import re
import asyncio
from datetime import datetime
from typing import (
    Tuple, Union, Callable, Iterable, Dict, Any, Optional, Sequence
)

from aiocqhttp import CQHttp
from aiocqhttp.message import Message

from . import permission as perm
from .helpers import context_source
from .expression import render
from .session import BaseSession

# Key: str (one segment of command name)
# Value: subtree or a leaf Command object
_registry = {}

# Key: str
# Value: tuple that identifies a command
_aliases = {}

# Key: context source
# Value: Session object
_sessions = {}


class Command:
    __slots__ = ('name', 'func', 'permission', 'only_to_me', 'args_parser_func')

    def __init__(self, name: Tuple[str], func: Callable, permission: int, *,
                 only_to_me: bool):
        self.name = name
        self.func = func
        self.permission = permission
        self.only_to_me = only_to_me
        self.args_parser_func = None

    async def run(self, session, check_perm: bool = True) -> bool:
        """
        Run the command in a given session.

        :param session: CommandSession object
        :param check_perm: should check permission before running
        :return: the command is finished
        """
        if check_perm:
            has_perm = await perm.check_permission(
                session.bot, session.ctx, self.permission)
        else:
            has_perm = True
        if self.func and has_perm:
            if self.args_parser_func:
                await self.args_parser_func(session)
            await self.func(session)
            return True
        return False


def on_command(name: Union[str, Tuple[str]], *,
               aliases: Iterable = (),
               permission: int = perm.EVERYBODY,
               only_to_me: bool = True) -> Callable:
    def deco(func: Callable) -> Callable:
        if not isinstance(name, (str, tuple)):
            raise TypeError('the name of a command must be a str or tuple')
        if not name:
            raise ValueError('the name of a command must not be empty')

        cmd_name = name if isinstance(name, tuple) else (name,)
        current_parent = _registry
        for parent_key in cmd_name[:-1]:
            current_parent[parent_key] = current_parent.get(parent_key) or {}
            current_parent = current_parent[parent_key]
        cmd = Command(name=cmd_name, func=func, permission=permission,
                      only_to_me=only_to_me)
        current_parent[cmd_name[-1]] = cmd
        for alias in aliases:
            _aliases[alias] = cmd_name

        def args_parser(parser_func: Callable):
            cmd.args_parser_func = parser_func
            return parser_func

        func.args_parser = args_parser
        return func

    return deco


class CommandGroup:
    """
    Group a set of commands with same name prefix.
    """

    __slots__ = ('basename', 'permission', 'only_to_me')

    def __init__(self, name: Union[str, Tuple[str]],
                 permission: Optional[int] = None, *,
                 only_to_me: Optional[bool] = None):
        self.basename = (name,) if isinstance(name, str) else name
        self.permission = permission
        self.only_to_me = only_to_me

    def command(self, name: Union[str, Tuple[str]], *,
                aliases: Optional[Iterable] = None,
                permission: Optional[int] = None,
                only_to_me: Optional[bool] = None) -> Callable:
        sub_name = (name,) if isinstance(name, str) else name
        name = self.basename + sub_name

        kwargs = {}
        if aliases is not None:
            kwargs['aliases'] = aliases
        if permission is not None:
            kwargs['permission'] = permission
        elif self.permission is not None:
            kwargs['permission'] = self.permission
        if only_to_me is not None:
            kwargs['only_to_me'] = only_to_me
        elif self.only_to_me is not None:
            kwargs['only_to_me'] = self.only_to_me
        return on_command(name, **kwargs)


def _find_command(name: Union[str, Tuple[str]]) -> Optional[Command]:
    cmd_name = (name,) if isinstance(name, str) else name
    if not cmd_name:
        return None

    cmd_tree = _registry
    for part in cmd_name[:-1]:
        if part not in cmd_tree:
            return None
        cmd_tree = cmd_tree[part]

    return cmd_tree.get(cmd_name[-1])


class _FurtherInteractionNeeded(Exception):
    """
    Raised by session.require_arg() indicating
    that the command should enter interactive mode
    to ask the user for some arguments.
    """
    pass


class CommandSession(BaseSession):
    __slots__ = ('cmd', 'current_key', 'current_arg', 'current_arg_text',
                 'current_arg_images', 'args', 'last_interaction')

    def __init__(self, bot: CQHttp, ctx: Dict[str, Any], cmd: Command, *,
                 current_arg: str = '', args: Optional[Dict[str, Any]] = None):
        super().__init__(bot, ctx)
        self.cmd = cmd
        self.current_key = None
        self.current_arg = current_arg
        self.current_arg_text = Message(current_arg).extract_plain_text()
        self.current_arg_images = [s.data['url'] for s in ctx['message']
                                   if s.type == 'image' and 'url' in s.data]
        self.args = args or {}
        self.last_interaction = None

    def refresh(self, ctx: Dict[str, Any], *, current_arg: str = '') -> None:
        """
        Refill the session with a new message context.

