#!/usr/bin/env python
# pylint: disable=missing-function-docstring, unused-argument
# This program is dedicated to the public domain under the CC0 license.

"""
Simple Bot to handle '(my_)chat_member' updates.
Greets new users & keeps track of which chats the bot is in.

Usage:
Press Ctrl-C on the command line or send a signal to the process to stop the
bot.
"""

import logging
from typing import Tuple, Optional

from telegram import Update, Chat, ChatMember, ChatMemberUpdated
from telegram.constants import ParseMode
from telegram.ext import (
    CommandHandler,
    ChatMemberHandler,
    Application,
    CallbackContext,
)

# Enable logging

logging.basicConfig(
    format="%(asctime)s - %(name)s - %(levelname)s - %(message)s", level=logging.INFO
)

logger = logging.getLogger(__name__)


def extract_status_change(
    chat_member_update: ChatMemberUpdated,
) -> Optional[Tuple[bool, bool]]:
    """Takes a ChatMemberUpdated instance and extracts whether the 'old_chat_member' was a member
    of the chat and whether the 'new_chat_member' is a member of the chat. Returns None, if
    the status didn't change.
    """
    status_change = chat_member_update.difference().get("status")
    old_is_member, new_is_member = chat_member_update.difference().get("is_member", (None, None))

    if status_change is None:
        return None

    old_status, new_status = status_change
    was_member = (
        old_status
        in [
            ChatMember.MEMBER,
            ChatMember.CREATOR,
            ChatMember.ADMINISTRATOR,
        ]
        or (old_status == ChatMember.RESTRICTED and old_is_member is True)
    )
    is_member = (
        new_status
        in [
            ChatMember.MEMBER,
            ChatMember.CREATOR,
            ChatMember.ADMINISTRATOR,
        ]
        or (new_status == ChatMember.RESTRICTED and new_is_member is True)
    )

    return was_member, is_member


async def track_chats(update: Update, context: CallbackContext.DEFAULT_TYPE) -> None:
    """Tracks the chats the bot is in."""
    result = extract_status_change(update.my_chat_member)
    if result is None:
        return
    was_member, is_member = result

    # Let's check who is responsible for the change
    cause_name = update.effective_user.full_name

    # Handle chat types differently:
    chat = update.effective_chat
    if chat.type == Chat.PRIVATE:
        if not was_member and is_member:
            logger.info("%s started the bot", cause_name)
            context.bot_data.setdefault("user_ids", set()).add(chat.id)
        elif was_member and not is_member:
            logger.info("%s blocked the bot", cause_name)
            context.bot_data.setdefault("user_ids", set()).discard(chat.id)
    elif chat.type in [Chat.GROUP, Chat.SUPERGROUP]:
        if not was_member and is_member:
            logger.info("%s added the bot to the group %s", cause_name, chat.title)
            context.bot_data.setdefault("group_ids", set()).add(chat.id)
        elif was_member and not is_member:
            logger.info("%s removed the bot from the group %s", cause_name, chat.title)
            context.bot_data.setdefault("group_ids", set()).discard(chat.id)
    else:
        if not was_member and is_member:
            logger.info("%s added the bot to the channel %s", cause_name, chat.title)
            context.bot_data.setdefault("channel_ids", set()).add(chat.id)
        elif was_member and not is_member:
            logger.info("%s removed the bot from the channel %s", cause_name, chat.title)
            context.bot_data.setdefault("channel_ids", set()).discard(chat.id)


async def show_chats(update: Update, context: CallbackContext.DEFAULT_TYPE) -> None:
    """Shows which chats the bot is in"""
    user_ids = ", ".join(str(uid) for uid in context.bot_data.setdefault("user_ids", set()))
    group_ids = ", ".join(str(gid) for gid in context.bot_data.setdefault("group_ids", set()))
    channel_ids = ", ".join(str(cid) for cid in context.bot_data.setdefault("channel_ids", set()))
    text = (
        f"@{context.bot.username} is currently in a conversation with the user IDs {user_ids}."
        f" Moreover it is a member of the groups with IDs {group_ids} "
        f"and administrator in the channels with IDs {channel_ids}."
    )
    await update.effective_message.reply_text(text)


async def greet_chat_members(update: Update, context: CallbackContext.DEFAULT_TYPE) -> None:
    """Greets new users in chats and announces when someone leaves"""
    result = extract_status_change(update.chat_member)
    if result is None:
        return

    was_member, is_member = result
    cause_name = update.chat_member.from_user.mention_html()
    member_name = update.chat_member.new_chat_member.user.mention_html()

    if not was_member and is_member:
        await update.effective_chat.send_message(
            f"{member_name} was added by {cause_name}. Welcome!",
            parse_mode=ParseMode.HTML,
        )
    elif was_member and not is_member:
        await update.effective_chat.send_message(
            f"{member_name} is no longer with us. Thanks a lot, {cause_name} ...",
            parse_mode=ParseMode.HTML,
        )


def main() -> None:
    """Start the bot."""
    # Create the Application and pass it your bot's token.
    application = Application.builder().token("TOKEN").build()

    # Keep track of which chats the bot is in
    application.add_handler(ChatMemberHandler(track_chats, ChatMemberHandler.MY_CHAT_MEMBER))
    application.add_handler(CommandHandler("show_chats", show_chats))

    # Handle members joining/leaving chats.
    application.add_handler(ChatMemberHandler(greet_chat_members, ChatMemberHandler.CHAT_MEMBER))

    # Run the bot until the user presses Ctrl-C
    # We pass 'allowed_updates' handle *all* updates including `chat_member` updates
    # To reset this, simply pass `allowed_updates=[]`
    application.run_polling(allowed_updates=Update.ALL_TYPES)


if __name__ == "__main__":
    main()