from collections import defaultdict, deque
import re

import regex
from telethon import events, utils

# Heavily based on
# https://github.com/SijmenSchoon/regexbot/blob/master/regexbot.py

last_msgs = defaultdict(lambda: deque(maxlen=10))


def doit(chat_id, match, original):
    fr = match.group(1)
    to = match.group(2)
    to = to.replace('\\/', '/')
    try:
        fl = match.group(3)
        if fl is None:
            fl = ''
        fl = fl[1:]
    except IndexError:
        fl = ''

    # Build Python regex flags
    count = 1
    flags = 0
    for f in fl:
        if f == 'i':
            flags |= regex.IGNORECASE
        elif f == 'g':
            count = 0
        else:
            return None, f"Unknown flag: {f}"

    def actually_doit(original):
        try:
            s, i = regex.subn(fr, to, original.message,
                              count=count, flags=flags)
            if i > 0:
                return original, s
        except Exception as e:
            return None, f"u dun goofed m8: {str(e)}"
        return None, None

    if original is not None:
        return actually_doit(original)
    # Try matching the last few messages
    for original in last_msgs[chat_id]:
        m, s = actually_doit(original)
        if s is not None:
            return m, s
    return None, None


async def group_has_regex(group):
    return any(getattr(x, 'username', None) == 'regexbot'
               for x in await borg.get_participants(group, search='@regexbot'))


@borg.on(events.NewMessage)
async def on_message(event):
    chat_id = utils.get_peer_id(await event.input_chat)
    last_msgs[chat_id].appendleft(event.message)


@borg.on(events.NewMessage(
    pattern=re.compile(r"^s/((?:\\/|[^/])+)/((?:\\/|[^/])*)(/.*)?")))
async def on_regex(event):
    if event.forward:
        return
    if not event.is_private and await group_has_regex(await event.input_chat):
        return

    chat_id = utils.get_peer_id(await event.input_chat)

    m, s = doit(chat_id, event.pattern_match, await event.reply_message)

    if m is not None:
        out = await borg.send_message(await event.input_chat, s, reply_to=m.id)
        last_msgs[chat_id].appendleft(out)
    elif s is not None:
        await event.reply(s)

    raise events.StopPropagation