import asyncio
import functools
import logging
import random
from asyncio import Lock
from collections.abc import Container
from functools import wraps
from typing import Callable, Optional, Union
from weakref import WeakValueDictionary

from discord import Colour, Embed
from discord.ext import commands
from discord.ext.commands import CheckFailure, Command, Context

from bot.constants import Channels, ERROR_REPLIES, Month, WHITELISTED_CHANNELS
from bot.utils import human_months, resolve_current_month
from bot.utils.checks import in_whitelist_check

ONE_DAY = 24 * 60 * 60

log = logging.getLogger(__name__)


class InChannelCheckFailure(CheckFailure):
    """Check failure when the user runs a command in a non-whitelisted channel."""

    pass


class InMonthCheckFailure(CheckFailure):
    """Check failure for when a command is invoked outside of its allowed month."""

    pass


def seasonal_task(*allowed_months: Month, sleep_time: Union[float, int] = ONE_DAY) -> Callable:
    """
    Perform the decorated method periodically in `allowed_months`.

    This provides a convenience wrapper to avoid code repetition where some task shall
    perform an operation repeatedly in a constant interval, but only in specific months.

    The decorated function will be called once every `sleep_time` seconds while
    the current UTC month is in `allowed_months`. Sleep time defaults to 24 hours.

    The wrapped task is responsible for waiting for the bot to be ready, if necessary.
    """
    def decorator(task_body: Callable) -> Callable:
        @functools.wraps(task_body)
        async def decorated_task(*args, **kwargs) -> None:
            """Call `task_body` once every `sleep_time` seconds in `allowed_months`."""
            log.info(f"Starting seasonal task {task_body.__qualname__} ({human_months(allowed_months)})")

            while True:
                current_month = resolve_current_month()

                if current_month in allowed_months:
                    await task_body(*args, **kwargs)
                else:
                    log.debug(f"Seasonal task {task_body.__qualname__} sleeps in {current_month!s}")

                await asyncio.sleep(sleep_time)
        return decorated_task
    return decorator


def in_month_listener(*allowed_months: Month) -> Callable:
    """
    Shield a listener from being invoked outside of `allowed_months`.

    The check is performed against current UTC month.
    """
    def decorator(listener: Callable) -> Callable:
        @functools.wraps(listener)
        async def guarded_listener(*args, **kwargs) -> None:
            """Wrapped listener will abort if not in allowed month."""
            current_month = resolve_current_month()

            if current_month in allowed_months:
                # Propagate return value although it should always be None
                return await listener(*args, **kwargs)
            else:
                log.debug(f"Guarded {listener.__qualname__} from invoking in {current_month!s}")
        return guarded_listener
    return decorator


def in_month_command(*allowed_months: Month) -> Callable:
    """
    Check whether the command was invoked in one of `enabled_months`.

    Uses the current UTC month at the time of running the predicate.
    """
    async def predicate(ctx: Context) -> bool:
        current_month = resolve_current_month()
        can_run = current_month in allowed_months

        log.debug(
            f"Command '{ctx.command}' is locked to months {human_months(allowed_months)}. "
            f"Invoking it in month {current_month!s} is {'allowed' if can_run else 'disallowed'}."
        )
        if can_run:
            return True
        else:
            raise InMonthCheckFailure(f"Command can only be used in {human_months(allowed_months)}")

    return commands.check(predicate)


def in_month(*allowed_months: Month) -> Callable:
    """
    Universal decorator for season-locking commands and listeners alike.

    This only serves to determine whether the decorated callable is a command,
    a listener, or neither. It then delegates to either `in_month_command`,
    or `in_month_listener`, or raises TypeError, respectively.

    Please note that in order for this decorator to correctly determine whether
    the decorated callable is a cmd or listener, it **has** to first be turned
    into one. This means that this decorator should always be placed **above**
    the d.py one that registers it as either.

    This will decorate groups as well, as those subclass Command. In order to lock
    all subcommands of a group, its `invoke_without_command` param must **not** be
    manually set to True - this causes a circumvention of the group's callback
    and the seasonal check applied to it.
    """
    def decorator(callable_: Callable) -> Callable:
        # Functions decorated as commands are turned into instances of `Command`
        if isinstance(callable_, Command):
            logging.debug(f"Command {callable_.qualified_name} will be locked to {human_months(allowed_months)}")
            actual_deco = in_month_command(*allowed_months)

        # D.py will assign this attribute when `callable_` is registered as a listener
        elif hasattr(callable_, "__cog_listener__"):
            logging.debug(f"Listener {callable_.__qualname__} will be locked to {human_months(allowed_months)}")
            actual_deco = in_month_listener(*allowed_months)

        # Otherwise we're unsure exactly what has been decorated
        # This happens before the bot starts, so let's just raise
        else:
            raise TypeError(f"Decorated object {callable_} is neither a command nor a listener")

        return actual_deco(callable_)
    return decorator


def with_role(*role_ids: int) -> Callable:
    """Check to see whether the invoking user has any of the roles specified in role_ids."""
    async def predicate(ctx: Context) -> bool:
        if not ctx.guild:  # Return False in a DM
            log.debug(
                f"{ctx.author} tried to use the '{ctx.command.name}'command from a DM. "
                "This command is restricted by the with_role decorator. Rejecting request."
            )
            return False

        for role in ctx.author.roles:
            if role.id in role_ids:
                log.debug(f"{ctx.author} has the '{role.name}' role, and passes the check.")
                return True