        :param ctx: new message context
        :param current_arg: new command argument as a string
        """
        self.ctx = ctx
        self.current_arg = current_arg
        self.current_arg_text = Message(current_arg).extract_plain_text()
        self.current_arg_images = [s.data['url'] for s in ctx['message']
                                   if s.type == 'image' and 'url' in s.data]

    @property
    def is_valid(self) -> bool:
        """Check if the session is expired or not."""
        if self.last_interaction and \
                datetime.now() - self.last_interaction > \
                self.bot.config.SESSION_EXPIRE_TIMEOUT:
            return False
        return True

    def require_arg(self, key: str, prompt: str = None, *,
                    prompt_expr: Union[str, Sequence[str], Callable] = None,
                    interactive: bool = True) -> Any:
        """
        Get an argument with a given key.

        If "interactive" is True, and the argument does not exist
        in the current session, a FurtherInteractionNeeded exception
        will be raised, and the caller of the command will know
        it should keep the session for further interaction with the user.

        If "interactive" is False, missed key will cause a result of None.

        :param key: argument key
        :param prompt: prompt to ask the user
        :param prompt_expr: prompt expression to ask the user
        :param interactive: should enter interactive mode while key missing
        :return: the argument value
        :raise FurtherInteractionNeeded: further interaction is needed
        """
        value = self.args.get(key)
        if value is not None or not interactive:
            return value

        self.current_key = key
        # ask the user for more information
        if prompt_expr is not None:
            prompt = render(prompt_expr, key=key)
        asyncio.ensure_future(self.send(prompt))
        raise _FurtherInteractionNeeded


def _new_command_session(bot: CQHttp,
                         ctx: Dict[str, Any]) -> Optional[CommandSession]:
    """
    Create a new session for a command.

    This will firstly attempt to parse the current message as
    a command, and if succeeded, it then create a session for
    the command and return. If the message is not a valid command,
    None will be returned.

    :param bot: CQHttp instance
    :param ctx: message context
    :return: CommandSession object or None
    """
    msg_text = str(ctx['message']).lstrip()

    for start in bot.config.COMMAND_START:
        if isinstance(start, type(re.compile(''))):
            m = start.search(msg_text)
            if m:
                full_command = msg_text[len(m.group(0)):].lstrip()
                break
        elif isinstance(start, str):
            if msg_text.startswith(start):
                full_command = msg_text[len(start):].lstrip()
                break
    else:
        # it's not a command
        return None

    if not full_command:
        # command is empty
        return None

    cmd_name_text, *cmd_remained = full_command.split(maxsplit=1)
    cmd_name = _aliases.get(cmd_name_text)

    if not cmd_name:
        for sep in bot.config.COMMAND_SEP:
            if isinstance(sep, type(re.compile(''))):
                cmd_name = tuple(sep.split(cmd_name_text))
                break
            elif isinstance(sep, str):
                cmd_name = tuple(cmd_name_text.split(sep))
                break
        else:
            cmd_name = (cmd_name_text,)

    cmd = _find_command(cmd_name)
    if not cmd:
        return None
    if cmd.only_to_me and not ctx['to_me']:
        return None

    return CommandSession(bot, ctx, cmd, current_arg=''.join(cmd_remained))


async def handle_command(bot: CQHttp, ctx: Dict[str, Any]) -> bool:
    """
    Handle a message as a command.

    This function is typically called by "handle_message".

    :param bot: CQHttp instance
    :param ctx: message context
    :return: the message is handled as a command
    """
    src = context_source(ctx)
    session = None
    check_perm = True
    if _sessions.get(src):
        session = _sessions[src]
        if session and session.is_valid:
            session.refresh(ctx, current_arg=str(ctx['message']))
            # there is no need to check permission for existing session
            check_perm = False
        else:
            # the session is expired, remove it
            del _sessions[src]
            session = None
    if not session:
        session = _new_command_session(bot, ctx)
        if not session:
            return False
        _sessions[src] = session

    try:
        res = await session.cmd.run(session, check_perm=check_perm)
        # the command is finished, remove the session
        del _sessions[src]
        return res
    except _FurtherInteractionNeeded:
        session.last_interaction = datetime.now()
        # return True because this step of the session is successful
        return True