[Python] Milestone Caculation

milestone.py

from typing import Optional


def roundup(x: int, tens: int) -> int:
    val: int = int("1" + ("0" * tens))
    return x if x % val == 0 else x + val - x % val


def halfway(x: int) -> int:
    val: int = int("5" + ("0" * (len(str(x)) - 2)))
    return val


def get_milestone(before: int, after: int) -> Optional[int]:
    """
    Calculate milestone with two integers

    :param before: Value from previous check
    :param after: Value at current check
    :return: Whether or not it's a milestone

    Milestone Pattern:

    10        | 15        | 20        | 25
    100       | 150       | 200       | 250
    1,000     | 1,500     | 2,000     | 2,500           ... 30, 35, etc...
    10,000    | 10,500    | 20,000    | 20,500
    100,000   | 150,000   | 200,000   | 250,000
    1,000,000 | 1,500,000 | 2,000,000 | 2,500,000

    ... Continues infinitely

    """

    # If it's smaller or equal, it can't be a milestone
    if after < before or after == before:
        return None

    # Less than 10 manual
    if before < 10 and after > 10:
        return 10

    before = before + 1 if (before % 10 == 0 or before % 5 == 0) else before
    rounded_up: int = roundup(before, len(str(round(before))) - 1)
    rounded_up_half: int = rounded_up - halfway(rounded_up)

    # Hit a halfway milestone
    if after >= rounded_up_half and not before > rounded_up_half:
        return rounded_up_half

    # Hit a tens/thousands/etc. milestone
    if after >= rounded_up:
        return rounded_up

    # There is no milestone
    return None

Can be used to calculate any milestone for incrementing forward values.