        log.debug(
            f"{ctx.author} does not have the required role to use "
            f"the '{ctx.command.name}' command, so the request is rejected."
        )
        return False
    return commands.check(predicate)


def without_role(*role_ids: int) -> Callable:
    """Check whether the invoking user does not have all of the roles specified in role_ids."""
    async def predicate(ctx: Context) -> bool:
        if not ctx.guild:  # Return False in a DM
            log.debug(
                f"{ctx.author} tried to use the '{ctx.command.name}' command from a DM. "
                "This command is restricted by the without_role decorator. Rejecting request."
            )
            return False

        author_roles = [role.id for role in ctx.author.roles]
        check = all(role not in author_roles for role in role_ids)
        log.debug(
            f"{ctx.author} tried to call the '{ctx.command.name}' command. "
            f"The result of the without_role check was {check}."
        )
        return check
    return commands.check(predicate)


def whitelist_check(**default_kwargs: Container[int]) -> Callable[[Context], bool]:
    """
    Checks if a message is sent in a whitelisted context.

    All arguments from `in_whitelist_check` are supported, with the exception of "fail_silently".
    If `whitelist_override` is present, it is added to the global whitelist.
    """
    def predicate(ctx: Context) -> bool:
        kwargs = default_kwargs.copy()
        allow_dms = False

        # Update kwargs based on override
        if hasattr(ctx.command.callback, "override"):
            # Handle DM invocations
            allow_dms = ctx.command.callback.override_dm

            # Remove default kwargs if reset is True
            if ctx.command.callback.override_reset:
                kwargs = {}
                log.debug(
                    f"{ctx.author} called the '{ctx.command.name}' command and "
                    f"overrode default checks."
                )

            # Merge overwrites and defaults
            for arg in ctx.command.callback.override:
                default_value = kwargs.get(arg)
                new_value = ctx.command.callback.override[arg]

                # Skip values that don't need merging, or can't be merged
                if default_value is None or isinstance(arg, int):
                    kwargs[arg] = new_value

                # Merge containers
                elif isinstance(default_value, Container):
                    if isinstance(new_value, Container):
                        kwargs[arg] = (*default_value, *new_value)
                    else:
                        kwargs[arg] = new_value

            log.debug(
                f"Updated default check arguments for '{ctx.command.name}' "
                f"invoked by {ctx.author}."
            )

        if ctx.guild is None:
            log.debug(f"{ctx.author} tried using the '{ctx.command.name}' command from a DM.")
            result = allow_dms
        else:
            log.trace(f"Calling whitelist check for {ctx.author} for command {ctx.command.name}.")
            result = in_whitelist_check(ctx, fail_silently=True, **kwargs)

        # Return if check passed
        if result:
            log.debug(
                f"{ctx.author} tried to call the '{ctx.command.name}' command "
                f"and the command was used in an overridden context."
            )
            return result

        log.debug(
            f"{ctx.author} tried to call the '{ctx.command.name}' command. "
            f"The whitelist check failed."
        )

        # Raise error if the check did not pass
        channels = set(kwargs.get("channels") or {})
        categories = kwargs.get("categories")

        # Only output override channels + sir_lancebot_playground
        if channels:
            default_whitelist_channels = set(WHITELISTED_CHANNELS)
            default_whitelist_channels.discard(Channels.sir_lancebot_playground)
            channels.difference_update(default_whitelist_channels)

        # Add all whitelisted category channels, but skip if we're in DMs
        if categories and ctx.guild is not None:
            for category_id in categories:
                category = ctx.guild.get_channel(category_id)
                if category is None:
                    continue

                channels.update(channel.id for channel in category.text_channels)

        if channels:
            channels_str = ", ".join(f"<#{c_id}>" for c_id in channels)
            message = f"Sorry, but you may only use this command within {channels_str}."
        else:
            message = "Sorry, but you may not use this command."

        raise InChannelCheckFailure(message)

    return predicate


def whitelist_override(bypass_defaults: bool = False, allow_dm: bool = False, **kwargs: Container[int]) -> Callable:
    """
    Override global whitelist context, with the kwargs specified.

    All arguments from `in_whitelist_check` are supported, with the exception of `fail_silently`.
    Set `bypass_defaults` to True if you want to completely bypass global checks.

    Set `allow_dm` to True if you want to allow the command to be invoked from within direct messages.
    Note that you have to be careful with any references to the guild.

    This decorator has to go before (below) below the `command` decorator.
    """
    def inner(func: Callable) -> Callable:
        func.override = kwargs
        func.override_reset = bypass_defaults
        func.override_dm = allow_dm
        return func

    return inner


def locked() -> Optional[Callable]:
    """
    Allows the user to only run one instance of the decorated command at a time.

    Subsequent calls to the command from the same author are ignored until the command has completed invocation.

    This decorator has to go before (below) the `command` decorator.
    """
    def wrap(func: Callable) -> Optional[Callable]:
        func.__locks = WeakValueDictionary()

        @wraps(func)
        async def inner(self: Callable, ctx: Context, *args, **kwargs) -> Optional[Callable]:
            lock = func.__locks.setdefault(ctx.author.id, Lock())
            if lock.locked():
                embed = Embed()
                embed.colour = Colour.red()

                log.debug("User tried to invoke a locked command.")
                embed.description = (
                    "You're already using this command. Please wait until "
                    "it is done before you use it again."
                )
                embed.title = random.choice(ERROR_REPLIES)
                await ctx.send(embed=embed)
                return

            async with func.__locks.setdefault(ctx.author.id, Lock()):
                return await func(self, ctx, *args, **kwargs)
        return inner
    return wrap