        assert self.valid_channel_name(channel), "Channel name not valid"
        # Add to group dict
        self.groups.setdefault(group, {})
        self.groups[group][channel] = time.time()

    async def group_discard(self, group, channel):
        # Both should be text and valid
        assert self.valid_channel_name(channel), "Invalid channel name"
        assert self.valid_group_name(group), "Invalid group name"
        # Remove from group set
        if group in self.groups:
            if channel in self.groups[group]:
                del self.groups[group][channel]
            if not self.groups[group]:
                del self.groups[group]

    async def group_send(self, group, message):
        # Check types
        assert isinstance(message, dict), "Message is not a dict"
        assert self.valid_group_name(group), "Invalid group name"
        # Run clean
        self._clean_expired()
        # Send to each channel
        for channel in self.groups.get(group, set()):
            try:
                await self.send(channel, message)
            except ChannelFull:
                pass


def get_channel_layer(alias=DEFAULT_CHANNEL_LAYER):
    """
    Returns a channel layer by alias, or None if it is not configured.
    """
    try:
        return channel_layers[alias]
    except KeyError:
        return None


# Default global instance of the channel layer manager
channel_layers = ChannelLayerManager()