bin

import configparser
import json
import asyncio
from datetime import date, datetime

from telethon import TelegramClient
from telethon.tl.types import PeerChannel

# some functions to parse json date
class DateTimeEncoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, datetime):
            return o.isoformat()
        if isinstance(o, bytes):
            return list(o)
        return json.JSONEncoder.default(self, o)

# Reading Configs
config = configparser.ConfigParser()
config.read("config.ini")

# Setting configuration values
api_id = int(config['Telegram']['api_id'])
api_hash = str(config['Telegram']['api_hash'])

phone = config['Telegram']['phone']
username = config['Telegram']['username']

# Create the client and connect
client = TelegramClient(username, api_id, api_hash)

async def main(phone):
    await client.start()
    me = await client.get_me()
    user_input_channel = input('enter entity(telegram URL or entity id):')

    if user_input_channel.replace('-100', '').isdigit():
        entity = PeerChannel(int(user_input_channel))
    else:
        entity = user_input_channel

    all_messages = await client.get_messages(entity, limit=None)

    with open('messages.json', 'w') as outfile:
        json.dump(all_messages, outfile, indent=4, sort_keys=True, cls=DateTimeEncoder)

with client:
    client.loop.run_until_complete(main(phone))