msgsplit.py

from typing import List


def split_message(input_msg: str, max_length: int, allocated_chars=None) -> List[str]:
    allocated_chars_arg = allocated_chars
    max_length_arg = max_length
    if allocated_chars_arg is None:
        allocated_chars = 6
    assert max_length > 1 + allocated_chars
    max_length -= allocated_chars

    msgs = []
    msg = ''

    def add_msg(msg):
        new_msg = msg.strip()
        msgs.append(new_msg)

    for word in input_msg.split():
        if len(f'{msg} {word}') > max_length:
            add_msg(msg)
            msg = ''
        msg = f'{msg} {word}'
    add_msg(msg)

    if len(msgs) > 1:
        msgs = [f"{msg} ({i}/{len(msgs)})" for i, msg in enumerate(msgs, start=1)]

    if len(msgs) >= 10 and allocated_chars_arg is None:
        allocated_chars = 6 + 2 * len(str(len(msgs)))
        return split_message(input_msg, max_length_arg, allocated_chars)
    return msgs


if __name__ == '__main__':
    print(split_message("Hi", 20))
    print(split_message("Hi Hello Wonderful World", 20))
    print(split_message("Hi Hello Wonderful World " * 20, 50))